|Publication number||US3568184 A|
|Publication date||Mar 2, 1971|
|Filing date||Sep 30, 1966|
|Priority date||Oct 14, 1965|
|Also published as||DE1541462A1, DE1541462B2, DE1541462C3|
|Publication number||US 3568184 A, US 3568184A, US-A-3568184, US3568184 A, US3568184A|
|Inventors||Drabowitch Serge V|
|Original Assignee||Thomson Houston Comp Francaise|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (6), Referenced by (12), Classifications (14)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent Inventor Serge V. Drabowitch Chatenay Malabry, France Appl. No. 583,309
Filed Sept. 30, 1966 Patented Mar. 2, 197] Assignee Compagnie Francaise Thomson Houston Hotchkiss Brandt Paris, France Priority Oct. 14, 1965, Nov. 2, 1965 France 34931 and 36937 DIRECTIONAL ANTENNA ARRAY HAVING IMPROVED ELECTRONIC DIRECTIONAL CONTROL 10 Claims, 14 Drawing Figs.
U.S. Cl 343/5, 343/100, 343/754, 343/854 Int. Cl G01s 9/02, HOiq 19/06, H0lq 3/26 Field of Search 343/753,
[5 6] References Cited UNITED STATES PATENTS 2,566,703 9 1951 Iams..... 343/100(.6) 3,192,530 6/1965 Small 343/854 3,245,081 4/1966 McFar1and.. 343/100(.6) 3,286,260 11/1966 Howard 343/100(.6) 3,305,867 2/1967 Miccioli et a1. 343/100(.6) 3,484,784 12/1969 McLeod 343/5 Primary ExaminerRichard A. Farley Assistant Examiner-T. H. Tubbesing Attorney- Karl F. Ross ABSTRACT: A plurality of transmitting and/or receiving radiators made operational in a predetermined sequence, confront a focusing assembly which includes an array of controllable phase shifters for converting planar waves into spherical waves or vice versa, the phase shifts introduced by this array being periodically altered under the control of a timer to center the spherical wave fronts on one side of the array successively upon the several radiators whenever the latter are made operational.
PATENTEDHAR 2197: 3,558,184
SHEET 1 BF 8 P2 P M t E T T INVENTOR JTRANSMITMRECEIVE 41mm Serge Vladimir Dra bowitch M Attorney PATENTED MAR 2197! SHEET 2 OF 8 CONTROL ,/8
INVENTOR Serge Vladimir Dra bowifch Attorney PATENTEUMAR 215m 3,568,184 saw 3 0P8 aw ar 1 Mm 2 at 233?; mm 1on2 AWER 10M ASSY ecoumcn W no s REG\STER- mwamoa Serge VladimirDrabowifdw Attorney PATENTED MAR 2 I971 SHEET [1F 8 INVENTOR Serge Vladimir Drabawifch Attorney PATENTEDMAR 2m: 3568.184
SHEET 5 OF 8 CONTROL f UNIT BNVENTQR Serge VladimirDrabou/Hc Attorney PATENTEUMAR 2l97| 3.568.184
SHEET 6 OF 8 INVENTOR.
Serge Vladimir Drabowifch WK g. Rm
Attorney PATENTEUHAR 2:971 3568 184 sum 8 BF 8 N4 N3 H2 ADDER INVENTOR Serge Vladimir Drabowiach Attorney BERE C'UQNAL ANTENNA ARRAY HAVING IMPWJVED ELECTRONIC DIRECTKGNAL CONTROL This invention relates to the directional transmission and reception of electromagnetic waves, and to directional antenna arrays therefor, of the type using electronic scan control.
In radar and similar directional systems, electromagnetic energy must be transmitted and received in the form of planar waves propagating in an accurately controllable scanning direction. In such systems, it has been proposed to use electronic scanning means for controlling the direction in which the planar waves are transmitted and received, thereby to do away with the cumbersome and complicated mechanical scanning equipment required with the conventional scanning antennas. In an electronically controlled directional antenna system, there is generally provided a matrixlike array of radiating elements, e.g. horns, to which the transmitted energy (and from which the received energy) is fed by way of controllable-phase-shift lines. By controlling the phase-shift distribution pattern to which the energy fed to (and from) the individual radiator elements is subjected, it is possible to cause said energy to be transmitted in the form of a planar equiphase wave propagating in a prescribed direction, and conversely to cause planar wave energy to be received from a prescribed direction of space.
Such electronic-scan directional antenna arrays have heretofore been provided in two main forms. In the so-called active arrays, energy was fed to and from the radiator elements of the array directly from and to a transmitter and a receiver, respectively. In the passive arrays, on the other hand, there is used a focusing assembly comprising two similar matrixlike arrays of radiating elements, corresponding elements in the two arrays being interconnected by the adjustable-phase-shift lines. There is further provided a primary radiator source (such as a horn) connected to the transmitter and receiver, by way of a suitable transmit-receive duplexing circuit. Energy from the transmitter is radiated as a divergent beam by the primary transmitter radiator at the secondary radiating elements of one of the arrays of the focusing assembly, then passed through the phase-shift lines to the corresponding elements of the opposite array, and thence radiated into space as planar waves in the prescribed direction. A reverse path is followed by the received wave energy.
These passive antenna systems have important advantages over the active type, since the separation of the primary sources from the focusing assembly has made it possible to select the primary source with optimal characteristics in each particular instance, as for example in the form of a monopulse receiver radiator, where this is desired.
However, passive arrays have heretofore had an important drawback, in the requirement of the duplexing means for switching between the transmitter and receiver. This introduces serious insertion losses, thereby reducing the range of the radar. Further, the construction of the duplexing means is complicated, especially in high power ranges. It is an object of this invention to provide an improved type of electronic scan control for passive focusing assemblies of the type indicated above, which will completely eliminate the need for transmit-receive duplexing.
Another object is to provide improved electronic control for directional antenna arrays, which will make it possible to combine the energy from a plurality of transmitters for the transmission of resultant radar pulses of greatly heightened energy content. A broad object of the invention is to provide improved digital controller means for directional transmitreceive systems. Further objects relate to the provision of improved digital phase-shift devices especially suitable for use in directional systems of the type specified above. Other objects will appear hereinafter.
Exemplary embodiments of the invention will now be described for purposes of illustration but not of limitation with reference to the accompanying schematic drawing, wherein:
FIG. 1 is a two-dimensional diagrammatic representation of a directionalantenna system according to a first embodiment of the invention, using a single primary radiator for transmission and a single primary radiator for reception;
FIG. 2 illustrates certain geometric relations in the system of FIG. l;
FIG. 3 is a time chart showing radar keying pulses and phase-shift adjustments over two successive keying cycles for a typical phase shifter of the array;
FIG. 4} is a simplified perspective view of a focusing assembly used in the directional antenna system;
FIG. 5 is a block diagram of a digital phase shifter comprising a chain of two-state phase-shift units, usable according to the invention;
FIG. 6 is a partly schematic view of a two-state phase-shift unit in the form of a hybrid junction, a plurality of which units may be used in the phase shifter of FIG. 5;
FIG. 7 is a block diagram of a digital controller according to the invention usable with the system of FIG. 1;
FIG. 8 is an expanded block diagram of a component of the system of FIG. 7;
FIG. 9 is a two-dimensional representation, similar to that of FIG. 1, but illustrating another embodiment of the invention using a plurality of primary transmitter radiators;
FIG. 10 shows time charts relatingto the embodiment of FIG. 9 the upper line showing the transmitted pulses, the middle line showing the angular correction for primary source position, and the lower line showing total angular signal;
FIG. 11 is a time chart showing the angular correction signal in a modification;
FIG. 12 is a block diagram of a digital controller usable with the system of FIG. 9;
FIG.. 13 is a logical diagram showing typical computer means for introducing the angular correcting signal in the system of FIG. 12, in a simplified case; and
FIG. 14 is a two-dimensional representation similar to FIG. 1 illustrating an embodiment of the invention using a reflective type of focusing assembly.
A directional antenna system according to this invention is diagrammatically shown in FIG. 1 as including a primary transmitter source 1. and a primary receiver source 2. Primary sources 1 and 2 are here shown as each consisting of a horn antenna, but may assume the forms of other suitable radiating elements capable of emitting and absorbing substantially spherical waves, centered at respective focal points indicated as F1 and F2.
In front of the pair of primary sources or radiators 1 and 2 there is positioned a device herein termed a focusing assembly and generally designated 3. The general function of the focusing assembly 3 is to convert the spherical waves emitted by emitter source it into planar waves of a predetermined, controllable, direction; and also to convert planar waves received from a predetermined, controllable direction into spherical waves centered at focus F2 so as to be absorbable by the receiver source 2. The focusing assembly 3 comprises a rearward array 4 on the side directed towards primary sources I and 2, and a forward array 5 spaced from said rearward array 4 in the direction away from the primary sources. While in the exemplary embodiment both arrays 4i and 5 are shown as being generally planar and normal to the plane of the drawing, it should be understood that they mayassume other general shapes and relative orientations depending on particular requirements.
Each of the arrays 41 and 5 comprises a set of secondary radiating elements, elg. horns, disposed symmetrically and in one-to-one correspondence as between the two arrays 4i and 5. While for simplicity the secondary radiating elements are shown as horns in both arrays 4 and 5,. it is to be understood that they may assume other forms, eg. dipoles, and that they are not necessarily the same as between the two arrays, though said elements are preferably made identical throughout each array. The arrangement of the elements in each array 4 and 5 is, of course, bidimensional, and the FIG. only shows one linear set of the elements in each array, designated 41, 42 through 4n in array 4, and 51, 52 through Sr: in array 5. Corresponding elements of the two arrays are interconnected by way of respective phase-shifter devices, designated 61, 62, through 6n. Each phase shifter may be connected with its associated elements in the two arrays through suitable coaxial lines or waveguides matched to the frequency band that is to be passed by the antenna system.
The phase shifters 61 611 are individually adjustable by electronic means, preferably digital in character, one exemplary embodiment of which will be later described. It can thus be understood that by suitable adjusting the phase shift introduced by each of the phase shifters into the wave energy passed therethrough, it will be possible to reshape a spherical wave, applied from primary transmitter l to the elements of array 4, into a planar' wave'of prescribed" direction retrans' rnitted from the elements of array 5.
Considering this condition in greater detail, it will first be assumed that the spherical waves issuing from the focus F1 of source l are to be converted into planar waves parallel to a given plane P1 normal to the plane of the drawing. Considering any two radial directions, such as el and e2, of the primary radiation issuing from source point F1, the corresponding primary electromagnetic fields, after absorption in elements of the input array 4, and phase shift in the associated phase shifters 6, are to be retransmitted by corresponding elements of the array 5 as the two output rays El and E2 which must both be perpendicular to the prescribed plane P1, and hence parallel to each other. The plane Pl is an equiphase plane for the outgoing radiation. It will therefore be apparent that the specified condition requires that the phase shifters 6 should be so adjusted that the propagation paths such as [F1 ABC and [Fl-1KLM are all equal. This condition can easily be accomplished by imparting linearly displaced phase-shift settings to all of the phase shifters 61 6n, in a manner that will later be discussed in greater detail.
As indicated above, it is also a function of the lens or focusing assembly 3 that incoming planar waves parallel to a prescribed direction, such as Pl, shall all be reshaped into concentric spherical waves centered at the focus F2 of the receiver source 2, which here is separate from the transmitter source 1. In practice, it will be understood that the antenna system of the invention will generally be used for transmission towards and reception from a common target, for example in radar work. The problem therefore arises of so controlling the phase shifters 6 as to accomplish the desired transmitreceive switching action. That is, during transmission periods the phase shifters 6 must all be adjusted so as to convert the Fll-centered spherical waves into planar waves parallel to a prescribed plane P1, while during the corresponding reception periods the phase shifters 6 must all be readjusted so that they will convert incoming planar waves, parallel to the same prescribed plane P1, into spherical waves centered at F2.
For converting the received planar waves parallel to plane P1 into F2-centered spherical waves, it will be evident from the explanations given above that the adjustment of phase shifters 61 should be such as to equalize all the propagation paths such as F2-GHI and F2-NPQ, in order that the received rays such as R1, R2 normal to the prescribed equiphase plane P1 shall be deflected as the rays rl, r2 into the focal point of receiver antenna 2. The geometric requirements involved in accomplishing the desired switching operation according to the invention will best be understood by reference to the schematic diagram of FIG. 2.
in this diagram, the target direction E is defined by its angle S to the axis xx of transmitter source 1, here assumed for simplicity to coincide with the axis of focusing assembly 3. As will be shown later, this simplifying assumption does not restrict the general validity of the results of the analysis. a designates the angle under which the segment F1F2 is seen from the center (i of the rear array 4, the array 4% being positioned at a distance sufficiently large from the primary sources that the line segment FEFZ is seen under substantially the same angle a from any point of the array 4, as indicated. Under these conditions, assuming the phase shifters 6 to be first adjusted so that the rays issuing from F1 are deflected into rays parallelto the prescribed direction E normal to the equiphase plane Pl, then, by the principle of reversibility of propagation of electromagnetic waves, incoming rays such as R parallel to direction E would be focused back into F1. The problem of transmit-receive switching stated above can be restated to mean that for reception, the phase-shift characteristics of the focusing assembly 3 are to be readjusted so that incoming rays such as R received from the prescribed direction E shall now be refocused into the receiver source-point F2, that is, that their angles of emergence from matrix array 4 shall all be increased by the common angle a. By the reversibility principle, this is the same as saying that the phase-shift readjustment for reception must be such that rays of a divergent beam issuing from the transmitter source-point Fl would be redirected into the direction E, at the angle a from the prescribed direction E and normal to the equiphase plane P2 which includes the angle a with plane P1. The requisite condition for the transmit-receive switching action, consequently, is seen to be the following: if the lens array is adjusted for transmission in the target direction defined by the angle 5, then it must be readjusted for reception in a direction defined by the angle (S or).
In the system just discussed with reference to FIGS. 1 and 2, the lens array 3 may be arranged vertically, and the primary sources F1 and F2 may be aligned in a vertical direction. In such a layout the angle designated S in FIG. 2 and defining the target direction would be purely an elevation angle. With the primary sources aligned on a horizontal direction parallel to the planes of arrays 4 and 5, the angle S would be an azimuth angle. It will readily be understood that the statements made in the foregoing discussion also hold in cases where the target angle S is a composite angle involving both an azimuthal and an elevational component, as would be the case e.g. if the target direction E' were out of the plane of FIG. 2. Also, the line segment FlF2 joining the point sources is not necessarily vertical and parallel to the planes of the arrays 4, 5, as assumed above, but may be oriented in any desired direction, so that the angle a may have azimuth and elevation components just as the target-direction angle E.
FIG. 3 is a timing chart in which the upper diagram shows radar keying pulses I produced at the keying-rate period T by a radar transmitter, not shown, with which the antenna system herein described is being used. The lower diagram illustrates the time variations of the phase shift, P to which a typical one of the phase shifters'61-6n, say phase shifter 6p, is adjusted. It will be seen that the phase shifter is adjusted to a first value, 1 for a short time period (7) encompassing each keying pulse I, and is adjusted to a different value 9, during the remainder of the keying period, for receiving the echo or response signals from the target. It will be understood that the transmission phase-shift angle 4%, for each phase shifter, such as 6p, of the focusing assembly is characteristic both of the position p of the phase shifter in the array and of the selected target direction as defined by the angle S; and the reception phase-shift angle I for the same phase shifter is determined simply by changing the angle S in the expression for P into the angle (S a), as indicated above and as will be made clearer presently. The time period 1' during which the phase shift is adjusted to its transmission value is a switching pulse somewhat wider than the keying pulses I, as shown, to allow for the response time of the phase shifters; thus, the complementary switching pulse T-r has a duration less than that of a keying pulse interval. It will be understood that in cases where the antenna is to describe a scanning motion, as is usually the case, the values 1 and P for the phase shifter 6p under consideration, would vary from each keying period to the next in accordance with the prescribed scanning cycle or program. This, as will be clear from the explanations earlier given, is equivalent to varying the angle S (e.g. elevation angle) of the target direction in FIG. 2, in accordance with the said prescribed scanning cycle.
The phase shifters 61 etc. may assume any of various suitaole types, for example devices using ferrite cores wherein the phase shift is varied by varying the current passed through the ferrite. This type of continuous phase shifter is well known and will not be described in detail here.
in a preferred embodiment of the invention, however, digital phase shifters are used of a kind schematically illustrated in FIG. 5. This FIG. shows in block-diagram form a phase shifter generally designated 6p interconnecting the radiator elements 4p and 5p of the respective arrays. The phase shifter is shown composed of several, here five, phaseshift elements or units numbered 71 to 75, connected in series and each having a control input 101 to 105 respectively, constituting an output of a digital control unit 8 Each control line 101 to 105 receives a two-valued signal from the control unit 8, say a direct voltage of one or the other polarity. The phaseshift units 7 are all generally similar and constructed as will be presently described with reference to FIG. 6. The construction is such that when any cell receives one type of signal at its input 101 etc., it introduces no phase shift into the electromagnetic energy transferred through it, while on receiving the other type of signal value at its control input, the cell introduces a predetermined fixed phase shift, the shift introduced by each element, whenthus energized, being the product of a corresponding power of 2 times the unit phaseshift increment introduced by the terminal element 75. Thus, the element 75 may conveniently introduce the unit incremental shift 1 1.25 (or 17/16); the second element 74 may provide a shift twice this value, 22.5 (or 11-13); the third element 73 may give a shift four times the initial value, 45 (or 1r/4); the fourth element 72 may cause a shift 8 times the initial value, 90 (or 1r/2); and the last element 71 may create a shift 16 times the initial value, i.e. 180 (or 1r). It will thus be apparent that depending on the pattern of energization of the control outputs 101 through 105, representing the thirty-two binary numbers from to 11111, the total phase shift through phase shifter 6p will assume a corresponding one of thirty-two angular values from 11/16 or 1 125 to 31 17/16 or 348.75. In these conditions, the phase error on the emergent wave never exceeds 17/32. The error can of course be reduced by using more than the five phase-shift units shown, should greater accuracy be desired.
FIG. 6 illustrates a preferred construction of each of the individual phase-shifter units 71 through 75in FIG. 5. It comprises a hybrid junction or magic-T having an input leg 709, an output leg 712 and the two unequal side legs 710 and 711, having shorted terminations 715 and 716. Diodes 713 and 714 are connected across the sidewalls of the respective side legs 710 and 711, at predetermined distances from their shorted ends 715 and 716. The diodes are connected in parallel 1 between the control line (1111 to 105, FIG. associated with the particular phase-shifter unit (71 to 75) and a common blessing-voltage source V through a resistor.
With such an arrangement, it will be understood that in the normal condition, i.e. in the absence of a positive signal voltage applied to the control line, the diodes 713 and 714 are both nonconductive, so that the effective short-circuited lengths of the side legs 7111 and 711 of the magic-T are the full lengths of said legs, as indicated at L1 and L2. On application of a positive control signal to the control line 101 to 105, sufficient to overcome the biassing voltage V, both diodes 713 and 7141 are made conductive, so that the side legs become short-circuited through the diodes, and the effective lengths of said side legs then become (L1 l1) and (L2 l2) respectively, l1 and I2 being the distances at which'the diodes 713 and 714 are respectively mounted as measured from the shorted terminations and 716 of the side legs.
The lengths L1 and L2 of the legs 710 and 711 are so predetermined that in the normal condition referred to above (no control signal applied), wave energy entering the hybrid junction through one of the input-output legs 7119 and 712, say leg 7%19, after two-way propagation through the side legs 711) and 711 including reflection from the shorted ends 715 and 716 thereof, reappears as a pair of reflected waves at the junction of the other input-output leg .712, both these reflected waves being in phase with the incident wave entering leg 7119. The resultant emergent wave appearing in output leg 712 then is in phase with the incident wave applied to input leg 709, that is, the device introduces zero phase shift into the wave energy transferred through it.
Further, the positions pf the diodes 713 and 714 are so predetermined that when these diodes are conductive (control signal applied), the split incident wave travelling down the side legs 710 and 711 and reflected from the shorted terminations represented by the diodes 713 and 714 reappears at the junction with the output leg (say 712) as two reflected waves cophasal with each other but difi ering in phase by a prescribed angular amount from the phase of the incident wave. The
emergent resulting wave in output leg 712 then is phase-displaced with respect to the incident'wave by the said angular amount; that is, the device has introduced a prescribed phase shift into the wave energy transferred-through it.
Further, the positions of the diodes 713 and 714 are so predetermined that when these diodes are conductive (control signal applied), the split incident wave travelling down the side legs 710 and 711 and reflected from the shorted terminations represented by the diodes 713 and 714 reappears at the junction with the output leg (say 712) as two reflected waves cophasal with each other but differing in phase by a prescribed angular amount from the phase of the incident wave. The emergent resulting wave in output leg 712 then is phase-displaced with respect to the incident wave by the said angular amount; that is, the device has introduced a prescribed phase shift into the wave energy transferred through it.
Each of the five phase-shift units 71 through 75 shown in FIG. 5 may be constructed in the general way just described with reference to FIG. 6, and the five units may differ only in the positioning of the diodes 713 and 714- therein, relative to the shorted side leg terminations 715 and 716. The dimensioning of the side legs 710 and 711 and the positioning of the diodes 713 and 714, in order to insure the type of operation just described, can be effected in various ways as will be readily understood by those skilled in the art from the above disclosure. However, the following additional dimensional data is given for illustrative purposes.
The lengths L1 and L2 of the side legs are preferably selected so that one of these lengths equals an integral number of half-waves of the transmitted energy, while the other lengths differs by one quarter wavelength from the first. Thus: L1=kh l2 and L2=.- (2k+ 1) A /4.
The common distance l2=l of each diode .713 and 714 from the respectively associated side leg termination 715 and 716 may be selected as indicated in the following table in order to obtain the elementary phase shifts described with reference to FIG. 5 (a power of two times the increment l 1.25"). In the table, column 1 indicates the phase-shift unit of FIG. 5, column 11 shows the phase-shift angle introduced by the unit on application of a control signal thereto, and column III indicates the distance I in terms of the wavelength of the transmitted energy, p being an arbitrary integer:
11.25 A l64+pl- /2 22.50 A /32 p A /2 45 A /16+p)\/2 A /8 p A /2 180 A /4+p)\/2 FIG. 5 further shows the phase-shifter chain 61 as including an additional phase-shift unit 76 which may be fixed in character and may comprise a hybrid junction generally similar to that described for each of the variable phase-shift units 7175 with reference to FIG. 6, with suitably dimensioned side legs 711) and 711, or may be of other suitable construction. The fixed unit 76 introduces a fixed phase-shift angle, depending only on the wavelength transmitted through the antenna system. This additional phase shift, designated f1 A serves to complete the conversion between the spherical waves at array 4 and the planar waves at the array 5, by compensating for second-order phase displacements present between the partial spherical wavelets associated with the respective radiating elements of the rear array 4. This function will be referred to later.
The means for switching the individual phase shifters 6 in the focusing assembly 3 according to the invention will now be described in greater detail. In this description, the simplifying assumption previously introduced as to the two-dimensional character of the operation of the system will be discarded, and
that operation will now be examined in its true three-dimensional aspect.
FIG. 4 is a simplified perspective view of the focusing assembly 3, in which each of the arrays 4 and 5 at the opposite sides of the assembly is shown as a four-by-four arrays of radiating elements for the clarity of the drawing, it, being understood that the radiating elements would actually be considerably more numerous. In the rear array 4, each radiating element is designated by a three-digit number in which the hundreds digit is 4, the tens digit designates the position of the element along the vertical or z coordinate of the array (from 1 to 4 in the downward direction) and the units digit designates the position of the element along the horizontal or x coordinate (from 1 to 4 in the rightward direction). Analogous schemes are used to designate the radiating elements of the forward array (hundreds digit 5) and also to designate the phase shifters interconnecting corresponding elements of both side arrays (hundreds digit 6), as well as the control lines connected to said phase shifters (hundreds digit 10).
It will be understood that each of the phase shifters shown in FIG. 4 may be similar in character to that earlier described with reference to FIGS. 5 and 6, in which case each of the control lines would actually consist of a bunch of five (or more) conductors.
Also shown in FIG. 4 is a reference system of rectangular coordinates in which the z axis is vertical, the x axis is horizontal and parallels the breadth dimension of the array, while the y axis is normal to the general plane of the arrays and serves as the azimuth reference. A target direction E is thus defined by the two angles G and S, G being the azimuth angle referred to the y axis and S the elevation angle referred to the xy plane.
The mesh dimensions of each of the arrays 4 and 5 are designated a (along the x coordinate) and b (along the z coordinate); they are not necessarily equal.
Assuming the side arrays 4 and 5 to be vertical planes as here shown, a straightforward analysis in spherical coordinates will show that to convert a spherical wave applied to a radiating element 4zx of the rear array 4 (i.e. that one of the elements of array 4 having the vertical coordinate z and horizontal coordinate x) into a planar emergent wave of azimuth angle G and elevation angle S, issuing from the corresponding radiating element 52 of the front array 5, the phase displacement 1 imparted to the wave by the phase shifter 6zx interconnecting said elements must have the value:
2 ZI:T7T(Z sinS+xsmGcosS) (I) In this expression, the coordinates z and x can be replaced by their values 2 v.h and x h.b, where v and a represent the vertical order number and horizontal order number of the phase shifter under consideration, in the focusing assembly (in the system of reference numerals used in FIG. 4, v represents the tens digit and h the units digit of the three-digit reference number designating the phase shifter).
If the arrays 4 and 5 are not vertical planes, so that the center axis of the assembly is inclined at an angle S to the horizontal plane, then S represents the reference elevation angle of the beam issuing from array 5 when all of the phase shifters 6 are adjusted to introduce zero phase shift. To allow for this, the elevation angle S in equation (1) should be replaced by (S S As earlier indicated, each phase shifter must introduce an additional, fixed, phase shift f1 A depending only on wavelength in order to compensate for phase displacements between individual wavelets. Hence a corrective term f1 A should be added to the second member of equation l It is further advantageous in many cases to control the radiation pattern of the antenna system. In a system of the type here disclosed, this pattern control can be simply accomplished by varying the total phase shift (i.e. the lens thickness of the focusing assembly 3), as a predetermined function of the transmitted wavelength, say the function f2 )t This will entail inserting an additional additive term f2 A into the second member of equation l When all of the above transformations have been made, the final expression for the phase-shift adjustment to be applied to the phase shifter identified as 6vh during periods of transmission, is seen to have the expression:
. u i I As earlier noted, for transmit-receive switching in an antenna system according to the invention, the phase shifts of all the phase shifters are readjusted to values which differ from the transmission phase-shift values as given by equation (2) in that the elevation and azimuth angles S and G are altered by appropriate amounts to take care of the rotation of the primary source focus from point F1 to F2 FIGS. 1 and 2). Assuming that the primary antenna elements, not shown in FIG. 4, are aligned in a direction such that the angle under which they are seen from the center of the rear array 4 has an elevation component a5 and an azimuth component aG, then it will be un derstood from earlier explanations that the equation for the individual phase-shift adjustments during reception is derived from equation (2) by replacing S by S a8 and G by G aG therein.
It is generally convenient to use different radiation patterns for transmission and reception. For example, it is often desirable to use a radiation pattern involving high antenna gain in the target direction with relatively large sidelobes during transmission, and use a pattern giving less gain and substantially smaller sidelobes during reception. This result can be accomplished by altering the term f2 A during reception periods, as by adding an additional term f3 A thereto. The same expedient can make it possible, where desired, to match the characteristics of the focusing assembly 3 to primary radiators 1 and 2 of different type. For example, the receiving radiator 2 may be a multimode radiator of the type disclosed in my copending application Ser. No. 315,949 filed 14 Oct. 1963, now Pat. No. 3,308,469, for optimizing the received sum and difference signals in a monopulse radar or for similar purposes.
It is seen finally that the individual phase-shift adjustment during reception periods is given by the equation:
' va sin (S+S +a )+hb sin 0M6 cos (S+S0+0z FIG. 7 illustrates in schematic form an embodiment of a computer generally designated 800 capable of controlling the individual phase shifters in an antenna system according to the invention in the manner just described. Block 802 represents a scan-cycle programmer of any suitable type operated from the time-base unit TB of the system and adapted to deliver at its output variable signals representative of the cyclically changantenna; alternatively the S and G signals may take the form of continuously varying voltage signals, or other forms. The S and G signals from programmer 802 are applied to respective digital counters 804 and 806.
Counters 804 and 806 may be conventional binary counters having any suitable number of stages, delivering at the counter-stage outputs a set of voltage states constituting a binary representation of the S and G values applied to the counter inputs, in the well-known manner. Counter 804 has associated with it an S register 808, which is preferably adjustable to preset the reference elevation value S as a fixed initial value in the counter whereby the output of counter 804 will represent the angle (S S rather than the angle S. The outputs of counters 804 and 806 are applied to a first set of inputs of each of the respective binary adders 810 and 812.
Each of the binary adders 810 and 812 has a second set of inputs, here shown as being two in number but which would be more numerous in practice, which are connected by way of respective sets of AND gates 814 and 816 to the outputs of respective registers 818 and 820. Register 818 has preset therein, in binary form, a quantity representing the elevation component a of the angle a under which the primary source foci F1 and F2 are seen from the center of the rear array 4, as earlier explained, and register 820 similarly has preset therein the azimuthal component 01 of said angle. The settings of registers 818 and 820 may be adjustable if desired.
The gates 814 and 816 have enabling inputs connected in parallel to the output of a monostable circuit 822 which has a setting input 824 and a timing input 826. Monostable circuit 822 may be any suitable type of multivibrator circuit capable of being switched from its stable to its unstable state on application of a pulse to its setting input 824, and relapsing into its stable state after a time that is accurately adjustable by means of the timing input 826. One form of circuit suitable for use as a monostable circuit 822 is disclosed, for example, in FIG. 13.62 of the General Electric Transistor Manual, 1964 Ed. In that circuit the timing control at input 826 is effected by adjusting a resistor of the circuit.
The setting input 824 is connected to receive the keying pulses I FIG. 3 from the time-base unit TB, by way of a suitable pulse-processing chain 828 which may include, in series: a pluse-differentiator circuit 828a, a suppressor rectifier 828b, and a delay circuit 828e, as shown. A keying pulse I applied to the input of circuit chain 828 is converted into a positive and a negative spike pulse in the differentiating circuit 828a, the positive spike pulse is suppressed in the suppressor rectifier circuit 828b, and the negative spike pulse, whose timing corresponds with the trailing edge of keying pulse 1, is delayed in the delay circuit 8280 prior to application to the setting input 824 of monostable circuit 822.
It will thus be apparent that monostable circuit 822 is switched from its stable to its unstable state a short, constant period after termination of each keying pulse I. Further, the timing input 826 can be adjusted so that circuit 822 relapses to its stable state a time (T 1) later (see FIG. 3), that is, a prescribed constant time before the start of the next keying pulses I. In other words, referring to FIG. 3, monostable circuit 822 will produce an output for enabling AND gates 814 and 816 during each receive period of the keying cycle, but not during the transmit period.
As a result, adder 810 will deliver a binary output representative of the angular value (S S during every transmit period, and a binary output representative of the angular value (S 8,, a during every receive period. Similarly adder 812 will deliver an output representing angle G during every transmit period, and an output representing angle (G 04 during every receive" period.
The outputs of adders 810 and 812 are applied to a Sine Function Generator, Selective Multiplier and Matrix Adder assembly generally designated 830. In this assembly, the binary numbers representative of elevation and azimuth angle data from adders 810 and 812 are converted into the appropriate trigonometric functions and these are combined with one another and with the remaining necessary data in dicated in equations (2) and (3) to provide the phase shift values 1 (or F for each of the phase shifters 61111 of the lens array (FIG. 4).
More specifically, referring to FIG. 8, computer assembly 830 may include sinecosine function generators 832 and 834 having the outputs of adders 810 and 812 applied to their inputs, respectively. Function generators 832 and 834 may be of any of the various types well-known in the art, capable of producing binary digit outputs representative of the sine and cosine functions of the angles that are represented by the binary numbers applied to their inputs. Thus, function generator 832 delivers at a first set of outputs 836 thereof a binary representation of sin( S S0)during transmit periods and of sin(S S a during receive" periods, and delivers at a second set of outputs 838 a binary representation of thecosines of the same angles. Function generator 834 delivers at its set of outputs 840 a binary representation of sinG (during transmission) and sin(G a (during reception).
The outputs 838 of function generator 832 are combined with the outputs 840 of function generator 834 in a binary multiplier 842 to provide the sinecosine product terms in equations (2) and (3). The sine outputs 836 of 832 and the product output of multiplier 842 are separately applied to the first inputs of respective multipliers 844 and 846, each of which receives at its second inputs the output of a register 848 which is preset to represent the constant factor 2 rrllt Starting with the outputs of multipliers 844 and 846, groups of conductors carrying binary digital information will be represented, in FIG. 8, as single lines for. the clarity of the drawing.
The output of multiplier 844 is applied in parallel to a set of constant-multipliers generally designated 850, here shown to be four in number, in which it is multiplied by the constant factors a, 2a, 3a and 4a. Similarly the output of multiplier 846 is multiplied by the constant factors I), 2b, 3b and 4b in the respective multipliers of a set 852. The outputs of the multipliers of the respective sets 850 and 852 are selectively added two by two in a matrix of adder circuits generally designated 854. Each of the (here sixteen) adders of the fourby-four matrix 854 operates to add the output of a related one of the multipliers 850 to the output of a related one of the multipliers 852. Thus, each of the output lines designated 1011 to 1044, of the adder matrix 854, digitally represents the phaseshift adjustment 1 (during Transmit) or 1 (during Receive) for a related one of the phase shifters 6hv, as given by equation (2) or 3), disregarding the additive terms f1, f2
and )3 in those equations. It will be understood that each of the output lines would actually represent a set of five digital conductors in the phase-shifter array disclosed with reference to FIG. 5.
The additive term f1 )t in this embodiment, is introduced by providing the fixed-delay element 76 FIG. 5 in each phase shifter 6hv, as earlier described.
The additive term jZA may be introduced by way of the computer assembly 830 from a register 858 (see FIG. 7) whose output may be applied to each of the adders of matrix 854 as a third input thereto, although this has not been shown in FIG. 8 for clarity. Alternatively, separate adders may be used for introducing the f2 term.
The additive term j3lt it will be recalled, is to be introduced only during the Receive periods of the cycle. For this purpose FIG. 7 shows an additional register 860 having the value 18 It preset therein, and having its outputs connected to inputs of register 858 by way of AND gates 862,. whose enabling inputs are connected in parallel to the output of monostable circuit 822.
As will be evident from the above description of FIGS. 7 and 8, the digital system shown operates to produce the desired switching actions for adjusting the phase shifters of the antenna system of the invention so as to perform a prescribed electronic scan action in accordance with the programmed cycle for the antenna while at the same time taking care of the requisite transmit-receive switching action whereby the two separate antennas I and 2 will, in each keying cycle, be transmitting and receiving, respectively, in and from precisely the same target direction. In addition, the system described includes means for automatically switching to different, predetermined radiation patterns during the transmission and reception periods.
In the invention as so far disclosed, the phase-shift switching action serving to alter the direction of wave convergence or focalization at the spherical-wave side of the focusing assembly, while maintaining a fixed direction of wave propagation at the planar-wave side of said assembly, is performed between only two directions of focalization or convergence; that is, the spherical waves are alternatively focused on a single primary transmitter radiator l and a single primary receiver radiator 2. It will, however, be evident that a generally similar switching principle can be applied in order to focus the spherical waves sequentially on any desired number of primary radiator sources :in' any'desired' cycle sequence. Thus, it is apparent that in the systems shown in FIGS. 1 and 2 if the antennas 1 and 2, rather than being a transmission antenna and a receiver antenna respectively as above described, were instead to constitute two transmitter antennas (or, for that matter, two receiver antennas), the mathematical analysis given earlier herein would remain true, and the conclusions inferred therefrom would hold, mutatis mutandis.
Accordingly, an important aspect of the invention, to be described with reference to FIGS. 9 and 10, is directed to an electronic-scan antenna system of the general type disclosed above, including improved means for switching between a plurality of separate primary transmitter sources without having to use the troublesome duplexing means heretofore required for a similar purpose.
FIG. 9 schematically shows a focusing lens assembly 3 similar to that shown in FIG. 1, including a rear matrix array 4 of radiating elements 41 4n and a front matrix array 5 of radiating element 51 5n interconnected by adjustable phase shifters 61... 6n, all of which components may be generally similar to the corresponding components in the embodiments earlier disclosed herein. A plurality of primary transmitter elements 11, 12, 1N and a single primary receiver element 2 are shown. While the primary radiator elements 11 etc. and 2 are shown as horn radiators, any suitable form of radiator may be used. The primary transmitter radiators 11 1N may be provided in any suitable number and may be arranged in any suitable configuration. Very desirably, the primary transmitter radiators are arranged in a part-circular or part-spherical array with their axes preferably converging at or near the center of the rear array 4 of the focusing lens assembly 3. It
.will be understood that while FIG. 9 is a two-dimensional representation (similar to FIG. 1) wherein the array of primary radiators l and 2 is shown as a circular are lying in a vertical plane normal to the vertical planes of the focusing arrays 4 and 5, this is by no means essential. The primary radiator elements may be disposed in a circular are (or other linear segment) lying on a plane having any desired orientation relative to the vertical and to the focusing assembly 3. Said primary radiator elements may also be disposed along a two-dimensional surface area rather than along a plane curve, for example a part-spherical surface area centered at 0. As shown, there is provided a single receiver radiator 2 which preferably is positioned centrally of the array of primary radiators, with its axis coinciding with the normal axis xx of the focusing assembly 3. Such central position of the receiver antenna element 2 minimizes undesirable aberration effects.
Each of the transmitter radiators ll IN is shown connected to an associated transmitter 91 9N respectively, over an individual transmission link such as a coaxial line or waveguide.
A controller unit generally designated 801 is provided and has as one of its functions the switching of the phase shifters 61 6n in a regular cycle sequence to cause the directions of the emerging planar waves from the outer array to sweep out a programmed scan cycle. The controller 801 is for this purpose shown as having an output line, generally designated 100, connected to control inputs of each of the phase shifters 61 etc. If the phase shifters 6 are constructed in the manner described with reference to FIGS. 5 and 6, each consisting of a set of five adjustable elements, then the line would actually consist of a bundle of as many bunches of five conductors as there are phase shifters in the array, each conductor in each bunch being connected to the two control diodes (713 and 714, FIG. 6) of a related phase-shift unit.
Controller 801 is further shown as having an output generally designated 110, comprising a set of control lines connected to an enabling input of each of the transmitters 91 9N. The purpose of these enabling connections is to place each of the transmitters in operation in cyclic sequence for a single keying period, at a predetermined time during the transmit period of every keying cycle. The operation of controller 801 in this embodiment is such, as will later appear more .clearly, that each of the. transmitters 91 9.N.(say transmitter 93) is enabled at that particular time in the keying-cycle transmit period when the combined adjustment of the phase shifters 6 has the precise configuration required to cause the spherical waves issuing from the particular primary radiator (say 12) associated with the transmitter (92) under consideration to be reshaped into planar waves propagating in the target direction prescribed for that keying cycle by the antenna scan program. After having thus successively enabled each of the transmitters 91 9N to transmit a pulse by way of its associated radiators l1 1N, all in the prescribed target direction, the controller 801 cuts off all of the transmitters throughout the Receive period of the keying cycle, while at the same time it sets the adjustment of all the phase shifters 61 etc. of the focusing assembly to a phase-shift distribution pattern such that incoming planar waves from a target, if present in the said prescribed direction, will be converted by focusing assembly 3 into spherical waves absorbed by receiver antenna 2. This receiving phase-shift distribution pattern is then maintained through the Receive portion of the keying cycle under consideration.
The manner of operation just outlined will now be considered more closely. It will be assumed that the primary radiators 11 1N and 2 lie on a circular arc in a vertical plane normal to the vertical planes of the focusing array 3. This simplifying assumption means that the term aG earlier defined and entering into eq. (3) is taken equal to zero. It will also be assumed that the referencedirection of the antenna for zero phase-shift is horizontal, i.e. the angle S in eqs. (2) and (3) is zero. Finally, the constant terms designated f1 A, f2 it andf3 A in eqs. (2) and 3) will here be disregarded, it being well understood that in practical utilization of the embodiment now being disclosed those terms would preferably be present, and that they can then be taken care of in ways that may be similar to what was described in detail in respect to the similar terms in the embodiment first disclosed. It will be evident therefore that the simplifying assumptions just set forth will in no way detract from the broad validity of the description to follow.
Let us write the equations, analogous eqs. (2) and (3) above, giving the phase-shift adjustment of any of the phaseshifters 6, defined by its vertical and horizontal coordinates u and h, in order that the focusing assembly 3 will convert energy between planar waves propagating at its outer array 5, in a direction defined by the elevation and azimuth angles S and G, and spherical waves propagating at its inner array 4 with wave fronts concentric with all the primary radiators l1 1N and 2. Remembering the simplifying assumptions made above, the equation can be written In this equation, the subscript is used to designate any one of the primary sources including both the transmitter sources 11 through 1N and the receiver source 2. Thus the symbol a, designates elevational angle of each of the primary-source foci as measured to the horizontal through the center 0 of the focusing array.
For the clarity of the ensuing discussion, it will now be assumed that the transmitter radiators are six in number, 11 to If, being symmetrically disposed with three above and three below the single reciever radiator 2. The primary sources will be assumed to be positioned at the following elevations:
a Receiver source: a 0
Referring now to FIG. 10, the upper one of the three time charts shows the timing of the pulses transmitted by the transmitters 91 to 96 during two consecutive keying cycles (called I and II). The six pulses are designated in the chart by the same numbers 11 to 16 as the primary transmitter radiators to which the pulses are applied. It will be seen that during the transmit time of every keying cycle, the six transmitter radiators 11 16 operate in succession for equal pulse periods of a duration designated T, with intervening short idle periods AT.
Thereafter the six transmitters are silent throughout the receive time of the keying cycle, when the receiver radiator 2 listens-in for incoming responses.
The middle chart of FIG. 10 shows how the angle a, in equation (4) must be varied during each of the keying cycles in order that the six pulses transmitted in the transmit period of the keying cycle shall all be directed in a common prescribed direction and that thereafter any response signals from that same direction shall be redirected into the receiver radiator, during the ensuing receive period. It is seen that the angle a,- is to vary stepwise through the values l5, 10, 5, 5, 10, 15, and then to the value zero for reception. Each step is coextensive with an enabled period of a corresponding one of the six transmitters (pulse period T), and the passing from one angular value to the next is effected during the interpulse periods (AT).
To improve the understanding of the way in which the system operates, the lowermost chart in FIG. 10 shows the variations of the angular sum (S 04,) entering in equation 4). It will be noted that the angle S is varied from one keying cycle to the next, owing to the action of the antenna-scan-cycle programmer, as earlier described. This variation of the angular term S in the sum imparts a shift to the total angular sum value, between consecutive keying cycles. ,The shift is made apparent in the chart by referring to the horizontal dotted extension lines shown.
The time variations of the phase shift 1 of an individual phase shifter would show a general appearance rather similar to the variations of (S 01,) as shown in the bottom curve of FIG. 10, except of course that all the ordinates would be altered as required by equation (4).
It should'be distinctly understood that the charts of FIG. 10 have been included chiefly for explanatory purposes and do not purport to illustrate the actual operation of a practical embodiment of the system of FIG. 9. For one thing, the number of primary sources would in practice be generally considerably greater than the six here assumed, so that the curves in the lower two charts would have a correspondingly increased number of steps. Further, the stepwise variations of the angular values need not be effected unidirectionally during each transmit period of a keying cycle, as is here shown. Instead, the array of primary transmitters 91 9N may be enabled by the controller in such a sequence that the curve described by the angular value a, will assume a sinusoidal" or oscillatory shape such that the angular excursions will be minimized at all times, including the start and termination of the tramrnit period. An example of such a curve, obtainable by a suitable sweep pattern through the primary radiators, is given in FIG. 11, where the transmitter sources are assumed to be twelve in number. A sweep pattern of this character has the obvious advantage of requiring minimum phase-shift adjustments to be performed in the phase shifters 6, thereby minimizing transients.
FIG. 12 illustrates in block form a suitable construction of the controller 801 usable in the embodiment of the invention shown in FIG. 9 in order to obtain the general manner of operation described above with reference to FIGS. 9, 10 and 11. In FIG. 12, components similar in function to components of the controller shown in FIG. 7 are designated by the same r ference numbers plus 1000, and will not again be described. A difference between the two embodiments is in the manner the adders 1810 and 1812 are controlled to receive their a and a inputs. It will of course be understood in this respect that in the event that the azimuthal component 04 of the a, angles is zero, as was assumed to be the case in the previous discussion of equation (4) and FIG. 10, then the adder 1812 shown in FIG. 12 can be omitted. So can the S register 1808 if 5 0 as was assumed in writing the equation (4).
For introducing the a and a values into the adders 1810 and 1812, there is here shown a digital counter (or adjustable register) 1874. There is further provided a multistage binary shift register 1878, having all of its stages connected by a shift line 1880 to an output of time-base unit TB so as to receive shift pulses therefrom at the same rate as the transmission pulse periods indicated as Tin FIG. 10. Shift register 1878 has as many stages as there are T pulse periods in a keying cycle. Further the input stage of the shift register is connected by a line 1882 with an output of timebase unit TB supplying a keying pulse thereto at the start of the transmission period of every keying cycle; This keying pulse is then shifted through the stages of register 1878 over the subsequent keying period, so that the successive stages of the shift register are sequentially energized at corresponding periods of the keying cycle. The initial stages of shift register 1878, energized within the transmit period of the keying cycle, have their outputs connected in one-to-one relationship with the enabling inputs of transmitters 91... 9N, as is schematically shown by the single connecting line 1884. Thus the desired sequential action of the transmitters to deliver radar pulses to their associated radiators, as earlier described, is ensured. Further, the outputs of the stages of shift register 1878 are'connected, as here shown schematically only, to the (r -counter 1872 and the a counter 1874 so as to control the counter logic to produce digital outputs at every pulse period, of the keying cycle, representing the proper values for the angles a and a at those periods. Counter 1872 is further shown as having an output connected to the AND gates 1862 in order to enable those gates during the receive" period of the keying cycle, for the purpose earlier described.
FIG. 13 indicates suitable logic circuitry for the (r -counter 1872 which is applicable to the simple numerical example illustrated in FIG. 10 and earlier described Counter 1872 is shown as comprising five digit lines N0, N1, N2, N3, N4, which are connected to respective inputs or adder 1810 so as to add 1, Z, 2 2 and 2, respectively, to the angular quantity, expressed in degrees, applied to the other set of inputs of the adder from computer 1804 as earlier described. Lines N0 to N4 have their input ends connected to a suitable voltage source V through resistances, and further through interposed AND gates G0, G1, G2, G3 and G4 respectively. The AND gates have their enabling inputs connected to the outputs of respective OR gates R0, R1, R2, R3, R41 Each OR gate has its inputs connected to selected ones of the six initial stages of shift-register 1878, as shown, and/or to the output of an OR- gate R5 having its inputs connected to the last ten stages of the shift register (which stages are energized during the receive" period of the keying cycle). The output of OR gate R5 is also connected to the line 1886 for enabling the gates 1862 to switch from the transmission radiation pattern to the recep tion radiation pattern as earlier described.
In the operation of this device, it is assumed that the adder 1810 has a count of 15 initially preset therein in order that the a -counter 1872 shall be required to introduce positive quantities exclusively. Thus, the chart of FIG. 10 shows that in pulse-period T1 (when primary radiator 11 is transmitting) the (r -counter must introduce a count of 15 15 30, or
1 1 1 10 in binary notation; in pulse-period T2 (12 transmitting) the a -counter must introduce 10 15 25 (11.001 in binary); in pulse period T3, (13 transmitting) the a -counter must introduce 15 20 (10100 in binary; in pulse period T4 (14 transmitting) the counter must introduce 5 15 (01010 in binary; in pulse period T5 transmitting) the counter must introduce 10 15 ="5'(00101); in pulse period T6 (16 transmitting) the counter must introduce 15 15 O; and throughout the receive period from pulse period T7 to the end of the keying cycle, the counter must introduce 0 +15 15 (01111 in binary).
A study of the logic of the a -counter 1872 in FIG. 13 shows that the-requisite counting operation is achieved. Thus, in the pulse period Tl stage 1 of the shift register 1878 has an energized output, and this is applied through the four OR gates R4, R3, R2 and R1 to enable the AND gates G4, G3, G2 and G1, whereupon the voltage from source V is applied to the four digital lines N4, N3, N2 and N1, introducing the binary count 11110 into adder 1810. It can readily be verified in similar fashion that the requisite counts are obtained in the remaining pulse periods of the keying cycle.
An important advance advantage of the embodiment of the invention using a plurality of primary transmission sources, as shown in FIG. 9 and as just described, lies in the possibility thus made available of greatly increasing the mean power that can be transmitted through an antenna system. Thus, the transmitters 91 9N may all be operated in coherent relationship so that the unit pulses transmitted by the transmitter array will then be practically equivalent to asingle pulse of greatly increased duration. Referring to the uppermost chart in FIG. 10, the effective duration of the resulting protracted pulse is seen to be substantially equivalent to NT, since the idle intervening periods AT can be made extremely short when using digital switching techniques of the general character disclosed herein. More precisely, if W is the instantaneous power delivered by each of the N transmitters, the transmitter array will deliver a total energy [NWT over a total time that is readily seen from said chart to be NWT (N 1) AT. ]This is practically equivalent to the delivery of a total pulse energy N times greater than the pulse energy derivable from a single source.
Since the resulting increase in means transmission power is obtained without any increase in the instaneous power transmitted from each primary source or through the component elements of the focusing array, the flow of damaging amounts of power is avoided.
Thus, the invention makes it possible to combine any number of transmitters for sequential operation so as to add the transmission energies developed by them, without having to use duplexing means as would otherwise be necessary for such purpose. The provision of such duplexing circuits for a large number of transmission sources would be complicated and would introduce considerable losses, which are almost completely absent in the system of the invention.
According to a further advantageous possibility afforded by the multisource switching system described above, the various transmitters such as 11... 1N (FIG. 9) may be operated so as to produce pulses that differ from one another in some selected characteristic in accordance with a predetermined modulation pattern. The resultant, combined pulse will then be modulated (or coded) in respect to the selected characteristic. This characteristic may be amplitude, but preferably is frequency or phase. The frequency modulation or coding of broad radar pulses provides a method of enhancing the resolving power of a radar system without detracting from its range, as is well known from current radar work.
This possibility is illustrated in FIG. 13 where each of the transmitters 91-96 is shown as having a frequency-control input such as 1888, the respective frequency-control inputs being connected to respective taps of a voltage divider 1890 connected between a voltage source 1892 and ground. In this manner, the partial radar pulses transmitted by the respective primary sources 11-16 (see FIG. 10 upper diagram) are assigned incrementally differing carrier frequencies, with the incremental frequency variation between consecutive partial pulses being made to follow a linear or any other desired law. The resulting high-energy pulse formed by the combination of said partial pulses will therefore be modulated or coded in a correspondingmanner.
While the phase-shift-control means used in the invention are preferably of the fully digital character here disclosed, some or all of the components thereof may be replaced by analogue components.
In an antenna system according to the invention, the focusing assembly used is not necessarily of the refracting'? or lens type so far considered. focusing assemblies of the reflecting type may be used with equivalent results. This is illustrated in FIG. 14, in which the same references as in FIG. 1 are used to designated components having corresponding functions. It will be immediately apparent that the layout of FIG. 14 differs from that of FIG. 1 essentially only in that the elements of array 5 are turned roundabout to face in the reverse direction, so that the planar waves propagate in the rear of the primary sources 1 and 2. More complex types of focusing assemblies, including assemblies using polarization rotation of the waves, and assemblies of the cassegrainian type used in certain types of my assignees tracking radar, installations, are likewise susceptible to adaptation in accordance with the teachings of the present invention, as will be readily apparent to those skilled in the art.
While in all of the disclosed embodiments the focusing assemblies are shown as converting wave energy between convergent first waves converging at a determined focal point at one side of the assembly, and second waves that are planar and propagate in a determined direction at the other side of the assembly, it will be evident that the same assemblies can be used for converting between first waves converging at a first focal point at one side, and second waves converging at a second focal point at the other side of the assembly. This would merely require correspondingly readjusting the patter of phase-shift distributions in the-phase shifters of the focusing assembly as well as readily understood by those skilled in the art. In this connection the elementary geometric truth should be recalled that planar waves propagating in a determined direction can be regarded as a special instance of convergent waves converging at a focal point removed to infinity along that direction.
In the appended claims as in the specification, the words radiate and its derivatives are to be taken with their broad meaning usual in radio engineering, as applicable both to transmitting and receiving antenna elements. Thus, an antenna element is understood as constituting a radiator both when it is acting to transmit electromagnetic energy fed to it, as waves propagating in space, and when it is absorbing or picking up space waves and transferring the energy absorbed therefrom to a receiver connected to the antenna element. Analogously, the word converging as applied to electromagnetic waves is to be understood as meaning both waves that are expanding from a focal point, in cases where the waves are being transmitted, and waves that are contracting toward a focal point (the commonly accepted meaning of convergence), in the case of waves being received.
1. In a directional antenna system, in combination:
focusing means including an array of controlable phase shifters;
a plurality of primary radiators including several transmitting radiators on one side of said focusing means;
a multiplicity of secondary radiators respectively connected to said phase shifters and confronting said primary radiators in transmit-receive relationship therewith;
control means for selectively adjusting said phase shifters to a plurality of different distribution patterns each adapted to convert a first beam with a predetermined wavefront into a second beam with a spherical wavefront centered on a respective primary radiator and vice versa;
and switchover means for individually making said primary radiators operational, with actuation of said transmitting radiators in rapid succession and in a predetermined sequence, while operating said control means to produce a distribution pattern centering said second beam on the operational primary radiator.
2. The combination defined in claim 1 wherein said primary radiators further include a receiving radiator, said switchover means comprising a source of recurrent keying pulses coinciding with operating periods of said transmitting radiators.
3. The combination defined in claim 2 wherein said control means includes circuitry for deriving from said keying pulses a train of first and second switching'pulses for alternately centering said second beam on said transmitting radiators and said receiving radiator, respectively, said second switching pulses occurring during part of the interval between successive keying pulses.
l. The combination defined in claim 2 wherein said first beam consists of substantially parallel rays, said controlmeans including circuitry for progressively modifying the phase shifts of said array in consecutive keying-pulse cycles with a resultant progressive change in the direction of said first beam.
5. The combination definedin claim 1 wherein said secondary radiators are coplanar, said primary radiators being disposed in a plane substantially parallel to that of said secondary radiators.
6. The combination defined in claim l wherein said secondary radiators are arrayed about a center, and primary radiators being disposed along a surface curved about said center.
7. The combination defined in claim 2, further comprising a source of modulable wave energy for said transmitting radiators responsive to said switchover means for energizing said transmitting radiators with different wave characteristics.
8. The combination defined in claim 1 wherein said control means comprises digital computer means.
9. The combination defined in claim 8 wherein each of said phase shifters comprises a terminal element for introducing a unit increment of phase shift and a plurality of supplemental elements connected in cascade with said terminal element and selectively actuatable by said computer means for multiplying said unit increment by respective powers of 2.
10. The combination defined in claim 1 wherein said primary radiators include a centrally positioned receiving radiator between two groups of said transmitting radiators.
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|U.S. Classification||342/157, 342/376, 343/754|
|International Classification||G01S13/42, H01Q25/00, H01Q3/00, G01S13/00, H01Q3/46|
|Cooperative Classification||H01Q3/46, G01S13/426, H01Q25/008|
|European Classification||H01Q25/00D7B, G01S13/42S, H01Q3/46|