US 3205501 A
Abstract available in
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Description (OCR text may contain errors)
Sept. 7, 1965 D. H KUHN 3,205,501
GLOSELY SPACED STOCKED WAVEGUIDE ANTENNA ARRAY EMPLOYING RECIPROCAL RIDGED WAVEGUIDE PHASE SHIFTERS Filed 001:. 1 1959 5 Sheets-Sheet l N 0 I SCI. SSO'I Q :0 N o o m 0 (I) g S :1: m n. o n: w o .1 o 5. u.
m 2 0a g o o o o o o o o 0 o o o m I n m $338930 3ONV/\CIV BSVHd L n J F T T 2 0 Q m E LLI INVENTOR:
' DONALD H.KUHN,
Sept. 7, 1965 D. H. KUHN 3,205,501
CLOSELY SPAGED STOCKED WAVEGUIDE ANTENNA ARRAY EMPLOYING RECIPROCAL RIDGED WAVEGUIDE 7 PHASE SHIFTERS Filed Oct. 1, 1959 s Sheets-Sheet 2 S338 EEG-M7130 BSVHd DONALD H. KUHN,
United States Patent This invention relates to electromagnetic wave phase shifter transmission systems, and has a particular object thereof the provision of systems having restricted transverse structural dimensions. The invention is particularly applicable to a scanning antenna utilizing an array of radiating elements.
Electromagnetic Wave phase shifting transmission lines employing magnetic materials are well known in the art. They normally comprise waveguide structures having a slab or rod of ferromagnetic material, such as ferrite, mounted within the waveguide and further having a magnetic field surrounding the material. The magnetic field strength is controlled so as to vary the tensor permeability of the ferromagnetic material, which can provide a phase shift of the electromagnetic energy traveling through the waveguide, A description of a recently developed reciprocal ferrite phase shifter having a longitudinally applied magnetic field, of special interest to the present invention, is given in an article by F. Reggia and E. G. Spencer, entitled A New Technique in Ferrite Phase Shifting for Beam Scanning of Microwave Antenhas, published in the Proceedings of the IRE, vol. 45, No. 11, pages 1510 to 1517, November, 1957. These phase shifting devices have previously been confined to conventional waveguide structures wherein the inside transverse dimension of the empty guide is equal to one half the Wavelength of the transmitted microwave energy at the cut-off frequency.
In some applications, it is necessary to use a plurality of parallel phase shifting waveguide transmission lines of reduced cross sectional dimensions wherein the spacing between individual guide structures is approximately one half wavelength of the transmitted frequency. One such application is in a wide angle antenna beam scanning system wherein it is desirable to utilize a large number of radiating elements, whereby the scanning is performed electrically by controlling the phase of the energy radiated from each radiating element, thereby controlling the direction of the maximum of the radiation pattern. So as to prevent the formation of high secondary lobes in a wide angle scan, it is required that each radiating element be spaced apart approximately one half Wavelength of the radiated energy. Where it is required to scan both in azimuth and elevation, the radiating elements are formed on a two dimensional plane which necessitates a critical half wavelength spacing existing between the radiating elements along both dimensions. In the past such a type of wide angle scanning in two dimensions was not feasible since the space required for the conventional sized Waveguide phase shifter feed structure coupled to the radiating elements exceeded the required half wavelength dimension.
It is accordingly an object of this invention to provide ferromagnetic phase shifting transmission systems for electromagnetic energy in the microwave frequency region having reduced transverse structural dimensions.
It is a more specific object of this invention to provide phase shifting transmission systems for electromagnetic energy in the microwave frequency region comprising a plurality of ferromagnetic phase shifting elements contiguously mounted along two dimensions, having transverse structural dimensions less than one half the free space wavelength of said energy and being spaced apart "ice approximately one half wavelength in either of said two dimensions.
It is another object of this invention to provide ferromagnetic phase shifting transmission systems for electromagnetic energy in the microwave region for application to an antenna scanning array making possible a solid angle scan.
Briefly, in accordance with one aspect of the invention, there is provided a reciprocal ferromagnetic phase shifting transmission system for electromagnetic energy in the microwave frequency region comprising a waveguide structure whose transverse electrical dimensions are one half or in excess of one half the free space wavelength of the electromagnetic energy propagated through said guide but Whose transverse structural dimensions are less than said one half Wavelength. An elongated slab of ferrite material is symmetrically mounted within said waveguide with its axis parallel to the longitudinal axis of said waveguide for producing a reciprocal phase shift to said transmitted electromagnetic energy, and a controllable magnetic field is applied along the axis of said ferrite slab for controlling the degree of phase shift, said magnetic field being of a Value to operate the ferrite in the region below magnetic saturation.
Considering a further aspect of the invention, there is provided a ferrite phase shifting transmission system comprising an enclosed stripline having top and bottom ground plates with a center conductor mounted therebetween by two slabs of ferrite material, said ground plates being joined along their length by two side plates so as to form an enclosed structure. The transverse dimensions of the enclosed stripline are less than one half the free space wavelength of the energy propagated therethrough. A controllable magnetic field is applied to said ferrite material for controlling the phase shift applied to said electromagnetic energy.
Considering still a further aspect of the invention, there is provided a two dimensional array of ferromagnetic phase shifting structures of reduced cross sectional dimensions mounted contiguously, the spacing between individual phase shifting structures being approximately one half the free space wavelength of the electromagnetic energy propagated therethrough.
Although the features of the invention which are be lieved to be novel are set forth with particularity in the appended claims, the invnetion itself both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings wherein:
FIGURE 1A is a partially exposed View in elevation of a ridged Waveguide ferrite phase shifter;
FIGURE 13 is an enlarged cross sectional view of the ridged waveguide of FIGURE 1A taken along the line 1B-1B;
FIGURE 2 is a graph illustrating certain electrical characteristics of the configuration of FIGURES 1A and 113;
FIGURE 3A is a partially exposed view in elevation of a dielectric load waveguide incorporating the principles of applicants invention;
FIGURE 3B is an enlarged cross sectional view of the dielectric loaded Waveguide in FIGURE 3A taken along the line 3B3B;
FIGURE 4 is a graph illustrating certain electrical characteristics of the configuration of FIGURES 3A and 38;
FIGURE 5A is an elevation view of an enclosed stripline ferrite phase shifter;
FIGURE 58 is a cross sectional view of the enclosed stripline configuration of FIGURE 5A taken along the line :iB-SB;
FIGURE C is an enlarged view, partially in section and partially exposed, of the right hand portion of FIG- URE 5A;
FIGURE 6 is a graph illustrating certain electrical characteristics of the configuration of FIGURES 5A, 5B and 5C;
FIGURE 7 is a perspective view of block form of a feed system for an antenna beam scanning array incorporating the principles taught by the invention;
FIGURE 8 is a schematic diagram of a portion of the system of FIGURE 7;
FIGURE 9 is a graphical showing of a normal radiation pattern of an array of radiating elements; and
FIGURE 10 is a diagram of an array of phase shifters useful in an antenna beam scanning system similar to that of FIGURE 7 and an exemplary control circuit which may be used to control said phase shifters.
In FIGURES 1A and 1B there is illustrated one embodiment of applicants invention, namely that of a reciprocal ridged waveguide ferrite phase shifter used at the S band of energy propagated in the TE mode. One may demonstrate that a ridged waveguide configuration has a reduced transverse structural dimension over that of waveguides of conventional design and of equal transverse electrical dimension. This is accomplished by forming ridges in the central portions of a conventional rectangular waveguide, which ridges extend along its length. A detailed disclosure of the ridged guide structure may be had by referring to an article by Samuel Hopfer, entitled The Design of Ridged Wave Guide, in the IRE Professional Group on Microwave Theory and Techniques, vol. 3, No. 5, October, 1955. The transverse structural dimension referred to appears in FIGURE 1B as dimension c.
The ridged guide 1, including flange members 2, may be of a silver plated brass material and comprises a ridged center portion and two outside portions running the length of the guide. The cross sectional view taken along line llB-IB in FIGURE 1A is shown in FIGURE 1B. An elongated rectangular slab of ferromagnetic material 3 is mounted in the center of the guide, with the axis thereof parallel to the longitudinal axis of said guide, to provide a phase shift of the propagated microwave energy. The slab abutts the inner walls 4 and 5, and may be cemented thereto. A ferrite material may be employed such as a magnesium ferrite aluminate. Other types of ferromagnetic material may be used such as a ferromagnetic garnet or a sintered nickel-zinc ferrite. A suitable magnesium ferrite aluminate has the following characteristics at room temperature:
Saturation magnetization, 41rm E1000 oersteds;
Tan A, the Rf loss factor, =.0005 at 3000 megacycles;
Line width, which is a measured of the resonance portion of the magnetization curve, 120 oersteds;
Curie temperature E190 C.
Measurements of the tensor permeabilities of ferrite materials is described in an article by R. C. LeCraw and E. G. Spencer, entitled Tensor Permeabilities of Ferrites Below Magnetic Saturation, in the IRE Convention Record, Part 5 for the year 1956.
It is a requirement that the ferrite material be placed within the ridged portion of the guide in order to obtain the maximum phase shift per unit length with a minimum of radio frequency power loss, since the microwave energy is concentrated in this portion of the guide. Further, in order to retain the reciprocal properties of transmission, the ferrite must be located symmetrically in the guide.
The ferrite slab extents for nearly the length of the waveguide, and has tapered portions at either of its ends so as to form an impedance matching section with the remainder of the hollow waveguide in a manner well understood in the art. This construction reduces reflections which are caused by impedance differences between the hollow guide and the material of the ferrite slab.
The ferrite slab can be matched by alternative means, such as by cutting quarter wave matching steps in the end of the ferrite slab or by adding quarter wave matching sections of a dielectrical material. The phase shifting property of the ferrite material is related to the cross sectional dimension and is proportional to the length of the material, so that in order to provide a useful phase shift it is required that the ferrite material be of sufficiently length and cross section.
The magnetic field is applied to the ferrite material and is produced by a solenoid composed of control windings 6 which extend along the length of and encircle the waveguide for the extent of the ferrite slab 3. The field is thus longitudinally related to the guide 1 and the ferrite therein. A source of control signals, applied to terminals '7 and 8 of the control windings, provides a magnetic field within a range of values so as to operate the ferrite material below magnetic saturation. A magnetic shield 9, composed of a .025 inch high permeability steel, surrounds the ridged guide assembly. The flux generated by the magnetic field structure essentially follows a path through the ferrite, across an air gap to the magnetic shield 9, through the shield, across a second air gap and back to the ferrite. Thus, as the control signals applied to the control windings varies the strength of the magnetic field traversing the ferrite, the permeability of the ferrite is changed. Hence, in accordance with the formula where v is the velocity of travel of the microwave energy through the waveguide; a is the effective permeability of the ferrite loaded guide; and s is the effective dielectric constant of the ferrite loaded guide, the phase of the microwave energy propagated through the waveguide is changed.
For purposes of illustration, the embodiment of FIG- URES 1A and 13 may have the following dimensions and data, which are merely exemplary of an operative structure and are not to be construed as limiting:
Magnetic shield width a: 1.750 inches Magnetic shield height b: 1.75 0 inches Overall guide inside width 0: 1.372 inches Overall guide inside height d:.622 inch Ridge inside width e:.625 inch Ridge inside height f:.l10 inch Ferrite cross section=.110 X .400 sq. inch Ferrite length=13 inches, 3% inch tapered ends Coil data: single layer, No. 15 wire, 208 turns There is shown in FIGURE 2, certain electrical characteristics of a ridged guide phase shifter, comparable to the one illustrated in FIGURE 1A, being energized at a frequency of 3200 megacycles. Plots of phase advance and radio frequency power loss versus applied magnetic field are given. It is seen that a phase advance of 360 and a power loss of approximately 1 db were obtained at an applied field of 4-0 oersteds.
It is noted that alternative arrangements may be devised without exceeding the scope of the invention. The magnetic field structure may alternatively comprise control windings mounted on a ferromagnetic core in the shape of an elongated U, which extends along the length of the waveguide adjacent to the ferrite slab. The legs of the U core structure contact the ridged portion of the waveguide at the extreme ends of the ferrite slab. This form of magnetic field structure can eliminate the requirement of a magnetic shield since a closed loop is formed for the flux through the core structure and the ferrite material, and this field structure may be more applicable when there are severe space limitations existmg.
In the field structure of the configuration of FIGURE 1A, the response time of the phase shifter is limited by the eddy currents flowing in the walls of the guide. The eddy currents are caused by the magnetic field and are in a direction opposite to the curent in the control windings. A slow response time, which is undesirable when operating the phase shifter by a switching action, may be appreciably improved by minimizing the eddy current flow. This can be done by cutting a narrow longitudinal slot in the center of the lidged portion extending throughout the length of the guide, which interrupts the eddy current flow. Cutting a slot in the center does not appreciably disturb the microwave current flow on the inside surfaces of the guide. Another solution is to use a plastic waveguide, the inside surface of which is coated with a thin layer of silver. This allows the structure to act as a waveguide while presenting a high impedance to the flow of eddy currents.
Some advantages accruing to applicants ridged guide construction are that the transverse dimensions of the guide are reduced substantially while maintaining an adequate phase shift of the microwave energy. The overall dimension of the construction, including the magnetic shield is 1.75 inches as compared to the half wavelength dimension at the S band of 1.97 inches. Further, the radio frequency power losses are linear and are low in value. In addition, low control power is required since operation of the ferrite is below saturation.
FIGURES 3A and 3B show a further embodiment of applicants reciprocal phase shifter, which is of the dielectric loaded type used at the S band of energy propagated in the TE mode. The rectangular waveguide 16 has its cross sectional dimensions reduced by being loaded with a dielectric material 23, in this instance Teflon. Other dielectric materials, such as polystyrene, may be employed. The effect of the dielectric material is to reduce the wavelength of the microwave energy in accordance with the formula )m e where is the wavelength of the microwave energy in the dielectric, h is the wavelength of the microwave energy in air, and e is the dielectric constant of the dielectric material, having a value greater than unity. The dielectric material completely fills the guide except for that portion in which is fitted the ferrite slab.
The waveguide 16, comprising flange members 17, is illustratively of silver plated brass, and is shown to be slightly longer than the 13 inch slab of ferrite material 18 contained therein. The inside cross sectional dimensions, indicated in FIGURE 38, are a:1.872 inches and b":.872 inch. The elongated ferrite slab, a magnesium ferrite aluminate, is mounted in the center of the guide within the dielectric material with its longitudinal axis parallel to the longitudinal axis of the guide. Optimum phase shift is obtained by extending the ferrite the full height of the guide. A suitable width has been found to be .800 inch. The ferrite is symmetrically located in the guide to retain the reciprocal properties of transmission. A longitudinal magnetic field, as in FIGURE 1A, may be produced by a solenoid composed of control windings 19 encircling the waveguide for the extent of the ferrite slab, or by control windings mounted on a ferromagnetic core which extends along the length of the waveguide adjacent to the ferrite slab. The ferrite char acteristics and coil data are the same as in the ridged guide configuration. The ferrite slab 24 is impedance matched to the hollow portion of the waveguide by its ends being tapered. A magnetic shield 20, 2.250 inches square, encompasses the waveguide assembly.
The control windings are energized by a source of control signals applied to terminals 21 and 22 which effects a varying magnetic field through the ferrite. As in the previous embodiment, the variable magnetic field maintains the operation of the ferrite in the region below saturation and produces a considerable phase shift for a low radio frequency power loss of the transmitted waves. In FIGURE 4- is shown certain electrical characteristics of a Teflon loaded guide operated at 2900 megacycles. A plot of phase delay and radio frequency power loss versus the applied field is presented wherein it is seen that a phase delay in excess of 360 is obtained for an applied field of 32 oersteds. For the same field the radio frequency loss variation is maintained within 1.3 db.
As suggested with the ridged guide embodiment, the eddy currents may be reduced and the response time of the phase shifter improved by cutting a slot in the center of the guide or by utilizing a silver coated plastic guide.
An advantage of the dielectric loaded guide is that a greater phase shift for a given magnetizing field is obtained than in the ridged guide construction. Further, being of a simple rectangular construction, it is readily fabricated and utilized.
Referring to FIGURES 5A, 5B and 5C, there is shown a further embodiment of applicants invention of an enclosed stripline phase shifter used at the S band. The stripline is a TEM mode transmission device and hence its transverse structural dimensions may readily be made less than one half a wavelength of the transmitted microwave energy.
In the illustrative embodiment shown, the stripline 31. is a reciprocal device composed of top and bottom ground plates 32 and $3 of a silver plate-d brass material. The center conductor 34 is mounted between the ground plates by two elongated symmetrically placed rectangular slabs of ferrite 35 and 36. The stripline is enclosed by two side silver plated brass plates 37 and 38 to prevent leakage radiation which would otherwise exist due to the introduction of the ferrite. The top ground plate 32 has cemented upon its inner surface a .0005 inch Mylar film insulation 39 to interrupt the flow of eddy currents around the enclosed stripline and hence improve the response time of the device. The ground plates and side plates are fastened together by means of nylon screws 40. The ferrite material, which may be of a magnesium ferrite aluminate, is shown tapered at either end to provide an impedance match. The length of the stripline is slightly in excess of the length of the ferrite material. A longitudinal magnetic field is provided by a solenoid composed of control windings 41 which are mounted on coil form 42 encircle the stripline along its length for the extent of the ferrite, as in FIGURES 1A and 3A. A ferromagnetic core structure can alternatively be utilized as described previously. A source of control signals is applied to terminals 43 and 44 of the control windings, maintaining the operation of the ferrite in the region below saturation, and providing the desired phase shift of electromagnetic energy traveling along the center conductor. Surrounding the stripline assembly is a magnetic shield 45. The stripline assembly is shown connected at either of its ends to a type N coax fitting, but may also be readily coupled to a conventional two plate stripline.
For purposes of illustration the embodiment of FIGURES 5A, 5B and 5C may have the following dimensions and data, which are merely exemplary of an opera- .tive structure and are not to be construed as limiting: Magnetic shield Width a=1.750 inches Magnetic shield height b=1.750 inches Enclosed stripline width c=1.000 inches Enclosed stripline height d=.500 inch Ground plate cross section, each=.125 x 1.000 sq. inches Side plates cross section, each=.250 .250 sq. inches Ferrite slab cross section, each=.250 .1l5 sq. inches Ferrite length, each=19 /2 inches, 3% inch tapered ends Center conductor cross section=.280 .020 sq. inches Coil data: single layer, No. 15 wire, 320 turns In FIGURE 6 is shown a plot of the phase advance and the radio frequency power losses versus the applied magnetic field for an enclosed stripline ferrite phase shifter of the type illustrated in FIGURE 5A, operated at 3200 megacycles. FIGURE 6 indicates that a phase shift in excess of 360 is obtained with an applied field of oersteds, and for the same applied field there is a power loss of approximately 1.5 db.
It is noted that in the operation of the device, the inside transverse electrical dimension between the side plates should be of a value less than one half the wavelength of the highest frequency energy to be applied to the device. If the inside dimension should be equal to or greater than this value, waveguide modes will be set up within the enclosed stripline which will interact with the energy propagated along the center conductor and result in undue losses.
This type of construction has the advantage of providing a large phase shift while maintaining the dimensions of the structure considerably less than one half wavelength of the microwave energy. As previously mentioned, in the enclosed stripline there is no half Wavelength limitation as with the waveguide configurations. In addition, the radio frequency power loss curve has a desirable substantially linear characteristic, as indicated in FIGURE 6.
In FIGURE 7 is shown a schematic diagram of a beam scanning microwave antenna equipment including an array of radiating elements having energy coupled thereto by a two dimensional array of ferrite phase shifter elements 51, in which one of the phase shifter configurations previously described is employed as the individual phase shifter element. We Will consider employment of the ridged Waveguide. The antenna equipment under consideration makes possible an electrical scan through a solid angle in excess of 90. The antenna structure is positioned at an angle of 45 to the horizontal so that the beam is actually directed 45 in the vertical direction to either side of the broadside position. An antenna system for scanning 360 in azimuth and 90 in elevation conventionally utilizes four such equipments positioned in 90 relationship to one another, each equipment comprising in excess of 1000 radiating elements in a rectangular or square configuration comprising m number of rows and 11 number of columns. For purposes of illustration we will consider a single equipment having an array of only sixty-four radiating elements, forming eight parallel rows and eight parallel columns. The principles of operation described herein apply equally to equipment of the larger number of radiating elements.
An S band microwave energy generator 52, which may for example be in the form of a klystron or a magnetron, is connected to several stages of power dividers 53. The power dividers successively divide the initial energy into sixty-four parallel paths which are connected to the inputs of the ferrite phase shifters 51, which in turn are connected to the radiating elements 50. When utilizing the ridge-d guide or the dielectric loaded guide phase shifters, as well as the enclosed stripline, the power dividers and feed lines to the phase shifters are conveniently in the form of striplines, to accommodate the reduced structural dimensions of the waveguides, although reduced dimensioned waveguide feed structures may alternatively be utilized.
FIGURE 8 shows the feed structure required for a single row or column of eight phase shifters. For sixtyfour phase shifters there are actually eight such structures as in FIGURE 8, requiring a total of sixty-three power dividers. Lines 56 to 72 are striplines and 89 to 95 conventional stripline power dividers, such as are described in an article by W. E. Fromm, entitled Characteristics and Some Applications of Stripline Components, pages 13-20, in the IRE Transactions on Microwave Theory and Techniques, March, 1955. Striplines to 72 are coupled to ridged Waveguides 73 to by transitional elements 81 to S8. The latter may be analogous to those described in an article by Norman R. Wil entitled Photoetched Microwave Transmission Lines, pages 21-30, in the IRE Transactions on Microwave Theory and Techniques, March, 1955. The phase shifters are connected to the radiating elements, shown as a horn construction in FIGURE 8, but which, using well known coupling techniques, may be in the form of dipoles, dielectric rods, narrow slots or other suitable radiating structures. The phase shifters and the radiating elements of the complete antenna equipment .are mounted contiguously on centers spaced apart in two dimensions approximately one half the free space Wavelength of the transmitted energy. This need not be an exact one half wavelength spacing as will be presently understood.
Electrical scanning may be accomplished in azimuth, elevation, or both, over a Wide angle, or the radiated beam may be merely directed to various fixed positions. The direction of the beam is determined by the respective phase conditions of the energy radiated from each radiating element. For a given set of phase conditions the energy in a single direction will add in phase, while the energy in other directions, being of different phases, will cancel. Scanning is performed by varying the respective phase conditions of the radiated energy so that the energy in succeeding different directions add in phase.
The respective phase conditions are derived in the following manner. For purposes of explanation the radiating elements and their respective phase shifters, whose centers are spaced at half wavelength intervals, are identified by location in 11 number of columns and in number of rows, referenced from a first reference plane AA in parallel with said columns and a second reference plane BB in parallel with said rows, as indicated in FIG- URE 7. Considering horizontal scanning, the magnitude of the instantaneous phase of the energy radiated from each radiating element is expressed in radians as:
(N. (Sin 9H) H= 'T' '27T where )t free space wavelength of the radiated energy expressed in inches N zthe number of quarter wavelength from the reference plane A-A to the centers of the radiating elements in column n fi zthe horizontal angle of the radiation measured from the broadside position Similarly for vertical scanning, the magnitude of the instaneous phase 6 of the energy from each radiating element may be expressed in radians as:
where N =the number of quarter wavelengths from the reference plane BB to the centers of the radiating elements in row in B ZthC vertical angle of the radiation measured from the broadside position These expressions may be simplified as =21rS sin 6H and =21rS sin 0 where S is the perpendicular distance from the reference plane AA to the radiating elements in column n, in terms of wavelengths, and S is the perpendicular distance from the reference plane BB to the elements in row in, in terms of wavelengths. It is noted that all elements, displaced the same distance from the reference plane A-A, will have the identical magnitude of horizontal phase, but those on one side of the reference plane will be of opposite sign to those on the other side of the reference plane. Similarly, all elements displaced the same distance from the reference plane BB will have the identical magnitude of vertical phase, but of opposite sign on either side of the reference plane. The total instantaneous phase, of the energy of each of the radiating elements is equal to the summation of the horizontal and vertical phases,
Thus, with the proper phase conditions applied to the radiated energy, the desired beam direction is obtained, and with a minimum of interfering secondary radiation, providing the radiating elements are of the proper spacmg.
In an antenna of this type, because of the tendency for secondary lobe formations, the spacing between radiating elements is critical. Referring to FIGURE 9, which is a graphical representation of a radiation pattern of an antenna array from the broadside position showing the primary and secondary lobes, the maximum allowable spacing of the radiating elements forming the indicated lobes may be given by the expression:
The maximum angle of scan possible in either direction is 0 =90. The minimum secondary lobe is formed when 0 :90". For this limiting condition A max By examining the radiation pattern formed by a single radiating element, it may be seen that the intensity of the radiation beyond an angle of 45 from the broadside falls off quite rapidly. Hence, although a maximum scanning angle approaching 90 is possible by employing applicants phase shifter structure, in actual practice a wide angle scane of 50 to either side of broadside is suflicient, resulting in a total angle of scan of 100". With four scanning antennas of such maximum scanning angle a full 360 azimuth scan is accomplished, with slight overlap. For a maximum scan angle of 50, the angle of the secondary lobe, 0 can be reduced to approximately 80 before the secondary lobe becomes large enough to be troublesome. For this condition Thus, the spacing of the radiating elements can be slightly in excess of one half the free space wavelength. For scanning in two directions, the horizontal and vertical, this critical spacing is correspondingly effective in two directions. Since each radiating element is directly coupled to the ferrite phase shifter, the spacing between phase shifters cannot exceed .57A in two directions. To accomplish this spacing of the phase shifters, considering the thickness of the waveguide structure itself, the coil assembly and the flare of the horn radiators, when used, it is required that the inside dimensions of the waveguide be cosiderably less than the conventional one half wavelength. With respect to the phase shifter configurations of the early figures, transverse structural dimensions of between 254k and .4757\ have been accomplished. Thus, such reduced dimensioned phase shifter structure makes possible a wide angle electrical scanning in two dimensions Without interfering secondary lobes, not previously achieved in prior art systems. It is noted that the height dimensions are less than the transverse dimensions and pose no space problem.
In FIGURE is shown an illustrative embodiment of the ferrite phase shifters, such as may be employed in the antenna equipment of FIGURE 7, together with an exemplary control system designed to control the individual phases of each of the ferrite phase shifters. The control system may include various types of conventional equipment and the details thereof are not intended to form a part of this invention. One such type is shown in FIG- URE 10, comprising an azimuth and an elevation control circuit, and 101. The function of the azimuth control circuit 100 is to provide magnetizing currents to the contol windings of a two dimensional array of phase shifters 102 to shift the phase of the energy therein in accordance with the expression =21rS sin 6 as given previously with relation to FIGURE 7. Similarly, the function of the elevation control circuit 101 is to provide magnetizing currents to the array of phase shifters 103 to shift the phase of the energy therein in accordance with the expression v=21rS sin 6 These functions likewise may be performed in a non-mechanical manner, as by an electronic computer, the inputs of which would contain information concerning the phase shift characteristics of each of the ferrite phase shifters plus the desired angle of beam direction, and the output would provide the individual currents necessary to provide the proper phase relationships in each of the ferrite phase shifters to attain the desired angle of beam direction.
The array of phase shifters 102 and 103 are normally directly connected but are shown in spaced relation for purposes of illustration. Array 102, connected to the radiating structure 104, provides horizontal movement of the radiated beam for an angle of 50 to either side of the broadside position. Array 103 provides vertical movement of the radiated energy for an angle of 50 to either side of the broadside, which exceeds the required 90 in elevation from the horizontal.
Considering array 102, control currents are supplied to the control windings of the individual phase shifter thereof by circular potentiometers 105 to 108 and 109 to 112 of the azimuth control circuit 100, energized by a voltage source +V. The potentiometers 105 to 112 having associated therewith, respectively, gear wheels 113 to and movable contact arms 121 to 128 which rotate with the wheels. The resistance of each potentiometer is nonlinear and conforms to the phase shift characteristics curve of the phase shifter employed through an angle of 360, so that the angle of rotation of the movable contact on the potentiometer provides the current producing a corresponding angle of phase shift. A tapped position on potentiometer 105 is connected by lead 129 to the control windings of each of the phase shifters in left-hand column 1L of array 102. correspondingly a tapped position on potentiometers 106 to 108 are connected through leads 130 to 132 to the phase shifters of columns 2L, 3L and 4L respectively. The tapped positions on potenti ometers 109 to 112 are similarly connected through leads 133 to 136 to the phase shifters in right-hand columns 1R to 4R respectively. A return path, not shown, is provided for the control windings of each of the phase shifters. The gear wheels 113 to 116, the diameters of which are in the ratio of 1:3 :5 :7 respectively, and similarly proportioned gear wheels 117 to 120 engage rack 137 at their perimeter and are driven in rotation by the axial movement of the rack. Rack 137 is driven by cam 138 by means of the roller 139 which rides on the surfaces of the cam. The cam is of symmetrical proportions, each side being shaped as a function of a sine curve so that for a given angle of rotation of said cam, corresponding to the horizontal angle of beam rotation, the rack is driven downward a distance corresponding to the sine of said given angle. Since the non-linear resistances of the po tentiometers conform to the phase shift characteristics of the phase shifters, current will be supplied to each phase shifter so as to effect the proper phase conditions. The cam is rotated in discrete steps by the drive motor 140 which in addition actuates pulsing circuit 141 to supply a clearing pulse to the control windings of each of the phase shifters during the interval of each stepping action. The pulsing circuit may take the form of a conventional uni-stable triggered multivibrator circuit. The clearing pulse consists of a highly positive pulse followed by a highly negative pulse of a given magnitude which drive the ferrite material beyond the operating range in both the positive and negative directions and return its magnetic properties to a fixed reference level before each control signal is applied, thereby consistently operating the ferrite on the same hysteresis curve. A switching circuit actuated by the cam and including contacts 142 and 143 supply the proper energizing potential to the potentiometers.
The elevation control circuit 101 associated with array 103 is identical to the one previously described and is shown merely in block form. The tapped positions of the otentiometers thereof are connected to the phase shifters of lower rows 1D to 4D of array 103 by leads 14S to 152 and to the phase shifters of upper rows 1U to 4U by leads 153 to 156.
As an example of the operation of the control circuits, we will assume the beam is to be directed at an angle 30 in azimuth and 90 in elevation. We will further assume employment of the ridged waveguide phase shifter which provides a phase advance, and the spacing between individual phase shifters to be exactly one half the free space wavelength of the transmitted energy. Considering the azimuth control circuit 101 cam 138 is rotated 30 counterclockwise. The cam engages contact 143 and a positive voltage is coupled from the top conducting surface 144 of the cam through conductor 145 to the left-hand terminal of each of the potentiometers 105 to 112. Simultaneously with the closing of this circuit, wheel contacts the lower left conducting surface 146 of the cam and a ground potential is coupled through conductors 147 and 14-8 to the right-hand terminal of each of the potentiometers 105 to 112. As the cam moves counterclockwise, the rack is moved axially in the downward direction rotating each of the gear wheels 113 to 120 in the direction shown by the arrows. Thus, the contact arms 121 to 124 of potentiometers 105 to 108 will move from ground towards the voltage +V, providing a phase shift increasing from and the fixed contact arms 125 to 128 of potentiometers 109 to 112 will move from +V towards ground, providing a phase shift decreasing from 360. Gear wheel 113 will rotate clockwise through an angle a, where x being expressed in degrees, to provide a control current from the potentiometer through conductor 129 shifting the phase in each of the ferrite phase shifters of column 1L through a corresponding angle of 45. Gear wheel 114 will rotate through an angle of 3a to provide a control current from its potentiometer to the phase shifters of column 2L to rotate the phases therein 135. Gear wheels 115 and 115 will rotate respectively through angles of a and 70c and provide control currents to the phase shifters of columns 3L and 4L to rotate the phase shifters therein 225 and 315 respectively. Correspondingly gear wheels 117 to 120 will rotate through respective angles so as to provide control currents to the phase shifters of columns 1R to 4R so as to shift the phase through angles of 315, 225, and 135, and 45 respectively. Thus, a phase relationship is set up in each of the columns such as to direct the beam 30 in azimuth.
The control circuit 101 for the elevation phase shifting array will operate similarly. The cam therein is rotated 45 in the counterclockwise direction. This will supply control currents to rows 1D to 4D rotating the phase of the energy therein 6, 3,8, 5B and '75 respectively, wherein b 0 6-41) sln 45 Control currents are supplied to rows 1U to 4U such as to shift the phase of the energy in these rows by the same amount, respectively, but in the opposite direction. Thus, a phase condition is effected in the eight rows such as to direct the beam in elevation.
It should be understood that when scanning to the other side of the reference lines, eg at an azimuth of 270 and an elevation of 0, the cams are rotated in the clockwise direction and by means of the switching circuit cause the voltages to the potentiometer terminals to be the reverse of what they were in the first example. In addition, when the dielectric loaded guide is employed, providing a phase delay, the cams are rotated in the opposite direction than when using a phase shifter which advances the phase.
A single array of phase shifters may be employed to perform the same function as performed by the two arrays in FIGURE 10, wherein each ferrite phase shifter applies a phase shift to the transmitted energy equal to the sum of the horizontal and vertical phase shifts. A mechanical computer, similar to the ones shown in FIG- URE 10, may be employed which provides a control current capable of providing the required summated phase shift to each individual phase shifter. Or in lieu thereof, and electrical computer can be employed which supplies the proper values of control currents to each of the phase shifters to yield the desired beam direction.
Although particular embodiments have been shown, the present invention is not to be construed as limited thereto. For example although the ferrite materials are shown as rectangular slabs, they, in some instances, may assume other suitable shapes, such as cylindrical. The appended claims are intended to include all modifications and variations that fall within the true scope of the invention.
What I claim as new and desire to secure by Letters Patent of the United States is:
1. A microwave waveguide for propagating energy of predetermined frequency axially therethrough, comprising a ridged waveguide structure defined by surfaces which maintain a constant polarization and whose transverse electrical dimensions are at least one half the free space wavelength of said propagated energy and Whose structural transverse dimensions are less than said one half wavelength throughout its length, an elongated slab of ferrite material symmetrically mounted within and substantially filling the ridged portion of said waveguide having its longitudinal axis in parallel with the longitudinal axis of said waveguide for reciprocally shifting the phase of said energy, and a controllable magnetic field applied along the axis of said ferrite material for controlling the extent of said phase shift.
2. A reciprocal microwave transmission system for propagating energy of predetermined frequency axially therethrough, comprising a two dimensional array of parallel waveguide structures arranged in rows and columns and mounted on centers spaced apart in both said dimensions approximately one half the free space Wavelength of said propagated energy, said waveguide structures each being defined by planar surfaces which maintain a constant polarization and having transverse electrical dimensions at least as great as said one half wavelength and having transverse structural dimensions less than said one half wavelength throughout the length thereof, each of said waveguide structures being in the form of a ridged waveguide, an elongated slab of ferrite material symmetrically mounted within the ridged portion of each waveguide structure and extending throughout the height of said ridged portion, said slab having its longitudinal axis in parallel with the longitudinal axis of said waveguide for providing a reciprocal phase shift to said energy, and means for applying a controllable magnetic field along the longitudinal axis of the ferrite members of selected waveguide structures for controlling the degree of said phase shift.
3. A reciprocal microwave transmission system for propagating energy of predetermined frequency axially therethrough, comprising a two dimensional array of parallel waveguides arranged in rows and columns and mounted on centers spaced apart in both said dimensions approximately one half the free space wavelength of said propagated energy, said waveguides each being defined by planar surfaces which maintain a constant polarization and having a ridged construction throughout their lengths for maintaining the transverse structural dimensions less than said one half wavelength, ferrite material of an elongated shape symmetrically mounted within the ridged portion of each waveguide and extending throughout the height of said ridged portion for providing a reciprocal phase shift to said energy, means for applying a controllable magnetic field to the ferrite material in each of said waveguides lying in a range of values to operate the ferrite material in the region below magnetic saturation, for controlling the degree of said phase shift in accordance with the expression:
where 5 is equal to the phase shift in radians of the propagated energy in the waveguide located in the row m, column 11 S =the perpendicular distance in wavelengths from the centers of the waveguides in row m to a first reference plane in parallel with said rows S =the perpendicular distance in wavelengths from the centers of the waveguides in column n to a second reference plane in parallel with said columns 14 =a first predetermined angle measured from said first reference plane 0 =a second predetermined angle measured from said second reference plane.
References Cited by the Examiner UNITED STATES PATENTS 2,602,856 7/52 Rumsey 333-84 10 2,692,336 10/54 Kock 343-778 2,832,938 4/58 Rado 333-24 2,850,705 9/58 Chait 333-24 X 2,960,974 9/59 Reggia 343-787 X 2,929,058 3/60 Blasberg et a1. 343-777 3,008,142 11/61 Salzman 343-787 X 3,041,605 6/62 Goodwin et a1. 343-854 X OTHER REFERENCES Pub. I: Proc. IRE Nov. 1957, pp. 1510-1517. Pub. II: Radio Electronics Engineering, Apr. 1925 p.
Pub. III: Journal of Applied Physics, Feb. 1957. p. 222.
Proceedings of the IRE, vol. 44, No. 10, Oct. 1956 page 1416.
HERMAN KARL SAALBACH, Primary Examiner.
GEORGE N. WESTBY, ELI LIEBERMAN, Examiners.