US 2283897 A
Description (OCR text may contain errors)
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l' IIIIlIlIIIIIlIlI/IIIIIIIII H. FS AFPA/mms [605 .1604 ATTORNEY May 26, 1942. A. ALFoRD ANTENNA SYSTEM Filed April 2e, 1959 6 Sheets-Sheet 5 FIGS.
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ATTORNEY May 26, 1942. A. ALFORD ANTENNA SYSTEM Filed April 26, 1939 6 Sheets-Sheet 6 710 sauna;
Patented May 26, 1942 ANTENNA SYSTEM Andrew' Alford, New York, N. Y., assignor, by mesne assignments, to International Telephone & Radio Manufacturing Corporation, a corporation of Delaware Application April 26, 1939, Serial No. 270,173
(Cl. Z50-33) 9 Claims.
My invention relates to antenna systems particularly for use with plane polarized waves.
' There appears to be considerable evidence favoring the use of directional and guiding systems using horizontally polarized waves for guiding aircraft in the horizontal plane.
A number of different kinds of radiators have been tried experimentally but it has been demonstrated that none of these radiators operates to radiate exclusively horizontally polarized waves` In order that this point may be made more clear, reference is made hereinafter to experiments which have been conducted with course beacon antenna systems. For this experiment the radiator consisted of two horizontal half-Wave dipoles crossed, that is, arranged at right angles to each other.
Since the electric eld around any linear radiator always points toward the radiator, it is clear that at any point lying above the plane of the two crossed half-way radiators used, the electric. fields at a point above the radiator and a, distance away therefrom in a horizontal direction, due to the individual radiators, are not horizontal but are inclined to the horizontal by an amount dependent upon the elevation of the point above the radiator and horizontal distance that it is spaced therefrom. For this reason if a pick-up antenna carried on an airplane be inclined at some angle to the horizontal in a direction transverse to the course of the airplane, the ratio of signals from the two crossed radiators will be changed and the course or apparent plane of equality will shift. These effects of shifting of the course due to imperfections in the horizontal radiation were observed during the experiments above mentioned. This effect is of considerable magnitude when the airplane is located at a large vertical angle with respect to the radiator.
When vertically polarized radiators are used this eiect is not observed because with the vertically polarized radiators the eld is vertical at all points, so that any deformation of the receiving antenna on the airplane will only decrease the magnitude of the received signal but will not decrease the signal from one radiator with respect to the other so as to produce a false or shifted course.
This problem is probably more serious than is at present appreciated because of the possibility that the airplane receiving antenna may be injured during take-oi or by sleet, or may simply be out of proper adjustment and thus produce entirely erroneous indications because of the presence of the vertical as well as the horizontally polarized components of the waves.
There is also another possibility which, so far as I am aware, has not at all been appreciated, namely, that parts of the airplane will pick up the vertically polarized waves and then re-radiate them into the supposedly horizontally polarized receiving antenna. Since each `airplane itself may be different in structure, these errors will be inherent in each type of airplane and will be different for each different airplane. This error will also be different for different ver.. tical angles and therefore is not subject to simple compensation. Since such errors will cause different cofurse indications for different airplanes in the field of the same beacon, it is quiteobvious that the situation would be intolerable because it would necessitate the individual investigations of each airplane.
All of these diierent diillculties, as well as some others not specifically enumerated would be eliminated if the electric field of the beacon or localizer antenna giving the course indication were made horizontal at all points. This may be accomplished by an antenna system constructed in accordance with my invention, for producing only plane polarized waves. Such an antenna system for producing only plane polarized waves is likewise readily applicable for stationary receiving systems and will result in a receiving arrangement superior/to those now in use since it will be more completely selective to reception of plane polarized Waves.
According to my invention I have devised an antenna system which substantially eliminates all of the vertically polarized wave components of a received or transmitted wave. This is accomplished by dimensioning the antenna and so energizing it that the vertically polarized components of a wave will be substantially neutralized in every direction from the antenna.
TheV provision of such a plane polarizing antenna is one of the principal objects of my invention.
A further object of my invention is to provide a radiating or receiving antenna which will have a radiant action substantially only for plane polarized waves forming substantially 9. circular radiation pattern in the plane of polarization.
ItA is a still further object of my invention to provide a'receiving system for plane polarized waves utilizing a receiving antenna subject to reception of only waves polarized in the pla'ne of the antenna.
It is a still further object of my invention to provide a radio beacon huilt up of antenna units radiating only horizontally polarized waves.
Other objects and advantages of my invention will be apparent from the particular description thereof made in connection with the accompanying drawings illustrating a few of the embodiments of my invention in which Fig. 1 illustrates in plan view one form of antenna constituting an embodiment in accordance with the principles of my invention;
Fig. 2 illustrates in plan view one form of constructive arrangement of the antenna of Fig. 1;
Fig. 3 illustrates in plan view a modification of the antenna arrangement of Fig. 1 utilizin only one loop conductor;
Fig. 4 illustrates a modied antenna structure embodying the principles of my invention;
Figs. 5 and 6 show a plan view and elevational view, respectively, of a practical constructive embodiment of the antenna illustrated in Fig. 4;
Fig. 7 illustrates a further practical embodirnen ofthe antenna of Fig. 4 arranged in circular form;
Figs, 8 and 8A illustrate still further embodi ments of my invention utilizing the principles outlined above;
Fig. 9 illustrates a vertical cross-section of the eld pattern radiated or received by the antenna system in accordance with the principles of my invention;
Fig. 10 is a diagrammatic illustration used to explain the cancellation of waves polarized in planes other than that of the antenna;
Fig. 11 illustrates a receiving circuit utilizing an antenna in accordance with my invention designed for the reception of more than the fre-l antennae constructed in accordance with the principles of my invention;
Fig. 15 illustrates a beacon transmitter system in accordance with my invention and using antennae of the type disclosed above and a coupling system permitting the simultaneous production of angularly related radiation patterns;
Fig. 16 illustrates the eld pattern radiation diagram for an antenna beacon such as shown in Fig. 15;
Fig. 17 shows another form of beacon in accordance with my invention;
Fig. 18 shows the ield pattern from the beacon of Fig. 17; and
Figs. 19 and 20 show views of an antenna structure particularly suited for beacon use.
Turning rst to Fig. 1, I have shown an arrangement utilizing an antenna indicated generally at coupled to a high frequency source or load 4l.
In Fig. 1, an embodiment of an antenna in accordance with my invention is disclosed. In this ligure the antenna 40 is shown coupled to a high frequency source or load 4l. The antenna is composed of two conductors comprising sections 42,` 43, 44, 45, 46 and 42', 43', 44', 45 and 46', respectively. The conductors are open circuited and are made electrically a halflwave long so that at the ends of the system will Occur current nodes.
Parts ol each conductor, namely, 42, 46, and 42', 46' are arranged close to each other and at the ends ol conductors 42, 42' is coupled a high frequency translator which may constitute a source of energy or a load. Sections 42, 42' and 46, 46' are preferably chosen of such length that the current maximum occurs at the center of the radiating portion of the conductors, namely, at the mid-point of conductors 44, 44', and the radiating sections comprising portions of the conductors 43, 44, 45 and 43', 44', 45', are made short relative to the operating wavelength so that asubstantially uniform current distribution is obtained. These radiating sections are made preferably of a length in the order of 116 to 1/5 of a wavelength, but should in any case not exceed 1/3 of a wavelength, while the total overall length of each conductor is preferably l a wavelength electrically.
The energy source 4| should beconnected to energize the conductors in phase opposition so that the instantaneous direction of current flow is around the periphery in the same direction in the radiant acting elements, and is opposite in the closely spaced conductors. In case 4l is a receiver the receiver is coupled at the same point as would be required for an energy source, in order to obtain the same operation. Itis well known that in any antenna system a receiver must be coupled at a point such that if it were replaced by a source the desired characteristics would be obtained. For this reason the connection of the translating device is made in terms of the effect of a source at this point because no other simple generic language is available.
In the illustration of Fig. 1, the two radiant acting portions are shown each substantially V3 of a wavelength long. The current distribution will then be substantially as indicated by the shaded portions 42'a-46a and 42'b-46'b. It will be noted that in 44, 44'; 43, 45; and 43', 45';
` the current distribution is equal so that at any point from the midpoints of these lines complete neutralization of vertical polarization may be achieved. The currents in the arms 44, and 43, 43', are not quite equal but are of the same order of magnitude and consequently substantial neutralization will occur at angles to the loop sides. A more complete explanation of this neutralization will be made later in connection with Fig, 10. This arrangement of antenna is particularly advantageous for use on portable receivers, since the antenna itself may be made very small still preserving a fair eciency and a high degree of discrimination against waves not polarized in the plane of the antenna.
In Fig. 2 is illustrated an antenna 50 in accordance with a practical structural arrangement of the antenna shown in Fig. 1. In this arrangement leads 56, 56' arebent downwardly and are enclosed in a grounded shield 51, and the feeders 52, 52', are also enclosed in a grounded shield 58. This construction prevents radiation from these portions of the system so that no vertically polarized waves will result therefrom. Because of the parallel capacity effect of the shield, conductors 56, 56' are considerably shorter in physical length to obtain the devised electrical length, than if no shielding is present.
In Fig. 3 is shown a modification of the arrangement illustrated in Figs. 1 and 2 utilizing a single leg of the loop, the other leg being constituted by the image conductors in the conductive surface. In this arrangement a high frequency source 6I is coupled over a shielded conductor 62 tor the radiating loop 63, the endof the conductor being constituted by shielded open ended conductor 64. The dimensions of the single conductor of this modified loop are preferably made the same as those illustrated in connection with a single conductor of Fig. 1. As a consequence the radiation pattern of the antenna of Fig. 3 is substantially similar to that produced by the structure illustrated in Figs. 1 and 2. Y
In Fig. 4 is illustrated a further embodiment of my invention utilizing four different radiating conductors instead of two as in the other embodiment. 'Ihis structure is especially adapted for use as a radiating antenna, since with the four conductors a larger radiation resistance and a consequent increase in energy radiation may be obtained. It is clear, however, that this antenna may also be utilized for reception, since it also provides an increased amount of pick-up.
In Fig. 4 is provided a high frequency source 10 coupled over conductors 1I, 'I2 to four radiators 13. 14. 15 and 16. High frequency source 10 is preferably connected to the mid-point of conductors 1I, 12 and the electrical length from the point of connection to the radiating conductors 13, 16 and to the ends thereof as shown at 13', 16' is made electrically equal to an integral half-wave length of the operating frequency. Conductors 13, 14, 15 and 16 are arranged in a square and the end of each radiator is bent inwardly as shown at 13', 14', 15', 16', so that only the central portions of the conductors are utilized for radiation. Radiators 13 and 16 are fed directly from high frequency source over conductors 1|, 12, and radiators 14, 15 are fed over conductors 12, 1l to a means for producing a 180 phase shift such as the transposition shown at 11. As a consequence the currents flow through they conductors in the direction indicated by the arrows, the current disposition in each of the four radiators is uniform, as indicated by the solid shaded area 13a to 16a. Each radiating section is preferably made short with respect to the operating wave length so that the current distribution is high throughout the length thereof, and since the current distribution is equal in each of the four arms, and is opposite in phase on the opposite sides thereof, the vertical field component will be substantially eliminated in every direction and for every vertical angle with respect to this radiator. Furthermore, since substantially uniform current distribution is provided in the radiator the resulting radiation pattern will be substantially circular.
An embodiment of the antenna in accordance with the principles set forth in connection with Fig. 4, is illustrated in Figs. 5 and 6. In this arrangement the radiators consist of four members 80|, 802, 803 and 804. These members may be comprised of hollow tubular conductor if desired to decrease the weight. Each of these radiators extends through entrance type insulators 805 into metallic shieldingboxes designated as 806. Tubular metallic shielding members 801 extend downwardly and inwardly to metallic shielding box 808 from the lower end of which extends the shield 809. The energy feeding leads of the antenna 8|0 extend downwardly from diagonal corners of the antenna to the metallic tube 801 into the shielding box 808 where the transposition is made and any necessary impedance matching of the antenna to the feed supply leads 813, is made. The other or reentrant end of the radiators 8H, 812 extend downwardly in the opposite diagonally arranged shielding tube 801 and so are completely shielded. With this arrangement only the parts of the whole radiating structure containing the current loops are exposed to the weather. The insulators 805 at the end of the radiators are near voltage nodes of the system, so that no high voltage strength existed thereacross. The entire supporting frame is arranged beneath the radiating structure and inside the patterns thereof so that no part of the supporting frame is in the eld of the radiators. The radiation resistance of this structure is high in comparison with the resistance of the wires or insulators so that a very high efficiency is obtained.
In an actual demonstration of an arrangement in accordance with this construction, it was found that the radiation pattern was substantially circular in the horizontal plane.
The radiator of the system according to my invention may be of shape other than straight conductors. In Fig. '1 is illustrated an arrangement similar to that shown in Figs. 5 and 6, except that the radiators are each curved so as to form substantially a circular pattern when assembled. Similar reference characters are used in Fig. '1 to designate the various elements corresponding to those shown in Figs. 5 and 6.
The radiating system may be composed of more than four conductors, for example, it may comprise eight units arranged in the form illustrated in Fig. 8. In this figure the high frequency load or source H00 is coupled to a pair of transposed conductors HOI. These conductors are connected to radiators H02, H03, H04 and H05. H08, H09 and H10 are arranged as shown in Fig. 8. In each of these conductors the terminating ends are bent inwardly as shown and arranged close thereto. This arrangement of the terminating ends of these radiators provides a coupling between the directly energized antennae elements H02, H03, H04 and H05, so that each of the other sections H01 to HIO, inclusive, are also energized. Thus is provided a radiating antenna for radiating only horizontally or other plane polarized waves into which a high radiation resistance may be obtained and consequently a greater eiiiciency of operaion.
Instead of using the nturned ends of conductors for coupling together the sections as shown in Fig. 8, condensers may be used as shown at H00', Fig. 8A. In this case it may be more convenient to make the condensers in the form of strain insulators and the radiant acting sections may be bent in their centers for fastening toa. support. p
In Fig. 9 is illustrated a vertical section vto the radiation pattern produced by antennae in'accordance with my invention. The horizontal axis is designated by HH and the Vertical axis by VV. The field is represented by the tangent curves F, F. The field is actually in the form of a lemniscate similar in pattern to that obtained from the radiation of a single dipole, but differs therefrom in that there are no vertically polarized components. The voltage at any point in the field may be expressed by equation ErEo cos 0 where Eo is the voltage in the horizontal frame and 0 indicates the angle of elevation.
The radiation resistance for antennae in accordance with my invention wherein the current Other radiating conductors H01,4
distribution throughout the arms is substantially uniform may be expressed by the equation where R is the radiation resistance, A is the area of the loop in given units and A is the working wavelength in the same type of units as area A. For the square loop arrangement such as shown in Figs. 4, 5 and 6, the radiation resistance i 4 It 820C?) ohms where l is the length of ,one of the radiators in the same units as the wavelength A. A preferred range of radiation resistance is between 7 and 20 ohms.
A more complete explanation of the operation of the antenna in accordance with the principles of my invention may be obtained by reference to Fig. 10, showing a three dimensional view of a quadrant of the radiation eld from a radiator similar to that illustrated in Fig. 4. The arms corresponding to the four radiators of the antenna are designated by letters A, B, C and D, as shown, with arms A and C being opposite each other and arms B and D being arranged opposite these planes being bounded by curves XY, ZY
and ZX, respectively. A third plane is passed through the diagonal of the radiator represented by the lines Z and W, and bounded by the curve w. At any point P on the line w, making a vertical angle with the plane of the radiator, can be assumed to be a receiving point. The dot-dash line starting at X and extending through point P, represents the meridian of polarization of energy from radiators A and C, and the broken line extending from Y through point P, represents the meridian of polarization from radiators B and D. At point P the radiation from radiator C will have a large horizontal component and a small vertical component as shown at c, and at the same time the radiator D will produce a horizontal component in the same direction as that from C and a small equal vertical component oppositely phased to that of point C. It is therefore clear that these two vertical components being equal and opposite will cancel, since P is equi-distant from both radiators B and D. Similarly at point P the vertical components from radiators A and B will cancel as shown at a, b, and the horizontally polarized components will add together in phase although they are of opposite phase from elements C and D. Since radiators A and B are at different distances from point P than radiators C and D, there will be a horizontally polarized component which can be received. The vertically polarized components, however, are completely cancelled as explained.
At points P1 still at the vsame vertical angle it can be seen that the radiation from elements from radiators B and D, will be largely vertical but will be in opposite directions. Since point P1 is equi-distance from radiators B, D, the vertically polarized waves will therefore be cancelled at this point. The horizontally polarized waves at point P1, arriving from radiators A and C, are of opposite phase but since they come from dif- 10" on the minor axis.
ferent distances, a horizontal component will be present for reception.,- Similarly at point Pz the horizontally polarized component from B and D will be received, whereas the vertically polarized component from A and C will be neutralized. If the vertical angle at which P is located is varied. the same effect will occur, since as shown, P represents a point at any vertical angle. Similarly, since the points 'chosen for illustration represent the extremes in so far as the radiator is concerned, it is clear that the vertically polarized components willbe neutralized everywhere about the loop regardless of the horizontal angle.
In planes intermediate the and 45 degree position discussed in detail above, for example, in a plane nearer the X axis, the vertically polarized components from B and D increase but will approach equality in opposite phases. 'I'he vertically polarized components from A and C will also approach equality in opposite phase. As a result the sum of the vertically polarized components at this intermediate point will be such that the components from A plus the components from D is equal in magnitude but opposite in phase to the vertically polarized components from B plus Ithe corresponding component from C. Accordingly, it is seen that the vertically polarized components will neutralize in every direction about the antenna. Careful test measurements of vertical components about` such an antenna verify this conclusion.
This explanation has been made with reference to the four armed loop such as shown in Fig. 4. It is clear that the same principles'apply in varying degrees to the other arrangements such as those shown in Figs. 1, etc.
In the arrangements as shown in Figa 1 the neutralization, however, will not be as complete in all directions because there is not a complete equality of currents in the loop sections. For example, turning to Fig. 1, it is clear that the current in 44', for example, is not exactly equal to the sum of the currents in 45 and 45' and for this reason a complete neutralization of the vertical components will not be present. However, a close approximation of complete compensation may be achieved by use of this loop.
In Fig. 11 is illustrated an installation of a loop according to my invention, for use as a receiver. This loop is designed for receiving two different frequencies and for this reason is somewhat of a. compromise in design. In this installation the two radiators |30| and |302 were arranged to form an oval loop approximately 1'7" long and The two frequencies fi, fz for which the circuit was designed, are 93 and 109 megacycles, respectively. The receivers are represented at |303, |304 in the drawing. A metal plate |305 mounted on an insulating handle |306 is provided for Vernier tuning of the circuit. The radiators are coupled over a special loaded line |301 across two shielded conductors |308, |309. Section |308 is made equal to onehalf of the wavelength k2, for which receiver |304 is designed. Thus the line is rendered tuned to f2 so that any addition at the termination of line |301 will not effect the line substantially for energy of fz. |304 is inductively coupled to line |308 by a tuned coupling so that energy other than that for which it is designed will not be received. Receiver |303 tuned to ,ii is coupled over a shielded pair symmetrically to the antenna over |309 and |301. The metal shields around line sections |308, |309 are conductively joined together. The line 301 is made by means of a special loading approximately a quarter of a wavelength long electrically although the actual length is much shorter. In the installation the actual length of line |301 was approximately 1l". A concentric line |3|0 is used to connect transmission line section |308 to receiver |304, and a shielded pair transmission line |3|| is used to couple section |309 to receiver |303. In the installation actually made the shields about line sections |309, |308 were made of concentric tubular conductors of outer diameter and the concentric transmission sections |3|0, |3|| were made of concentric transmission lines of onequarter inch outer diameter'.
The loaded line I 301 has a relatively high value of surge impedance. This extra high value of surge impedance was found desirable in order to reduce the circulating current in the half-wave length line. 'I'he impedance of the loopitself at the upper terminals may be very high,.for example, say the value is R. Then the impedance at the bottom of the special section line |301 is where Zo is the 4surge impedance of the line. When Zo has a low value, impedance r is very low and consequently there is a large current owing into the half-wave length line. This large current produces losses in the conductor shield. Actual tests have shown that when special loaded line |301 was replaced by an open air line consisting of two copper rods a quarter inch in diameter and spaced three-quarters of an inch apart, the total loss at |09 megacycles was about four decibels. With the loaded line which was made of number I4 tinned wire and loaded with four coils of about twelve turns each, with an outer diameter of about a quarter of an inch, spaced ar half an inch apart the total loss was reduced to one decibel. In order to complete the shielding, screening boxes |3|4, |3|5 may be provided.
A further modication by way of improvement ofthe antenna shown in Fig. 11 is illustrated in Fig. l2. In the loop installation such as shown in Fig. l1, a considerable voltage exists in the loop at the ends of the loop where it is supported by its insulators. The consequent high impedance at the insulators leads to two troubles. (1)
The tuning of the loop is relatively sensitive to additions of capacity, for example, snow may produce a effect, and (2) the high impedance of the insulator requires the use of such a loaded line to reduce loss in the two frequency, tuning circuit illustrated.
Even with the specially loaded line it may still be necessary to use fairly large concentric tubing for the half-wave line section to reduce losses to a reasonable value. The use of a lighter con` centric line. for instance, a quarter-inch line would be preferable because of the ease in bending and lighter weight.
, In order to improve the operational characteristics in so far as this voltage distribution is concerned, the loops may be constructed in accordance with the showing of Fig. 12. In this arrangement each of the arms |40|, |402, are broken up by means of condensers |403. The voltage distribution about the loop becomes about 1n the form represented at V. At the same time the current distribution in these parts of the conductors is approximately as represented at Io in t' e lower half of Fig. 12. Considering the surge impedance of the loop conductors as Zo, and the distance between two consecutive condensers as 20, then V=Zo sin 0 In. Where Io is the new loop current which occurs half-way between the condansers; the general current i=Io cos 0; the capacity C of a condenser is determined from the following formula,
where w=21r X frequency.
For example when m. c. Z0=500 Ohms that is 20 about 6",^then It is seen that the capacity C of condenser |403 is very small. This capacity may be obtained by a very simple fitting such as illustrated in Fig. 13. In this arrangement the conductor forming the radiators I, |502, may be a metal tube, for example, aluminum tubing. Into the ends of these tubes is inserted an insulator |503, which may be a ceramic tube. Through the tube is inserted a metallic rod |504 provided with enlarged ends |500, |506, which will serve as the seats of capacity for the condenser. Tube |504 may also be of aluminum. The two conductors |50|, |502 are then clamped in position on insulator |503, by means of clamping rings |506', |501.
By replacing the loop shown in Fig. 11 by a loop provided with condensers such as shown in Figs. ,"2 and 13, the voltage at the insulators would e reduced to about one-third of the value without the condensers and the impedance would' be reduced to about one-ninth of the value obtained otherwise. It is clear that with this type of loop, the circuit will be much less sensitive to capacity changes such as caused by snow or ice, and furthermore the loss in tuning the circuit will be considerably reduced.
Because of the substantially complete absence of vertically polarized components the antennae in accordance with my invention are particularly suitable for use as horizontally polarized guiding beacons or runway localizer beacons, since they will not produce faulty shifting of courses due to variations in polarization at vertical angles. One form of radio beacon arrangement utilizing antennae in accordance with my invention is illustrated in connection with Figs. 14 to 16.
In Fig. 14 two antennae |60| and |602 are shown, preferably mounted a ,half a wavelength of the operating frequency apart. These antennae are preferably of the type illustrated in Figs. 5 and 6, but may be of any of the other types illustrated in the application. Antennae and |602 are connnected together over a transmission line |603. Coupled to the transmission line |603 is high frequency apparatus |604 connected by means of line section |605 midway between antennae |60| and |602. A 180 phase shift is provided, for example by a transposition provided in line |603 at |606. Thus antennae |60I, |602 are located a half-Wavelength apart and are energized in phase opposition. This energization of the loops in phase opposition producesY a. radiation pattern having a null point midway between the two antennae, as shown in Fig. 16 at F1. If a transposition |600 is omitted. then antennae |60|, |602 will be energized in phase. rI'his will produce a radiation pattern having a null in the direction of the extension of the antennae, as illustrated at F2, in Fig. 16. These variations in radiation pattern may be produced by any suitable keying means for alternately transposing the line.
In Fig. is illustrated an arrangement for producing a guiding course by simultaneous energization of two antennae spaced a half wavelength apart. The antennae |10|, |102 are connected over transmission lines |103, |104', to opposite corners of a balanced network indicated generally at |104. This network is preferably made of open lines and is provided with two sets of arms |105, |100, a transposition is arranged in arms |105. Because of this transposition energy introduced or withdrawn at any corner of the network will have no eiect on the apparatus connected diagonally opposite therefrom as long as the impedances are balanced, although it may eifect any apparatus connected to the other corners. A transmitter which may be a common high frequency source |1|0 is provided, from which is derived two separate signalling energies which may be differently modulated with frequencies F1, F2. The energy thus modulated is transmitted from the separatetransmitter output |1||, |1|2. Energy from |1|| modulated at F1 is applied to one corner of the bridge |104, so that radiators |10I, |102, are energized over the transposed section and thus radiate the pattern F1 of Fig.` 16. `Simultaneously the energy from |1|2 is applied to the diagonally opposite corner of the network |104 so as to feed antennae |10| |102 in phase. Thus there results a pattern such as shown at F2 of Fig. 16.
The four arms of bridge |104 are preferably in length equal so that at point b looking in from a, the eiect is the same as though a short circuit existed at this point. However, arms |105, |108, and |106, |101 may not present an impedance match with respect to energy entering from point a, and reections from b, will result. Similarly energy from point b will be reflected at a. By properly dimensionng the arms the lengths may be 'so chosen that the reected energy will just compensate for the mismatch and the circuit will operate so as to prevent reflections on the u feeding lines. I have discovered that in order to provide for this effect the individual arms of the bridge network should be substantially .l5 of a wavelength long at the operating frequecy.
As shown in Fig. 16 the radiation patterns are not circular but are deformed so that pattern F1 is somewhat attened and F2 is elongated. The courses are consequently at an angle less than 90 as in the case of circular radiation patterns. The courses actually extend at about 60" with respect to one another. There is provided a beacon arrangement for forming four separate guiding lines towards the beacon. Since the antennae units also are provided to cause substantial neutralization of the vertical i'leld component,
. the beacon signals will be derived solely from horizontally polarized waves. Thus any receiver coupled to this system will operate to give the proper course, regardless of any variation in the polarization of the receiving antennae.
In Fig. 17 is illustrated another form of beacon particularly useful for the utilizing antennae in accordance with the principles outlined above. In this figure high frequency source |1|0 is coupled to two modulators |1|| and |1|2 and to a bridge network |104, similarly to the arrangement illustrated in Fig. 15. The arms of the bridge network are preferably made .15 of a wavelength long as explained in connection with Fig. 15. However, instead of only two antennae, four antenna units |12| and |124 are provided. Units |12| and |124 are connected together by a transmission line in which is provided the phase reversal means, such as the transposition |120, so that they are energized in phase opposition. Line |125 is connected to one corner oi bridge |104 by line |121, at a point electrically midway between 12| and |124. Two other antennae |122, |123 are connected together by a transmission line |120 which is connected `by means of aline |129 to the corner of bridge |104 diagonally opposite the point of connection of |121. Line |129 is made 90 shorter electrically than |121 so that these units are energized in llniase quadrature with respect to units |12| and The energy supplied from modulator |1| modulated at frequency f1 then energizes antennae |12|, |124 at 180 phase difference, as indicated in the drawings, and simultaneously energizes antennae |122, |123, in phase with energy at +90 phase displacement with respect to energy supplied to the other two antennae. Similarly, energy from |1 2 modulated at f2 energizes antennae |12|, |124 at 180 phase difference but also at 180 out of phase with energy from |1||. The antennae |12|, |124 are displaced a distance a from the center line of the array and antennae |122, |123 are spaced apart a distance 1S. The radiation pattern from these arrays will then be formed somewhat as shown in Fig. 18. In this figure the broken line curve F'1 represents the transmission pattern from modulator and the solid line curve F'z represents the energy transmitted from |1|2. The modulator |1|| may be provided to furnish a modulation frequency, for example, 170 cycles, and modulator |1|2 a modulation of different frequency, for example, 90 cycles, so that the signal equality course may be readily determined on a craft. Both patterns F1, Fz have some minor lobes of radiation but these are of such small amplitude as to be neglected with respect to the main guiding part.
The spacing between the antennae may be varied to change the shape of the radiation pattern. However, a preferred form using a spacing in which a equals 170 electrical degrees, and is made equal to electrical degrees, produces a very sharp pattern free from bothersome minor lobes of radiation.
For use as radio beacons, the structure shown in Figs. 5 and 6, presents some diculties since the shielding arrangements such as 801, are at an angle to the vertical and are also disposed in the radiation eld of the other antenna unit. For this reason these angularly disposed sections will pick-up and reradiate some energy and for this reason interfere with the pure horizontal polarization. In order to overcome this diiliculty the antenna may be constructed in the manner shown in Figs. 19 and 20 so that substantially no vertically polarized radiation will be produced.
In Fig. 19 a front view of this antenna is shown with the cover of central boxes removed so as to show the construction. According to this arrangement, two hollow metal boxes |90|, |902 are provided. To the other side of each of these boxes is fastened a concentric cable arrangement |903, |904, the center conductor of which may be used to feed the antennae. In the sides of boxes |901,
|902, at the point where they are adjacent each other, a hole is provided so that a transposition of the feeding conductors may be achieved. These conductors |905, |906 are led through suitable shields to the radiant acting conductors |9|| to IBM, inclusive. Conductors |9|| to |0|4 are preferably made heavy and may be as shown, made of strips of metal, such as copper. By making these elements of large dimension, the resistance thereof is greatly decreased. This is of importance since by decreasing the surge impedance of the radiators themselves, considerable reduction of the voltage across the insulators connecting conductors |906, |905, may be achieved. The inturned end of conductors |9|| to ISM, are supported by means of a plate |9|1 and may be covered by suitable weatherproof covering |9|8. By this arrangement all of the angularly related conductor portions are obviated, and consequently harmful vertically polarized radiations are averted.
It should be noted that the beacon arrangements disclosed herein are well suited for producing radiation beacon patterns. It is further noted that the spacing between the antennae units is such that radiators of a half wavelength could not be used. Therefore, the particular antennae units in accordance with my invention are admirably suited for this purpose. It should be understood, however, that the particular balancing arrangement and the beacon system may be utilized also, with other forms of antennae, than those producing horizontal polarization.
While I haveillustrated a few preferred embodiments of my invention, it should be distinctly understood that this description is made merely by Way of illustration and is not intended as a limitation on the scope of my invention. What I intend to cover as my invention is dened in the accompanying claims.
What I claim is:
1. A radio antenna system comprising a peripherally arranged planar radiant acting linear conductor means of small dimensions relative to the operating wavelength arranged along a planar periphery, a transmission line section directly connected to and forming a continuation of said radiant acting conductor means said section being dimensioned to tune said system to the operating frequency to produce substantially uniform current distribution in said radiant acting conductor means, energy transfer means coupled to said transmission line section in energy transfer relation at a point such that if energy were supplied thereat current would circulate about said periphery in the same sense at all points, whereby radiant action of said system is substantially uniform in all directions about said periphery and has everywhere a polarization substantially parallel to said plane.
A2. A radio antenna system according to claim 1 wherein said radiant acting conductor means is not over one-third of a wavelength long at the operating frequency.
3. A radio antenna system according to claim '1, wherein said radiant acting conductor means comprises a plurality of separate radiant energy conductors, and said transmission line section comprises at least one part consisting of two con-l ductors connected to at least two of said radiant energy elements, said conductors being adjacent each other and energized in phase opposition, whereby radiation therefrom is substantially neutralized.
4. A radio antenna systemaccording to claim 1, wherein said radiant acting conductor means comprises two radiant acting elements, and said transmission line section comprises at least one part consisting of two parallel, closely spaced conductors connected to respective ones of said radiant acting elements and energized in phase opposition, whereby radiant action thereof is substantially neutralized.
5. A radio antenna system according to claim 1, wherein said radiant acting conductor means 'comprises two radiant acting conductors arranged to substantially enclose said periphery,'
and said transmission line section comprises a pair of parallel conductors connected each to one end of a respective one of said radiant acting conductors, further comprising another pair, of parallel conductors connected to the other end of said radiant acting conductors at one end and open circuited at the other end, the total overall electrical length of one transmission section conductor, one radiant acting conductor and one of said other conductors being substantially onehalf of said operating wavelength.
6. A radio antenna system according to claim 1, wherein said radiant acting conductor means comprises four substantially equal radiant acting conductors arranged with ends adjacent to define said closed periphery, and said transmission line se` tion comprising a first pair of conductors connected to the adjacent ends of two of said radiant acting conductors, and a second pair of conductors transposed with respect to one another and connected to the adjacent ends of the other two radiant acting conductors,said Wave energy transfer means being connected to said first and second conductor pairs at a point equidistant from said radiant acting conductors, further comprising other open ended conductors connected to each of the other ends of said radiant acting conductors, said other conductors connected to adjacent ones of said other ends extending parallel to one another to neutralize radiant action thereof, said radiant acting conductors, said transmission line section conductors and said other conductors being so dimensioned that the current distribution in each of said radiant energy conductors is substantially uniform.
7. A radio transmitting arrangement including a radio antenna system comprising radiating means of small dimensions relative to the operating' wavelength arranged in a single plane, a transmission line section forming a continuation of said radiating means dimensioned to tune said radiating means electrically to said operating wavelength, the conductors of said section being arranged close to each other and wave transmitting means coupled to said transmission line section, in such a manner as to cause instantaneous current flow in all parts of said radiant energy means in the same sense, whereby the radiant action of said system is substantially uniform in` all directions and has everywhere a polarization parallel to said plane.
8. A radio translating system including a radio antenna comprising a plurality of radiant acting conductors arranged with ends adjacent to form a closed coplanar periphery, each of said radiant acting conductors being short with respect tothe operating wavelength, conductor means connected to the ends of each of said radiant acting elements, said conductor means at each of the adjacent ends of said radiant acting elements being arranged close to each other,
said conductor means from two oppositeiy positioned adjacent ends being connected to an energy transfer means. means for producing 180 phase shift in one o! said connected conductor means. and energy` translating means coupled to 5 said energy transfer means, whereby current distribution throughout said radiant acting conductors is substantially uniform and the direction o1 energization thereof is all in the same sense.
9. A radio translating s stem according to claim 8, wherein each of sai radiant acting conductors is from one-tenth to one-fifth of a Wavelength long at the operating frequency.
. ANDREW ALFORD.