US2981946A - Antenna feed system - Google Patents

Description

April 1961 N. 1. KORMAN 2,981,946

ANTENNA FEED SYSTEM Filed Sept. 30, 1947 2 Sheets-Sheet 2 FROM TKJNFDRMER .6 TRANSMITTER pzoww ,41 11 5 ;p

JNTEN 45 FEED 4 T0 AMTEA/Mq 7'0 SWITCH/N6 VOL 777615 in van for: Maiizafljelllfbrman Attorney 2,981,946 ANTENNA FEED SYSTEM Nathaniel I. Korman, Camden, N.J., assignor to Radio Corporation of Americana corporation of Delaware Filed Sept. 30, 1947, Set. No. 776,927 11 Claims. (Cl. 343-756) This invention relates to antenna feed systems, and

particularly to improvements in lobe switching antenna systems. A lobe switching antenna is a directive radiator or collector having a single-lobe pattern; lobe switching consists in changing the direction of the lobe with reference to a physical axis of the antenna. Lobe switching ordinarily is cyclical, and may be made along'one coordinate, for example alternately left and right, or may comprise a cycle of four positions such'as up, left, down and right.

The principal object of this invention is to provide methods and means for lobe switching which involve no moving parts and enable maximum eifective utilization of the efiective aperture of the directive radiator structure.

Another object is to provide feed-networks for simul taneous lobing of a directive radiator, i.e. to separate thecomponentsof a received signal in accordance with the deviation ofthe direction of arrival of said signal from a reference line.

The invention will be described with reference to the accompanying drawings, wherein:

Figure 1 is a schematic diagram in elevation of a directive structure of one type which may be used with the present invention,

Figure 2 is 'a group of graphs representing typical directive patterns which can be produced with the device of Fig. l, V I

Figure 3 is a group of schematic diagrams illustrating types of feed cavity excitation required to produce the respective patterns shown in Fig.

Figure 4 is a further group of graphs showing directive patterns obtainable by simultaneous excitation of the feed cavity in two of the modes shown in Fig. 3,

Figure 5 is a perspective diagram of a complete feed system embodying the instant invention,

Figure 6 is a sectional view of one of the elements of Fig. 5,

Figure 7 is a sectional elevation of another of the elements of Fig. 5, and

Figure 8 is a perspective view of a wave guide junction used in the system of Fig. 5.

Similar reference characters are applied to similar elements throughout the drawings;

Referring to Fig. 1, a type of directive structure, commonly used for the relatively short waves (1 to 10 cm.) associated with microwave radar, comprises a parabolic reflector 1 and a radiator source 3' at the focal point of the reflector. The effective area or opening of the reflector is known as its aperture and it is the aperture which determines how sharp the directive beam or lobe can be made. The larger the aperture in relation to a wavelength, the sharper is the beam.

To achieve the maximum effectiveness of the reflector,

.the source 3 must be directive so as to illuminate or substantially cover the reflector with radiation. If the beam from the source is too sharp, reflector is utilized; if it is too broad,

only a part of the some of the energy Figs. 3A, 3B and 3C, or combinations thereof, depend-' 2,981,946 Patented Apr. 25, 1961 .1 and the cavity 3, and provides a beam from the reflector 1 as indicated by the lines 5 in Fig. 1. Referring to Fig. 3A, the cavity 3 is seen to be of square cross section. 2A, the cavity 3 is excited by a field whose electric vectors extend vertically across the cavity.

Figure 2B shows a radiation pattern comprising two lobes extending to the left and right respectively of the reference axis. The showing of the right hand lobe below the abscissa in Fig. 2B is to indicate that the energy in this lobe is degrees out of phase with that in the left hand lobe. The excitation required in the cavity 3 to produce the pattern of Fig. 2B is shown in Fig. 3B. This mode is that known in the wave guide art as the T13 2, and that shown in Fig. 3A is theTE mode. Either of the patterns shown in Figs. 2A and 2B may be reversed in phase by reversing the excitations shown in Figs. 3A and 3B.

The excitation shown in Fig. 3C requires the presence of a horizontal conductive septum 7 across the cavity 3.

This part, although not shown in Figs. 3A and 3B, does" The directive pattern illustrated by Fig. 4A results from the simultaneous presence of the excitation patterns of Figs. 3A and 3C, and is the sum of the radiation patterns of Figs. 2A and 2C. The directive pattern of Fig. 4B is obtained by reversing the phase of either of its two components, for example that of Fig. 3C. Similarly, Fig. 4C shows the result of combined excitation in the modes of Figs. 3A and 3B, and Fig. 4D represents the effect of reversing one of the components for example that of Fig. 3B. The foregoing description is based on the assumption that the feed cavity 3 is energized by a generator, and is used for transmission of signals. However, received energy striking the reflector will also be appliedto the cavity and will set up excitation patterns like those of ing upon the direction of arrival of the incident waves. Thus'energy may be transmitted or received directively in a lobe extending straight along the axis of thereflector 1, or in'a lobe which deviates either laterally or verticallyfrom the axis, by coupling the cavity 3 to a utilization device (transmitter or receiver) in such manner as to produce or respond to the proper mode or combination of two of the modes shown in Figs. 3A, 3B and 3C.

.The dimensions of the mouth of the cavity 3 must of necessity be a compromise between the most efiective aperture for excitation like that of Fig. 3A and the best for excitation like that of Fig. 30. Preferably the design is such that little or none of the radiated energy misses the reflector 1 when the beam lobe is off-axis. This implies that not all of the reflector area is eifective simultaneously. However, the use of a single feed cavity as described enables a closer approach to ideal illuminationof the reflector than can be obtained by meansof separate individually excited cavities, since it afiords maximum utilization of the space in the vicinity of the focal point. n

This represents a single radia-' To provide the radiation pattern shown in Fig.

cavity 3 in the configuration of Fig. 3A. This energizes.

the four wave guides7, 9, 11 and 13 equally. The guides 11 and '13 are supplied in phase with .each other, and

the guides 7 and 9 in phase opposition with each other. Accordingly, all the energy reaching the hybrid T along the guides Z and 9 goes out the guide 19. Owing to the different arrangement of the hybrid T 33, the inphase energy supplied to it by the guides 11 and 13 all goes out the guide 35. At the hybrid T 39, the energy arriving on the'guides 19 and 35 combines in phase and goes up the main wave guide 41. It is reflected by the stub 49, whose ATR tube is open at this-time, and goes out the guide 45 to the. sense receiver.

. Return signals which do not arrive along the axis, such as. thoserefiected by an off center target, will induce fields inthe cavity3 like those shown in Fig. 3B or 3C, or a combination thereof if the target is off both in azimuth and in elevation. Suppose the configuration to be, that of Fig; 3 0. No energy is accepted by the guides-121 and 13 because they cannot propagate this mode. The guides 7 and 9 are excited in phase with each other, and equally. At the hybrid T- 15, the incoming energy combines in phase and all of it goes out the wave guide 17. The

ATR gap near the junction with the wave guide 53 prevents-any flow further up the guide 17, so all of the energy goes-out the guide53 to the up-down receiver;

' The phase of the energy at this point will reverse if the field in the cavity 3 is reversed in phase. The intensity of the field in the cavity, and hence the voltage appearing on the guide53, depends on'theangular deviation of the return signal from the reference axis.

Suppose now that the field inducedin the'cavity 3 by the return signal is of the form shown in Fig. 3B. In this case the wave guides 7 and 9 accept no energy, and the guides 11 and 13 are energized out of phase, causing flow up the arm 37 of the hybrid T 33. Substantially all of the energy goes to the waveguide 61 leading to the left right receiver. By means which are not a part of the present invention and hence will not be described or claimed, the outputs of receivers connected to the wave guides 45, 53, and 61 are combined to provide control signals for indicating target deviation and/or correcting such deviation. r r Relatively low power pulses are applied to the wave guide 67. These are to be radiated selectively indirective beams above, below, to the left and to the right of the'axis. The power is insufficient to closethe gap 69 or the ATR gap associated with it, and cannot close any of the switching gaps 71, 73, 75, or '77. However all of the latter except one are held closed byapplication of a high D.-C. voltage from a control source, not shown. Which one is left open depends upon .which of the four available directive patterns is bcing selected.

Assume for example that the gap 75 is open. Energy applied to the wave guide 67 is barred by the associated ATR gap (un-ionized) and must go down the guide 41. At the junction with the guides 57, 59, 63 and 65 it divides, part going into the open guide 63 and the remainder continuing down the main guide '41. The TR gap 47 and ATR gap 51 both close, barring the wave guide 45 and allowing the energy to flow to the hybrid T 39. Here it divides equally between the guides '19 and 35, is again divided at the hybrid Ts 15 and 33, and provides a field like Fig-3A in the cavity 3.

The other part of the supplied energy goes down the guide 37, past the barred junction with the guide 61, to the hybrid T 33. Here it divides equally, exciting the guides 11 and 13 equally but in opposite phases. This induces a field-like Fig. 3B=in the cavity 3. ,The combination of the fields of Figs. 3A and 3B provides a tionship between the energy travelling directly down the guide 41 and that in the guide 63. Assume it to be that of Fig. 4C. Then the pattern of 4D can be obtained by closing the guide 63 and opening the guide 65, thus reversing the phase of the energization of the guide 37.

The wave guide 17 can be energized by opening either of the switching gaps 71 and 73., This provides a field in the cavity 3 of the form shown in Fig. 3C. Combined with the field of Fig. 3A, the field. provided by opening the gap 71 will result in the directive pattern shown in Fig. 4A. The phase of the component corresponding to Fig. 30 may be reversed by opening the gap 73 instead of the gap 71, producing the directive pattern ofFig. 4B. 7

From an examination of Fig. 3 it will be apparent that the mode of excitation illustrated by Fig. 3A is one of even symmetry with respect to the vertical plane through the wave guide. axisand also having even symmetry with respect to the horizontal plane through the wave guide axis. Referring to Fig. 3B, it is clear that the, mode of excitation therein illustrated is one of odd symmetry with respect to a vertical plane tbrough'the wave guide axis, although possessing even symmetry with respect to the horizontal plane. Conversely, the mode illustrated in Fig. 3C has odd symmetry with respect to the horizontal plane and even symmetry with respect to the vertical plane. vIt will be clear that thephasal rela- 'The phasal relationship in the sensing wave guides 45 or 61 may be related to the transmitted or received energy in wave guide 41 or to the energy in the principal mode illustrated in Fig. 3A.

When referring to the horizontal plane of symmetry or the vertical plane of symmetry in the foregoing, applicant refers, of course, to the central plane through the waveguide mouth Thus, for example, theplane 7 in FigureV3C is the horizontal plane of symmetry. With reference to the even and odd symmetry, the definition of these as classically established will be recalled. In a system of mutually perpendicular axes X, Y and Z along which are measured variables x, y and z, the definition is, as appears in numerous standard mathematical texts, the function f(x,yrz) is even with respect to the Y-"Z plane if f(x,y,z) equals f( .352) and the function is odd if f(x,y,z) is equal to f(x,y,z). Accordingly, referring to Figure 3C and the plane 7, it is clear that the mode there illustrated has odd symmetry because the value of the vectors an equal distance normally above and below any chosen point in the plane is the same in magnitude but reversed or negative in direction. a The invention has been described as an improved feed system for high frequency antennas of the type comprising a. radiation source and a director device such as a reflector. Lobe switching and similar effects are achieved with maximum utilization of the director aperture and without moving parts, by making the radiator in the form of a single cavity with plural excitation means, and en 1. In a simultaneous lobing antenna system including .a radiation focussing device, a radiator substantially at the focal point of said device, said radiator comprising a Fig. 40 or 4D, to the left or to the right of the axis, depending upon the phase relastew spect ely of said cavity device; acommon Wave guide,

two further wave guides enteringthe top and bottom reand a hybrid T connecting both of said first mentioned 7 wave guides in phase oppesitidn with "each other to said common Wave guide, a second common wave guide and a hybrid 1 connecting both of said second mentioned wave guides in phase opposition with ea chlotherto" said Second common wave guide; a main wave guide, and'means connecting said main wave guide to both of said hybrid Fri to connect said first mentioned two wave guidcscophasally to said main wave guide and said second mentinned two'wave guides cophasally with each other to said mainwave guide; four branch wave guides, two connected in parallel to each of said common wave guides, means connecting each of said branch wave guides cophasally with abranch wave guidefrom the other of guides to said main wave guide, and;

said common wave switching means included ineach of said branch guides to render itselectively effective and ineffective to transrnit energy.

2. A lobe switching antenna system including a wave focussing devicepa single radiator fixed with respect to said lfocussing device at the focal point thereof, said "focussing device, a

radiator comprising a cavity device in the form of a rectangular parallelepiped and includinga substantially squaresopening facing said focussing device, fourfwave guides entering said cavity device respectively at the four surfaces adjacent the open side thereof, a main wave guide, and [means interconnecting said four wave guides in pairs selectively in phase agreement andin phase opposition to said main wave guide. 7 r

, 3. A lobe switching antenna system including a wave focussing device, a radiator fixed with respect to said focussing device, said radiator comprising a cavity device including an opening facing said focussing device," four wave guides entering said cavity device respectively at the four surfaces adjacentthe open side thereof, a main wave guide, and means interconnecting said four wave guides in pairs selectively in phase agreement and in phase opposition to said main wave guide. a

4. A feed system for directional antennas, comprising a cavity device having an openingof substantially square cross section, four orthogonally related wave conduit means entering said cavity device in directions respectivelyperpendicular to the'sides of said opening and termin atin g within said cavity device, a main Wave conduit, and means connecting said first mentioned conduits in pairs selectively in phase agreement and in phase opposition to said main conduit. S. In a" simultaneous lobing antenna system including a radiation focu ssing device, a radiator substantially at the focal point of said device,said radiator comprising a cavity device of substantially square cross section open at the front and closed at the back, two wave guides each entering one side of said cavity device respectively, and

two further wave guides entering the top and bottom respectively of said cavity device; a common wave guide, and a hybrid T connecting both of said first mentioned wave guides in phase opposition with each other to said common wave guide, a second common wave guide and a hybrid T connecting both of said second mentioned wave guides in phase opposition with each other to said second common wave guide; a main wave guide, and means connecting said main wave guide to both of said hybrid T,s to connect said first mentioned two wave guides cophasally to said main wave guide and said second mentionedtwo wave guides cophasally with each other to said main wave guide.

, 6, In a lobe switching antenna system including a radiation focussing device, a radiator substantially at the focal said device, said radiator comprising a cavity device of substantially square cross sectionopen at the tering one side of said cavity device respectively, and two further wave spectively of saidcavity, device; a common wave guide,

and means connecting bothof said, first mentioned wave guides in phase opposition with'each other to said, common wave guide, a second common vvave guide and means connecting both of said second mentioned wave guides in phase opposition with each other to said second commonwave guide; a main wave guide, and means connecting said main wave guide to said first mentioned two wave guides and'to said secondmentioned two wave guides cophasally. q I

j 7. In a lobe switching antenna including a radiation radiator substantially at the focal point of said device, said radiator comprising a cavity device of substantially square cross section open at the front and closed at the back, twowave guides each entering one side of said cavity device respectively, and two further wave guides entering the top and bottom respectivelyof said cavity device; a common wave guide,

and means connecting both of said first mentioned wave guides in phaseopposition with each other to saidcommon wave guide, a second common wave guide and means connecting both of said second mentioned waveguides in phase opposition with each other to said second common wave guide; a main wave guide, and means connecting said main wave guide to said first mentioned two wave guides and, to said second mentioned two wave guides cophasally,

reception of electromagnetic energy, said portion having a longitudinal axis and having transverse dimensions to propagate at an operating frequency a first mode having odd symmetry with respect to a plane passing through said axis and to propagate energy at said frequency in'a second mode having even symmetry with respect to said plane, means to excite said wave guide portion in said first mode at said frequency, and meansto excite said wave guide portion simultaneously with the excitation of said first mode selectively cophasally and antiphasally in said second mode at said frequency, thereby to direct radiation on one side or the other of said plane in accordance with the cophasal and antiphasal relationship between said modes.

9. The combination claimed in claim 8, said means to excite said first mode including a transducer coupled to saidwave guide portion to energize and to be energized solely by energy in said first mode, whereby the phasal relationship to energy coupled to said transducer means is dependent upon the cophasal and antiphasal relationship between said modes to provide a sensing in accordancewith the direction of radiated or received energy on one side and the other of said plane.

10. In a simultaneous lobing antenna system, a wave guide having an open mouth portion for radiation or reception of electromagnetic energy, said portion having a longitudinal axis and having transverse dimensions to propagate energy at an operating frequency in first and second modes of odd symmetry respectively with respect to first and second planes normal to each other and passing through said axis and to propagate at said frequency a third mode symmetrical with respect to both said planes, means to excite said wave guide portion in said third mode at said frequency, and means to excite said wave guide portion simultaneously with the excitation fronta'nd closed at the back, twowave guides each en:

guides entering the top and bqttom reof said third mode in at least'one of said first two modes selectively cophasally and antiphasally at said frequency whereby the radiation or reception pattern of said open mouth wave guide portion is lobed at an angle with respect to said axis.

11. In a simultaneous lobing antenna system, the combination of a wave guide having an open mouth portion for radiation or reception of electromagnetic energy, said portion having a longitudinal axis and having transverse dimensions to propagate energy at an operating frequency in first and second modes having odd symmetry respec tively with respect to first and second planes normal to each other and passing through said axis and to propagate energy at said frequency in a third mode having even symmetry with respect to both said planes, means to excite said Wave guide portion in said third mode at said frequency, and means to excite said wave guide portion simultaneously with the excitation of said third mode in at least one of said first two modes at said frequency selectively cop-basally and antiphasally with respect to said third mode, said last named means including two transducers coupled to said wave guide portion, one coupled solely to energize and to be energized by energy in 16 said wave guide portion in said first mode, and the other coupled solely to energize and to be energized by energy in said wave guide portion in said second mode, each in a phasal relationship dependent on the phase of its coupled mode with respect to enegy in said third mode, whereby said transducers each provide sensing means in accordance with the phaseof its energy corresponding to the position of the lobe pattern of said wave guide portion on one side or the other of the plane of odd symmetry of its coupled mode.

References Cited in the file of this patent UNITED STATES PATENTS Southworth July 9, 1940 2,403,302 Richmond July 2, 1946 2,407,068 Fiske et al. Sept. 3, 1946 2,412,315 Brown Dec. 10, 1946 2,423,072 :Willoughby June 24, 1947 2,434,253 Beck Jan. 13,1948 2,436,408 Tawney Feb. 24, 1948 2,441,574 Jaynes May 18, 1948

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