US3293648A

US3293648A - Monopulse radar beam antenna array with network of adjustable directional couplers

Info

Publication number: US3293648A
Application number: US148271A
Authority: US
Inventors: Donald H Kuhn
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1961-10-27
Filing date: 1961-10-27
Publication date: 1966-12-20
Anticipated expiration: 1983-12-20

Description

Dec. 20, 1966 D H KUHN MONOPULSE RADAR BEAiVI A NTENNA ARRAY WITH NETWORK OF ADJUSTABLE DIRECTIONAL COUPLERS Filed Oct. 27. 1961 LINE OF SIGHT FIG.IA VEVEN ILLUMINATION 3 /LINE OF SIGHT -\I 000 ILLUMINATION /LINE OF SIGHT COMPRISED EVEN AND FIG-IE 00o ILLUMINATIONS /LINE OF SIGHT OPTlMlZED EVEN AND ODD ILLUMINATIONS 5 Sheets-Sheet l SIGNAL STRENGH FIGJB CENTER LINE CENTER LINE\ FIGID CENTER LINE\ l4 AND 15 I4} CENTER LINE p l6 FIGIH INVENTORI DONALD H. KUHN,

BY J 2 M m? AGENT.

Dec. 20, 1966 BEAM ANTENNA ARRAY WITH NETWORK OF ADJUSTABLE DIRECTIONAL COUPLERS Filed OOL. 27. 1961 5 Sheets-5heet 2 FIG.2 r IsI 'I I30"I 3 I I2l I DIRECTIONAL DIRECTIONAL 'T X [I37 I COUP ER L2 COUPLER I I l I IsIL I TRANSMITTER V V V L W l I I I22'\ {I36 l E' DIRECTIONAL DIRECTIONAL I I I COUPLER COUPLER I DUPLExER I I I I I I3I I I63\ I53 I I23\ DIRECTIONAL DIRECTIONAL I I I COUPLER I COUPLER SUM 52 I l RECEIVER I g I I DIRECTIONAL DIRECTIONAL I I COUPLER COUPLER I u c 0 c I I I5 O I I HYBRID I39A HYBRID 38A I I I398 I385 I I I I Ies Iss I I I DIRECTIONALT DIRECTIONAL I I25 5 I g COUPLER COUPLER I I I g I l I45 I I66\ I I56\ I DIFFERENCE I DIRECTIONAL DIRECTIONAL I I26\ RECEIVER I COUPLER COUPLER l I I I 4s I34 I I I I67-I I51 I DIRECTIONAL T DIRECTIONAL I27 I COUPLER COUPLER I I I I I4? I I l68 Isa I58L I I DIRECTIONAL DlRECTlONAL' I I28 I COUPLER COUPLER k I I I48 I INVENTOR- DONALD H. KUHN,

BY J 7 HI AGENT.

Dec. 20, 1966 D. H. KUHN 3,293,643

MONOPULSE RADAR BEAM ANTENNA ARRAY WITH NETWORK OF ADJUSTABLE DIRECTIONAL COUPLERS Filed Oct. 27. 1951 5 Sheets-Sheet 5 FIQZA I2I I22 l4| I42 I43 I44 I45 I45 I47 I48 1 I53 I56 l6! I68 1 I54 I55 I I52 (y I67 I55 1 1 I66 1 I64 I65 I58A I385 FROM DUPLEXER \F'ROM RECEIVER I34 INVENTORI DONALD H. KUHN,

HIS AGENT.

Dec. 20, 1966 D. H. KUHN 3,293,648

MONOPULSE RADAR BEAM ANTENNA ARRAY WITH NETWORK OF ADJUSTABLE DIRECTIONAL COUPLERS Filed 001;. 27. 1961 5 Sheets-Sheet 5 FIG.4 6

Y Y Y Y Y Y A I I I I I I I I BEAM (FIG.2 525 SYNTHESIS NETWORK OR FIG.3I

Y Y Y Y Y)? 380 Y m8 390 (b, (b 2 I I 9 I I I I I I I I BEAM (FIG.2 330B SYNTHESIS NETWORK R F163) BEAM BEAM SYNTHESIS A SYNTHESIS NETWORK NETWORK TO NETWORK 3300 TO NETWORK 3300 A I I I I i I I I I l I I I TO NETWORK 33OH TO NETWORK 33OH I AZIMUTH k ELEVATION DIFFERENCE SIGNAL SUM SIGNAL I DIFFERENCE SIGNAL ELEVATION AZIMUTH DUPLEXER RECEIVER RECEIVER l I I 336 334E 334A INVENTOR DONALD H KUHN,

BY J 7 HIS AGENT.

Patented Dec. 20, 1966 MONOPULSE RADAR BEAM ANTENNA ARRAY WITH NETWORK OF ADJUSTABLE DIRECTION- AL COUPLERS Donald H. Kuhn, North Syracuse, N.Y., assiguor to General Electric Company, a corporation of New York Filed Oct. 27, 1961, Ser. No. 148,271 9 Claims. (Cl. 343-854) The present invention relates to signal distribution networks for monopulse radar. More particularly, this invention relates to efficient networks of transmission lines 7 or waveguides and directional coupler devices which are arranged between a single multi-element antenna array and a radio receiver and/or transmitter and which distribute signals in such a manner that both the even and odd aperture illumination functions are independently selectable. This enables beam synthesis which optimizes antenna directivity, minimizes side lobes, and produces other advantages obtainable from beam tailoring.

In monopulse radar, the transmitted pattern desired is generally a single symmetrical lobe in a given direction which can be along the line of sight of a mechanically tracking antenna or in an instantaneous electronic scanning direction provided by a given phase relationship in the radiation from individual elements in an antenna array. Considering receiver operation in a plane of constant elevation or azimuth, received signals from each half of the antenna system are combined into two parts: a first part provides A sum signal by a process which is the reciprocal process relative to the single lobe illumination used for transmission and therefore has the same even directivity pattern relative to the center line of the lobe of radiation (the signals from opposite sides of the center line have the same polarity and have a symmetrical distribution of amplitudes) as illustrated in FIGURE 1A; and a second part provides a difference signal which has a null in the direction of the center line of the lobe of radiation and has an odd directivity pattern relative to the center line as illustrated in FIGURE 1C. The received sum signal is generally utilized to produce range data in a conventional manner and as a normalizing factor for the difference signal. The difference signal is utilized to produce directional data in either elevation or azimuth. The sum signal-as the name implies-usually denotes an addition in phase of the voltages from both halves of the antenna system whereas the difference signal de notes the addition of the voltages out of phase. For monopulse radar mechanical tracking, the difference signal has opposite signals of opposite phase relative to the sum signal for received signals on opposite sides of the line of sight and therefore provides a convenient error signal which is utilized to automatically maintain the an tenna (and relatively fixed apparatus) aimed at the target.

The present invention is concerned with the distribution network between an antenna system of a class having many radiating elements and a receiver and/ or transmitter which can provide the optimum directivity patterns for both the even and odd illuminations. In a monopulse radar system, as described above, only a sum signal is generally employed for illumination and both sum and difference signals are employed for received signals. However, radiation and reception are reciprocal functions so that both functions are implemented by the same structure. The specific embodiments disclosed herein are generally described in terms of radiation for convenience, but it is to be understood that the structures described in respect to one function are also suitable for the other function. It is also to be understood that the properties essential to the operation of the disclosed systems are those of wave propagation in general, and systems employing sonic radiation or electromagnetic radiation at frequencies differing from those generally designated as radio frequencies may be constructed with corresponding components.

In monopulse radar, the design of antenna systems to provide optimum illumination patterns presents many problems. For example, high directivity is generally de sired in order that operation over the greatest range is obtained for a given amount of energy. Such directivity is usually produced by narrowing the lobe of illumination. However, narrowing the principal lobe tends to introduce side lobes which are undesirable. Accordingly, it is necessary to design the antenna system with the desired directivity but without significant side lobes as represented by the beam pattern 1 of FIGURE 1A which is produced by a representative electromagnetic radiation aperture illumination function 2 in FIGURE 1B. A desired odd beam pattern 3 having a slope of large magnitude at the null point for monopulse radar is illustrated in FIGURE 1C which is produced by the aperture illumination function 4 in FIGURE 1D. This large slope of the illumination pattern is desirable because it determines the error signal sensitivity or the angular resolution.

As is well known, multi-element antenna arrays are advantageous for their flexibility in lobe synthesis. They are also advantageous for their adaptability to electronic scanning. That is, the directive pattern of an array can be swept in azimuth and/or elevation by introducing the proper phase differentials in the signals fed to the individual antenna elements. This enables rapid tracking of a plurality of targets within a given time interval. However, the combination and distribution of microwave signals is limited by the nature of electromagnetic wave propagation. The process of forming components from a plurality of signals, and the distribution and combination of these components for an antenna array and the inverse process are difficult to perform. The limitations arise not only from losses in microwave components, but primarily because any given practical microwave device has inherent restrictions on the choice of the relations of the input and output signals. In a directional coupler in which one pair of isolated ports are considered as input ports, the relative distribution of the signals to the output ports can be varied over a wide range. However, the selection of the relative amplitudes of the signals at the output ports for an input signal at one port will place an absolute constraint on the relative amplitudes for the output signals for signals applied at the second input port (the inverse ratio). Also, there are strict limitations upon the relative phases of the output signals of a directional coupler for signals applied to the input ports.

In monopulse radar apparatus which employs an array of many antenna elements, the beam pattern is determined by the relative amplitudes and phases of the signals applied to the respective elements which produces the aperture illumination function. To provide the even and odd illumination patterns from a single array, it is the usual practice to apply one set of signals to the antenna elements in accordance with an even aperture illumination function 14 such as that illustrated in FIGURE 1F and to apply a second set of signals in accordance with an odd aperture illumination function 15 which has the same relative amplitudes but has opposite polarities on opposite halves of the aperture.

This distribution of signals is generally realized by having a sum signal and a difference signal transmitted along the array of antenna elements with the sum and difference signals being of the same polarity for one-half of the array and being of opposite polarity for the other half. The sum and difference signals are coupled to each antenna element with a coupling coefficient (which is the same for both sum and difference signals) corresponding to the chosen functions such as illustrated at 14 and 15 3 in FIGURE 1F. The result is that the sum and difference signals are distributed with the same relative amplitudes. As can readily be seen in FIGURES 1A D, the requirements for optimum illuminations are conflicting. For example, an even illumination requires large signal feeds to the center elements of an array and an odd illumination requires small signal feeds to the center. With this type of arrangement, it is necessary to compromise between the optimum requirements of the even and odd illuminations.

It is accordingly an object of the invention to provide an efficient signal distribution network for a monopulse radar system which is interposed between a common multi-element antenna array and a receiver and/or transmitter and which enables independent selection of the even and odd illumination patterns.

It is a further object of the invention to provide an efficient signal distribution network for a monopulse radar system in which sum and difference signal components are produced and combined without reliance upon attenuators which remove substantial useful signal energy.

It is also an object of the invention to provide a distribution network which does not introduce differential phase shifts with variations in signal frequencies and thereby permits broadband operation.

Briefly stated, in accordance with one aspect of the invention, novel signal distribution networks are provided between a conventional multi-element antenna array and a conventional radio receiver and/or transmitter which enables the synthesis of independently selected even and odd m-on-opul se illuminations. The networks utilize directional coupler devices which are arranged in such a manner that sum and difference signals are simultaneously processed in accordance with the desired aperture illumination functions and with all of the useful energy directed to the receivers during reception and to the antenna array during transmission. Sum and difference sets of directional couplers are arranged between sources of sum and difference signals and a multi-element antenna array. Each antenna element is fed from a directional coupler which provides both the sum and difference signals. However, the sum and difference sets of directional couplers are interconnected and adjusted in specific configurations which compensate for interactions without signal energy loss (except for insertion loss within the individual directional couplers).

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with durther objects and advantages thereof, may best be understood by reference to the following description when taken in connection with the drawings, wherein:

FIGURES 1A and 1B are respective diagrams of a beam pattern and a corresponding aperture illumination function for an even radar illumination function. FIG- URES 1C and ID are respective diagrams of an odd beam pattern and a corresponding odd aperture illumination function. FIGURES LE and IF are respective diagrams of a beam pattern and a corresponding aperture illumination function for a monopulse radar system utilizing a multi-element antenna array in which the even and odd aperture illumination functions have the same relative amplitude signal distributions. FIGURES 1G and 1H are respective diagrams of an optimum monopulse beam pattern and corresponding independent even and odd aperture illumination functions.

FIGURE 2 is a schematic diagram of a first embodiment of a beam synthesis network between a m-onopulse radar antenna array and a receiver and transmitter. FIG- URE 2A is a schematic diagram of an arrangement of the FIGURE 2 network which compensates for frequency variations.

FIGURE 3 is a schematic diagram of a second embodiment of beam synthesis network.

FIGURE 4 is a block diagram of a three-dimensional monopulse radar system incorporating a plurality of linear antenna arrays of the FIGURE 2 or FIGURE 3 type.

Referring now to the drawings, FIGURE 2 illustrates a first embodiment of a radar beam forming network for illuminating one angular dimension which can be in azimuth or elevation. A conventional multi-element antenna array is comprised of several elements (more than two) such as dipoles or horns 121-128 which are symmetrically arranged to radiate or receive monopulse radar waves. These elements are conveniently aligned and equally spaced in such a manner that signals applied thereto in phase and having relative amplitudes corresponding to well known aperture illumination functions, such as Dolph-Tchehytchef or Taylor distributions, will produce a desired illumination beam pattern. The signal components applied to the individual antenna elements are provided by a signal distribution network generally designated as 139. The network 136 is in turn connected to conventional receiver and transmitter apparatus for monopulse radar operation by a common sum signal transmission line or waveguide 131 and a common difference signal transmission line or waveguide 132. (For convenience, transmission lines and waveguides are hereinafter generically termed microwave transmission lines.) The common sum signal microwave transmission line .131 is connected to a sum receiver .133 and transmitter 137 through a duplexer switch 136. The difference microwave transmission line 132 is connected to the difference receiver 134.

The distribution network is arranged between the array of antenna elements 121128 and the duplexer 136 and difference receiver 134 to enable the synthesis of independently selected even and odd aperture illumination functions. The arrows represent the direction of energy flow for the radiation of a radar signal. It is to be understood that the flow of energy is in the reverse direction for received radar signals. Therefore, although the arrows for the difference signals indicate transmission, no actual odd illumination is expected. However, the relations required for transmission and reception are essentially the same, and the consideration of transmission is less complex.

A set of :feed transmission lines 141-148 connect each antenna element to the distribution network 130. The feed transmission lines 14 L148 are connected to a sum

distribution transmision line

138A or 138B by respective directional coupler devices 151-154 and 155-153. The directional coupler devices 151-158 are adjusted so that signal power from the individual antenna elements 121- 12-8 are coupled in accordance with the desired aperture illumination functions. The

sum transmission lines

138A and 138B are connected to the sum transmission line 131 by means of a hybrid 150. The hybrid 150 is connected to duplexer 136 and operates as a power splitter whereby transmitted signals are equally divided between lines 138A and 1388. Similarly, the

difference transmission lines

139A and 139B are connected to difference receiver 134 by means of hybrid 160. The directional couplers 151-158 and 1614.68 are preferably of a type permitting adjustment of the coupling coefficient so that a variable proportional distribution of power is made between a first input port and two output ports. The distribution of power from the remaining port to the pair of output ports has the proportions reversed. Each of these pairs of ports has the two ports isolated and the input and output relations of the pairs are interchangeable. Of course, directional couplers having fixed, but properly selected, coupling coefficients can be used; or any four port coupling device, with or without auxiliary adjustment means, which has the properties of the adjusted directional coupler described above is suitable.

The adjustment of the directional couplers in FIG- URE 2 is as follows. The sum signals applied to and received from each half of the multi-ele-ment array are the same and the distribution of signals from hybrid 150 to antenna elements 121-124 through line 138A and directional couplers 151-154 is the same as the distribution to antenna elements 125-128 through line 138 13 and directional couplers 155-158. The directional couplers 151-154 and line 138A are connected in series. Transmission line 138A is connected to an input port 154a of directional coupler 154 which is adjusted to pass a proportion of the sum signal power to antenna element 124 through output port 154d. However, most of the sum signal power is passed through port 154a to the input port 153a of the next series connected directional coupler 153. This second directional coupler taps off a portion of the sum signal for antenna element 123 in the same manner as directional coupler 154. The series connected directional couplers 152 and .151 are adjusted in the same manner as

directional couplers

153 and 154.

The above described sum signal distribution fixes the coupling coefficients of the directional couplers 15 1-158. The common difference transmission line is coupled to the common antenna array through these same directional couplers and the same feed transmission lines 121-128. It is accordingly necessary to compensate for this fixed coupling which distributes part of the difference signal through the series of sum directional couplers 151-158. The difference signals are distributed to the antenna elements 121-1 28 by means of directional couplers fled-168 in a manner similar to the sum signal distribution by means of directional couplers 151-158. For the difference signals, hybrid 160 is coupled equally to each half of the antenna array but combines the signals from each half with a relative phase differential of 180. Directional couplers 1 61-164 are connected in ser'es, with each directional coupler providing the desired coupling for one of the antenna elements. For example, hybrid 160 is connected to port 164a of directional coupler 164 and the output ports 164d and 1640 are respectively connected to the next directional coupler input port 163a and the sum directional coupler 154 at port 15%. Similarly, the next directional coupler 162 has its input port coupled to the output of directional coupler i163 and the directional coupler 161 has its input port coupled to the output port of directional coupler .162 to effect serial energization. The signals connected to directional couplers 151-154 from directional couplers 161-164 are partly coupled directly to respective antenna elements 121-124 and partly to the next directional coupler of the series 151-154. For example, the output of directional coupler 164 at 164d passes through port 1541) of directional coupler 154- and part is passed directly to antenna element 124 and part to directional coupler 153. The relative amplitudes of the portions of the difference signal passed through ports 154a! and 154c are the reverse of the distribution of the sum signals applied to port 154a. Since only part of the difference signal derived from directional coupler 164 is coupled to antenna element 124-, the adjustment of the coupling coefficient of directional coupler 164- is made to compensate therefor. The adjustment of subsequent directional couplers 161-163 which are coupled through couplers 151-153 to antenna elements 121- 123 respectively must compensate not only for partial coupling through the respective associated directional coupler (151-153), but must also allow for the portions of the difference signals distributed from other ones of the directional couple-rs 151-154. For example, a portion of the difference signal from port 154d of directional co-upler 154 will be coupled to antenna element 123 through directional coupler 153 in the same manner as the sum signals.

For the second half of the difference signal, the directional couplers 165-168 are employed. They are serially interconnected in the manner illustrated in FIGURE 2 6 and are adjusted in the same manner as the directional couplers 161-164. FIGURES 1A to 11-1 illustrate the aperture illumination ".fiunctions and thereby the adjustment of the individual directional couplers forming the sum and difference signals.

As is evident from the foregoing, the even and odd illuminations are individually adjusted and substantially all of the useful energy of the sum and difference signals (except for insertion losses of the directional couplers) is coupled between the antenna array and the receiver and/ or transmitter. However, there may be some losses in the loads 15 1L and 158L at the ends of the distribution networks. This loss, particularly in a large antenna array, will be a negligible part of the transmitted power. The last directional couplers in each set, 161 and 168, 151 and 158, are not required for signal distribution to subsequent antenna elements. These directional couplers simplify operation by enabling adjustment of the last di rectional couplers without readjustment of all. If all of the signal energy appearing at the ends of the distribution network must be applied to the end antenna elements, all of the directional couplers must be critically adjusted so that an exact amount of power is delivered to the last two antenna elements. But with a small load such as 161L a negligible amount of power will be lost while enabling easy adjustment of the last directional couplers.

These considerations which permit independent adjustment of the even and odd illuminations also permit an interchange of the sum and difference sets of directional couplers such that the difference set is connected directly to the radiators. With such an arrangement, the difference directional couplers are first adjusted and then the sum directional couplers are adjusted with allowance being made for contributions through the several difference directional couplers.

FIGURE 2A illustrates an arrangement of the FIG- URE 2 network in which the corresponding components are represented with the same reference characters. In this arrangement, the signal paths for both the sum and difference signals are equalized in length to avoid relative phase shifts due to variations in frequency. A transmitted signal component traverses a geometrical path from a common point at either hybrid or 160 which is effectively on a geometrical line through the center of the linear antenna array and normal thereto. The transmission lines are arranged so that waves propagating towards the antenna array are always directed at the same angle a relative to a line parallel to the array. Accordingly, the length of all paths from the transmitter to the antenna elements are equal and phase coherence of the components is maintained regardless of the signal frequency. The same relation holds for received signals in respect to both sum and difference illuminations.

FIGURE 3 illustrates a second embodiment of a distribution network for forming independent even and odd aperture illumination patterns. The distribution network 230 is interposed between the array of antenna elements 221-228 and duplexer 236 and receiver 234. The distribution network 230 is essentially comprised of two tree networks of directional couplers 241-247 and 251- 256. The first tree is comprised of directional couplers 244-247, each of which feeds a pair of antenna elements, and directional couplers 241-243, which are connected as a tree to divide the sum signals into symmetrical portions which are applied to couplers 244-247. The directional couplers 241-247, in addition to distributing the sum signal in accordance with the desired even aperture illumination function, also distribute in part the difference signals to the antenna array. The second tree of directional couplers 251-256 distributes difference signals to the antenna array, partly through the first tree of directional couplers. Directional coupler 251 divides the difference sigral into two portions, the first portion is applied to the antenna array through directional coupler 241 in accordance with a. sum illumination pattern. The second 7 portion is applied through directional couplers 252256 to provide the difference aperture illumination pattern. As in FIGURE 2, the flow of energy is indicated by arrows for transmission of both sum and difference signals. Although transmission of ditferenoe signals is not eX- pected, consideration thereof is convenient and provides the proper reception relations.

In several respects the adjustment of the directional couplers in FIGURE 3 follows the same principles of FIGURE 2. For the sum signals, the distribution is symmetrical so that the distribution to each half of the antenna array is identical. Similarly, the difference signal distribution is anti-symmetrical and the distribution to each half of the antenna array is provided with the same relative amplitudes but with opposite polarities. The sum signals are distributed by the tree of directional couplers 24 L247. Signals from the common sum signal line 261 are equally divided by directional coupler 24 1 and applied to directional couplers 2 42 and 24 3. Each half of the tree is then adjusted to provide the desired aperture illumination function for the antenna array. The difference signals are distributed partly through the first tree of directional couplers 241-247 and partly through a second tree of directional couplers 252256 and 2 44-24-7. The signal from the common difference signal transmission line is divided between the two trees of directional couplers by directional coupler 2511. The portion of the difference signal applied to the first tree through directional coupler 2 41 is supplied into equal parts having opposite phase. Accordingly, the portion of the difference signal distribution provided by the first tree will tend to assume the function .15 in FIGURE =1F. However, the distribution of the difference signals through the second tree of directional couplers modifies this function to form an optimum odd illumination.

For the purpose of illustration, all the directional couplers can be assumed to be 180 directional couplers, but to those skilled in the art, it will be obvious that 90 directional couplers in conjunction with fixed phase networks can be used.

The specific adjustments for the individual directional couplers in FIGURE 3 are made in accordance with the following considerations. If the ports of a directional coupler are designated in a clockwise consecutive order 8 Specifically, the scattering matrix S, for a four port, 180 directional coupler is:

S O O VF? From the desired aperture illumination iiunction, the relative amplitudes of the sum signals applied to the individual antenna elements are 0 (r etc. Accordingly, the coupling coefficients for directional couplers 24 L247 are as follows:

The above relations determine the coupling coeflicients of the first tree of directional couple-rs 24 1-247 and the part of the second tree of directional couplers which is common to the first, 2 42-247. By a similar process, the coupling coefiicients of

directional couplers

251, 252, 255 and 256 are determined for the odd illumination. This requires only three equations since directional couplers 255 and 25 6 are reciprocally related as :given above. Accordingly, the three remaining coupling coefiicients are chosen to satisfy the following three equations which provide the desired relative difierence signals 6 6 etc., at the respective antenna elements:

as 1, 3, 4 and 2 the input and output waves at the four ports are related by the following matrix equation:

These equations are derived by a straightforward expression of the multiplied effect of the tree of coupling c0- eflicients of the directional couplers between the individual antenna elements and difference receiver 234 along the various signal transmission paths.

These equations are derived 'for an eight element antenna array. The adjustments are determined by the relationships for the sum signals, the properties of directional couplers, and the desired relative amplitudes of the signals applied to pairs of antenna elements. This process can be applied to larger antenna arrays, preferably having 2 antenna elements, by the same type of interlocking trees.

FIGURE 4 is a block diagram of a three-dimensional monopulse radar system in which scanning is provided in both azimuth and elevation. Three-dimensional scanning is enabled by an antenna array in which the antenna elements are arranged in two dimensions. In this embodiment, a plurality of linear arrays of antenna elements are provided such as 321A, 322A, etc., and 321B, 3223, etc., each linear array being of the same form as the antenna arrays 121-128 or 221 22? in FIGURE 2 and FIGURE 3. Each linear antenna array is provided with an individual beam synthesis network which distributes sum and difference signals in accordance with a desired aperture illumination function, for one angular coordinate in the same manner as in FIGURE 2 or FIGURE 3. However, additional beam synthesis networks are provided which distribute common sum and difference signals to the plurality of individual beam synthesis networks in a manner similar to the signal distribution within each individual beam synthesis network in order to provide independent beam synthesis in a second angular coordinate.

As illustrated in FIGURE 4, a plurality of linear antenna arrays are provided. The first linear array is comprised of

individual antenna elements

321A, 322A, etc., which are respectively coupled to a beam synthesis network 33tlA through individual phase shift elements 379A. The beam synthesis network 33lA is preferably identical with either the network 13f) or 235) of FIGURE 2 or FIGURE 3. Accordingly, sum and difference signals applied to this network will be distributed to the individual antenna elements in accordance with an optimized aperture illumination function :for both the even and odd illuminations. The phase shifter elements 376A are conveniently conventional equipment for electronic scanning. The second linear array of antenna elements 3218, 3223, etc., is arranged in the same manner as the first linear array.

The distribution of sum and difference signals to the individual linear antenna arrays is provided by the beam synthesis networks 380 and 399. The beam synthesis network 385 couples the duplexer 336 and the elevation receiver 334E to the individual linear arrays. Network 380 is comprised of a plurality of directional couplers and/ or hybrids which distribute the sum signal and the elevation difference signal in the same manner as the beam synthesis network SStPA. Similarly, beam synthesis network 390 couples the azimuth receiver 334A to each of the beam synthesis networks 33tiA33tiH. With this arrangement the sum signals are distributed with a taper such as that illustrated at -16 in FIGURE lI-I in both angular dimensions. Similarly, in the two dimensions corresponding to azimuth and elevation, the difference signals are distributed in each dimension in accordance with the distribution function 17 in FIGURE 11-1. The result is that a radar beam is synthesized with a cross section of the pattern as illustrated in FIGURE 1G and the beam is scanned in azimuth and elevation in accordance with the phase shifts introduced by phase shift elements 37iiA-H.

While the fundamental novel features of the invention have been shown and described as applied to illustrative embodiments, it is to be understood that all modifications, substitutions and omissions obvious to one skilled in the art are intended to be within the spirit and scope of the invention as defined by the following claims.

What is claimed is:

1. A monopulse radar, beam synthesis, signal distribution network, interposed between a common multi-elernent antenna array and equipment including a receiver, for providing individually adjusted even and odd aperture illumination functions comprising:

(a) a plurality of feed transmission lines adapted to feed components of both sum and difference signals to respective elements of the antenna array;

(b) a first signal transmission line;

(c) a first hybrid connected to said first signal transmission line to distribute energy into two equal parts;

(d) a first series of directional couplers symmetrically connected to said first hybrid, each directional conpler being connected to distribute energy partly to a first port of the successive directional coupler and partly to a respective said feed transmission line in accordance with a first monopulse aperture illumination function;

(e) a second signal transmission line;

(f) a second hybrid connected to said second signal transmission line to distribute energy into equal parts; and

(g) a second series of directional couplers symmetrically connected to said second hybrid, each second directional coupler being connected to distribute energy partly to the successive directional couplers and partly to a respective said feed transmission line through a second port of a corresponding first directional coupler isolated from said first port, said distribution of energy by said second directional couplers being selected in accordance with a second monopulse aperture illumination function with allowance for partial energy distribution through said first series of directional couplers.

2. A monopulse radar, beam synthesis, signal distribution network, interposed between a common multi-element antenna array and equipment including a receiver, for providing individually adjusted even and odd aperture illumination functions comprising:

(b) a common sum signal transmission line;

(c) a first hybrid connected to said common sum signal transmission line to distribute energy into two equal parts;

(d) a first and second series of directional couplers con nected to said first hybrid to distribute said energy, each directional coupler being connected to distribute energy artly to a first port of the successive directional coupler and partly to a respective one of said feed transmission lines in accordance with an even monopulse aperture illumination function;

(e) a common difference signal transmission line;

(f) a second hybrid connected to said common difference signal transmission line to distribute energy into two parts; and

(g) a third and fourth series of directional couplers connected to said second hybrid to distribute said energy, each one of said third series of directional couplers being connected to distribute energy partly to the successive directional couplers of the same series and partly to a respective one of said feed transmission lines through a second port of a corresponding one of said first series of directional couplers isolated from said first port, said distribution of energy by said one of said third series of directional couplers being selected in accordance with an odd monopulse aperture illumination function with allowance for partial energy distribution through said first series of directional couplers and each one of said fourth series of directional couplers being connected to distribute energy partly to the successive directional couplers of the same series and partly to a respective one of said feed transmission lines through a second port of a corresponding one of said second series of directional couplers isolated from said first port, said distribution of energy by said one of said fourth series of directional couplers being selected in accordance with an odd monopulse aperture illumination function with allowance for partial energy distribution through said second series of directional couplers.

3. The monopulse radar system of claim 2 further comprising:

(h) a plurality of phase shift elements connected to respective ones of said feed transmission lines, said phase shift elements being adapted to provide electronic beam scanning.

4. The monopulse radar system of claim 2 wherein said directional couplers are arranged in a configuration which equalizes the length of the tranmission paths for the signal components from said common sum and said common difference transmission lines to the individual antenna elements.

5. A monopulse radar, beam synthesis, signal distribu tion network interposed between a multi-element antenna array and equipment including a receiver for providing individually adjusted even and odd aperture illumination functions comprising:

(a) a plurality of feed transmission lines adapted to feed signals to respective antenna elements of an antenna array to produce said first and second aperture illumination functions for desired monopulse radar beam patterns;

(b) a first common signal transmission line for said first illumination function;

(c) a first plurality of directional couplers connected in a tree configuration to said first common signal transmission line, said tree being coupled to said feed transmission lines in accordance with said first desired aperture illumination function; said tree consisting of an initial directional coupler forming a first rank, two directional couplers, each coupled to the coupler of the first rank, forming a second rank, and 2 couplers, each coupled to a coupler of the prior rank, forming the (N[1)' rank, where N is a plural integer;

(d) a second common signal transmission line for said second illumination function;

(e) and a second plurality of directional couplers connected between said second common signal transmission line and said feed transmission lines to couple said signals in accordance with said second desired aperture illumination function through the first directional coupler tree and adjusted to allow for signal distribution through the other directional couplers; said second plurality of directional couplers being connected into a succession of trees, each tree being branched to consolidate into a single trunk each plural membered rank of said first tree; additional branches consolidating said trunks so formed; and a final directional coupler coupled to said initial coupler of said first tree and the directional coupler in which said trunks are consolidated.

6. A monopulse radar, beam synthesis, sign-a1 distribution network interposed between a mu-lti-element antenna array and equipment including a receiver comprising:

(a) a plurality of feed transmission lines adapted to feed signals to respective antenna elements of an antenna array to produce an aperture illumination function for a desired radar beam pattern;

(b) a common sum signal transmission line;

(c) a first plurality of sum directional couplers connected in a tree configuration to said common sum signal transmission line, said tree being coupled to said feed transmission lines in accordance with a desired even aperture illumination function; said tree consisting of an initial directional coupler forming a first rank, two directional couplers, each coupled to the coupler of the first rank, forming a second rank,

and 2 couplers, each coupled to a coupler of the prior rank, forming the (N-l-l) rank, where N is a plural integer;

(d) a common difference signal transmission line; and

(e) a second plurality of difference directional couplers connected between said common difference signal transmission line and said feed transmission lines to couple said difference signals in accordance with a desired odd aperture illumination function through said sum directional coupler tree and adjusted to allow for signal distribution through the sum directional couplers, said second plurality of directional couplers being connected into a succession of trees, each tree being branched to consolidate into a single trunk each plural membered rank of said first tree; additional branches consolidating said trunks so formed; and a final directional coupler coupled to said initial coupler of said first tree and the directional coupler in which said trunks are consolidated.

'7. A three-dimensional, monopulse radar, beam synthesis, signal distribution network interposed between a multi-element antenna array and transmitter-receiver equipment comprising:

(a) a plurality of sets of feed transmission lines adapted to connect sum and difference signals to respective sets of antenna elements arranged in a two-dimensional array to produce an aperture illumination function for a desired radar beam pattern;

(b) a plurality of individual distribution networks, each individual network being connected to a respective set of feed transmission lines to couple sum and difference signals to one of the linear sets of antenna elements in accordance with the desired even and odd aperture illumination functions over a first angular dimension;

(c) a first common distribution network connected between a transmitter-receiver and a first difference receiver and said plurality of individual distribution networks arranged to couple a common sum signal and a common first difference signal to said plurality of individual networks in accordance with respective even and first odd aperture illumination functions; and

(d) a second common distribution network connected between a second difference receiver and said plurality of individual distribution networks and adjusted to provide a second odd aperture illumination function.

87 The monopulse radar system of claim 7 further comprising:

(e) a plurality of phase shift elements connected to respective ones of said feed transmission lines, said phase shift elements being adapted to provide electronic beam scanning.

9. The monopulse radar system of claim 7 wherein said directional couplers are arranged in a configuration which equalizes the length of the transmission paths for the signal components from said common sum and difference transmission lines to the individual antenna elements.

References Cited by the Examiner UNITED STATES PATENTS 2,286,839 6/1942 Schelkunoff 343-853 2,818,549 12/l957 Adcock et al 343-854 3,093,826 6/1963 Fink 343854 X 3,222,6177 12/1965 Fink 343854 OTHER REFERENCES Blass, A New Approach to Stacked Beams, IRE International Convention Record, 1960, vol. 8, Part I, pages 48-50.

Shel-ton, Perrino, Davis, Scanning Techniques for Large Flat Communication Antenna Arrays, Jan. 31, 1960, ASTIA No. AD 235571, pages 4959.

HERMAN KARL SAALBACH, Primary Examiner. CHESTER L. JUSTUS, Examiner.

P. M, HINDERSTEIN, E. LIEBERMAN,

Assistant Examiners,

Claims

1. A MONOPULSE RADAR, BEAM SYNTHESIS, SIGNAL DISTRIBUTION NETWORK, INTERPOSED BETWEEN A COMMON MULTI-ELEMENT ANTENNA ARRAY AND EQUIPMENT INCLUDING A RECEIVER, FOR PROVIDING INDIVIDUALLY ADJUSTED EVEN AND ODD APERTURE ILLUMINATION FUNCTIONS COMPRISING: (A) A PLURALITY OF FEED TRANSMISSION LINES ADAPTED TO FEED COMPONENTS OF BOTH SUM AND DIFFERENCE SIGNALS TO RESPECTIVE ELEMENTS OF THE ANTENNA ARRAY; (B) A FIRST SIGNAL TRANSMISSION LINE; (C) A FIRST HYBRID CONNECTED TO SAID FIRST SIGNAL TRANSMISSION LINE TO DISTRIBUTE ENERGY INTO TWO EQUAL PARTS; (D) A FIRST SERIES OF DIRECTIONAL COUPLERS SYMMETRICALLY CONNECTED TO SAID FIRST HYBRID, EACH DIRECTIONAL COUPLER BEING CONNECTED TO DISTRIBUTE ENERGY PARTLY TO A FIRST PORT OF THE SUCCESSIVE DIRECTIONAL COUPLER AND PARTLY TO A RESPECTIVE SAID FEED TRANSMISSION LINE IN ACCORDANCE WITH A FIRST MONOPULSE APERTURE ILLUMINATION FUNCTION; (E) A SECOND SIGNAL TRANSMISSION LINE; (F) A SECOND HYBRID CONNECTED TO SAID SECOND SIGNAL TRANSMISSION LINE TO DISTRIBUTE ENERGY INTO EQUAL PARTS; AND (G) A SECOND SERIES OF DIRECTIONAL COUPLERS SYMMETRICALLY CONNECTED TO SAID SECOND HYBRID, EACH SECOND DIRECTIONALY COUPLER BEING CONNECTED TO DISTRIBUTE ENERGY PARTLY TO THE SUCCESSIVE DIRECTIONAL COUPLERS AND PARTLY TO A RESPECTIVE SAID FEED TRANSMISSION LINE THROUGH A SECOND PORT OF A CORRESPONDING FIRST DIREC-