GB1558794A

GB1558794A - Electronic scanning antenna

Info

Publication number: GB1558794A
Application number: GB4579376A
Authority: GB
Original assignee: Thomson CSF SA
Current assignee: Thales SA
Priority date: 1975-11-04
Filing date: 1976-11-03
Publication date: 1980-01-09
Also published as: DE2650220A1; IT1068659B; FR2331164B1; DE2650220C3; NL7612093A; DE2650220B2; FR2331164A1

Description

(54) ELECTRONIC SCANNiNG ANTENNA (71) We, THoMsoN-CSF, a French Body Corporate, of 173, Boulevard Haussmann, 75008 Paris - France. do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by Lii following statement: The present invention relates to an electronic scanning antenna of the type in which a plurality of directional beams are produced which point in directions defined by different angles of elevation, these beams being capable of passing from one angle of elevation to another under the control of phase shifters associated with radar equipment radiating the electromagnetic energy transmitted or receiving the part of the energy returned by a target.

Antennas of this type, which are moreover given a movement of rotation in azimuth, permit the determination of the altitude of the located objects and also the tracking of these objects. However, if it is desired while effecting tracking also to maintain surveillance, it is necessary to provide another antenna associated with another detecting equipment.

The applicants have already proposed a system comprising a number of radiators, also termed elementary sources, which are spaced apart vertically and excited simultaneously through phase shifters which are associated therewith and produce a number of beams stacked in elevation, the angle of elevatio of these beams being made variable in accordance with concurrent adjustments of the phase shifters. This system was more particularly adapted for the evaluation of the altitude of tracked targets and was associated with an additional radar equipment provided with a particular antenna rotating in azimuth and effecting a surveillance.

In one embodiment, such an antenna comprises a number of radiators which are spaced vertically and coupled through phase shifters with two feed waveguides which were parallel to each other. One of these waveguides is connected through a rotary coupling and a multiplexer to three transmitters transmitting at three different frequencies, whilst the other of these wave g-.'des is connected directly to the receiver of the radar equipment and the couplers connecting it to the radiating sources enabling the detection of intercepted echos in a difference mode. Such an assembly consequently constitutes a transmitter-receiver operating as a monopulse radar.

In order to effect a surveillance which might be considered necessary during the evaluation of the altitude of the objects or their tracking, another radar equipment was provided.

The drawback which arises with such an arrangement is that it requires two different equipments operating differently, the surveillance radar being a panoramic radar in which the rotation of the antenna has to be synchronized with that of the waveguides of the electronic scanning antenna.

An object of the present invention is to avoid or substantially reduce the drawback of the arrangement mentioned hereinbefore by eliminating the particular radar whose function was to effect the surveillance and to incorporate this function in the radar provided with the electronic scanning antenna.

The present invention consists in an electronic scanning antenna comprising a number of aligned radiators capable of transmitting and receiving electro-magnetic energy, a first waveguide connected with a first transmitter transmitting at a first frequency and with a receiver through a duplexer, a first group of fixed phase shifters connecting said radiators to said first waveguide through a first group of couplers producing a first beam fixed in elevation, a second waveguide parallel to said first one and located behind it relative to said radiators, said second waveguide being connected with a second transmitter transmitting at a second frequency and with a second receiver through a duplexer, a group of variable phase shifters connecting said radiators to said second waveguide through a second group of couplers, producing a second beam which is movable in elevation.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: - Fig. 1 is a diagram showing the fixed and movable beams obtained with the antenna according to the invention; - Fig. 2 is a block diagram of an embodiment of antenna with two feed waveguides; - Fig. 3 is the radiation patterns of the sources fed at the same frequency by the feed waveguides G1 and G2; - Fig. 4 shows the angular deviation curve in the case shown in Fig. 3; - Fig. 5 is a block diagram of an embodiment of antenna having three feed waveguides; - Figs. 6, 7 and 8 are radiation patterns of the sources for different aiming of the movable beam; - Fig. 9 shows the curves of the distribution of the power exciting the waveguide G2 as a function of the aiming-off; and - Fig. 10 is a block diagram of an embodiment of antenna with a plurality of transmitters and receivers.

As already mentioned in the introduction of the present description, antenna arrays are capable of producing one or several fixed beams for given values of frequency and/or phase and one or more movable beams if there are defined phase shifts between the radiators, which phase shifts are usually given by electronically controlled phase shifters. However, it does not seem that there has been constructed, in particular for the purpose of effecting simultaneously tracking and surveillance with the same radar antenna, one antenna array giving simultaneously fixed and movable beams as concerns angles of elevation.

The present invention provides a solution to the problem of simultaneous tracking and surveillance and relates to the construction of an antenna array producing, as shown in Fig. 1, at least one first beam FAl preferably established with a. fixed low angle of elevation and allowing a surveillance, and at least one second beam or movable beam FA2 allowing the tracking and/or the determination of the altitude of the targets which have been detected by the first beam FA which is movable as concerns bearing.

Fig. 2 shows a block diagram of an embodiment of an antenna array according to the invention.

A plurality of radiating elements or radiators, for example in the form of horns Al to An, are disposed one above the other and capable of transmitting energy into space and receiving energy. These sources are part of an assembly which rotates in azimuth about a vertical axis in the illustrated embodiment. The radiators may be associated with a reflector which, however, has not been shown in the Figure. These radiators Al to An are connected through phase shifters DF1 to DF" having a fixed phase shift value, with a waveguide G1 connected, on the one hand, through a rotary coupler JTl and a duplexer DUl, to a transmitter El operating at a frequency fl and on the other hand, to a receiver Rl. The connection of the different radiators to the waveguide is achieved by directional couplers C1 to Cn respectively. A dissipative load CHi is provided at the other end of the waveguide G1.

A second waveguide G2, disposed at the rear of the first waveguide G1, relative to the radiators, is also connected to the different radiators and the waveguide G1 through transmission lines carrying the phase shifters DVl to DVn which are variable and controlled by an element which may be a computer (ST. The connection to the guide G2 is achieved by directional couplers c')i to CD" one branch of each of which is respectively connected with a load CL1 to C The waveguide G2 is connected at one of its ends, through a rotary coupler JT2 and a duplexer DU2, with a transmitter E2 operating at a frequency f2 and with a receiver R2. At its other end the waveguide G2 is connected to a dissipative load CH2.

The device shown in Fig. 2 operates in the following manner. The electromagnetic energy produced by the transmitter El feeds the different radiators Al-An in series through the different directional couplers C1 to Cn The waveguide G1 dispersive and propogates a travelling wave; the direction of the maximum radiation of the beam FA1 produced depends on the frequency of the transmitter El. At this frequency and with the phase shifters DFl to DFu inserted in the connections between the waveguide G1 and the radiators Al-An which are fixed, that is to say given a value which does not vary, it is possible to obtain a first beam FAl fixed in elevation which is aimed at a well-determined given direction. Normally it is advisable that this direction be such that this first beam is aimed at a direction having a low angle of elevation, thereby enabling a surveillance to be made.

The waveguide G2 located, relative to the radiators, behind the waveguide G1 with which it is parallel, is fed by a second transmitter E2 operating at a frequency f2.

Through the agency of directional couplers CD1 to CUn, the main output of which is connected respectively to one arm of the coupling elements C1 to Cn through a transmission line, the elements Al to An radiate a second beam FA2 independent of the first beam FAl. As can be seen, the feeds of the waveguides G1 and G2 are independent and the inputs of the waveguides are decoupled from one another. As the phase shifters DV, to DVn respectively inserted in the transmission lines coupling the waveguide G2 with the couplers C1 to Cn are variable and controlled electronically by the computer CT,, the beam FA2 is movable as concerns its angle of elevation and is capable of aiming, depending on the values set in the variable phase shifters DV1DVn, in several directions stacked in elevation, the higher of which may reach 50 degrees.

The above described antenna may be used with a monopulse radar by setting the variable phase shifters so as to permit the beam FA2, produced by the waveguide G2, to point at a given instant in the same direction as the first beam FA1. With this arrangement there is produced in this direction, by means of the waveguide G2, a difference pattern, which permits the first heam FA1 to have a reception on the sum pattern established by the waveguide G1 and on the difference pattern established by the waveguide G2. However, in this case, the waveguide G2 is connected with a receiver R21 set at the frequency fl via the switch SW2.

Fig. 3 shows these sum and difference patterns S1 and D1 respectively obtained from the waveguide G1 for the sum and the waveguide G2 for the difference.

Fig. 4 partly repeats Fig. 3 as concerns the radiation patterns S1, D1 but there has been added the angle deviation curve T1 plotted with respect to the axes T, angle of elevation and u. It will be noted that the angle deviation curve has a large linear part.

Except in the particular case which is referred to above, the movable beam produced by the waveguide G2 radiates a pattern of the sum type.

Fig. 5 shows a modification of the antenna according to the invention in which there has been added a third waveguide G3 which is parallel to the first two waveguides already mentioned. This waveguide G3 is connected at one of its ends to receiver R3 set at the frequency f2 and at its other end to a load CH. It is connected to the radiating sources A1--An through couplers CP1 to CP. The connection between the couplers and the radiators is achieved through fixed phase shifters DP to DP,. This connection is continued through the couplers of the waveguide G2, the variable phase shifters DVt to DV", the couplers of the waveguide G1 and the fixed phase shifts DFl to DF. The radiators fed by said third waveguide at frequency f2 exhibit a radiation pattern of the difference type. Since the radiators fed by said second waveguide G2 exhibit a radiation pattern of the sum type, the electronic scanning antenna described provides a first beam fixed in elevation a second beam radiating a sum pattern and a third beam having a different pattern. The equipment comprising such an antenna is a monopulse radar which is able simuftane ously to perform both tracking and surveillance.

As the above antenna is movable in azimuth, rotary joints JT1, JT2 and JT3 are provided on Fig. 5, on which duplexers DUl and DU2 have also been shown.

Figs. 3 and 4 showed the patterns obtained for the radiators fed by the waveguide G1 and by the waveguide G2 for the same fre quency and for a fixed aiming in the direction of the normal to the array, and the corresponding angle deviation curve.

Figs. 6 to 9 show patterns obtained by the feeding of the antenna by the waveguide G2 as a function of aiming orders with omission for convenience, of the linear law function.

The diagrams are thus superimposed upon a certain aiming error.

In a concrete case the antenna comprises about 40 sources spaced apart 83 mm in the S band, thus producing a beam of 2" in width at half power, the beam aimed at 30 has a first lobe at 19 dB and that aimed at 4" has a first lobe at 23 dB.

In Fig. 6 there are shown patterns obtained from the waveguide G2 as a function of the beam aiming at 1 , 2" and 3 respectively by P1, P2 and P3.

Fig. 7 shows the patterns P4, P5 and P6 for the beam aiming corresponding to 40, 50 and 6" respectively. Fig. 8 shows the pattern P7 for a beam aiming corresponding to 10 .

Other patterns of the same type could also be represented which would show, as those illustrated in the Figures, that the sum patterns of the radiators fed by the waveguide G2 are of a quality which improves progressively as one moves away from the first beam.

Fig. 9 shows the distribution of the power between the radiation and the loads CH1 and CH2 at the end of the two waveguides G1 and G2 respectively, when waveguide G2 is energised for various aiming orders. From the aiming of 3 on, the power dissipated in the load of the waveguide G1 is acceptable and of the order of one percent. However, it may be noted that the load of the waveguide G2 dissipates the same power as that of the waveguide G1 when it is excited, that is to say 1 to 2% of the total power.

The curve A gives the power radiated as a function of the aiming-off of the beam FA2; the curve B gives the power dissipated in the load of the waveguide G1, and the curve C the power dissipated in the waveguide G2.

Note that the couplers employed in the different feed waveguides of the radiating sources have no particular features. They are generally constituted by waveguide junctions the branches of which have coupling factors or transfer coefficients determined in such manner that the energy is correctly distributed throughout the length of the array.

The foregoing description discloses the production of a first beam fixed in elevation and also a movable beam, which enables a single radar equipment to have simultaneously a surveillance channel at a low angle of elevation for example and a surveillance channel or tracking channel with a variable angle of elevation. However, the invention is not intended to be limited to this case and it is easy to multiply the number of transmitters and receivers to obtain with the described antenna a multibeam coverage with, for example, two beams having fixed low angles of elevation and one or more beams movable in a group.

Fig. 10 shows an embodiment of electronic scanning antenna according to the invention in which it is desired to have two beams fixed in elevation and two movable beams.

This Figure repeats, with the same reference characters, a large part of Fig. 2.

There has merely been added to the end of the waveguide G1 adjacent the rotary joint JT1, a low-level multiplexer Ml 1 connected to the duplexer DU1 and also connected with two receivers RM11, RM,2 and high-level multiplexer M12 connected with two transmitters EM11 and EM,2 operating at two different frequencies.

Likewise, there is disposed at the end of the waveguide G2, adjacent the rotary joint JT2, a low-level multiplexer M21 connected to the duplexer DU2 a second high-level multiplexer M22. The multiplexer M21 is connected. with two receivers RM,, and RM22 and the multiplexer M22 with two transmitters EM21 and EM22 operating at two different frequencies which are also different from those of the transmitters associated with the waveguide G1.

The operation of a system such as that diagrammatically represented in Fig. 10 is not basically different from that of the system of Fig. 2 or of Fig. 5 in which a third feed waveguide G3 was added. The energy delivered respectively by the transmitters EMll and EH12 at frequencies which are different but close to each other, for example, and with an appropriate setting of the values of the fixed phase shifters DFl to DF,, contributes to the production of two beams fixed in elevation which are in the neighbourhood of each other and aimed at two angles of elevation in the neighbourhood of each other.

Likewise, the energy delivered respectively by the transmitters EM21 and EM22 at two different frequencies which differ from those of the transmitters EM11 and EM,2 and with an appropriate setting of the variable phase shifters DV1 to DVn, contributes to the production of two movable beams in the neighbourhood of each other and movable together as concerns angle of elevation.

Moreover, it is evident that the number of transmitters and receivers may be diiicrent from that shown in Fig. 10.

There has thus been described an electronic scanning antenna, which produces simultaneously one or more beams fixed in elevation and one or more beams which are movable as concerns angle of elevation, and allows a surveillance and tracking to be made simultaneously with one and the same equipment.

WHAT WE CLAIM IS:- 1. Electronic scanning antenna comprising a number of aligned radiators capable of transmitting and receiving electromagnetic energy, a first waveguide connected with a first transmitter transmitting at a first frequency and with a receiver through a duplexer, a first group of fixed phase shifters connecting said radiators to said first waveguide through a first group of couplers producing a first beam fixed in elevation, a second waveguide parallel to said first one and located behind it relative to said radiators, said second waveguide being connected with a second transmitter transmitting at a second frequency and with a second receiver through a duplexer, a group of variable phase shifters connecting said radiators to said second waveguide through a second group of couplers, producing a second beam which is movable in elevation.

2. Electronic scanning antenna according to claim 1, wherein a rotary joint is provided in the connection of each waveguide with its corresponding transmitter and receiver, for enabling the antenna to rotate in azimuth, each said waveguide being further connected to a respective dissipative load.

3. Electronic scanning antenna according to claims 1 or 2, wherein the first beam radiates a pattern of the sum type.

4. Electronic scanning antenna according to claim 1 or 2, wherein the second beam is adapted to radiate a pattern of the difference type by setting the variable phase shifters so as to aim said second beam substantially in the direction of the first beam, there being provided a second receiver connected to said second waveguide.

5. Electronic scanning antenna according to claim 1 or 2, comprising further a third waveguide parallel to said first and second waveguides respectively and located behind said second waveguide relative to said radiators, a third receiver tuned to said second frequency and connected to said third waveguide, said third waveguide being further connected to a third dissipative

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. distributed throughout the length of the array. The foregoing description discloses the production of a first beam fixed in elevation and also a movable beam, which enables a single radar equipment to have simultaneously a surveillance channel at a low angle of elevation for example and a surveillance channel or tracking channel with a variable angle of elevation. However, the invention is not intended to be limited to this case and it is easy to multiply the number of transmitters and receivers to obtain with the described antenna a multibeam coverage with, for example, two beams having fixed low angles of elevation and one or more beams movable in a group. Fig. 10 shows an embodiment of electronic scanning antenna according to the invention in which it is desired to have two beams fixed in elevation and two movable beams. This Figure repeats, with the same reference characters, a large part of Fig. 2. There has merely been added to the end of the waveguide G1 adjacent the rotary joint JT1, a low-level multiplexer Ml 1 connected to the duplexer DU1 and also connected with two receivers RM11, RM,2 and high-level multiplexer M12 connected with two transmitters EM11 and EM,2 operating at two different frequencies. Likewise, there is disposed at the end of the waveguide G2, adjacent the rotary joint JT2, a low-level multiplexer M21 connected to the duplexer DU2 a second high-level multiplexer M22. The multiplexer M21 is connected. with two receivers RM,, and RM22 and the multiplexer M22 with two transmitters EM21 and EM22 operating at two different frequencies which are also different from those of the transmitters associated with the waveguide G1. The operation of a system such as that diagrammatically represented in Fig. 10 is not basically different from that of the system of Fig. 2 or of Fig. 5 in which a third feed waveguide G3 was added. The energy delivered respectively by the transmitters EMll and EH12 at frequencies which are different but close to each other, for example, and with an appropriate setting of the values of the fixed phase shifters DFl to DF,, contributes to the production of two beams fixed in elevation which are in the neighbourhood of each other and aimed at two angles of elevation in the neighbourhood of each other. Likewise, the energy delivered respectively by the transmitters EM21 and EM22 at two different frequencies which differ from those of the transmitters EM11 and EM,2 and with an appropriate setting of the variable phase shifters DV1 to DVn, contributes to the production of two movable beams in the neighbourhood of each other and movable together as concerns angle of elevation. Moreover, it is evident that the number of transmitters and receivers may be diiicrent from that shown in Fig. 10. There has thus been described an electronic scanning antenna, which produces simultaneously one or more beams fixed in elevation and one or more beams which are movable as concerns angle of elevation, and allows a surveillance and tracking to be made simultaneously with one and the same equipment. WHAT WE CLAIM IS:-

1. Electronic scanning antenna comprising a number of aligned radiators capable of transmitting and receiving electromagnetic energy, a first waveguide connected with a first transmitter transmitting at a first frequency and with a receiver through a duplexer, a first group of fixed phase shifters connecting said radiators to said first waveguide through a first group of couplers producing a first beam fixed in elevation, a second waveguide parallel to said first one and located behind it relative to said radiators, said second waveguide being connected with a second transmitter transmitting at a second frequency and with a second receiver through a duplexer, a group of variable phase shifters connecting said radiators to said second waveguide through a second group of couplers, producing a second beam which is movable in elevation.

load, a third group of couplers and a second group of fixed phase shifters connected to said couplers respectively and connecting said third receiver to said radiators and said second group of fixed phase shifters being set so as to detect echoes intercepted at said second frequency in the difference mode.

6. Electronic scanning antenna according to claims 1, 2, or 5 wherein the transmission lines coupling said radiators with the different feed waveguides are terminated by loads at the side opposite to said radiators.

7. Electronic scanning antenna according to claim 1 or 2, comprising a plurality of transmitters connected via a multiplexer to an input of the respective duplexer, a plurality of receivers connected via another multiplexer to an output of the respective duplexer, the operating frequencies of all the transmitters being different from one another, whereby a plurality of first and second beams are generated.

8. Electronic scanning antenna substantially as hereinbefore described with reference to Figs. 1 to 4 of Figs. 5 to 9 or Fig. 10 of the accompanying drawings.

9. Radar equipment including an electronic scanning antenna scanning as claimed in any preceding claim.