Radar transmitters

Abstract

 Recent proposals to use multiple solid state amplifiers to energise different elements of an antenna array are accompanied by problems in providing the required amplitude control at the individual elements.
This can be improved by having twelve antenna elements (2) driven from a common line (1) from which is taken a signal at line (3). This is passed via phase shifters (9 and 10) and identical amplifiers (11 and 121 to a hybrid (13). One output of this is transmitted via phase shifters (19 and 20) to another hybrid (21). The outputs of the hybrids are used to power three antenna elements (2A,2B and 2C). A similar process is applied to signals taken from lines (4,5 and 6).
By adjusting the phase shifters (9,10,19 and 20), the required control can be obtained over the power distribution across the antenna aperture.

Description

[0001] This invention relates to a radar transmitter having an array of antenna elements.

[0002] Conventionally such transmitters have employed a single vacuum tube amplifier the output of which is distributed between individual elements using appropriate amplitude and phase control techniques to provide the desired amplitude and phase at each element. More recently there has been a proposal to use, instead of a single high power amplifier, a number of relatively low power solid state amplifiers. This can give a saving in cost if the solid state amplifiers are all manufactured to the same specification i.e. if they are nominally identical. It does however present certain problems in obtaining the required phase and amplitude at the individual antenna elements and existing proposals using multiple solid'state amplifiers have not completely solved these problems. It was against this background that the present invention arose.

[0003] According to the invention there is provided a radar transmitter comprising a plurality of power feed systems each for feeding a signal to be transmitted from a common line to two or more elements of an array of antenna elements, each power feed system having: means for feeding signals from the common line to amplifiers; means for controlling the relative phase of the signals to the amplifiers; a mixer system having inputs connected to receive signals from the amplifiers and outputs between which the mixer system, in operation, distributes the_/received power in a manner depending on the relative phase at its inputs, the mixer-outputs being connected to respective antenna elements.

[0004] By employing the invention and by suitably selecting the antenna elements to be fed from each individual power feed system, it is possible to obtain a good degree of control over the power levels at the different antenna elements. Since this is done using a phase control technique at the inputs to the amplifiers, there need be only a small power loss.

[0005] For reasons of economy previously explained, all the amplifiers are preferably nominally identical though it may be -practicable in some circumstances to use two or more batches of amplifiers where those of each batch are nominally identical but different from those of another batch.

[0006] The features of the invention described above do not necessarily give the required phase control over the output from each antenna element so it.is preferable that means are included for controlling the relative phase of the power from the mixer outputs.

[0007] This facility could conveniently be provided by phase shifters arranged only in connections to those output ports having lower power levels, since this reduces losses.

[0008] Preferably three outputs of the mixer system are connected to respective antenna elements although two, or more than three, outputs could be so connected. It will usually be desirable for one output of each power feed system to be connected to an element near the centre of the antenna and two others to be connected to outer elements, the power being distributed so that most of it goes to the centre element.

[0009] There are many different ways in which the mixer system can be provided. One possibility, which is preferred, is to use two hybrids arranged so that an output of one of them provides inputs for the other.

[0010] The array is preferably a linear array, but the invention is also applicable to antenna systems having a plurality of linear arrays, a curved or a circular array.

[0011] One way in which the invention may be performed will now be described by way of example with reference to the accompanying drawing of a radar transmitter in accordance with the invention.

[0012] Referring to the Figure , the radar transmitter leads signals to be transmitted along a channel 1 from which the signals are divided equally onto four lines 3,4,5, and 6 to four power feed systems.

[0013] The signals on line 3 are further divided into lines 7 and 8 and passed through two phase shifters 9 and 10 respectively. The outputs of the phase shifters 9 and 10 are applied to two nominally identical solid state amplifiers 11 and 12, the outputs of which are applied to input- of a hybrid 13. The hybrid 13 is of the type such that the relative phase between signals at its inputs determines the relative amplitude of power at its outputs. Thus the phase shifters 9 and 10 determine the power at the outputs on lines 14 and 15.

[0014] The power on line 14 is applied to an element 2A of the central four of an array of twelve antenna elements via a T.R. cell 16.

[0015] The power on line 15 is further divided between two other lines 17 and 18 each having a phase shifter 19 or 20 on it through which the power passes. This power on lines 17 and 18 is applied to the inputs of a second hybrid 21. The output power level of the hybrid 21 is again controlled by the relative phase of its inputs and is applied to two channels 22 and 23.

[0016] The power on channel 22 is passed via phase shifter 24.and a T.R. cell 25 to an antenna element 2B spaced three elements from the element 2A. The power on channel 23 passes via a T.R. cell 26 to the other of the elements 2C spaced three elements from element 2A.

[0017] The.phase shifter 24 introduces phase control for the element 2B and phase shifters 19 and 20 allow both amplitude control of the outputs on channels 22 and 23 and phase control for the element 2C. The phase shifters 9 and 10 provide amplitude control of the outputs of the hybrid 13 and phase control for the element 2A fed by line 14.

[0018] The signals on the other three lines 4,5 and 6 to other feed systems are similarly processed, those elements fed initially from signals on line 4 being adjacent to those fed by signals on line 3.

[0019] The power distribution required from the particular antenna described above is one which requires most of the power to be transmitted to the most central element 2A of the three fed by the illustrated feed system and the outer most element 2B fed by power along channel 22 receives the least amount of power. The phase shifters of the illustrated feed system are positioned and adjusted so that lines carrying the highest level of power contain the least number of phase shifters and vice versa, hence giving low power loss.

[0020] Another variation (not shown) includes a three line coupler which is a device having three inputs and three outputs and designed so that incoming energy is distributed between the outputs according to the relative phases at its inputs. Similarly a coupler having five lines or any other number of lines can be used.

Claims

1. A radar transmitter characterised by a plurality of power feed systems each for feeding a signal to be transmitted from a common line to two or more elements of an array of antenna elements, and further characterised in that each power feed system has: means (3) for feeding signals from the common line (1) to amplifiers (11,12) ; means (9,10) for controlling the relative phase of the signals to the amplifiers (11,12); and a mixer system (13,15,17,18,19,20,21) having inputs connected to receive signals from the amplifiers (11,12) and outputs (14,22,23) between which the mixer system (13,15,17,18,19,20,21), in operation, distributes the received power in a manner depending upon the relative phase at its inputs, the mixer outputs (14,22,23) being connected to respective antenna elements (2A, 2B, 2C).

2. A radar transmitter as claimed in claim 1 and characterised in that all of the amplifiers (11,12) are nominally identical.

3. A radar transmitter as claimed in claim 1 or 2 characterised in that the spacing between antenna elements of all adjacent pairs are equal.

4. A radar transmitter as claimed in claim 1, 2 or 3 characterised by means (9,10,19,20,24) for controlling the relative phase of the power from the mixer outputs.

5. A radar transmitter as claimed in any preceding claim characterised in that three outputs (14,22,23) of the mixer system are connected to respective antenna elements (2A, 2B, 2C).

6. A radar transmitter as claimed in claim 5 -characterised in that the mixer system (13,15,17,18,19,20,21) includes two hybrids (13,21).

7. A radar transmitter as claimed in any preceding claim characterised in that the said array is a linear array.

8. A radartransmitter as claimed in any preceding claim characterised in that the amplifiers (11,12) are solid state amplifiers..

Drawing