GB1085071A - Radar target simulators - Google Patents

Abstract

1,085,071. Radar simulators; aerials. ELLIOTT BROTHERS (LONDON) Ltd. Nov. 5, 1964 [Nov. 15, 1963], No. 45208/63. Headings H4A and H4D. To enable a radar system to be tested a radar target simulator is provided whereby a radar pulse is received, heterodyned down to an I.F. pulse, delayed for a period consistent with the target range to be simulated, heterodyned up to a pulse of the original radar frequency, and then attenuated by an amount consistent with the target range and size to be simulated, to provide a simulated target echo pulse for transmission back to the radar system. The radar pulse is received by aerial 1, Fig. 1, and is fed, via circulator 7 and fixed attenuators 11, 12, to a first mixer 13, where it is heterodyned with a signal from local oscillator 14 at such a frequency that the output pulse from the mixer has a frequency of 150 Mc/s. The pulse frequency is further heterodyned down to 15 Mc/s. in mixer 16, with the aid of the output of local oscillator 17 at 135 Mc/s. The frequency of the output of the mixer 16 is monitored in discriminator 36 and any frequency deviation from 15 Mc/s. causes a servo control to operate to readjust the frequency of oscillator 14. The I.F. pulse at 15 Mc/s. is delayed in a mercury delay line 19 under the control of a servo 31 which is fed with signals representing the range and range rate to be simulated. The delayed I.F. pulse is heterodyned up to its original radar frequency by means of mixers 21 and 23 and local oscillators 14 and 17. The system so described should be such that the amplitude of the radar pulse at the output filter 24, is the same as its amplitude at the input of attenuator 20. This equality is checked by means of comparator 43 comparing said amplitudes and feeding any correcting signal to control a variable gain amplifier 20. The delayed radar pulse is now passed to attenuator 25 where it is attenuated in accordance with the simulated target area. The attenuated radar pulse is further attenuated in attenuator 26 which is varied, via specially profiled cam 32, by servo 31, such that as delay 19 is varied to simulate the range, the radar pulse is attenuated by attenuator 26 according to the fourth power of the range. The thus delayed and twice attenuated radar pulse is retransmitted by aerial 1. The operation of the simulator may be checked using pulse generator 64. The waveform of the I.F. pulse may be observed on C.R.O. monitor 39. The aerial 1 may be a simple horn radiator mounted on a tripod and backed with a screen of radar wave absorbing material, Fig. 2 (not shown), or the horn may be mounted on a carrier which is movable along rails under the section of a motor-driven pulley when it is desired to vary the bearing of the simulated target. The rails are mounted such that they can be pivoted from horizontal to vertical, Fig. 3 (not shown). Where noise-free simulator is desired the aerial may be replaced by a probe, which is inserted in a hole in a waveabsorbing cone which is placed over the radar transmitting aerial, Fig. 2 (not shown).