GB924208A - Improvements in and relating to the testing of radar apparatus - Google Patents

Abstract

924,208. Radar. A. C. COSSOR Ltd. Aug. 4, 1959 [Aug. 1, 1958], No. 24945/58. Class 40 (7). In an arrangement for testing pulse radar apparatus of the type adapted to indicate moving objects only, energy from the apparatus 11 (Fig. 1) is received at a predetermined position 15 and there, prior to being reflected back to the apparatus 11, subjected to a phase modulation by means of a device 17 to simulate a moving target. In one embodiment the device 17 consists of a waveguide 18 (Fig. 2) provided with a load impedance comprising the series arrangement of a resistor 20 and a crystal diode 21 connected across two opposite walls of the waveguide. By varying a voltage supplied between terminal 22 and the waveguide casing (i.e. the voltage across the diode) the impedance of the load and hence its absorption of energy may be varied to vary the phase of the energy reflected back to the apparatus 11. To check the operation of the apparatus with respect to a fixed target the load impedance 20, 21 is made fully absorbing and a peg 23 of conducting material then determines the level of the reflected energy. Fig. 3 shows a second embodiment in which the required phase variation to simulate moving targets is produced by rotation of a two vaned metallic paddle 24, 25 in the waveguide 18. In other arrangements for producing phase variations in the received energy the waveguide 18 is dispensed with and a rotating paddle, or the parallel combination of four crystal diodes across which a varying voltage is supplied, is positioned at the focus of reflector 15 (Figs. 4 and 5, not shown). The variation of the voltage control in the cure of the impedances employing crystal(s) is preferably effected by a square-wave signal of one half the repetition frequency of the pulses transmitted by the apparatus 11.