Patent GB-1039406-A (GB)
Title: Improvements in radar testing systems
IPC: G01S7/40
Filed: 1963-07-30
Abstract: 1,039,406. Pulse radar test equipment. CANADIAN WESTINGHOUSE CO. Ltd. July 30, 1963 [Sept. 28, 1962], No. 30195/63. Heading H4D. A radar test arrangement comprises a test area, a plurality of antennas at one end of the test area, an opening at the opposite end of the test area to receive the antenna of the radar equipment to be tested, a source of radio frequency signals simulating the normal signals produced by reflection of signals from the radar equipment, means to apply the signals from the source to the antennas, including means to independently modify the characteristics of said signals applied to each of the antennas. In one arrangement according to the invention, wherein the response of a radar equipment 21, Fig. 3, having a downwardly directed radiation beam, to a distributed ground portion 22, 24, 23, is simulated, two antennas 12 and 8 are provided, mounted one above the other. A signal generator 5 produces output signals of the same frequency as those radiated from the radar, under the control of a signal on line 17. A remote control unit 13 feeds control signals to the signal generator, such that the generator feeds its output signals to two modulators 6 and 9, in bursts having the envelopes shown in Fig. 2 (B), where time 20, measured with respect to the corresponding pulse transmitted by the radar equipment, represents the distance 21 to 24, and the burst duration 19, represents the extent 25, measured along the beam, of the ground portion. The remote control 13 also feeds control signals to a waveform generator 14, which produces output signals on lines 15 and 16, as shown in Fig. 2 (C) and (D) respectively. These latter output signals are used to control modulators 6 and 9, respectively, such that the envelopes of the signal bursts fed from the generator 5 to the modulators, are changed from rectangular to the shape of the corresponding waveform generator signal. The output of modulator 6 having the envelope shown in Fig. 2 (C) is fed, via attenuator 7, to antenna 8, for radiation thereby. The output of modulation 9 having the envelope shown in Fig. 2 (D) is similarly fed via attenuator 11 to antenna 12. If the slope and maximum values of the output signals are equal, the latter being determined by the attenuators, the radar antenna interprets the signals radiated by the two antennas as follows. At the beginning, at a time representing minimum range, all the energy is received from antenna 8. Point 22 is thus simulated. After an interval 19, Fig. 2 (B), corresponding to a increase of range 25, all the energy is being received from antenna 12 at a higher elevation than antenna 9. Point 23 is thus simulated. In between these times the rest of the ground portion is simulated. Due, however, to the bore sight of the beam 21, 24 not bisecting the line between the two antennas, the simulated line will be a curve. The curvature can be lessened by reducing the slope of the envelope of the output of antenna 8, or by increasing the slope of the envelope of the output of antenna 11. A phase shifter 10 is provided in one output line to bring the outputs of the two antennas into exact phase. If it is desired to simulate only a part of the ground portion, the envelopes of the antenna signals are caused to vary as shown by the dotted lines in Figs. 2 (C) and (D). A change in the slope of the simulated ground portion may be caused by changing the dimension 19. If the radar equipment is of the phase sensing type the amplitude modulators 6 and 9 are replaced by phase modulators, and the waveforms at Fig. 2 (C) and (D) represent the phase shift of the signal from a datum position. In an alternative arrangement whereby a moving point target is simulated, the duration of the waveform generator pulses of Fig. 2 (C) and (D) may be extended to many times the pulse repetition rate of the radar and the durations of the pulses from signal generator 5 shortened to that of a point echo return, such that the pulses radiated by the antennas 8 and 12 have respective successively decreasing and increasing amplitudes and producing the simulation of a point target moving from the lower to the upper antenna. If each signal generator pulse is displaced in time relative to the preceding one, a radial movement of the target may also be simulated.