Patent GB-980217-A (GB)
Title: Improvements in radar testing equipment
IPC: G01S7/40
Filed: 1963-07-29
Abstract: 980,217. Radar testing equipment; testing aerials. CANADIAN WESTINGHOUSE CO. Ltd. July 29, 1963 [Sept. 4, 1962], No. 30003/63. Headings H4A and H4D. A test equipment for a radar system 2, Fig. 1, comprises a signal generator 22 for producing signals simulating the signals received by the radar system reflected from a target, a plurality of spaced antennas 4, 5, 6 and 7, and switching means 8 for selectively connecting any one of said antennas to said generators to permit the radiation of said signals from said antennas in accordance with a predetermined sequence and thereby create a simulation of relative angular motion between the radar system and a target. The antennas are mounted at the end wall of an anechoic chamber 3 having an opposite open end through which the antenna of the radar system to be treated is introduced. A separate antenna 9, adjacent the open end receives the pulses radiated by the radar. Part of the thus received energy is taken off by a directional coupler 20 to an automatic frequency control system 21, whereby the frequency of the energy produced by the signal generator 22 is continually caused to equal that of the signals received by the antenna 9. The said frequency is read off of knob 33. Most of the energy received by antenna 9 is passed to a microwave detector 11 which produces the envelope, Fig. 3A, of the received radar pulses. This envelope signal is passed to a system trigger 12 which squares off the pulses to produce the waveform shown in Fig. 3B. This waveform is then passed on two lines to a precision delay 13 and a range sawtooth generator 14. The range sawtooth generator produces the sawtooth output shown in Fig. 3D having the same repetition period as, and in synchronism with the received radar pulses. A velocity ramp function generator 17 produces a ramp voltage having a duration extending over many of the sawtooths produced by the generator 14. The ramp and sawtooth voltages are shown together in Fig. 3E, the scale of this figure being smaller than that of Fig. 3D. The two voltages are compared in a comparator 18 such that the pulses shown in Fig. 3F are fed to a pulse generator 19 every time the sloping parts of the two waveforms become equal. Each pulse fed to the pulse generator lays the corresponding received radar pulse by an amount increasing with end pulse at a rate depending on the slope of the ramp voltage, and can thus be used to simulate the echo return of a target changing its range with respect to the radar system. The slope of the ramp voltage and thus the simulated target velocity is controlled by a signal or line 16 from a remote control and monitor unit 15. The precision delay 13 may be of the magnetostrictive type and introduce a fixed delay in the pulses from the system trigger 12 to produce a train of pulses for simulating the echo return of a fixed target at a known range whereby the range measuring apparatus of the radar system may be checked and/or calibrated. A control pulse from the remote control and monitor unit 15 on line 25 determines whether the output of the comparator 18 or the precision delay 13 is to be fed to the pulse generator. When it is desired to simulate a fixed target at a range other than that determined by the delay introduced by the precision delay 13, the control voltage on line 16 can be dropped to zero and a constant voltage fed to the second input of comparator 18, in lieu of the ramp voltage. Whichever output is passed to the pulse generator 19 causes the production of corresponding pulses operating microwave switch 23 to pass the energy from the microwave signal generator 22 to the antennae, via an attenuator 34 and an antenna switch unit 8. To simulate the effect of the echo return momentarily fading, a pulse generator 55 may be provided controlled by the remote control and monitor unit 15, to block the pulse generator 19 for the requisite time. The radar transmitter power can be monitored by means of a transmitter power monitor 28 which is fed with the radar energy received by antenna 5 under the control of the remote control and monitor unit 15. The simulated echo pulses from the microwave switch 23 can be fed to any of the antennae 4, 5, 6 and 7 under the control of the antenna switch unit 8, in any order, such that an angularly moving target as well as a radially moving target may be simulated. The antenna switch unit 8 is shown in detail in Fig. 2, together with the four antennae. The four antennae are arranged in two pairs, each pair having a two-way input switch 41 and 42 controlled by the remote control and monitor unit, such that either of the antennae in each pair may be energized. A switch 36 is also provided which can be rotated through 90 degrees to couple modulators 38 and 37 to attenuator 34, and the set attenuator 45 to the terminator. With the switch positions as shown the unit is arranged for monitoring the transmitted power of the radar system. Energy from the radar system is received by antenna 5 and is passed via set attenuator 45, switch 36 and attenuator 34 to lead 35 which is connected to the transmitter power monitor 28. Any energy picked up by the antennae 4 and 6 is absorbed in the termination. When it is desired to transmit microwave energy from the antennae for simulation purposes, switch 36 is rotated through 90 degrees. To simulate a moving target, the microwave energy from microwave switch 23, Fig. 1 is fed via line 47, attenuator 34 and switch 36 to modulators 37 and 38. A signal on line 51 stops the energy from passing through modulator 37, whilst a signal on line 50 allows the full amount of energy to pass through modulator 38 to attenuator 44 and antenna 4. A signal is subsequently fed to switch 49 to change it over such that the energy is now radiated by antenna 5. The signals on lines 50 and 51 are then reversed such that the energy is finally radiated from antenna 6. By adjustment of attenuator 34, the sensitivity of the radar system may be checked. The equipment may comprise an infra-red source mounted with the antennae for testing fire control systems in the aircraft. To check the accuracy of the bore sighting of the antenna 2 illuminated cross hairs may be mounted with the antennae on a movable panel. Antenna 5 then radiates energy, and is moved with the cross hairs until it is on the electrical axis of the antenna 2. An optical system on the aircraft is then used to sight along the bore of the antenna to detect the cross hairs. The change of intensity of the echo signals with range may be simulated by controlling microwave switch on attenuator 34 by a signal from the velocity ramp function generator 17.