Patent GB-1049361-A (GB)
Title: Improvements in methods of and apparatus for measuring distances
Inventor: LERWILL WILLIAM EDWARD
IPC: G01S13/76
Filed: 1962-05-08
Abstract: 1,049,361. Radar; transponder apparatus. SEISMOGRAPH SERVICE (ENGLAND) Ltd. May 8, 1963 [May 8, 1962], No. 17628/62. Headings H4D and H4L. [Also in Division G1] In a secondary radar system comprising an interrogator apparatus and a responder, the interrogator apparatus comprises pulse-generating means, means for expanding the pulse to produce an expanded pulse having a characteristic which varies along it according to a predetermined non-repetitive pattern, means for transmitting the expanded pulse for reception by the responder to cause the responder to transmit a return signal having a characteristic pattern related to that of the expanded pulse, means for compressing the received return signal, and means responsive to the time interval between the expanded pulse and the resulting compressed return signal for measuring the distance between the interrogator and the responder. In the described embodiment the interrogator comprises, Fig. 2, a crystal controlled oscillator 6 which feeds pulses at 500 c.p.s. to a pulse generator 5 which sends pulses of short duration to a pulse expander 2. The pulse expander 2 comprises a rod, wire or tube delay member 21 of magnetostrictive material, terminated in two matched resistive loads 22 and 23, two single coil transducers 24 and 26 and a multi-coil transducer 25, the windings of which are distributed in accordance with the predetermined characteristic pattern. The pulse from generator 5 is fed to one end of the transducer 25, resulting in an expanded pulse output from transducer 26. This output is fed to an R.F. amplifier 3 and a modulator 4 which causes the amplitude modulation of the output of a V.H.F. transmitter 1 by the said output. The resulting amplitude modulated signal 13 is radiated by antenna 12 to the responder. The responder replies with a signal containing the same amplitude modulation as signal 13 which is received at the interrogator by antenna 14 and passed to a receiver 7. The output of the receiver 7 which should be the same as the output of the pulse expander 2, is passed to a pulse compressor 8, which comprises the same elements as pulse expander 2. In this ease however the receiver output is fed to the right-hand transducer 34 and the output is taken from the transducer 35 which, except for possible difference to be mentioned later, is constructed of coils distributed the same as the coils in transducer 25. The output of the pulse compressor represents the cross-correlation between the expanded pulse as transmitted to the responder and the expanded pulse as returned by the responder, and should, assuming no system induced distortion, result in a short duration pulse similar to that produced by generator 5. The pulse compressor output is amplified at 9 and fed to a C.R.T. display 10 to provide a type A range display. The C.R.T. scan is controlled by a time base and stroke generator 11 and is supplied with calibration pips from oscillator 6. To produce a zero time datum and indicate any distortion produced by amplifier 3, a portion of the output of this amplifier is fed from potential divider 40 to the input of the pulse compressor 8. The resulting compressed pulse is displayed on the C.R.T. in a position representing the zero time datum and shows by its shape the presence of any distortion from amplifier 3. The correct shape is restored by adjusting the distribution of the coils in transducer 35. Phase distortion introduced by the responder is corrected by adjustment of a phase-shift device 27. The return signal produced by the responder may be as shown at 19, comprising a carrier signal of a different frequency produced by heterodyne means, Fig. 4 (not shown), or it may comprise the modulation signal only, produced by rectifying either the received signal shown at 13, Fig. 3 (not shown), or its heterodyned equivalent, Fig. 5 (not shown). Either or both the responder and interrogator signals may be ultrasonic signals. Alternative means for expanding and compressing pulses are given, including the correlating devices described in Specification 1,029,833, and a dispersive delay line having a delay varying linearly with frequency. The interrogation signal may comprise a frequency modulated carrier-wave. Alternative correlating devices may use a magnetic recording medium and magnetic correlators.