GB1219072A - Pulsed doppler radar system - Google Patents

Abstract

1,219,072. Pulse radar. CANADIAN ARSENALS Ltd. 18 Sept., 1958 [24 Sept., 1957] No. 29990/58. Heading H4D. A pulsed Doppler system has a duty ratio of 0À05-0À5 and uses a " comb " filter to reject returns from fixed targets. Various methods of obtaining coherence between transmitted pulses and reference oscillations are described. The filter has a number of stop bands at multiples of the P.R.F. with an attenuation of at least 50 db obtained by the use of high Q ferrite core inductances. Fig. 4 shows the transmitter and local oscillator both locked to the IF reference frequency. The transmitter frequency and local oscillator frequency are arranged to differ by the IF, so that mixing the local oscillator and reflected pulses gives IF pulses which are compared with the IF reference frequency at 12. The output of the phase detector 12 passes to the filter 13 which rejects fixed target returns. Fig. 5 shows a system using a duty ratio about 0À5. Part of each transmitted pulse is fed to a mixer 24 to form an IF pulse which is delayed and compared directly with the reflected pulse. The P.R.F. is adjusted so that the leading edge of any reflected pulse is at the antenna before the transmitted pulse ends, so that the lengths of the IF pulses are proportional to the ranges of the reflecting objects. The system in Fig. 6 uses stable RF and IF continuous wave sources. CW RF is mixed with gated IF, the difference product filtered out, and the pulses transmitted. Return pulses are mixed with the RF and the resulting IF pulses are compared with oscillations from the stable IF source and filtered as above.