GB920700A - Radar system - Google Patents

Abstract

920,700. Radar. STANDARD TELEPHONES & CABLES Ltd. (Nippon Electric Co. Ltd.). Jan. 1, 1960, No. 27/60. Class 40 (7). A radar system comprises means for transmitting some side bands of the transmitted wave in predetermined phase relationships with respect to one another, filter means in the high or intermediate frequency stage of the receiver section for separating the side bands from one another, and phase-shifting means in the stage for making the phases of the side bands coincide with one another. In one example the transmitter transmits three bands of frequencies, one centred on a frequency f 0 , one centred on a 2T frequency f 0 +-, where T is the pulse width, 3 2T and one centred on a frequency f 0 - -, the two 3 outer bands being 180 degrees out of phase with each other. At the receiver one of the side bands is altered in phase to bring it into phase with the other side band. The effect is to transmit wide pulses to gain the advantage of large mean power, and to receive narrow pulses to give accurate ranges. In Fig. 4, an oscillator 15 operating at the I.F. of the receiver feeds a phase shifter 16 which applies a leading phase of 90 degrees and feeds a balanced modulator 17; the modulator 17 combines this input with an input of frequency 2T/3 from oscillator 18 to produce the sum and difference frequencies out of phase with each other. These two signals, together with another output from oscillator 15, are heterodyned at the mixer 19 with the output of local oscillator 20, amplified and pulse modulated in unit 21, and fed to the aerial through T-R unit 25. The pulses generated in unit 22 and used to pulse modulate the transmission are derived from a frequency divider 23 which divides the frequency of oscillator 18 so that the pulse modulation has a predetermined phase relationship and the waveforms are the same for all pulses. Received signals pass through T-R unit 25 to mixer 26 where they are heterodyned with an output from local oscillator 20 and passed through an I.F. amplifier 27 to unit 28. Unit 28 comprises three filters in parallel 2T tuned to frequencies f 0 and f 0 Œ-; the filter 3 2T tuned to f o - -is connected to a phase-shifting 3 circuit which shifts the phase by 180 degrees and this output is combined with the outputs of the other two filters and fed to a detector 29 and a display 30 triggered by pulses from unit 22.