Patent GB-1026387-A (GB)
Title: A radio system using spaced pulses for intelligence transmission
IPC: G01S13/28
Filed: 1962-10-23
Abstract: 1,026,387. Pulse radar; pulse signalling. GENERAL ELECTRIC CO. Oct. 23, 1962 [Oct. 23, 1961], No. 40113/62. Headings H4D and H4L. In a pulse expansion-compression radar or communication system the effects of large Doppler frequency shifts are reduced by using expansion and compression means having a substantially logarithmic phase/frequency characteristic which in the case of pulse expansion results in a hyperbolic frequency modulation in place of the linear frequency modulation produced by known expansion means having a parabolic phase/frequency characteristic. For pulse expansion the substantially logarithmic phase/frequency characteristic is produced by dividing the total frequency spectrum of the RF pulses into N contiguous segments and subjecting each segment to (1) a linear phase/ frequency transformation produced by a non- dispersive delay line; (2) a parabolic phase/ frequency transformation produced by an active modulator or a known form of linearly dispersive delay line, e.g. a wire or strip solid acoustic waveguide, and (3) a uniform phase shift, the phase/frequency transformations and phase shifts differing for the different segments such that the resultant characteristic, Fig. 4D (not shown), is substantially logarithmic. As described, with reference to Fig. 3 (see below) a system of frequency conversion is used so that all the delay lines operate at the same centre frequency # 0 , where # 0  is the centre frequency of the frequency spectrum of the input pulses, Fig. 4A (not shown). Pulse compression is effected by a corresponding complementary process but in the case of a radar system the same dispersive line may be used for both expansion and compression, the required complementary operation being obtained by inverting the constituent frequencies of each frequency segment. Pulse radar. As shown in Fig. 3, the output from the RF pulse source 21 (frequency spectrum, Fig. 4A, not shown), is applied in parallel to N channels each comprising an amplifier 39 of centre frequency # 0  and band width ##, a non-dispersive delay line 31 producing the linear phase/frequency transformation, Fig. 4B (not shown), a linearly dispersive delay line 32 which causes pulse expansion and produces a parabolic phase/frequency transformation giving a resultant phase/frequency characteristic, Fig. 4C (not shown), and a frequency changer comprising a local oscillator 34, phase shifter 34<SP>1</SP> and mixer 33. The frequencies #<SP>1</SP>n of the N local oscillators 34 are spaced apart by ## so that the outputs from the N dispersive lines 32, each of which is centred on the frequency # 0 , are transposed into N contiguous frequency segments, Figs. 4D and 4H (not shown), and the phase shifters 34<SP>1</SP> are adjusted so that adjacent segments of the resultant phase/frequency characteristic are continuous. In a modification the value of t n  is the same for all the delay lines 38. The reflected echo signal is applied from the receiver 106 in parallel to the N channels each of which includes a frequency changer comprising a local oscillator 37, a phase shifter 37<SP>1</SP> and a mixer 36 whose output is applied to the dispersive delay line 32 through a linear delay line 38 having a delay (T-t n ) complementary to that, t n , produced by the linear delay line 31, T being the duration of the pulse from the pulse source 21. The frequencies of corresponding local oscillators 34 and 37 are chosen to satisfy the relationships so that each of the N contiguous frequency segments of the received signal are transposed to a common frequency segment of centre frequency # 0  the frequency spectrum of which is inverted relative to the spectrum of the output from the corresponding dispersive line during transmission so that on reception the dispersive line compresses the pulse. The outputs from the delay lines 32 are applied to corresponding mixers 101 which transpose the outputs to N contiguous frequency segments, the outputs being combined and applied to a utilization circuit 109. Fig. 5 (not shown) illustrates the application of the invention to a pulse communication system using binary phase modulation.