Patent GB-1524079-A (GB)
Title: Methods of deriving for comparative vetor measurement measured values of a keyed radio signal pulse
IPC: G01S3/46
Filed: 1975-11-12
Abstract: 1524079 Radio direction finding SIEMENS AG 12 Nov 1975 [13 Nov 1974 27 May 1975] 46640/75 Heading H4D A pulse of radio radiation, in particular a TACAN pulse, is received at a plurality of aerials 4, 5, 6, Fig. 1, the aerials being close enough together that the pulses at the outputs of the aerial receivers, eg. ZF1, ZF2, seem to have in-phase envelopes but on closer inspection exhibit a phase difference in their carriers, said phase difference being indicative of the incoming direction of the pulse. The invention is concerned with the measurement of said carrier phases whereby amplitude overloading of measuring circuitry caused by the rapid increase in the amplitude of the pulse is stopped by the pulses passing through a variable attenuator or amplifier, the attenuation being increased or the amplification being decreased in discrete steps in step with the rising front of the pulse. To determine the relative phases of the carriers of the pulses a reference measuring time t is established whereat the amplitude A and phase # of the attenuated or amplified carrier are simultaneously determined for all the pulses. For each pulse the carrier vector M, Fig. 4, is analysed in terms of two orthogonal components thereof A1 = cos # and A2 = sin # where A is the magnitude of the vector M. To produce these orthogonal components the carrier may be passed directly to a storage device 19, Fig. 6, via a rapid acting switch 17 closed at time t whereby 19 stores component A cos # and via a 90 degree phase shift 21 to a similar storage device 20 and switch 18 whereby the component A sin # is stored. Instead of using the 90 degree phase shifter 21 the sampling or closure times of the switches 17 and 18 may be staggered by an equivalent amount, Fig. 7 (not shown). This variation is only possible if the vector amplitude A does not change significantly during said staggering period. Even if the amplitude does change, by taking two samples instead of one for the A sin # component said two samples being equally spaced before and after the sampling time of the A cos # component and the resulting two samples then being averaged, Fig. 8 and 9 (not shown), said variation can be averaged out. The above methods require a plurality of expensive rapid acting switches 17, 18 (22). Said requirement can be overcome and said switches replaced by corresponding sequentially operating slow acting switches 30, 31, 32, Fig. 10, if a single rapid acting switch 29 is placed immediately in the output of variable attenuator or amplifier 15 together with a storage means 25, said single rapid acting switch 29 acting three times synchronously with the actions of switches 30, 31, 32. Since sinusoidal functions are being sampled period integrators 41, 42, Fig. 12 (not shown), may be used instead of the instantaneous samplers the periods of the two integrations, Fig. 13 (not shown), being staggered to produce the required sin and cosine component outputs. If the pulses are mixed, Figs. 14, 15 (not shown), with quadrature reference signals at the carrier frequency a D.C. envelope type pair of signals, Fig. 16 (not shown) results. These vary according to the required cosine and sin components and can be sampled (49, 50) to give the required components. Doppler shift or frequency shift of either carrier changes the output variation of the mixers but still allows a viable sampling to be taken, Fig. 17 (not shown). The above mixing to D.C. can also be used with the integration method, Figs. 18, 19 (not shown). Fig. 20 (not shown) shows a case where the mixers (43, 40) are ring modulators and the output signals a, b from the mixers are commutated by the reference frequency, the integration period (t1 to t2) being an integral multiple of the reference frequency half period. Figs. 21 (not shown) shows how with pulses of very low aspect ratio D.C. error produced when using ring modulator mixers can be eliminated by means of dividing capacitors. Figs. 23 and 24 (not shown) show how clamping can overcome said D.C. error. The quotient of the differential of the variation of the envelopes amplitude and the said amplitude can be used to identify any particular part of the envelope, Fig. 25 (not shown).