Patent GB-719131-A (GB)
Title: Radio navigation systems
IPC: G01S1/30
Filed: 1949-03-01
Abstract: 719,131. Radio navigation. TORCHEUX, E. L. G., and HONORE, E. A. H. March 1, 1949 [April 24, 1948; Jan. 17, 1949 ; Feb. 22, 1949], Nos. 5614/49, 5617/49 and 5618/49. Class 40 (7)  Re!ates to c.w. radio navigation systems of the type in which a number of primary signals of different frequency are radiated from spaced aerials and the signals received at a mobi'e receiver, or signals derived there'rom, are mutually heterodyned to give two comparison signals having a common low frequency, e.g. 10, 20, 30 or 50 c/s. so that a locus or contour of constant phase difference between the comparison signals defines a position line. At the receiver the required phase difference may be measured directly or it may be measured indirectly by controlling the phase of a heterodyne oscillator so as to maintain the two comparison signals co-phasal, the amount of phase adjustment necessary being a measure of the required phase difference. The most useful phase contours are hyperbolic but other forms are described. Such a system defining a single family of phase contours is defined as an elementary system and the density or phase gradient of the phase contours of the system depends upon a "characteristic" frequency Fc which is a function of the transmitted frequencies and of the grouping of the frequencies radiated by the different aerials, the shape of the phase contours depending on the relative locations of the aerials. In order to eliminate or reduce phase ambiguities further sets of signals having different frequencies constituting further elementary systems of differing characteristic frequency may be radiated from the same spaced aerials resulting in further families of phase contours with the same shape as and coincident with the first family but having different phase gradients, the resultant system being a "multiple" system; in such a system some signals may be common to each constituent elementary system. In order to obtain a fix, a further multiple system may be established producing a further set of multiple phase contour families intersecting the set produced by the first multiple system, some of the aerials and signals in the two multiple systems being common to each other, the resultant system being a " complete " system. A " combined " system comprises (1) a number of spaced complete systems, (2) a number of spaced multiple systems any two of which form a complete system, or (3) a large number of spaced transmitters any two of which form a multiple system and any three of which form a complete system, the frequencies employed being such that the frequencies of any constituent multiple system may be readily selected by a heterodyne receiver. According to the present invention an elementary system comprises. at least two spaced aerials and n primary signals where n is at least three, the frequencies and phases of (n-1) of the primary signal being independent and the frequency and phase of the nth primary signal being controlled to satisfy the condition K1Q1+K2Q2 +KnQn=C where Q1-Qn are the respective phases of the n signals at a fixed location, C is a constant and K1-Kn are integers of which at least two are of opposite sign. As described the control is effected by a monitor receiver at the fixed location, the two comparison signals at the receiver being applied to a frequency and phase discriminator which controls the frequency and phase' of the nth primary signal to maintain the frequencies of the two comparison signals equal and to maintain their phase difference equal to some predetermined value.  In the embodiments of the invention described, n is 4 or 5 and the number of spaced aerials per elementary system is 2, 3, 4 or 5. Multiple, complete and combined systems are described only for the aerial elementary systems with n equal to 4 resulting in hyperbolic phase contours but it is stated that combined systems may be produced by combining intersecting hyperbolic and non-hyperbolic systems.  Elementary systems, n=4  In a four-wave elementary system, the difference between two of the radiated frequencies is equal to the difference between the other two and tne radiated, frequencies preferably comprise two pairs of adjacent frequencies, e.g. F1, (F1+f) and F2, (F2-f) where F1=500,000 c/s, F2=520,020 c/s and f=20 c/s. Four types of systems are described, the characteristic frequency Fc being respectively equal to (1) the sum of the mean frequencies of each pair, (2) the difference of the mean frequencies of each pair, the mean frequency of all four frequencies. A fourth type, not within the scope of the present invention; is also referred to in which the characteristic frequency is equal to the mean frequency of one pair only. Types 1, 2 and 4 are described as producing hyperbolic contours and type 3 as producing non-hyperbolic contours. Type 1.-In this type pairs of frequencies F1, F2 and (F1+f) (F2-f) are radiated from spaced aerials A and B, the phase of the beat frequency f produced at the mobile receiver by heterodyning Fl and (F1+f) being equal to 2# F1/C (DB-DA)+ 2#f/c DB where DA and DB are the distances of the receiver from A and B respectively and c is the velocity of propagation and the phase of the beat frequency f produced by heterodyning F2 and (F2-f) being equal to 2#F2/c (DADB)+2#f/c DB, so that the phase difference q is equal to 2#/c (F1+ F2) (DA-DB), i.e. the phase contours are hyperbolic, Fig. 13 (not shown), with A, B as foci and the characteristic frequency Fc=(F1+F2). Type 2.-In this type, Fig. 14 (not shown), the frequencies F2 and (F2-f) are interchanged so that the phase of the corresponding beat frequency is 2#F2/c (DB-DA)+2#f/c DA and the phase difference q is now 2#/c (F1-F2+f) (DB-DA), i.e. the characteristic frequency Fc= (F1-F2+f). Type 3.-In one embodiment of this type the frequencies F2, (F2-f); (F1+f) and F1 are radiated respectively from aerials A, B, C, D, Fig. 11, located at the corners of a rectangle to produce phase contours of the type shown and in another embodiment, Fig. 12, frequencies F2 and F1 are radiated respectively from spaced aerials A and D, frequencies (F2-f) and (F1+f) being radiated from a central aerial B to produce closed phase contours, as shown, in these figures. R and Rr denote the mobile and monitor receivers respectively.  Type 4.-In one example illustrating this type, similar to the system disclosed in Specification 452,235, frequencies F2 and (F2-f) are radiated from spaced aeria's A and B and the frequencies F1, (F1+f) are radiated from A or B or from a third aerial whose location is not critical. Mobile receiver.-When the four frequencies radiated comprise two pairs of adjacent frequencies each pair is selected at the receiver and applied to a mixer giving a beat frequency f, the two beat frequencies being app'ied to a phasemeter, Figs. 5 and 6 (not shown); if required the received frequencies may be heterodyned by a local oscillator before separation, Fig. 7 (not shown). If the four radiated frequencies do not comprise 2 pairs of adjacent frequencies-they may be transformed to such in the receiver by heterodyning them, with or without preliminary separation, in separate mixers with the outputs from two local oscillators of differing frequency, Figs. 8-10 (not shown) and when four mixers are employed the required phase difference may be measured by controlling the phase of one of the outputs from one of the local oscillators to one of the mixers, Fig. 9 (not shown), so that the two comparison signals are automatically maintained co-phasal, the amount of phase adjustment required being a measure of the required phase difference. Elementary system, n=5 A system of this type producing substantially circular phase contours is described in which frequencies (F-530), (F+500), (F-300) and (F+330) are radiated respectively from four aerials, A, B, D, C, located at the corners of a square, Fig. 3 and Fig. 1 (Cancelled, not shown) and a frequency F=1.5 Mc/s is radiated from a central aerial E, the frequency of the comparison signals being 30 c/s., and the characteristic frequency Fc being equal to the main value of the frequencies, i.e. Fc=F so that by analogy with the types defined in the n=4 elementary systems, the system may be said to be type 3. At the mobile receiver, Fig. 4, the five frequencies are applied via a band-pass filter 30 to a mixer 32 where they are heterodyned with a frequency of 1972 Kc/s from a local oscil'ator 31 giving beat frequencies (F<SP>1</SP>+530), (F<SP>1</SP>-500), (F<SP>1</SP>+300), (F<SP>1</SP>-330) and F'=472 Kc/s respectively which are se'ected by filter 33 and applied to mixer 34 where the frequency F<SP>1</SP> beats with the other four frequencies producing beat frequencies of 530, 500, 300 and 350 c/s whose phases are respectively proportional to (DE-DA), (DB-DE), (DE-DD), and (DC-DE) where DA-DE are the distances of the receiver from aerials A-E. The frequencies 530 and 500 are selected by filter 35 and mutually heterodyned in mixer 37 giving a first comparison 30 c/s beat frequency whose phase is proportional to f(DE-DA)-(DB-DE)] and a second 30 c/s comparison beat frequency whose phase is proportional to [(DC-DE)- (DE-DD) is produced in a similar manner by filter 36 and mixer 38, the two comparison frequencies being applied through filter 39, 40 to a phasemeter 41 indicating the relative phase # which is equal to 2# F/c (DA+DB+DC+DE- 4 DE). The distance r from aerial E to each of the other aerials is preferably 5# F where # F is the wavelength corresponding to frequency F and when DE is greater than r, ° is approximately proportional to r<SP>2</SP> /DE, the phase contours being then substantially circular. Monitor receiver. In any of the elementary systems, the monitor receiver is similar to the corresponding mobile receiver except that the transmitted frequencies may be conveyed thereto by line, Fig. 2 (not shown), and the two comparison signals are applied to a two-phase