Patent GB-1428682-A (GB)
Title: Elevation-measuring system
IPC: G01S1/30
Filed: 1973-06-08
Abstract: 1428682 Radio-navigation; aerials INTERNATIONAL STANDARD ELECTRIC CORP 8 June 1973 [22 June 1972] 27326/73 Headings H4A and H4D In an elevation measuring system a ground station has a vertical linear aerial array of n equally spaced radiators which are cyclically and sequentially excited with pulses of R.F. energy having equal magnitudes and the same phases, a characteristic pulse train being radiated before each cycle of pulses. At an airborne receiving station the phase and amplitude of each pulse in a cycle are measured relatively to one of them, for example, to the first pulse, and at least two different groups are formed, each containing m successive received pulses (where m is less than n). The phase and amplitude of each pulse in each group are changed, the changes for corresponding pulses of all groups being the same, and the vector sum of the changed pulses of each group is determined. The elevation is determined from the phase differences of the said vector sums. As described, the ground station aerial array comprises 40 parallel dipoles, at half-wavelength spacings. In a cycle, the characterizing pulse train is first sent from radiator no. 1. The radiators are then connected in order, from no. 1 to no. 40, to the transmitter and radiate pulses of R.F. waves, whose amplitudes and phases are equal for all radiators. At the airborne station the characterizing pulse train, after conversion to I.F., is recognized by a device 15, Fig. 3, which alerts a computer 13 and sets a switch 8 to its upper contact (as shown). The first received pulse (from radiator no. 1) is applied at I.F. to an oscillator 10, which is thereby synchronized with respect to amplitude and phase. After the first pulse, the switch 8 is changed to its lower contact, and the succeeding pulses are applied through an I.F. amplifier 9 to an amplitude meter 11 and a phase meter 12. The phase and the amplitude of the output signal of the oscillator 10, which is coupled to second inputs of the meters 11, 12, serve as reference quantities for the measurements made in respect of the second to fortieth pulses. The outputs of the meters 11, 12 are connected to the computer 13, output from which operates an indicator 14. The stored values of phases and amplitudes are processed by the computer in groups of twenty successive pulses each, i.e., those corresponding to respective radiators nos. 1 to 20 (group O), nos. 21 to 40 (group F), nos. 2 to 21 (group G), and nos 5 to 24 (group Z). The changes effected to the pulses in each group may be such as to produce a virtual radiation pattern for use at high elevations in which the field strength is approximately equal at all angles, or to produce a peaked virtual radiation pattern for use at low elevations (Figs. 1, 2, not shown). In determining the elevation, use of the two groups O and F provides maximum accuracy, but the result is ambiguous, since their equivalent phase centres on the transmitting array are ten wavelengths apart. Use is therefore made of the groups G and Z, each taken with the group O, to resolve the ambiguity, since their equivalent phase centres are respectively only a half-wavelength and two wavelengths from that of the group O. Specification 1,410,121 is mentioned.