Patent GB-1410121-A (GB)
Title: Radiolocation system and method
IPC: G01S1/44
Filed: 1973-01-23
Abstract: 1410121 Radio-navigation; aerials INTERNATIONAL STANDARD ELECTRIC CORP 23 Jan 1973 [25 Jan 1972] 3457/73 Headings H4D and H4A At a ground transmitting station n like, equally spaced radiators 1.1, 1.2, 1.3, ... of a linear array 1 are cyclically and sequentially excited with pulses of R.F. energy having the same phase, a characteristic pulse train being radiated before each cycle of pulses. At an airborne receiving station the phase and amplitude of each pulse as received are measured relatively to one of them (e.g. the first pulse). If # is the angle between the broadside axis of the array and the line from its centre to the receiving station, d the spacing between array radiators, and # the operating wavelength, then the phase difference # between the pulses received from adjacent radiators will be: In one aspect of the invention, the measured values relating to the pulses are vectorially added, and the absolute value of their sum is determined. The phase of the pulse received from the first radiator 1.1 is then changed by an angle alpha, and the phases of the pulses received from the radiators 1,2, 1,3, ... are changed by 2x, 3x, .... Vectorial addition is carried out and the absolute value of the sum is determined. This process is repeated for various values of alpha, and from that value which gives the greatest sum, # may be determined, i.e. In another aspect of the invention, the pulses received from one half of the array are phase shifted by # relative to those received from the other half of the array, and # is determined from that value of alpha which gives the smallest sum. Either azimuth or elevation may be determined in this way and, as described, a ground station for the former purpose comprises an array of six dipoles 1.1 to 1.6 which are arranged collinearly with each other, at full wavelength spacings. The amplitudes of all pulses are the same, and their transmission sequence is 1.1, 1.2, ... 1.6. At the receiving station the initial pulse train, after conversion to I.F., is recognized by a device 15, Fig. 8, which alerts a computer 13 and sets a switch 8 to its upper contact (as shown). The first received pulse (from the radiator 1.1) 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 following 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 following pulses. The outputs of the meters 11, 12 are connected to the computer 13, whose output operates an indicator 14. This embodiment requires a fast computer, because all arithmetical operations must take place between two receiving cycles. In another embodiment, alpha is changed with each receiving cycle, and # is determined from observation of a number of successive cycles. The received signal at I.F. is applied through a phasechanging device, an amplitude-changing device, and several converter stages, to a filter, whose output is measured. The pulses may be tapered in amplitude, instead of being of equal magnitudes, to reduce side-lobe effects. Furthermore, in order to promote secrecy, the radiators may be excited in a predetermined coded sequence, which is de-coded at the receiving station.