GB677913A - Improvements in or relating to radar systems - Google Patents

Abstract

677,913. Radiolocation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. July 13 1950 [Oct. 11, 1949], No. 26137/49. Class 40 (vii). A radar system comprises a plurality of common-transmitting - and - receiving aerials A1 ... A5 mounted at different heights above the ground plane or other reflecting surface GP and arranged all to have at all times the same momentary orientation in azimuth, each aerial having its respective radio-frequency for transmission and reception so that each receives echoes due only to its own transmissions, and means for determining the elevation angle of a target by determining upon which aerials echo signals exceeding a predetermined proportionate amplitude are received. Due to interference with its image in the plane GP each aerial has a multilobed vertical polar diagram and it may be shown that with the aerials spaced vertically as shown in Fig. 1 and by the use of limiting devices in the receiving circuits, the aerials may be restricted to reception of echoes from within elevationangle bands as indicated by the lines in Fig. 3. It will be seen that between elevation angles of 0 and 6 degrees the elevation angle is uniquely determined by an assessment of those aerials which are receiving echo signals. The invention is preferably employed in conjunction with a system providing a P.P.I. display. In the preferred embodiment, Fig. 7, exploring pulse signals are transmitted from each aerial on closely adjacent radio-frequencies and echo signals are applied to respective gate circuits G1 ... G5 whereby strobe pulses applied over line RAS are also applied to gate circuits G1 ... G5 to allow only pulses of the selected azimuth and/or range to pass. The gate circuit outputs are applied to respective automatic-gain control circuits having a common AGC line so that the gain of each circuit is controlled by the greatest amplitude signal delivered by the gate circuits. The gaincontrol-circuit outputs are applied to delay circuits D1 ... D5 whereby simultaneously received pulses are separated in time from one another, and thence to amplitude-selecting circuits AS1 ... AS5 which comprise biased diodes which permit only signals having an amplitude greater than one half the maximum established by the AGC circuits to pass. The outputs from the amplitude-selecting circuits are applied to respective " valuer " circuits VC1 ... VC5 which multiply the values of the inputs, i.e. amplitude or pulse length, by 31, 15, 7, 3, 1, respectively. By suitably combining the outputs in circuit SS and integrating in circuit JC a signal having an amplitude corresponding uniquely (within 0-6 degrees) to the elevation angle may be obtained. Signals from buffer amplifiers BA1 ... BA5 are applied to a circuit SC which controls the manner in which the combination is effected in circuit SS. Synchronizing pulses corresponding to each pulse transmission are fed to circuits SC and JC over lines PS and PSC to re-set these circuits for each fresh set of echo signals. The integrated signal derived by circuit JC is stored in circuit ST which is periodically operative to receive the output of circuit JC by signals sent from circuit SC. The voltage or charge stored in circuit ST is indicated by any suitable means, preferably a mechanical counter giving a direct reading of elevation. In a modification, Fig. 6 (not shown), which is of particular use when only a small number of aerials are used, means are also provided for measuring the ratio of the signal amplitudes received by the two uppermost aerials, whereby the accuracy of the elevation-angle measurement may be improved.