Aerial arrangements

Abstract

Abstract 1388114 Aerials; radio direction-finding ELLIOTT BROS (LONDON) Ltd 6 July 1972 [6 July 1971] 31772/71 Headings H4A and H4D An aerial arrangement suitable for use in a monopulse radar system comprises a feed horn 1 adapted to transmit signals in even and in odd modes, a directional coupler 7 having two channels coupled to respective ports, one on each side of the axis of the horn, and comparator means 5 coupled to the directional coupler and adapted to produce sum and difference output signals. The purpose of the directional coupler 7, which provides a relative phase shift between the two channel signals in dependence upon its coupling coefficient, is to counter the effects of differing propagation coefficients of the said odd and even modes. As described, two horn parts P1, P2 are coupled by waveguide to the directional coupler 7, which comprises two side-by-side waveguides with coupling holes in a common wall within a portion 8. The horn 1 is formed with discontinuities at the neck portion such as to propagate the H 01 , H 03 even modes and the H 02 odd mode. The comparator means 5 comprises a 3dB directional coupler 4 having a quadrature phase-shifter 3 in one input channel. The output channels of the comparator provide sum and difference signals in quadrature which are brought into phase (or into antiphase) by a further quadrature phase shifter 6. The horn 1 may be mounted at the centre of the main reflector of a Cassegrain aerial system, and be directed at the sub-reflector thereof. In another embodiment, two superimposed feed horns each propagating even and odd mode signals in respective parallel planes enable sum and difference signals to be derived relative to those planes, and also relative to planes which are perpendicular thereto. Alternatively, a single horn may be adapted to propagate even and odd signals in perpendicular planes, from which corresponding sum and difference signals are derived.

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