GB1409749A - Waveguide antenna - Google Patents

Abstract

1409749 Filters STANDARD TELEPHONES & CABLES Ltd 6 Dec 1973 [14 Dec 1972] 57690/72 Heading H1W [Also in Division H4] A frequency scan aerial comprises a multisection evanescent mode waveguide bandpass filter with radiating slots along its length. As described, the filter is basically to Specification 1,129,185 and comprises a rectangular crosssection waveguide 1 containing spaced-apart adjustable capacitive elements, such as tuning screws 2, by means of which the necessary conjugate match condition may be obtained to achieve evanescent mode resonance for energy transfer along the waveguide over a required pass band of frequencies below the dominant mode cut-off frequency. Radiating longitudinal slots 3 are provided on alternate sides of the centre line of the broad wall of the waveguide, the transverse centre line of each slot being midway between adjacent screws 2. The filter acts as a slow wave structure, and a comparatively small change of frequency results in a comparatively large change of phase between adjacent slots, with a correspondingly large beam deflection. The radiating slots may alternatively be provided all on the same side of the broad wall centre line, or they may be provided in the narrow wall of the waveguide. As shown in Fig. 7, the far end of the waveguide 1 may be terminated in a reflecting wall 4. In this case, the last three or five of the capacitive elements are made lossy, and no radiating slots are associated with them. A matched termination is thereby obtained.