Abstract: A directive antenna (for a groundstation or a satellite) has a plurality of discrete receptional states which provide predetermined electronic displacements from boresight of the optimum direction of reception. The direction of the target is obtained by rapid switching from one receptional mode to another. The receptional modes are preferably provided by switchable mode converters, e.g. 6A, 6B, 7A and 7B, which are coupled with the waveguide so as to convert higher order propagation modes, e.g. TM01, TE21(H) and TE21(V), to the fundamental.

Abstract: The invention relates to mode filters for millimetric waves. The mode filter provided includes a circularly sectioned waveguide divided into a number of equal sectorial channels. Dielectric mode perturbing material is provided in all but one of the channels. This material extends in the direction of the H-field so as not to interfere with a wanted mode of a propagated signal but to perturb the current lines of an unwanted TE.sub.On mode so that an -unwanted TE.sub.On mode in the channel containing the dielectric material undergoes a .pi.radian phase shift relative to the TE.sub.On mode in the remaining channel which remaining channel has a conductive sectorial ridge of the same cross section as the sectorial channels and extending in the direction of the H-field the ridge being of such a radius that differential phase shifts produced by the perturbation effect of the mode perturbing material of the wanted mode cut-off frequency are substantially reduced.

Abstract: A microwave band branching arrangement for successively coupling frequency sub-bands of a broad frequency band of energy has a coupler for coupling the highest sub-band of frequencies at one end of the arrangement and a series of successive couplers which are each arranged to sequentially couple frequency sub-bands of energy in an ascending order of frequency from the coupler which couples the highest frequency sub-band. By arranging that the highest frequency sub-band is coupled first, it is subjected to a lower attenuation. In further embodiments of the invention, where the arrangement is used, for example, in a repeater station, sub-bands of energy are coupled out, regenerated and amplified, and reinserted by a further coupler into the arrangement for further transmission.