Abstract: A zero-dB hybrid or directional coupler includes a first through waveguide extending between first and third ports and a second through waveguide, parallel to the first waveguide, and extending between second and fourth ports. A plurality of branch waveguides extend between the first and second through waveguides, and are adjusted to couple signal from the first port only to the fourth port, and from the second port only to the third port (within in limits of systems isolation). Particular normalized branch line impedances provide best operation. A communication system especially adapted for use as a spacecraft uses a zero-dB coupler in a "planar" waveguide system to transpose or "crossover" the positions of two system ports, whereby the physical positions of the various ports are arranged in the same relation as their phase progression.

Abstract: Arrays of helical antennas are desired for operation at spaced-apart frequencies, such as 1.5 and 2.5 GHz. In order to reduce mutual coupling between the antenna elements of the lower-frequency array, they are spaced apart by more than .lambda.. Grating lobes occur due to the spacing. The lengths of the lower-frequency helices are adjusted to move the nulls in their radiation patterns into congruence with the unwanted peaks of the array pattern, thereby suppressing the grating lobes. In order to reduce the total area of the combined arrays, the higher-frequency antennas of the second array are interleaved with the elements of the first array. At the higher frequency, the antenna elements of the second array are spaced apart even further, in terms of wavelength, than the elements of the first array, so mutual coupling of the antennas of the second array is reduced even more than in the first array.

Abstract: A waveguide termination includes a rectangular waveguide having a pair of spaced-apart broad walls and a pair of narrow walls equally spaced from a plane of symmetry. The termination has a block or wedige of absorber material. The width of the absorber material is approximately half the width of the waveguide as measured between the narrow walls. The absorber material is located asymmetrically in the waveguide so that substantially all of the absorber material is on one side of the plane of symmetry.

Abstract: A family of waveguide branch directional couplers having various coupling values is adapted for using the same housing dimensions for all members of the family. The housing includes a conductive block defining first and second spaced-apart parallel rectangular through waveguides. The block also defines a chamber extending between the through waveguides. One or more further conductive blocks in the form of rectangular parallelepipeds are fastened within the chamber and dimensioned to coact with the chamber dimensions to define at least two rectangular branch waveguides extending between the through waveguides. The dimensions of the further blocks are selected to adjust the branch waveguide dimensions to provide the various coupling values.

Abstract: A waveguide branch directional coupler having a pair of parallel main waveguides defining four ports and a plurality of branch waveguides interconnecting the two main waveguides to establish a predetermined amount of coupling between the ports has the coupling between ports adjusted by mechanically changing the height dimension of the main waveguides.