Microwave branching systems

In multi-channel microwave radio relay systems it is sometimes necessary to have a number of transmitters and receivers simultaneously utilizing the same aerial. This is advisable from economic considerations because of the saving entailed in feeder and aerial costs. To achieve this a complex branching system is necessary. The object of this paper is to describe the design and development of such a branching system in the 7000 Mc/s frequency band. The branching system contains a number of branching units connected in cascade. Each unit consists of a number of microwave band-pass niters and 3 dB short-slot couplers in a suitable configuration. By means of detailed experimental investigation and theoretical analysis a design procedure for band-pass niters in waveguide is derived and normalized design curves are plotted. Filter characteristics calculated on a theoretical basis are compared with those obtained from experimental prototypes. The design data for broad-band short-slot couplers is derived. On the basis of the information obtained a prototype 3 dB coupler is developed and its characteristics measured. The operation of a branching unit is described. Finally, the specification of the complete branching system is outlined and a prototype constructed. A description is given of the tests carried out on it and the results of these tests.