"The Field Focusing Filter" a Novel form of Microwave Band Branching Filter

The paper describes a new form of microwave branching filter which may be realised in either waveguide or a microstrip form. The filter incorporates a semicircular non resonant cavity in which the various output frequency bands are focused to emerge at different output ports. This concept can provide a large number of matched output channels without the use of circulators and the shape of the output frequency responses can be varied by control of the geometry of the filter design. Theoretical and experimental results are presented for prototype filter units operating at different microwave frequencies. Proposals are made to incorporate electronic control of bandwidth and centre frequency of such filters.