Miniaturized directional filter multiplexer for band separation in UWB antenna systems

In this paper, new design of miniaturized coupled-line directional filter multiplexer allowing for band separation in UWB antenna systems has been proposed. To achieve small size of the directional filters, hence entire multiplexer, directional couplers constituting the filter have been miniaturized following the approach, in which the coupler is realized as a connection of tightly coupled and uncoupled lines. Moreover, sections of quarter-wave-long transmission lines have been designed with quasi-lumped elements approach, which allows for further miniaturization of the structure. Theoretical analysis of the circuit has been provided. Moreover, performance of the presented approach has been verified by the design and measurement of an exemplary single directional filter multiplexer covering ISM 2.4 GHz band.