Planar Microstrip Diplexer for a Multifunctional Antenna

A compact wide-band microstrip diplexer working in the 0.9÷2.5 GHz frequency range is presented. This component is a key part of the feeding network of a multifunctional antenna, working at five frequency bands associated to terrestrial and satellite radio services. By using interdigital capacitors in conjunction with the stepped impedance technique, very good results in terms of compactness and performances have been obtained. An unconventional arrangement of the filters has led to a further reduction of the dimensions.