Multilayer dual-band filter using a reflector cavity and dual-mode resonators

A dual-band filter has been designed using a multilayer approach. The structure includes a reflector cavity and dual-mode resonators. The walls of the reflector cavity have been designed using metalized vias enabling the integration characteristics of standard planar microwave circuits. The principle includes the passband division of a fourth-order fully canonical form into two narrowband second-order passbands. The designed topology exhibits a dual-band response with center frequencies of 5.2 and 5.7 GHz and in-between isolation of 30 dB created by two in-band transmission zeros. The enclosing cavity reduces radiation loss and increases the unloaded Q of the resonant modes. The hybrid design provides insertion losses better than 1.7 dB and narrow fractional bandwidths of 2.5%.