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 5.7GHz and in-between isolation of 30 dB created by two in-band transmission zeros. The enclosing cavity reduces radiation loss and increases the unloaded of the resonant modes. The hybrid design provides insertion losses better than 1.7 dB and narrow fractional bandwidths of 2.5%.