Novel Dual-Band Microwave Filter Using Dual-Capacitively-Loaded Cavity Resonators

We present a novel design concept for low-loss dual-band cavity filters based on dual-capacitively-loaded (DCL) cavity resonators. The relatively independent control over the center frequencies, inter-resonator and external coupling coefficients makes the DCL resonator an ideal building block for dual-band filters with widely separated passbands. The high unloaded quality factor (Q
_u
) of the DCL cavity resonator ensures a low insertion loss. An example 2-pole dual-band filter at 2.4 and 5.0 GHz is demonstrated with an insertion loss of 1.47 dB at 2.4 GHz, 1.01 dB at 5.0 GHz and a bandwidth of 24.8 MHz (~1%) at 2.4 , and 51.2 MHz (~1%) at 5.0 GHz.