Dual-Band Bandpass Filter Design with Novel Double-Layer Mixed Coupled SIR/CPW-SIR Resonators

This paper presents a compact 2.4-/5.2GHz dual-band bandpass filter (BPF) design using novel double-layer mixed coupled SIR/CPW-SIR resonators. To miniaturize the footprint, the SIR is built on the top layer with CPW-SIR on the bottom layer. The coupling is tunable by modifying the resonator geometries. The characteristics of the novel resonator are studied which is suitable for dual-band applications. The fractional bandwidth (FBW) design graph is constructed for a straightforward dual-band filter synthesis. To validate our design theory, a fourth-order dual-band BPF prototype is design and fabricated. The measurement shows insertion losses of 1.7/2.95 dB with a 3-dB FBW of 12/10% at 2.4-/5.2-GHz bands, return loss of greater than 10 dB, inter-band isolation of greater than 30 dB, and stopband rejection above 15 dB up to 10 GHz. The filter has a compact size of 500×500 mil².