Single-/Dual-BPF Using Coupled-Line Stepped Impedance Resonators (CLSIR)

Abstract

This brief presents a new coupled-line stepped impedance resonator to design single-/dual-bandpass filters (BPFs). To verify the validity of the design concept a single-band filter with central frequency at 5.2 GHz and a dual-BPF with central frequencies at 3.2 and 5.2 GHz were fabricated and tested. Measured results show low insertion loss (less than 0.8 dB) for the single-band BPF with passband centered at 5.2 GHz with −3 dB fractional bandwidth (FBW) of 9.49% and a dual-band BPF with two passbands centered at 3.2/5.2 GHz with lower and higher passband insertion loss less than 0.6 dB and 0.8 dB respectively, having −3dB FBW of 16.2%/8.2%. The single-band BPF can be used for IEEE802.11a systems, and the dual-band can additionally be used for WiMAX applications. Unwanted spurious frequencies for the two BPFs are cancelled by transmission zeros produced by means of open-ended stubs resulting in extremely wide upper stopband. A thorough derivation is conducted to extract the resonating modes, which are calculated analytically.