Design of wideband CPW bandpass filters using phase comparison method and oblique air bridges

This work presents two wideband coplanar-waveguide bandpass filters using open-circuited stubs (Design 1) and short-circuited stubs (Design 2), respectively. The electrical lengths of stubs were accurately determined by a phase comparison method. In Design 1, a spurious resonance was found at the high band edge of the passband. The problem was solved by introducing oblique air bridges to ruin the undesired resonance path for the suppression of the spurious resonance. Design 1 achieves bandwidth of 38.1% and low insertion loss of 0.7 dB. Another CPW filter, Design 2, was constructed with short-circuited stubs for compact size, which can achieve a very wide bandwidth of 70.8% and insertion loss of 0.9 dB.