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Compact wideband and highly selective bandpass filters (BPFs) implemented in coplanar waveguide technology are presented. The high frequency selectivity is achieved by the presence of shunt-connected stepped impedance resonators which introduce a transmission zero at both band edges. The circuit model of the filter as well as the design procedure to synthesize the required bandwidth, based on such model, is presented. An order-3 prototype BPF with 38% fractional bandwidth, central frequency fo = 6.3 GHz and 0.03 dB bandpass ripple is designed and fabricated as proof-of-concept demonstrator. The measured filter response is in good agreement with the model predictions. Filter dimensions are as small as 0.16λ0 × 0.29λ00 , λ0 being the free-space wavelength at the central filter frequency.
Date of Publication: Dec. 2011