Broadband Impedance Inverters for Application in Synthesis and Realization of Bandpass Filters

A novel circuit of impedance inverter has been proposed, which allows for efficient design of bandpass microwave filters. The synthesis approach relies on direct application of Richard’s transform to a lumped element prototype. Further impedance inverters are applied, which are composed of transmission-line sections with quarterwave-long shorted sections having negative impedance. The proposed impedance inverters are well suited for filters having from narrow to broad bandwidths. The proposed design method has been applied in the design of exemplary 5th and 9th order badndpass filters with directly connected transmission-line sections. The obtained measurement results support the proposed design method showing a good agreement with the theoretical results.