Compact dual‐mode differential bandpass filter using stepped impedance resonators

A compact dual‐mode differential bandpass filter using a pair of identical stepped impedance resonators connected by a short microstrip line is presented in this letter. The proposed filter showcases good differential‐mode (DM) bandpass response centered at 2.5 GHz (f 0 ) while possesses inherent bandstop effect across the differential passband for the common‐mode (CM) signal. In addition, there is a transmission zero for the CM operation located within the DM passband. Accordingly, the loaded lumped element or stub for the CM suppression is not required in this design. In addition, compact size and wide stopband of the differential filter are both achieved, and the DM stopband rejection is more than 30 dB up to 8.0 GHz (3.2 f 0 ). © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2055–2058, 2014