A Wideband Differential BPF With Multiple Differential- and Common-Mode Transmission Zeros Using Cross-Shaped Resonator

Wideband differential bandpass filter (BPF) with multiple differential-mode (DM) and common-mode (CM) transmission zeros (TZs) is presented in this letter. This filter is designed based on Cross-Shaped Resonator (CSR) alone that is intrinsically attributed by three DM transmission poles (TPs), four DM TZs and one CM TZ. Adding loaded coupled structures, two extra DM and CM TZs are generated respectively. A prototype differential BPF centered at 3.5 GHz with 40% fractional bandwidth (FBW) is designed and experimentally characterized. The experimental results are in good agreement with theoretical and simulated results. Allocating three CM TZs in the DM passband, the suppression is better than 40 dB in average, and the maximum rejection is as high as 80 dB, while the DM passband is sharpened by two extra DM TZs.