Wideband balanced filter using T-shaped multi-mode resonators

A novel high selectivity wideband balanced filter using T-shaped multi-mode resonators is proposed in this paper. Two transmission zeros near the passband for the differential mode can be easily achieved for the balanced filter. In addition, the common mode can be suppressed with three transmission zeros with insertion loss greater than 15 dB over a wide frequency band. A prototype with 3-dB fractional bandwidth of 67.6% for the differential mode with insertion loss greater than 15 dB (7.0-12.7 GHz) is designed and fabricated. Good agreement can be observed between measured results and theoretical expectations.