A Compact Balanced Filtering Crossover with Wide Stopband Rejection

This paper proposes a balanced filtering crossover composed of five stub-loaded ring resonators. This circuit exhibits third-order bandpass response for differential-mode signals, and has high suppression level for in-band common-mode signals. The fabricated prototype operating at 0.95 GHz is measured and the results validate the theory. The overall size is 0.46 λg × 0.46 λg, where λg is the guided wavelength at the operating frequency. With the stub-loaded ring resonators, this circuit has a 40-dB rejection level in the stopband up to 5.7 f₀.