A high-selectivity ceramic bandpass filter with controllable transmission zeros

This paper proposes a microstrip filter with controllable transmission zeros based on the lambda/4 stepped impedance resonator. This filter utilizes hybrid electric-magnetic coupling to generate transmission zeros, which can improve selectivity and stop-band performance. A fifth-order filter is designed and manufactured on a ceramic substrate with a center frequency of 26 GHz, bandwidth of 2 GHz and the signal suppression level is better than 42.51 dB from 10 to 22.8 GHz and 48.23 dB from 29.1 to 40 GHz. Furthermore, the proposed filter has a compact size of 2.074 x 1.071 mm (0.566 lambda(g) x 0.292 lambda(g) ).