Wide tunable range bandpass filter with three transmission zeros

This paper proposes a reconfigurable bandpass filter with a wide tunable range, which is achieved by connecting two tunable passbands with switching diodes. A pair of transmission zeros (TZs) are introduced through the cross-coupling structure to improve the passband selectivity of the filter, and one more transmission zero is added by the interdigital coupling line to enhance the out-of-band suppression and broaden the upper stopband. The simulation and experimental results show that the designed filter with an absolute bandwidth of 100 MHz realizes a tunable frequency band covering 1.5–3 GHz, corresponding to a fractional tunable range of 66.7%. The dimension of the fabricated filter is 0.32 λg × 0.34 λg.