Reconfigurable Hairpin Filter with Tunable Center Frequency, Bandwidth and Transmission Zero

This paper presents a twofold tunable hairpin filter with continuously controllable center frequency and bandwidth. Stopband attenuation and band isolation is increased by introducing one tunable transmission zero for the upper frequency bands. Center frequency tunability is achieved by loading the filter resonators, while the bandwidth is controlled by varactors between adjacent resonators, which control the inter-resonator couplings. The presented filter is designed for a center frequency range from 900MHz to 1.1GHz and for a bandwidth between 40MHz to 80GHz. The tunable transmission zero frequency range is between 1GHz to 1.3GHz to achieve a stopband attenuation above 30dB for the upper bands. The filter performance is experimentally validated.