Reconfigurable Differential Filter With Constant Absolute Bandwidth and High Common-Mode Suppression

A reconfigurable differential filter with constant absolute bandwidth (ABW) and high common mode (CM) suppression is proposed in this letter. The design is aiming to achieve the constant ABW under the differential mode (DM) by choosing the loading place of the varactors on the resonators and adjusting the external quality factor. Under the DM and CM bisection, the frequency of the CM differs from that of the DM, which results in the wide CM suppression without loading extra elements. The transmission zeros are introduced by source-load coupling, which lead to high selectivity. The simulated and measured results are presented with a good agreement to verify the theory and design.