Spatially decoupled varactor biasing for a tunable staircase filter

A spatially decoupled biasing circuit is proposed for the biasing of varactor diodes in a tunable staircase X‐band suspended substrate filter. The biasing lines are vertically aligned with lines of zero electric field which are created by the symmetric capacitive loading of half‐wave planar resonators. A prototype filter is designed and a tunable centre frequency of between 11.75 and 12.15 GHz is measured.