Tunable band rejection in a tightly-coupled array using varactor diodes

A mechanism for tunable band rejection in the reconfigurable balun of an ultra-wideband (UWB) tightly-coupled array (TCA) is presented. A variable capacitor increases and controls the effective length of the balun's short stub, shorting out the dipoles of the array at a specific frequency. The practical implementation of the rejection scheme using varactor diodes is discussed. A number of different varactor diodes has been measured using a custom-made evaluation board to model their actual behavior. Simulation results, including the characterized components and their DC biasing network, verify the design. A fabricated prototype of the reconfigurable array will be presented at the conference.