UWB arrays with tunable band rejection

A mechanism for tunable band rejection within an ultra-wide bandwidth, 0.6-4GHz (6.7:1), of a tightly-coupled array (TCA) is presented. Specifically, a variable capacitor, placed in the folded Marchand balun, feeding the array, is used to create a tunable mismatch resonance. Both the center frequency and the bandwidth of the resonance can be controlled via the capacitor value and position, respectively. The proposed scheme achieves >15dB rejection and operates unhindered as the array scans ±60° from boresight in all directions. To the authors´ knowledge, this is the first reconfigurable array to be presented for tunable band rejection. The validity of the concept is verified via fabrication and measurement of isolated baluns with fixed capacitance values, which achieve the expected rejection. A reconfigurable 8×8 array with varactor diodes, as tunable capacitors, is being fabricated with test results to be presented at the symposium. The proposed array enables realization of practical UWB systems by reducing interference risk. This is achieved via continuous, dynamic tuning without additional loss. The proposed method does not entail any theoretical limitations and can be applied to other types of antennas or output loads.