Unbalanced-Fed TCDA Performance Improvement Using a Scan Impedance Model

Abstract

Unbalanced-fed Tightly-Coupled Dipole Arrays (TCDAs) allow for the realization of ultrawideband, wide-scanning phased arrays without the need for baluns, which may increase size, weight, and cost. However, unbalanced-fed TCDAs often have additional radiating modes and common-mode resonances which may degrade performance. In this paper, a scan impedance model is presented which describes performance in terms of a combination of even and odd monopole and dipole radiating modes. An intermodal coupling term is included to account for performance when scanning in the E-plane. Each mode is calculated individually in a full-wave solver and the model is then validated by comparing the proposed combination to a full simulation of the unbalanced-fed TCDA. A coaxial extension technique is then introduced to increase the impedance of the monopole-like radiating even mode, allowing the unbalanced-fed array to match the performance of the balanced-fed version without shorting posts or significant redesign of the elements or lattice.