UWB Low-Profile Tightly Coupled Dipole Array With Integrated Balun and Edge Terminations

Tightly coupled phased arrays (TCPAs) provide UWB performance due to their strong inter-element coupling. However, in finite tightly coupled phased array realizations, mutual coupling is reduced near the array edges, causing the edge elements to become narrowband. To address this issue, a nonuniform array excitation scheme, referred to as “characteristic mode (CM) excitation,” was recently proposed. A more practical alternative for designing UWB tightly coupled phased arrays is proposed here. In this paper, we present a strategy that employs uniform excitation of the central array elements and short-circuits the periphery elements. We report that at least for medium size arrays, this approach provides up to 3 dB more gain and 50% higher efficiency than typical resistive termination. This concept is demonstrated using a 7 $,\times,$ 7 linearly polarized dipole array, 60.96 cm $,\times,$ 60.96 cm (2 $\´\times$ 2 $\´$ ) in size, for operation from 200 MHz–600 MHz . Feeding of the active elements is challenging due to several constraints on the feed design, including balanced to unbalanced transitions, impedance transformations, common mode suppression, compact size, low cost, etc. To address these issues we propose a novel array feed using a compact, ultrawideband balun (with 10:1 bandwidth for ${\hbox {VSWR}} < 2$ ). Simulated and measured data are provided for broadside and 30 $^{\circ}$ scan in the H-plane.