Ultra-Wideband Tightly Coupled Dipole Array Fed by a Tapering Meandered Balun

An ultra-wideband (UWB) phased array is presented operating from UHF to C-bands (0.14 to 5.85 GHz). This new design employs an integrated, compact tapered spline balun in conjunction with a triple-layer semi-resistive frequency selective surface (FSS) network. Notably, the integration of the meandered balun within a dual-polarized tightly-coupled dipole array (TCDA) allowed for a contiguous bandwidth of 40:1 with VSWR < 2.5 at broadside. Moreover, the use of the semi-resistive FSS superstrate enabled scanning down to +/- 60degree celsius with a VSWR < 3.5 in the E-, H-, and D-planes. The overall array thickness is lambda(Low) / 17.93$ (where lambda is the wavelength at the lowest frequency of operation, 140 MHz), and the array's radiation efficiency is 75% on average across the operational bandwidth. That is, compared to previous UWB TCDAs with contiguous operational bandwidths of 40:1 or greater, the proposed array is 30% thinner and has equally good or better efficiency. This paper presents the analysis and design of the dipole array, with emphasis on the spline balun. An 8 x 8 prototype (12 x 12 element FSS network footprint) was fabricated and measured to validate the performance of a finite array.