An Ultrawideband Frequency-Reconfigurable Tightly Coupled Dipole Array With Wide Beam-Scanning Capability

An innovative ultrawideband (UWB) frequency-reconfigurable tightly coupled dipole array (FR-TCDA) is presented. The design realizes high radiation efficiency and wide beam-scan angles with its custom-designed reconfigurable layer and wide-angle impedance matching (WAIM) structure. The reconfigurable layer is p-i-n-diode based; it functions as a phase-shifting structure that transforms an undesirable out-of-phase ground-plane reflection into a desirable in-phase one with low insertion losses in each of its two contiguous bands. The WAIM element is obtained by integrating dual-level, double-sided capacitively loaded loops (DLDS-CLLs) in a co-planar configuration with the dipoles and leads to enhanced beam-scanning performance. Each array unit cell is fed by a Klopfenstein tapered balun that incorporates a capacitance-loaded shorting pin, leading to a feeding scheme free from common-mode resonances across the entire working bandwidth. A $14\times 14$ prototype was fabricated and tested; the measured results confirm the simulated performance characteristics. The developed array’s two frequency-reconfigurable states cover 0.37–0.93 GHz and 0.85–5.85 GHz at broadside with a VSWR <3 and a radiation efficiency greater than 95%. These two contiguous operating bands combine to effectuate an overall bandwidth of 15.8:1 (0.37–5.85 GHz). When scanning up to {±70°, $\pm 70^{\circ },\pm 50^{\circ }$ } in the {E, D, H} planes, they achieve a combined bandwidth of 13.7:1 (0.42–5.77 GHz).