Ultrawideband (UWB) phased arrays play an increasingly indispensable role in emerging communication and sensing systems. Multifunctional apertures, advanced radars, software-defined radios, electronic countermeasure systems, and radio telescopes all demand wideband beamforming front ends. Tightly Coupled Arrays (TCAs) have emerged as a very attractive option for these wideband systems, as they provide large bandwidths in low profile implementations. This work presents three novel TCAs which address the following challenges: 1) the need for increased bandwidth (>10:1) in low-profile arrays; 2) the need for integrated baluns in these extremely wideband array designs; 3) the high component cost of large UWB arrays.
First, the Superstrate-Enhanced Substrate-Loaded Array (SESLA) is presented, which represents a novel scheme for bandwidth enhancement of UWB ground plane backed arrays. The SESLA employs resistive substrate loading to suppress destructive ground plane interference that limits array bandwidth. This translates to an improvement in bandwidth by a factor of two or more. Of course, if used alone, this loading can lead to severe degradation of radiation efficiency. However, a key innovation of the SESLA is that in addition to the loading, it uses a synergistically designed superstrate which dramatically mitigates the efficiency degradation. A very simple equivalent circuit is presented which is used to co-optimize the loading and the superstrate. The SESLA approach is validated through measurements of a 4x4 prototype array.
As balanced feeding is a major challenge in UWB arrays, a version of the SESLA with an integrated feed is also presented. The design uses a stripline-based folded Marchand balun. At broadside scan, it is matched across a 13.9:1 bandwidth (VSWR<2.4, infinite array) and shows good scanning capability out to θ=45°. Extensive measurements of a prototype 8x8 array validating this design are presented.
Finally, an UWB beam-scanning horn antenna is presented. This design incorporates an UWB Tightly Coupled Dipole Array (TCDA) into a horn antenna to provide a high gain scanned beam with reduced element count, compared to a conventional phased array. For limited-scan applications, this translates to major savings in cost and complexity. The design is a truncated pyramidal horn fed by a TCDA, where the horn structure augments the gain of the array, but still allows some scanning. This allows for navigation of the design space between an UWB array and a fixed aperture. This design concept is validated with a measured prototype.