Superstrate-Enhanced Ultrawideband Tightly Coupled Array With Resistive FSS

An efficient low-profile ultrawideband tightly coupled array employing a resistive frequency selective surface (FSS) and a superstrate is introduced. The FSS suppresses destructive ground plane interference, resulting in an increase in the array bandwidth by a factor greater than two. A superstrate is used to alleviate losses due to the resistive FSS. It is shown that a properly designed superstrate reduces losses by about 2.5 dB. The proposed array, which employs tightly coupled bowtie elements, achieves very low profile (0.055λ_low) , 21:1 bandwidth, and radiation efficiency greater than 73% across the band. This paper presents the analysis and design of the array, particularly the FSS and superstrate. To validate the design, measurements of a prototype array are presented as well.