Ultra-wideband small antenna subarray module with narrow elevation pattern

We propose a small ultra-wideband antenna subarray module with narrow elevation pattern for future use in antenna arrays providing spatial processing capabilities such as Direction-Of-Arrival estimation in the azimuth plane, for the frequency range from 5 GHz to 8 GHz. The proposed subarray design is based on four mutually coupled Vivaldi antennas stacked on a common substrate in the E-Plane, with an element distance of d_elem ≤ λ_{0, high}/2. We optimize the antenna element in an infinite E-plane array configuration and show that the truncation effects when reducing the infinite array to only four elements do even improve the total scan element reflection for broadside excitation. In addition our design does not utilize a parallel-plate to microstrip balun at the feed point of each antenna element. Instead we use a novel ultra-wideband and geometrically small hybrid ring coupler to realize an ultra-wideband corporate feed network directly in parallel plate technology.