Octave-Band Three-Beam Scalable Antenna Array Fed by Broadband 4 × 4 Butler Matrix

A novel concept of a three-beam antenna array operating over a one-octave frequency range is proposed in this paper. The antenna array allows stable beams’ direction and beamwidths. To achieve constant radiation patterns, the antenna elements are appropriately spaced and fed by a network consisting of a broadband Butler matrix to which outputs directional filters are connected. The radiating elements are placed in such a way that two similar subarrays can be distinguished, one for the lower and another for the higher end of the desired frequency range. Signal switching between the subarrays and differential phase between pairs of radiating elements is ensured by directional filters and Butler matrix, respectively. The concept has been verified by measurements of the antenna array operating in a 2–4 GHz frequency range.