Contents I. Introduction
Recently, multi-beam antennas have attracted much attention because of its multi-direction and high gain. Compared with the various feeding mechanisms of multi-beam antennas, such as Nolen matrix [1], Rotman lens [2], and Blass matrix [3], Butler matrix (BM) [4]–[5] has advantages of simple configuration, low loss and wide operating bandwidth at millimeter wave band[6]. Until now, most of the works are focus on H-plane BM, while the E-plane BM is seldom reported due to the limitation of the E-plane crossover.
