A Multibeam Antenna Using Compact Low-Profile Wideband 4 × 8 Butler Matrix Incorporating Diverse Transmission Lines

This letter introduces a multibeam antenna that employs a compact, wideband 4 × 8 Butler matrix (BM), incorporating diverse transmission lines such as substrate-integrated coaxial line (SICL), grounded coplanar waveguide (GCPW), and substrate-integrated waveguide (SIW) without increasing the number of dielectric substrate layers. This approach enhances the topology of the 4 × 8 BM. By replacing crossovers with spatially crossed GCPW transmission lines at the top and bottom layers, the configuration of the network is greatly simplified, facilitating the miniaturization of the BM. Furthermore, an ideal 180° phase-shifting scheme is proposed that not only addresses the issue of signal lines not being on the same layer but also achieves 180° phase shifting across the wide operating band by transitioning the GCPWs on the top and bottom layers to the SIW cavity. Finally, eight magneto-electric dipoles (ME-dipoles) were connected to the output ports of the 4 × 8 BM, forming the proposed multibeam antenna. A prototype of this multibeam antenna was fabricated and measured, it is evident that a compact structure and an impressive operating bandwidth of 20.56% [(24 to 29.5) GHz] has been achieved. The measured data confirms its potential as a promising candidate for B5G/6G millimeter-wave communications.