PMC Packaged Single-Substrate 4 × 4 Butler Matrix and Double-Ridge Gap Waveguide Horn Antenna Array for Multibeam Applications

Abstract

A perfect magnetic conductor (PMC) packaging concept is utilized at 30 GHz, which suppresses the higher order cavity modes, improves insertion losses, and helps in developing packaged microstrip lines (PMSLs) and double-ridge gap waveguide (DRGW) transmission lines. The Quasi-TEM PMSLs are used to design quadratic hybrid, crossover, and phase shifters as components of a wideband <inline-formula> <tex-math notation= LaTeX >$4\\times 4$ </tex-math></inline-formula> Butler matrix (BM) on a single substrate. Two types of electromagnetic bandgap (EBG) unit cells—full height and half height—are investigated to realize artificial magnetic conductors (AMCs) required for the present design. A parametric study is performed for all components. BM is numerically assembled from these components and analyzed. It achieves a 5-GHz (28–33 GHz) bandwidth with return loss and isolation, both better than 15 dB. At 30 GHz, the insertion loss is 0.8 ± 0.3 dB, and antenna-ports’ phase distributions are ±° and ±°. <inline-formula> <tex-math notation= LaTeX >$E$ </tex-math></inline-formula>-plane-flared horn antennas terminate the BM antenna ports as a linear array. The DRGW horn antenna is designed to reduce the scan loss within an array environment. The <inline-formula> <tex-math notation= LaTeX >$H$ </tex-math></inline-formula>-plane fan-beam switching covers ±° with a maximum gain of 11.7 and 11.2 dBi for <inline-formula> <tex-math notation= LaTeX >$1R$ </tex-math></inline-formula> and <inline-formula> <tex-math notation= LaTeX >$2R$ </tex-math></inline-formula> beams, respectively. The <inline-formula> <tex-math notation= LaTeX >$H$ </tex-math></inline-formula>-plane element pattern and the half-height EBG AMC at the array aperture help to maintain 0.5 dB of gain loss for the outer beams (<inline-formula> <tex-math notation= LaTeX >$2R$ </tex-math></inline-formula> and <inline-formula> <tex-math notation= LaTeX >$2L$ </tex-math></inline-formula>) compared to the inner beams (<inline-formula> <tex-math notation= LaTeX >$1R$ </tex-math></inline-formula> and <inline-formula> <tex-math notation= LaTeX >$1L$ </tex-math></inline-formula>). The multibeam prototype is the right candidate for millimeter-wave 5G base station and can easily be scaled to higher frequency bands.