Coexistence-Mode CRLH SIW Transmission Line and Its Application for Longitudinal Miniaturized Butler Matrix and Multibeam Array Antenna

Abstract

The miniaturization design of the beamforming network (BFN) is the key to improving the application value of the multibeam array antenna. The traditional miniaturization method of the BFN mostly solves the miniaturization of the transverse width, while the miniaturization of the longitudinal length is rarely involved. In this article, a coexistence-mode (Co-mode) composite right-/left-handed (CRLH) substrate-integrated waveguide (SIW) transmission line technology is proposed, and this technology aims to solve the problem of miniaturization in the longitudinal length of the Butler matrix (BM). Its core is to introduce a longitudinally extended interdigital slot (IDS), force the SIW to incorporate an interdigital capacitor, and realize the phase constants of the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode and the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> mode reverse change. Then, the coupling region length of the couplers based on the Co-mode CRLH SIW transmission line can be reduced, and the longitudinal miniaturized directional coupler and the longitudinal miniaturized cross coupler are obtained. Finally, three types of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> longitudinal miniaturized BMs based on the Co-mode CRLH SIW transmission line are designed, whose longitudinal lengths are reduced by 32%, 22.1%, and 30.7% compared with those of their SIW counterparts. In addition, a miniaturized multibeam array antenna based on the Co-mode CRLH <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> H-plane SIW BM is fabricated and measured, which verifies the applicability of Co-mode CRLH SIW transmission line technology.