Coupled Composite Right/Left-Handed Leaky-Wave Transmission Lines Based on Common/Differential-Mode Analysis

A systematic analysis for two types of symmetrical coupled composite right/left-handed (CRLH) leaky-wave (LW) transmission lines (TL) based on the common/differential-mode excitations is presented. The first proposed coupled CRLH LW-TL is a 4-port via-free coupled CRLH LW-TL that behaves as a conventional CRLH LW-TL under differential-mode excitation. But when common-mode excitation is applied, the structure has the ability to suppress the left-handed waves by operating in the cutoff mode, and only supporting right-handed guided as well as radiating waves. The second type of the proposed coupled CRLH LW-TL is a modification of the first type by inserting vias at the center of the left-handed stub of each unit-cell along the symmetry plane to provide a physical short-circuit to the ground. This structure behaves as a conventional CRLH LW-TL under both common- and differential-mode excitations but with orthogonal polarizations when operating in the fast-wave region. As a result, a dual polarized CRLH LW-TL is obtained.