Evolution of Composite Right/Left-Handed Leaky-Wave Antennas

In this paper, the evolution of the composite right/left-handed (CRLH) leaky-wave antennas (LWAs) yielding several novel CRLH LWA is reviewed. Starting with the concept of CRLH LWAs, the concave and convex passive CRLH LWAs are discussed along with the conformation effects in each case and a dispersion engineering method is introduced to compensate for the conformation effect to refocus the main radiation beam. Next, planar and conformal varactor-based electronically controlled CRLH LWAs are reviewed. In the planar case electronic beam steering and beamwidth controlling are discussed while in the case of conformal version electronic radiation aperture selectivity as well as electronic beam focusing is discussed. Finally, a dual polarized CRLH LWA is presented which is a balanced four-port coupled CRLH LW-TL that conserves its CRLH nature under both common-mode and differential-mode excitations but with two orthogonal E-planes resulting in two orthogonal polarizations for the radiated fields.