Highly Directive Resonator Antennas based on Composite Right/Left-Handed (CRLH) Transmission Lines

A composite right/left-handed (CRLH) series mode zeroth order resonator antenna (ZORA) and a CRLH half-wavelength antenna (HWA) with tunable directivity are presented and demonstrated to exhibit substantially higher directivity than a conventional patch antenna in the case of a 2.4 GHz (WLAN) design. Due to the special dispersion relation of a CRLH transmission line (TL), the length of CRLH TL resonators can be enlarged while keeping their resonance frequency constant, which yields enhanced directivity. The ZORA has been shown to have a higher efficiency (η
_ZORA
> 70%) than the CRLH HWA (η
_HWA
≈40%), comparable to that of a patch antenna, as a result of the perfectly uniform current distribution in the zeroth order mode. In particular, the ZORA due to its versatile characteristics and high performance, is expected to find wide applications in the future.