A small patch antenna using a single CRLH TL unit cell

This paper presents the design of a small patch antenna, which consists of one unit cell of composite right/left handed transmission line (CRLH TL). Due to the resonant frequency of the CRLH TL unit cell is determined not by the physical length but by the inductance and capacitance values loaded in the cell, the size of the patch antenna consisting CRLH TL unit cell can be reduced by tuning the LC values. The antenna is fed by a microstrip line. In order to improve the matching, a thinner microstrip line and two rectangular notches etched on the patch are used. The patch antenna including the feeding line is fabricated on a 3×3 cm² substrate with ε_r of 3.5 and thickness of 1.5 mm. The size of the patch is reduced to 9 mm×12.9 mm, which is 0.18 λ_g×0.26 λ_g at the resonant frequency of 3.59 GHz, owing to the characteristic of the CRLH TL unit cell. The measured results exhibit a bandwidth of 24 MHz and conventional patch-like radiation pattern. The gain of -4.7 dBi and efficiency of 20% are achieved.