A Compact Co-Planar Waveguide-Fed Zeroth-Order Resonant Antenna

Zeroth-order resonant (ZOR) antenna manufactured on microstrip transmission lines has attracted great interest in the small antenna applications. Many techniques have been employed in order to miniaturize the composite right/left handed (CRLH) transmission line (TL) unit cell size, such as using meander line shunt stubs [1] or using the Sievenpipe

r`s mushroom structure[2]. In[2], a mushroom-type two unit-cells ZORA with the small size of 0. 17 »0 0. 17 »0 at 3. 38 GHz was presented. The peak gain and radiation efficiency of this antenna were 0. 87 dBi and 70%, respectively. In order to further reduce the antenna size, a spiral slot structure on the ground was used[3]; the measured peak gain and radiation efficiency of this antenna were 0. 28 dBi and 62%, respectively. However, small ZOR antennas employing a CRLH resonator made up of two or three cells suffer from a low radiation efficiency and poor gain in the zeroth-order resonant mode[4]. Various solutions designed to improve the ZOR an- tenna`s efficiency have been under investigation. One approach used for ZOR antenna radiation efficiency has been to increase the vertical via-hole height over the improvement ground plane using an air substrate[5]. The drawbackof this design is in the difficulties found in manufacturing the antenna. Recently, a 0. 145 »0 0. 172 »0 at 2. 03 GHz co-planar waveguide (CPW) type ZOR antenna was presented in[6]. However, its measured peak gain and radiation efficiency were only 1. 35 dBi and 62%, respectively. This is thought to be due to the small radiator size, as well as from losses caused by the antenna structures, such as the shorted meander lines. In order to achieve an efficient ZOR antenna with a high gain, it is thought that the number of CRLH resonator unit cells needs to be...

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