The characteristics of coplanar waveguide (CPW) fed ring antennas (such as gain, efficiency and polarization purity) are degraded by the dielectric losses and excitation of surface waves on the substrates. To counteract such effects, we propose to remove some portions of the substrate in the vicinity of the metallic patches, which effectively eliminates the conditions for the generation of surface waves. The proposed technique is applied to a CPW-fed ring antenna and a prototype model is fabricated. The measurement data and the computer simulation results agree well and indicate the efficacy of the technique for the improvement of antenna gain and efficiency.
It is desirable to improve the antenna radiation efficiency by using suitable methods to decrease the substrate dielectric losses and limit the spurious surface waves. Although the dissipation losses of available substrates are usually low, the excitation of surface waves degrades the printed antenna performance such as polarization purity and radiation efficiency [1-3]. The surface waves are always present, because the cut-off frequency of their dominant mode is zero. Surface waves move towards the antenna edges, where they radiate into space. Consequently, it is advisable to devise some techniques to suppress the surface waves and prevent them from deteriorating the antenna efficiency and generating cross-polarized fields which spoil the antenna characteristics and polarization purity.
In this paper, we propose to remove the substrate in the neighborhood of the antenna, which counteracts the conditions for the excitation of surface waves. The proposed technique is applied to a printed CPW-fed ring antenna. A prototype model of the proposed antenna is fabricated and its Characteristics are measured and compared with computer simulation results.
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