Coaxially Fed Antenna Composed of Monopole and Choke Structure Using Two Different Configurations of Composite Right/Left-Handed Coaxial Lines

Two kinds of composite right/left-handed coaxial lines (CRLH CLs) are designed for an antenna element. The dispersion relations of the infinite periodic CRLH CLs are designed to occur -1st resonance at around 700 MHz, respectively. The designed CRLH CLs comprise a monopole and a choke structure for antenna elements. To verify the resonant modes and frequencies, the monopole structure, the choke structure, and the antenna element which is combined the monopole and the choke structures are simulated by eigenmode analysis. The resonant frequencies correspond to the dispersion relations. The monopole and the choke structures are applied to the coaxially fed antenna. The proposed antenna matches at 710 MHz and radiates. At the resonant frequency, the total length of the proposed antenna which is the length of the monopole structure plus the choke structure is 0.12 wavelength. The characteristics of the proposed antenna has been compared with that of the conventional coaxially fed monopole antenna without the choke structure and the sleeve antenna with the quarter-wavelength choke structure. The radiation pattern of the proposed antenna is omnidirectional, the total antenna efficiency is 0.73 at resonant frequencies, and leakage current is suppressed lesser than -10 dB at resonant frequency. The propose antenna is fabricated and measured. The measured |S11| characteristics, radiation patterns, and the total antenna efficiency are in good agreement with the simulated results.