Bandwidth Improvement of Omni-Directional Monopole Antenna with a Modified Ground Plane

摘要

This study introduces a new design of low profile, multi-resonance and omni-directional monopole antenna for Ultra-Wideband (UWB) applications. The proposed antenna configuration consists of an ordinary square radiating patch and a ground plane with pairs of inverted fork-shaped slits and inverted Gamma-shaped parasitic structures, which provides a wide usable fractional bandwidth of more than 135%. By cutting a pair of inverted fork-shaped slits in the ground plane and also by inserting a pair of inverted Gamma -shaped conductor-backed plane in the feed gap distance, additional resonances are excited and hence much wider impedance bandwidth can be produced; especially at the higher band. By obtaining the third and fourth resonances, the usable lower frequency is decreased from 3.12 GHz to 2.83 GHz and also the usable upper frequency of the presented monopole antenna is extended from 10.3 GHz to 14.87 GHz. The proposed antenna has symmetrical structure with an ordinary square radiating patch; therefore, displays a good omni-directional radiation patterns, even at the higher frequencies. The antenna radiation efficiency is greater than 87% across the entire radiating band. The measured results show that the proposed antenna can achieve the Voltage Standing Wave Ratio (VSWR) requirement of less than 2.0 GHz in frequency range from 2.83 GHz to 14.87 GHz, which is suitable for UWB systems.