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An optimum quarter-wave impedance matching feedline for circular UWB array antenna with high gain performance

The goal of this paper is to designed ultra-wide band (UWB) array antenna for biomedical application. The array arrangement is introduced to improve the performance of the antenna in terms of return loss, gain, bandwidth, and directivity. In this paper, a four-element antenna array is presented. The antenna array is composed of quarter wave feed network along with four-identical circular patch antenna elements designed and simulated using Computer Simulation Tool (CST) Microwave Environment software. The performance of the designed array antenna evaluated in term of return loss, Voltage Standing Wave Ratio (VSWR), bandwidth, radiation pattern, directivity and gain. The array elements and its feed network are properly designed to have a very wide useful band and high gain antenna against frequency. Introduction of unique mitered structures along the feedline and low right side feed realize UWB array antenna with high gain. The simulation result of return loss shown that the operating bandwidth less than -10 dB is start from 4.5 GHz until more than 20 GHz at gain range of 4.2 dB until more than 8 dB at VSWR less than 2. The antenna has an excellent averaged directivity of 7 dBi and a widespread functioned fractional bandwidth of more than 129%. Simulated result shows that the array has a peak gain of more than 8 dB at 9 GHz. These features lead the UWB antenna array appropriate for microwave imaging purposes. The antenna is fabricated on the low cost FR-4 substrate with dielectric constant of 4.7 and thickness of 1.6 mm. Less complicated fabrication methods is possible due to the feeding network placement is on the same level with the antenna patch elements.