Investigations on Input Impedance and Radiation Pattern of a UWB Antenna for Microwave Imaging

Abstract

Investigations carried out on the Input Impedance and Radiation Pattern of an Ultra-wideband (UWB) antenna are presented in this study. The proposed antenna is fabricated on an FR4 printed circuit board with a rectangular aperture. Major applications of UWB technology are presented. The fundamental characteristics of the antenna, such as input impedance, return loss, radiation pattern, and realized gain, are obtained. Investigations on how to improve the directivity of the proposed antenna are also presented in this study. The antenna demonstrates good impedance bandwidth (S11≤ -10dB) from about 4GHz to 10.6GHz, except in the case when the width _W_ of the T-shaped stub was varied. A commercial simulation tool – CST Microwave Studio – is used for the optimization of the proposed antenna. The proposed antenna operates almost over the entire UWB band (3.1-10.6GHz), except at lower frequencies of 3.1-4GHz. The response of the designed UWB signal starts at 3.1-10.6GHz, giving a good performance between 4GHz to 10.6GHz with an operational bandwidth of 6.6GHz. The input impedance is well matched, as a return loss of 10dB is obtained between 4-10.6GHz. The return loss decreases even more at 4-5GHz and at 8-10GHz, which means that the proposed UWB antenna transmits a high percentage of its power while a very low power is reflected back.