A Compact Rectangular Monopole Antenna Design with a Novel Feed for an Improved UWB Performance

Abstract

Printed wideband antennas, if not optimised both in frequency & time domain, often fail to qualify for UWB applications. This is primarily observed in designs based on multiple resonances. The excitation of different modes causes variation in the position of the antenna phase centre and radiation patterns with frequency. In this paper, we propose a novel compact UWB antenna design with optimised resonances within the 3.1 – 10.6 GHz band. The design comprises of a rectangular CPW-fed monopole. The novelty in the design lies in the impedance transformer arrangement at the antenna feed which not only maintains constant impedance over the wide band but contributes towards maintaining uniformity in the radiation patterns over the frequency band. The proposed antenna is characterized, both in the frequency and time domain, confirming its suitability for UWB operation. The impedance bandwidth of the antenna is from 2.9-11.5GHz with an omni–directional radiation pattern over the full band, unlike most of the planar UWB antennas reported in literature whose pattern deteriorates particularly at the upper end of the band. It also exhibits appreciable polarization purity and radiation efficiency. The time domain parameters, Full Width Half Maxima (FWHM) and Ringing, are computed from the measured antenna transfer function. The computed Fidelity of the transmitted pulses indicates superior pulse handling capabilities. The antenna is suitable for commercial hand held devices as its PCB area is just 30 x 12mm2 when fabricated on the FR4 substrate with permittivity 4.4 and height 1.6mm.