Modified Designs for UWB Planar Monopole Antennas

This paper reports a theoretical study of a planar monopole antenna for use in the 3.1 GHz-10.6 GHz UWB band for later integration into consumer electronic products. Therefore the emphasis of the research is related to minimizing the size of the monopole while maintaining the matching in the desired frequency range. Simulations, using the Empire Software Suite, show that the impedance matched bandwidth (RL>10 dB) can be significantly increased by bevelling the bottom edge of the monopole and also the impedance match at the lower end of the band can be improved by judicious placement of a shorting pin. The use of a 1 mm wide shorting pin yields a structure that resembles a PIFA antenna. It is possible to treat the monopole antenna as a modified PIFA and apply transmission line theory to predicting the resonant frequencies and the return loss. A combination of shorting pin with bevel shows significant promise in the size reduction of the UWB antennas. The key point is the careful position of the shorting pin (with the bevel) on the monopole that to give a very good match through out the UWB band. This paper reports an investigation of the effect of the antenna dimensions (height, bevel angle and position of shorting pin) on its broad band response. The results of this study show that it is possible to reduce the size of the antenna elements significantly below lambda_max/4, when additional shorting pins are used on the antenna. The distributed shorting pins can be understood to work as a matching network for the antenna.