Tuesday, July 1, 2008

BW Enhancement using Proximity Coupling

Proximity coupling is basically a feeding mechanism which gives the highest bandwidth and low spurious radiation. In general, we use two substrates of different thicknesses and permittivity. A short tuning stub is connected in shunt with feedline at some distance from edge of the patch. The fabrication of such an antenna is difficult. Length of feeding stub and the width-to-line ratio of the patch is used to control the match.

BW Enhancement by Impedance Matching Network

The method is unique in that it does not alter the radiating element itself. Instead, a reactive matching network is added to compensate for the rapid frequency variations of the input impedance. The validity of the technique is based upon the relative frequency insensitivity of the radiation pattern and gain characteristics as compared to the resonant behavior of the input impedance. Thus what happens is a matching network is so designed which alters its impedance in such a way that it acts as a parallel resonant circuit over a range of frequencies.

Fig:i) Basic form of impedance matching ii)Comparison of structure of impedance matched antenna and reference antenna