Shorted patches mounted on high impedance ground planes

Recently, we presented a variant of the shorted microstrip patch antenna that improved the efficiency of the small antenna, whilst not compromising the size advantages of the shorted patch (Pavlickovski, D. and Waterhouse, R.B., IEEE Trans. Antennas & Propag., vol.51, p.2472-5, 2003). This shorted microstrip patch was mounted on a high impedance ground plane (HIGP) and showed an increase in gain, compared to a conventional shorted patch, of more than 3 dB. The new shorted patch also had significantly lower cross-polarization levels, more than 20 dB below the copolar levels of the conventional shorted patch. We now investigate several parameters that have an impact on the performance of this antenna. These include the radius of the conducting via that connects the metal elements in the HIGP to the continuous bottom metal layer and the size of the HIGP. The latter is important given that the purpose of the HIGP is as a substitute the PEC ground plane in small microstrip antennas, and it is therefore desirable that the HIGP be as small as possible. For each variation in design parameter, a shorted patch on an HIGP is developed; the measured return loss, radiation pattern and gain are given for each configuration. The cross-polarization levels can be substantially reduced with a small HIGP, although the gain of the antenna is compromised by reducing the number of HIGP elements.