The Significance of Ground-Plane Size and Antenna Location in Establishing the Performance of Ground-Plane-Dependent Antennas

The performance properties of small, multi-band, device-integrated antennas are significantly affected by the ground-plane structure on which they are mounted. In many cases, the time-varying current on the ground plane is the primary source of radiation that determines both the antenna's impedance and radiation-pattern properties. With device-sized or integrated antennas, it is sometimes presumed that the primary factor affecting or establishing the antenna's performance is the significantly reduced size of the ground plane. Here, we consider both the ground plane's size and the location of the antenna on the ground plane in terms of how these factors affect the antenna's performance. We demonstrate that often, it is the location of the antenna and its feeding point on the ground plane, rather than the size of the ground plane itself, that primarily establishes the antenna's performance in terms of its impedance, bandwidth, and radiation mode. We also show that in many cases, the method used to feed the antenna and how the feed couples to the ground plane can be significant factors in establishing the current distribution on the ground plane, and therefore the antenna's performance. We demonstrate these effects for several single and multi-band antenna designs.