Gain enhancement of a thick microstrip antenna by suppressing surface waves

The most detrimental aspect of microstrip antennas for more widespread usage is their inherent narrow bandwidth. One simple way to increase the bandwidth is to use a thick substrate. As the layer thickness increases, the surface waves become highly excited. The surface waves are eventually dissipated at the substrate edges. This unwanted radiation reduces the antenna gain. In addition the radiation is uncontrollable and usually interferes with the main beam destructively to degrade the radiation quality. The purpose of this paper is to introduce a new device to reduce the surface wave excitation. The reduction of the surface waves is achieved by using parasitic elements next to the radiation edges of regular microstrip antennas. Such parasitic elements are usually used for increasing the bandwidth. These patches are placed on a surface coplanar to the main radiation patch. In the proposed antenna, the parasitic elements are between the top radiation surface and the ground plane. The surface waves reflected from the parasitic elements feed back to the microstrip cavity, thus enhancing the radiation efficiency. A simple cavity model is used for the analysis.<>