Radiation pattern of a microstrip antenna located on a finite size ground plane with small vertical wall at the edges

Abstract

The radiation pattern of a microstrip antenna is often calculated in the assumption of infinite ground plane dimensions. This approach gives a good approximation for the radiation pattern above the ground plane if the ground plane dimension is relatively large. The radiation pattern under the ground plane is not taken into consideration by this approach but it is considerably lower than in the above half-space and in many cases this approximation is acceptable. In many practical situations the microstrip antenna is located in such an environment that small vertical walls at the edges of the ground plane are used. The presence of a small wall has a large effect on the radiation pattern. It disturbs considerably the radiation pattern not only under the ground plane but also above it. Therefore there is a growing need for models which are able to take these effects into consideration. Our method takes the reflection of the surface wave from the edge into consideration. It is based on the postulates of the geometrical theory of diffraction (GTD). The size of the ground plane has to be considerably larger than the size of the microstrip antenna in order to ensure the correct application of the GTD. The main advantage of GTD is that the diffraction effects are taken into consideration separately from the primary source contribution. This approach is simpler and it is compatible with existing models for microstrip antennas. The complete calculation time does not depend on the size of the ground plane. This method can be applied also to antenna arrays.