A beam steering technique using dielectric wedges
The thesis describes a method of' beam steering aimed at producing a useful amount of deflection of an antenna beam from boresight, by a simple and Inexpensive method. For large antennas, It is difficult, as well as expensive, to steer the beam by more than a few beamwidths. The method studied was developed with particular reference to the beam steering requirements of Direct Broadcast Satellite flat plate antennas. The method involves two dielectric wedges, having circular faces, placed In front of the antenna. By adjusting the relative angular position of the wedges, the beam can be steered In any direction, up to a maximum value from the antenna boresight direction. The maximum value of the deflection is determined by the wedge angle and the dielectric constant of the wedge material. This method of beam steering Is Independent of frequency. Frequency limitations are, however, set by the need for a matching layer on the wedge faces to reduce the loss due to reflection and also due to interference of multiple reflection effects on the radiation pattern. Extensive investigations are made (both theoretical and experimental) to predict the performance of the wedges as the beam Is steered. The effect of reflection is studied and a new matching technique is devised. Other practical considerations for example, stepping the wedges for weight reduction, the effect of loss in the dielectric material and cross polar performance are also taken into account. Some effort is given to explore the possibility of using metal loaded artificial dielectrics using polyurethane as the base material. Finally, a number of charts are presented to determine the amount of beam steering for an arbitrary position of the wedges.