The electromagnetic modelling and optimization of planar holographic antennas
Antennas based on holographic principles are attractive at millimetre wave frequencies because of their potentially relatively high directivity and low profile. Most published design work on planar holographic antennas has been based on approximate expressions and experimental experience. Little attempt appears to have made to use some computational electromagnetics approach to model these antennas. Thus no numerical optimization has been possible. One aspect that makes the modeling/optimization process difficult is that such planar holographic antennas are electrically large. For instance, in the case of a holographic antenna of directivity 18 dBi, the combined length of the conducting strips on the antennas can be more than 100lambda 0. In this thesis we formulate and implement a two-dimensional electromagnetic analysis that allows one to determine the H-plane radiation characteristics of the holographic antenna. This analysis consists of an integral equation formulation for a line source illuminating a structure consisting of conducting strips and dielectric material, plus feedhorn walls, and its solution using the method of moments. We demonstrate how it can be applied in the modeling of the holographic antennas in question. It is possible to model the holographic antenna's feedhorn, the holographic antenna proper, and its interaction with the feedhorn. In addition, we have integrated the electromagnetic analysis with numerical optimization algorithms, and show what antenna geometries (such as the distribution of conducting strip widths) are obtruded by such algorithms as being optimum in some sense. Experimental validation is provided, and shows that it is possible to improve the gain of the holographic antenna by up to roughly 2 dB.
Engineering, Electronics and Electrical.
Source: Masters Abstracts International, Volume: 43-06, page: 2363.
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