Design of antennas through optimization of geometry

Summary form only given. Increased flexibility in design of antennas such as cylindrical horns and planar microstrip antennas is possible by allowing the layout in the selected geometry to be chosen as part of meeting the performance objectives. An example is the design of the profiles of electromagnetic horns and dielectric rod antennas. Starting from an initial cross-section geometry the horn profiles are chosen so that desired performance objectives are ultimately achieved. The profiles are obtained by means of standard optimization methods with constraints in order to satisfy the design specifications. Implicit in this is the availability of accurate and fast method for analysing the basic horn structure. These can range from standard computer packages to dedicated packages that are often faster and more accurate. A further example of the approach is the design of planar microstrip patch antennas for a desired bandwidth and radiation performance. The initial antenna is chosen as the driven element and small patches are introduced as part of the optimization process. These patches can be parasitically excited or directly linked to the feed through a power divider. In this paper the type of geometric constraints are discussed and some optimization methods are compared for handling problems that involve the variation of the geometry, and also bounds that may be required to eliminate overlap and abrupt changes in geometry. Most conventional numerical optimization methods can be used for the design. These range from evolutionary methods such as the Genetic Algorithm, and swarm methods such as the Particle Swarm Optimization. These mentioned techniques are especially valuable in a wide domain search as they balance the fittest location uncovered by an element against others uncovered by neighbours, all of which are subject to constraints. Conventional gradient methods, such as steepest descent, can be advantageous in reaching an optimum solution in fewer function eva- uations though once a broad coverage technique has reached a sub-optimum solution. The paper will review some techniques that have been employed to design a range of antennas by optimization of geometry.