Multi-Objective Genetic Algorithm Optimization of Antennas for use in LWA

Many of the technical requirements proposed for the LWA are significantly expanded compared with the LWDA. Among the most significant changes in requirements is the wider operating band of the LWA, nominally 20 MHz to 80 MHz [1], compared with 60 MHz to 80 MHz for the LWDA. This presents new challenges in designing many of the system components including the antenna. Requirements for an LWA antenna include good impedance matching and high radiation efficiency to enable sky noise limited operation in the receiver. The antenna must also exhibit wide beamwidth and omnidirectional radiation patterns with low axial ratio circular polarization. All of these characteristics must be maintained over the full 20 MHz to 80 MHz operating band. Additionally, the antenna should be mechanically robust to withstand long-term field operations. Of course, the performance characteristics must be traded against the cost of the antenna which must be low in order to achieve a low station cost. An effort is discussed in this document in which multi-objective genetic algorithm optimization is applied to the design of antennas for use in LWA. First, some background information is provided in the area of multi-objective optimization, and a Pareto-based genetic algorithm (GA) optimization code developed by ARL:UT is briefly discussed. A new simulation code, which can be used for the efficient analysis of planar antennas is described and its performance is compared against other simulation codes and measurement results. Recent results of applying the Pareto GA optimizer coupled with this antenna simulation code to the design of planar (or “blade”-like) dipoles for use in LWA are presented. Finally, upcoming work involving the Pareto GA optimizer is discussed. Planar dipole antennas were selected for initial study with the Pareto GA optimizer since this type of antenna was used in LWDA, and scaled versions of the LWDA antenna have been considered for use in LWA. As a result, a good amount of reference data is already available for this type of antenna in order to rate the performance of the optimizer. Additionally, it is believed that compared with simpler antenna structures consisting of wire or tubular elements, planar dipoles bound the electromagnetic performance that can be achieved in a dipole antenna for LWA. Therefore, the results yielded from optimization of planar dipoles should be useful in judging the relative quality of other types of antennas considered for LWA as well. The optimizer may also be equally well applied to wire or tube based antennas. Therefore, follow-up studies to the planar dipole study could involve such antenna types as they are identified in the LWA effort.