Multi-level antenna pattern representation for the synthesis of multi-beam coverage

In the design of multi-beam antennas, several synthesis methods have been developed, but usually little importance has been given to the representation of the antenna far field. The goal of this paper is to find an efficient representation of the desired field, that concentrates the information of the design task in a few basis functions; if properly coded, this enables synthesis algorithms to converge faster. An adaptive wavelet expansion of the far field of multi-beam circular aperture antennas is presented, and applied in the synthesis of the satellite coverage of Europe. Two synthesis techniques are considered, a simple projection method and a genetic algorithm (GA) based optimization. The developed wavelet basis allows most of the information of the desired pattern to be concentrated in a few basis functions; as a result, we have verified better convergence with both synthesis algorithms, and an improvement in the final synthesized directivity with respect to that using the standard beam basis. We consider a circular aperture; extending the technique we previously applied a hexagonal lattice array (Vipiana, F. et al., AP-S Digests, vol.1, p.575-8, 2004). A key ingredient of the proposed representation is that the wavelet generation scheme has been made adaptive to the desired mask, taking advantage of the explicit hierarchical, multilevel nature of the basis. The developed multi-level wavelet-based representation of the radiated field is then tested employing a projection and a GA synthesis method, showing an improvement in the performances.