Design of Beam-Forming Networks for Fermat Spiral Antenna Arrays

This paper presents a novel design technique using beam-forming networks based on CORPS (coherently radiating periodic structures) technology to achieve the simplification of the feed network of Fermat spiral antenna arrays. The use of one-layer CORPS structures generates the values of co-phasal excitation required for the feeding network system based on subarrays. The setting of subarrays has been achieved through the study of the behavior of phases of each antenna element in scanning. In this way, elements that exhibit linear behavior in scanning can be grouped. Furthermore, the geometry of the antenna array system using a Fermat spiral configuration applies methods for side lobe level (SLL) reduction such as: a raised cosine amplitude excitation and optimization of the amplitude excitations through the method of genetic algorithms (GA), CORPS amplitude distribution and uniform distribution. The contribution of this paper is to provide a design of a phased antenna system for a Fermat spiral array geometry considering the analysis and study in the performance of SLL, scanning range, and the phase shifters reduction. Full-wave electromagnetic results are provided for the full phased antenna system by using circular patch antenna elements at a frequency of 6 GHz. If our system using CORPS is compared with the use of a conventional feeding network where every antenna in the spiral array is fed with a phase shifter, the benefits of using this phased spiral array system are: a phase shifters reduction capability of 33%, steering ranges of ±22° in the elevation plane, low SLL using the proposed distribution techniques. Furthermore, the choice of CORPS 2×3 networks would allow the integration of the antenna system where one layer is proposed for the feeding network and another layer for the antenna array with the aim of avoiding crossings and unwanted radiation.