| Antenna arrays have been used in many radio frequency (RF) applications from high frequency (HF) to sub-millimeter waves. Arrays, and especially phased arrays, are popular because they allow the user to fully customize the radiated far-field including beam-shape, beam steer location, and gain levels. This customization is achieved by controlling spatial, amplitude, and phase distributions for each antenna element in the array. Since the World War II era, there has been extensive research on the effects of amplitude, phase, and spatial distributions for the performance of linear, rectangular, and circular arrays, as well as other topologies. Methods for steering the beams of these different geometrical configurations have also been well researched. Until recently, circular array research has focused primarily on arrays with a single ring, almost completely ignoring arrays with concentric rings.;To achieve the desired phase and amplitude at each antenna element, transmission lines, power dividers, and phase shifters are typically used. To reduce the array losses and far-field degradation, it is very important that the transmission lines, power dividers, and other components comprising the array's beam-forming network (BFN) are designed for low loss, and minimal phase imbalances. The research of this thesis primarily focuses on methods for reducing transmission line losses for a corporate BFN of multi-element and multi-ring circular arrays. The types of transmission lines investigated in this research include shielded microstrip, rectangular coax, and suspended stripline. The line losses and phase stability are analyzed in combination with discriminators such as cost and weight to determine which type of transmission line would provide the best performance. A demonstrator array is composed of 2 concentric rings and a single center element. The inner and outer rings have 6 and 12 elements, respectively. The array is designed for L-band operation with a bandwidth of 10-30%. The far-field pattern is optimized to have a single main-beam with a 3dB beam-width of 20°. The side-lobes are designed to be 25-30dB down from the main-beam. A genetic algorithm is used to determine the necessary distributions of amplitude, phase, and spatial location for each antenna element.;Dual-band and single wideband patch antennas with circularly polarized symmetric beams are developed and used as the baseline elements in the array. Using the methods researched and developed in this thesis, it is shown that an air-loaded trans- mission line can provide 0.2dB/m of loss, as compared to 0.4dB/m from traditional coaxial cable. Also, a corporate BFN that feeds 19 patch elements in a concentric circular array with suspended stripline will have between 0.4 and 0.8dB of loss. Comparing this to 3-4dB that is typically found when using conventional transmission lines and power dividers, it is a significant increase in efficiency. The low-loss system also enables lower cost, weight, and space; all of which are extremely important in space-based applications. The 19-element array designed in this thesis has a directive gain of 20dBi, a 20° main-beam, and side lobe levels that are at least 25dB down from the main-beam. |
