Design and Optimization of a Wideband Feed Antenna for the Onsala 20-m Telescope

Abstract

Wideband feed antennas are an essential part of reflector antenna systems, as they affect the radiation characteristics and, in turn, the reflector performance, which is the focus of the present thesis. A wideband quad-ridge horn feed was designed and optimized for the Onsala Cassegrain reflector system. The main objective of this work was to achieve a narrow radiation beam that satisfies the required edge taper while providing acceptable impedance matching and antenna efficiency. The antenna geometry is determined and studied by means of electromagnetic simulation. The ridge profile, horn geometry, and backshort, as well as antenna dimensions and radiation characteristics, were studied in detail. The 3D spline-based approach was used to design the ridge profile, providing flexibility in controlling the antenna geometry. Several geometric configurations and scaling factors were investigated to study their influence on radiation beamwidth and efficiency. The scaled design of 1.8 has shown approximately a 12-degree beam width at -12 dB point at 4 GHz and has retained a narrow beam with the increase of frequency and better antenna efficiency. The efficiency of the antenna has been assessed through simulated reflection coefficient, radiation patterns, spillover efficiency, illumination efficiency and combined aperture efficiency as measuring parameters. Although the target beamwidth could be achieved or closely approached, the overall efficiency remained below the target value of 60%. The results indicate that modifying the geometry and scaling of a wideband quad ridge horn provides significant control over its radiation pattern. Nevertheless, further optimization and validation are required to improve the overall efficiency while maintaining the required beam characteristics.