Design and Simulation of Dielectric Load Ultra-Wide Band Corrugated Feed for FAST

Five hundred-meter aperture spherical radio telescope (FAST) is a multi-disciplinary basic research platform that is used for a wide range of astronomy research. Currently, narrow-band multi-beam feed are primarily employed for observation. The development of ultra-wide broadband feed system is beneficial for covering more scientific objectives, while also giving full play to the advantages of the FAST huge reception area in wider frequency band. This paper focuses on the 0.5-3.3GHz feed design, which has better than 10 dB simulated return loss across the bandwidth with the method of using fitting curves and dielectric loading and adding corrugated structures to improve the performance of quad ridge flared horn (QRFH). A centrally positioned PTFE dielectric rod regulates electromagnetic wave phase velocity, enhancing radiation directivity and main lobe symmetry. The dielectric rod is formed by two concentric layers with the same dielectric constant but different structures. The outer layer is evenly slotted to reduce its dielectric constant. The addition of the above technical means ensures the symmetry of the E-plane and H-plane far-field patterns, making the aperture efficiency of the feed relatively balanced over 6.6:1 bandwidth. This kind of feed is designed with an emphasis on performance, ease of tuning and manufacturability compared to the case of multi-layer dielectric rods.