Design Of Ultra-wideband Directional Antennas As A Feed For Reflectors

The feed as the core components of the radiotelescope has direct influences to the performance of the radiotelescope.Compared with the ordinary antenna,the feed requires the characteristics of high efficiency,stable phase center,constant radiation pattern and so on.With the needs of the astronomical detection,many radiotelescope project with great influence in the word has been launched,such as the SKA project,the FAST projec,the "Tianlai" project and more.The "Tianlai" project is developing a special radiotelescope for indirect observation of the the dark energy,the radiotelescope is working in a frequency band of 400?1400 MHz,the bandwidth of the feed was 3.5:1.The "Tianlai" project adopted a novel four square plate ultra-wideband feed,however it could only work in the frequency of 600-1200 MHz,the bandwidth of the feed was only 2:1,so the novel feed could not meet the requirements of the "Tianlai" project.This paper will research a new model to provide new design ideas and alternative for upgrading the "Tianlai" project.Aiming at deficiency of the feed of the "Tianlai" project,some research results have been obtained on the study of the new model,summary of work as follows:1.The paper makes an intensive study of the effect of the director and the reflector from two aspects of impedance matching and radiation characteristics.On the basis of sufficient study of this kind of model,the directional ultra-wideband antenna is designed,the antenna achieved a nearly 3:1 operating bandwidth(2.2-6.5 GHz)with a return loss higher than 10 dB,nearly constant radiation pattern and high aperture efficiency have got over the entire operating band.The simulated and measured results indicate that the antenna works well.2.This paper derives equations associated with the total return loss for multi-port antenna.According to the above design method,the dual polarized feed has been designed,the antenna also achieved a nearly 3:1 operating bandwidth(2.1-6.2 GHz)with a return loss higher than 10 dB.3.The ultra-wideband feed for the "Tianlai" project has been designed in this paper,the simulated results shows that the feed can operate from 450-1400MHz,nearly constant radiation patterns and high aperture efficiency have got over the entire operating band.Compared with the feed working on 600-1200MHz,the novel feed has a wider working bandwidth.