Dual Band Prime Focus Feed for Satellite Earth Terminals

Licentiatavhandling, 2009

Satellite Communication systems have been studied and developed since long. With more high frequency satellite bands coming in the market, there is a need to develop such systems with multi-band or wideband operation with reconfigurable antennas which can provide simultaneous transmit receive capabilities on different polarizations as well as have properties suitable to track the satellite. This thesis is primarily focused on developing a satellite communication system which operates simultaneously over X (7.25-8.4 GHz) and Ka (20.2-31 GHz) band using the new wide band technology referred to as Eleven feed with broad band choke horn. This type of system finds commercial applications in satellite earth terminals for voice, video or data communication for news broadcast or military warfare applications. The first section of this thesis describes basic blocks of such a satellite communication system and emphasizes on the feed with prime focus reflector which is very common type of antenna for these applications. Furthermore, it gives details of the ‘Eleven’ feed geometry formed by two parallel (linear as well as circular) dipoles above ground plane and describes how dipole separation and height above ground plane influence radiation performance characterized by feed aperture efficiency. In order to achieve dual band performance, different technologies like Eleven feed, Hat feed, Choke Horn, stacked patch arrays are briefly discussed in section two and combination of Eleven Feed with Choke Horn giving better than -2dB aperture efficiencies in both bands is considered as potential technology to explore further. Finally, the simulated performance of X band ‘Eleven’ feed integrated with Ka band choke horn is presented in section three. The estimated performance show feed aperture efficiency better than -3dB for prime focus reflector with half subtended angle of 50°. The matching of the antenna impedance to system characteristic impedance is found to be better than -15dB in X band and better than -20dB in Ka band.