Performance of a small reflector with a splashplate feed

Reflector antennas with aperture diameters of less than ten wavelengths are difficult to design with good sidelobe performance because of blockage problems. A small prime focus reflector for 8.4 GHz has been designed using mode-matching techniques. The design was aimed at providing sidelobes of less than -20 dB without degrading the gain excessively. In order to minimise blockage problems, a splashplate feed was chosen. The diameter of the integrated subreflector must be small and has to be optimised in order to offset blockage losses against diffraction and spillover losses. The feed dimensions must also be optimised to reduce blockage losses. The measured results agree well with predictions. The target of less than -20 dB sidelobes was achieved with an aperture efficiency of 60% and the authors conclude that mode-matching is a useful approach to the design of such small antennas. >