Analysis of radiation pattern and G/TA for shaped dual-reflector antennas

An accurate calculation of the radiation pattern from shaped Cassegrain-type dual-reflector antennas is given. In the forward axial region this is achieved by using the classical methods of physical optics and aperture field. Elsewhere we use the g.t.d. in the analysis, utilising a recent solution for the double knife-edge diffraction phenomenon between the two reflector edges. The result is used to compute the antenna temperature TA at a number of frequencies in the 1¿¿100 GHz region commonly used for radio astronomy and space communications. The use of shaped reflector profiles to maximise G/TA consistent with other requirements such as acceptable sidelobe levels is discussed.