In this paper the mode conversion and propagation behaviours are analyzed systematically and a strict calculation of conversion between corrugated-wall hybrid modes and smothed-wall modes is made. Moreover

the effect of the TE12 mode in section C is also taken into consideration. By using the method of optimization

eight parameters including the three parameters of the corrugated-waveguide are selected optimally. It is shown that the amplitude and phase radiation patterns in E and H planes are very approximately equivalent for both 4/6 GHz bands. It can be used as the ideal feed of antenna for satellite earth-station.