Abstract:In the design of the Ultra-wideband(UWB) reflector antenna，the most important problem is the matching between the radiation pattern of feeding antenna and the reflector. A rule in designing the reflector antenna in the frequency domain is that the radiation of the feeding antenna on the edge of the reflector is about -11 dB. The radiation patterns of Transmission Electron Microscopy(TEM) horn are simulated in different parameters，then some proper UWB reflector antennas are added and simulated to obtain higher amplitude of the far-field radiation by Computer Simulation Technology(CST) in 0 GHz–1 GHz. In the end，the simulation results are analyzed in the time domain. It is concluded that the radiation pattern of the TEM horn cannot match up with the reflector as the phase center of the TEM horn is uncertain, and when the TEM horn moves along the central axis，the field of the reflector surface changes，which leads to the change of the far-field radiation. At the same time，the effect of the shade of TEM horn should not be neglected.