Design of Low-frequency Separation Structure for Ultra-wideband TEM Horn Antenna

In the design of ultra wideband TEM horn antenna, it is difficult to combine both the character optimization in low frequency and the miniaturization of an antenna, which always limits the usage of TEM horns in some applications. For the problem of low-frequency reflection, a structure, which is referred to the principle of band-pass filters in parallel and different from the conventional ones, is proposed in this paper for separating a fraction of low-frequency electric field component on the plates linking excitation port to radiation plates. It can greatly reduce the reflection of low-frequency component at the edge of radiation plates to improve the low frequency character of the antenna. In this paper, an ultra-wideband TEM horn antenna improved with the proposed structure is presented. Finally, the comparison of the improved antenna and the original one is exhibited, which shows that the impedance bandwidth is 12.5% wider with the low-cutoff frequency decreasing to 0.1 GHz and simultaneously the port-fe