Resonance based reflector based UHF/S bow-tie antenna with two opposite uni-directional radiation bands

Two ring-shape resonance based reflectors (RBR) with different operating frequencies are used to design a broadband directional bow-tie UHF/S antenna with two opposite uni-directional radiation bands. The RBR has the characteristic of "in-phase reflection" in a wide frequency band and it does not need a periodic structure. Therefore, the distance between antenna and RBR is much smaller than λ/4 and the whole area is relatively small when the RBR is used as the reflector for an antenna. The two ring-shape RBRs have different sizes and they are placed over and under the antenna, respectively. Though one RBR is placed on the radiation (reflecting) direction of the other, the radiation to each other still exists. Thus, the radiations of the lower UHF and the upper S-frequency bands of the antenna point to the+z axis and the—z axis, respectively. The antenna is fed from its side not back to avoid the effect to the antenna radiation. Though two reflectors are used, the overall size of the antenna is only 0.45λ×0.4λ×0.2λ, and the impedance bandwidth is more than 100%.The antenna demonstrates good uni-directional performance, while its relative directional bandwidths (front-to-back ratio > 5 dB) at the lower and higher frequency bands are 58% and 41.6%, respectively.