基于谐振式反射器的UHF/S双频双定向蝶形天线

利用两个工作在不同频率的圆环型谐振式反射器设计了一款小型化、低剖面的"双频（UHF/S）辐射"宽带双定向蝶形天线.谐振式反射器在很宽的频带内具有"同相反射"的特点且无需周期结构，因此作为天线反射板时与天线间的距离远小于λ/4且面积较小.两个反射器大小不同且分别置于蝶形天线的上方和下方.虽然这两个反射器分别位于另一反射器的辐射（反射）方向上，但它们不会阻止彼此的辐射，因此所提出的天线在工作频带的UHF低频段与S高频段分别向+z轴与-z轴辐射.所设计的蝶形天线采用微带线从侧边馈电，避免了从天线背面馈电可能对天线辐射特性的影响.虽然该天线使用了上下两层反射器，其整体尺寸仅为0.45λ×0.4λ×0.2λ.天线的阻抗带宽超过100%，低频和高频的相对定向带宽（前后比> 5 dB）分别为58%和41.6%，具有良好的双频双定向性.

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,whileits relative directional bandwidths (front-to-back ratio＞ 5 dB) at the lower and higher frequency bands are 58％ and 41.6％,respectively.