A Method of Side-lobe Suppression for Reactance Modulated Antennas

This paper reveals the mechanism of the high side-lobe level (SLL) phenomenon in reactance modulated antennas (RMAs) and proposes a method to suppress the side-lobe for RMAs. The wave-guiding mode in RMAs is a surface wave with considerable EM field exposed to the free-space. We found that it is the exposure of EM power results in the slow-wave radiation phenomenon deteriorating the SLL, which is always neglected in conventional waveguides with local EM confined structures, such as rectangular waveguides and microstrip lines. To eliminate the slow-wave radiation, a `complementary decoupling' method is proposed in this paper by introducing another RMA with inverse periodic variation to the original one. The two parallel antennas are excited with equal amplitude and reversed phase forming a complementary radiation pair. With the proposed method, the slow-wave radiation is eliminated and the SLL is improved. Meanwhile, all of the even radiation modes are also suppressed. Especially for the -2
^nd
mode, which also carries considerable power and often appears in most RMAs.