Abstract: A two-arms planar spiral antenna was designed for long-narrow confined space like tunnels. The antenna is composed of two symmetrical arms which are structured by four equiangular helix lines. Compared with traditional omni-directional antenna, the antenna has greater potential for reducing reflection loss of radio waves by tunnel walls. Because of circular polarization characteristics, the antenna has potential for weakening influence of multi-path effect, and bidirectional radiation characteristic can make the antenna to improve radiation efficiency. The simulation results show that when the antenna with five cores works at 2.4 GHz, half power beam width in 3 dB is more than 60 degree and gain is more than 4 dB while the antenna with ten cores is 120 degree and 6 dB seperately.