A Broadband Planar Spiral Antenna Design for Electromagnetic Signal Monitoring

In order to meet the wide-band full-space radio monitoring task, the design of a circular-polarized planar dual-arm composite spiral antenna is presented in this paper. The antenna operation covers the L-band and S-band frequencies ranging from 200 MHz to 6 GHz (relative bandwidth is 187.1%). The equiangular spiral is applied to the beginning of the Archimedean spiral, which reduces the input impedance of the antenna, thereby reducing the length of the cross-section of the feed balun and realizing the miniaturization of antenna. The antenna is designed to be simple in structure and small in size. The diameter of the radiating surface and the length of the section are only 1/5 and 1/50 of the working wavelength. The simulated and measured results show that the antenna has a very good impedance matching (standing wave ratio of less than 2.5), and the antenna has good symmetry, and has good circular polarization and wideband characteristics. Finally, the antenna is applied with an USRP (universal software radio peripheral) to carry out the electromagnetic signal monitoring experiment outdoors. The results show that the designed antenna can receive electromagnetic signals in the 200 MHz - 6 GHz band and can be used for full-space radio monitoring.