Designs of spiral slot antennas with dual‐frequency operation

Dual‐frequency slot antennas with different polarization combinations are studied in this article. The antenna is a single‐arm spiral slot fed by a microstrip line. A comparison between the circular polarization (CP) design methods of a shorted ring slot antenna and a spiral slot antenna is first made. By the comparison results, a design for dual‐frequency CP spiral slot antennas is then drawn. Moreover, it is found that, by rotating the spiral slot, the polarization senses at the two operating frequencies can be varied among three different combinations, including (left‐handed CP, right‐handed CP), (right‐handed CP, left‐handed CP), and (linear polarization, linear polarization). Simulation and experimental results for the performances of the antenna operating at each polarization combination are shown in detail. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2294–2297, 2014