Frequency reconfigurable circularly polarized slot antennas with wide tuning range

Frequency tunable annular‐ring slot antennas with circularly polarization (CP) operation are studied in this article. The annular‐ring slot antenna operates at one full‐wavelength resonant mode and it is excited by an L‐shaped coupling strip with a reactive loading. It is found that the operating frequency of the slot antenna can be tuned by varying the capacitance values of four capacitors, which are symmetrically placed along the circumference of the ring slot. Moreover, for each operating frequency in the tunable range, good CP performance can be obtained as long as the reactance of the loading is properly adjusted. Both measured and simulated results indicate the CP operating frequency of the proposed design can be tuned between 1.58 and 2.59 GHz. A prototype integrating with two varactor diodes is also implemented so that the CP operating frequency can be switched by controlling dc biases. Details of the antenna designs and measured results are presented and discussed.