Reconfigurable square-ring microstrip antenna

A reconfigurable design for a dual-feed square-ring microstrip patch antenna is described. The dual feeds are used to excite two orthogonal modes of the antenna, and each feed network is composed of a coupling patch, an impedance transformer, and a variable capacitor. In addition, the two feeds are connected to a single input port through a T-junction power divider. The proposed design can perform polarization diversity at different frequencies by tuning the capacitance values of the two capacitors. A prototype integrating with a pair of varactor diodes and related dc bias circuits is constructed. Typical experimental results are shown along with numerical simulation results. Both of them demonstrate that the prototype can provide one linear polarization and two circular polarizations at one operating frequency; moreover, the operating frequency can also be tuned to adjacent frequencies.