Frequency-Reconfigurable Microstrip Patch Antennas With Circular Polarization

A simple design of circularly-polarized (CP) microstrip antennas with frequency agility is described. The reconfigurable antenna is composed of a square radiating patch, four varactor diodes, and two lumped capacitors. With a coaxial probe, two orthogonal resonant modes of the square patch antenna are simultaneously excited. When the equivalent capacitance values of the varactors are increased, the resonant frequencies of the two modes are decreased, and at the same time the lumped capacitors with a specific value are introduced to produce a difference between the two resonant frequencies so that a CP operating frequency can be generated and tuned. For the proposed design, only one dc voltage is required to vary the CP operating frequency, and experimental results indicate that the CP frequency can be switched between 1.97 GHz and 2.53 GHz; in addition, good CP performances can be obtained at each CP operating frequency.