Frequency Reconfigurable Antenna With Conical Radiation Pattern And Wide Tuning Range

The antenna is mainly composed of a suspended circular patch, eight shorting posts, and a ground plane. The circular patch is loaded with two concentric annular slots, and four varactors are placed across the outer annular slot to vary the resonant frequency of the antenna. Simulated results show that the resonant frequency can be tuned from 3.25 to 5.7 GHz as the capacitance of the varactors is varied from 0.2 to 12 pF, and conical radiation patterns are obtained when the antenna is operated at each resonant frequency. In the simulation, the reversed-bias circuit of the varactor is also included, and it is found that a bias tee or an inductor is not necessary for the proposed reconfigurable antenna. Experiments are also realized using two different varactors, and the measured results indicate that the peak gains of the conical radiation patterns occur around theta = +/- 40 degrees, and they are about 4.5 +/- 1.5 dBi when the constructed prototypes are operated in the frequency range from 3.1 to 5.7 GHz.