Polarization-Diversity Ring Slot Antenna With Frequency Agility

A design for polarization-diversity slot antennas with switchable frequency is described. The antenna structure is mainly composed of a radiating annular slot backed with a reflector and a quasi-lumped coupler with two different operating modes, quadrature hybrid mode and T-junction power divider mode. The resonant frequency of the slot antenna and the operating frequencies of the two modes of the coupler can be tuned with variable capacitors. First, the effects of changing capacitance values on the performances of the antenna and coupler are respectively analyzed. Then, according to the simulation results, validated with experiments, a reconfigurable antenna prototype integrating with several diodes and their related dc-bias networks is constructed. The prototype is designed to be with three working frequencies, and moreover it can provide one linear polarization and two circular polarizations at each working frequency. Details of measured antenna performances are shown.