Impedance Matching of a Frequency- and Pattern-Reconfigurable Antenna

The authors have recently proposed a frequency- and pattern-reconfigurable antenna based on center-shorted patch antenna, which is tuned with six stub-loaded varactors. This antenna has the capability of switching between a broadside radiation pattern and monopole-like omni-directional pattern across a frequency tuning range of 2.7 GHz to 3.5 GHz. Using a single tuning bias voltage, the measured return loss was between 9.8 dB and 15 dB at the resonance frequencies across the tuning range. It will be demonstrated in this paper that the return loss at the resonance frequencies can be significantly improved to more than 30 dB with virtually no cost by using two reverse bias voltages controlling two groups of three tuning varactors. It is noted that the antenna design employing open-circuited loading stubs allows the use of different bias voltages on different varactors.