Electrically small antenna tuning techniques

Cognitive radio systems require antennas and microwave components to be actively tuned for different parts of the frequency spectrum. In this paper results of a study of three antenna tuning techniques are presented here. The first tunable antenna is a liquid crystal (LC) tuned microstrip patch antenna operating in the 2 GHz range. The simulated tuning range is 8% while the measurements showed a range of 3.8%. Losses in the LC material at these frequencies give rise to antenna efficiencies ranging from 25% to around 7% when the LC is in the unbiased state. The second antenna is a reconfigurable PIFA which is able to cover 7 frequency bands by controlling the combination of 4 MEMS switches mounted on the radiator. The third antenna is a dual-port antenna which is comprised of two capacitive-fed plates sharing one lower-band patch, operating for 5 mobile phone bands.