Study on tunable electrically small antennas

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 two antenna tuning techniques are presented here. The first tunable antenna is a liquid crystal (LC) tuned microstrip patch antenna operating in the 5 GHz range. The simulated tuning range is 8% while the measurements showed a range of 4%. Losses in the LC material at these frequencies give rise to antenna efficiencies ranging from 40% to around 20% when the LC is in the unbiased state. The second antenna is a reconfigurable PIFA which is able to cover 7 frequency bands by changing the combination of 4 MEMS switches.