Liu, Luyi; Langley, Richard (EEE Department, University of Sheffield, Mappin Street, Sheffield, S1 3JD, United Kingdom)
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.