The design of a compact frequency-reconfigurable slot antenna for cognitive radios is proposed in this paper. The antenna consists of a rectangular-ring slot, a T-shaped feed line, an inverted T-shaped stub and two varactors. The length of the rectangular-ring slot is designed to resonate at about 2.4 GHz. The inverted T-shaped stub is used to extend the current path, making the total size of the antenna smaller for low frequency operation. The two varactors are used to achieve continuous tuning. The proposed antenna is studied and designed using computer simulation. The simulated return loss, radiation pattern, realized peak gain and efficiency of the antenna are presented. Results show that the antenna has a wide tuning range from 2.14 to 3.33 GHz (43.51%) and is a potential candidate for use in cognitive radios.
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