A compact monopole antenna with reconfigurable band notch for underlay cognitive radio applications

A compact printed ultra-wide band (UWB) antenna with a switchable band notch for underlay cognitive radio applications is presented in this paper. The antenna patch is partially covered by a ground plane with a staircase slot in order to enhance the matching between the feed line and the antenna. A broadband notch centered at 3.5 GHz and extended along the frequency range (2.9-3.9) GHz is produced by etching a complementary split-ring resonator on the radiating patch, while the presence and absence of this band notch are controlled by a PIN diode. On the other hand, the sensing mode of the proposed antenna scans a frequency range with a fractional bandwidth equal to 130.6% over the range (2.3-11.16) GHz. The results show that the proposed antenna has reasonable radiation characteristics with omnidirectional radiation pattern suitable for portable devices. The gain value surpasses 2.5 dBi over the entire sensing range, but it drops to value less than -4 dB within the notched band. Furthermore, the fabricated version of the proposed antenna gives measurements that are in good agreement with the simulated results.