A Sensing and Tunable Two‐Element MIMO Unified Five‐Antenna via Circuit Model for WLAN Cognitive Radio

ABSTRACT This paper presents a five‐element antennas system formed by integrating one sensing and four reconfigurable communicating antennas on a single substrate for cognitive radio applications in the 2.4 and 5 GHz WLAN bands. The five antennas are termed as A‐1, A‐2, A‐3, A‐4, and A‐5, where A‐1 is designed to sense in the 2.4 (2.4–2.484 GHz) and 5 GHz (5.15–5.875) bands. Antenna A‐2, exhibiting two‐element MIMO configuration with A‐3, is designed to communicate in the 5 GHz band, whereas Antenna A‐4, also exhibiting two‐element MIMO configuration with A‐5, operates in the 2.4 GHz band. Each communicating antenna is incorporated with a varactor diode to accomplish continuous frequency tuning operations. Simulated maximum peak gains of A‐1, A‐2, and A‐4 are 7.07, 2.65, and 2.15 dBi, respectively. A good mutual coupling, of less than −15 dB, is noted between the sensing and communicating antennas. MIMO diversity parameters are found to be ECC ≤ 0.01, TARC ≤ −10 dB, DG ≤ 10 dB, and CCL ≤ 0.4. Overall dimensions of the proposed structure are 80 mm × 100 mm × 1.2 mm. The antenna lumped element circuit models developed in ADS software also present good matching with EM simulation. A prototype of the proposed antenna system is fabricated to validate the simulation results. Because the proposed antenna can sense the WLAN bands using the dual‐band antenna (A‐1) and can be able to communicate at the identified spectrum holes using the reconfigurable NB antennas (A‐2 to A‐5), this antenna system is an appropriate module for the cognitive radio applications in WLAN bands.