High-Isolation Frequency-Reconfigurable UWB-MIMO Antenna with T-Shaped Decoupling for Cognitive Radio Systems

Abstract This study presents a UWB antenna for spectrum sensing and a reconfigurable communication antenna with dynamic frequency selection designed for cognitive radio applications. The UWB antenna (ANT1) is used for spectrum sensing while the PIN diode-integrated frequency-reconfigurable antenna (ANT2) is used for communication. The antenna is designed on a FR-4-based dielectric material with dimensions of 25 × 35 × 1.6 mm 3 (0.175 λ ₀ × 0.245 λ ₀ × 0.011 λ ₀) and sized at the wavelength ( λ ₀) corresponding to the lowest resonant frequency in free space. The UWB antenna (ANT1) operates at a bandwidth of 2.1–12 GHz and the communication antenna (ANT2) operates at 3.8–6.3 GHz and 2.4–3.5 GHz; 8.6–12 GHz, respectively, depending on the pin diode off/on states. To increase the isolation between the antenna components and the impedance bandwidth, a T-shaped extension is integrated into the ground plane, which significantly enhances the isolation levels. The proposed antenna structure is transformed into a 4 × 4 8-port MIMO antenna architecture. A total of four PIN diodes are integrated into the MIMO antenna structure to provide frequency reconfigurability. The simulated and fabricated antenna structures are comprehensively evaluated in terms of MIMO performance parameters, including mutual coupling, diversity gain (DG), and envelope correlation coefficient (ECC).