A novel triple-band MIMO antenna for multi-frequency wireless applications

Abstract This paper presents the design and experimental validation of a compact triple-band two-port MIMO antenna based on a star-shaped slot-loaded circular radiator for multi-frequency wireless applications. The proposed antenna operates over three distinct frequency bands of 3.1–4.2 GHz, 6.3–8.4 GHz, and 10.1–12.3 GHz, with overall dimensions of 87.5 mm × 35 mm × 1.6 mm (approximately 1.0 λ × 0.4 λ × 0.0187 λ at 3.5 GHz). A key feature of the design is the use of a segmented ground-plane architecture , which effectively confines surface currents and suppresses mutual coupling, enabling high isolation despite a compact edge-to-edge radiator spacing of only 17 mm (≈0.2 λ at 3.5 GHz). As a result, the antenna achieves isolation better than 20 dB in the first band, above 18 dB in the second band, and greater than 11 dB in the third band without employing bulky or complex decoupling structures. Circular polarization is realized in the upper band (10.1–12.3 GHz) through controlled perturbation of higher-order modes using symmetrically placed star-shaped slots, with the axial ratio maintained below 3 dB. The antenna provides a peak gain of up to 8 dBi, with gains ranging from 2 to 8 dBi across the operating spectrum. A fabricated prototype was measured, and the results show good agreement with simulations. The MIMO performance metrics demonstrate excellent diversity characteristics, with ECC < 0.01 , DG ≈ 9.9–10 dB , CCL < 0.4 bits/s/Hz , and TARC < −10 dB across the operating bands, confirming the antenna’s suitability for compact triple-band MIMO systems supporting sub-6 GHz 5G, emerging upper-midband, and X-band wireless applications.