Design Process of a Four‐Port Fractal MIMO Antenna: Boosting Isolation and Diversity for Ultra‐Wideband and X‐Band Systems

Abstract

ABSTRACT This work offers a novel fractal multiple‐input multiple‐output (MIMO) antenna system designed for robust isolation at ultra‐wideband (UWB) frequencies and suitable for X‐band applications. The MIMO design includes four identical fractal antenna units spaced 5 mm apart and oriented orthogonally. Each unit features a circular ring with smaller rings and a plus sign, enhancing impedance matching and bandwidth. Fabricated on a Rogers RT 5880 substrate with dimensions of 1.2λo × 1.2λo × 0.0218λo (λo at 4.15 GHz), the antenna covers 2.05–14.5 GHz, including UWB (3.1–10.6 GHz) and X‐band (8–12.5 GHz). A neutralization line (NL) reduces mutual coupling (MC), achieving isolation of up to −90 dB and improving parameters like diversity gain, total active reflection coefficient (TARC), and envelope correlation coefficient (ECC). The antenna provides a maximum gain of 8 dBi with an efficiency ranging from 95% to 97%, making it ideal for UWB and X‐band applications.