A Fractal-Shaped Wideband MIMO Antenna for C, X, Ku, and K Band Applications

This paper introduces a compact wideband MIMO antenna design having coverage across C, X, Ku, and K bands. The proposed antenna comprises four identical circular fractal-shaped elements, arranged orthogonally and fed through 50-ohm microstrip lines. Both the patch and ground are made of copper, while the substrate is made of FR-4 lossy material with a relative permittivity of 4.3. A modified partial ground plane is used to achieve a large bandwidth, complemented by the fractal geometry of the antenna elements. The overall antenna dimensions are 32 x 32 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, and it operates effectively across a frequency range of 4 GHz to 24 GHz. The design achieves excellent isolation with values less than -15 dB and below -20 dB across most operating range. An envelope correlation coefficient (ECC) of less than 0.01 ensures minimal signal interference between elements, while the diversity gain (DG) is 9.95 dB. The total active reflection coefficient (TARC) reaches very low values, with a minimum of -70 dB observed at 180° phase difference. Additionally, The mean effective gain (MEG) ranges from -3.70 dB to -3.05 dB and the antenna exhibits a gain of over 5 dB with an efficiency of 75%. Simulations were performed in CST Microwave Studio to evaluate the antenna’s performance.