Design of a high-gain, MIMO Diagonal Square Fractal antenna for dual-band vehicular communication

A low-profile, dual-band, high-gain, 2-port MIMO Diagonal Square Fractal (DSF) antenna is proposed for vehicular communication applications in the DSRC and X-band frequencies. The design addresses key challenges such as reducing mutual coupling between closely spaced elements, miniaturization for space-constrained platforms, suppression of undesired frequencies, and achieving high gain with high radiation efficiency. Two rectangular slots are incorporated into the ground plane to control the gain by transmitting the EM wave through the slots to the radiating element, thereby minimizing the mutual coupling effect and improving transmission coefficient. The antenna has a compact size of 20.41 × 45.44 × 4.72 mm3 (0.402λ × 0.92λ × 0.093λ), where λ is the free-space wavelength at the lowest working frequency, fabricated on RT/duroid 5880 substrate. It achieves simulated gains of 17.98 dBi and 23.19 dBi, and measured gains of 16.86 dBi and 21.78 dBi, respectively, at the targeted frequencies of 5.9 GHz and 9.5 GHz, respectively, with radiation efficiencies of 95.10% and 95.40%. S-parameters from the equivalent circuit agree with HFSS 2023 R1 simulation. Measured radiation patterns closely match simulated E- and H plane results. Vehicular testing using a dummy car with ADAS confirms stable 3D polarized gain. Performance metrics including ECC, DG, TARC, and MEG validate reliable communication suitability.