To improve 5G base station antenna performance, the study presents a novel dual-band high-gain four-port MIMO antenna with a frequency selective surface (FSS). The antenna resonates at 37.5 GHz (7.8% fractional bandwidth) and 3.5 GHz (53.3% fractional bandwidth), covering the sub-6 GHz and mmWave bands crucial for 5G. It has a straightforward monopole design with a cross slot and partial ground, it measures 82×76×1.524 mm³. Using frequency selective surface (FSS) for every band for beam steering, increases antenna gain, and isolation. Four different radiation patterns are displayed, with isolation levels of -15 dB and -34 dB and maximum gains of 8.5 dB and 11.2 dB. FSS is enhancing data rates and throughput for single or array antenna elements across both frequency ranges has been verified by practical experiments conducted with the FEKO-WinProp platform. Significant performance improvements are demonstrated by the results, which include a 25% increase in throughput (150 MB/s to 187.7 MB/s) and a 20% increase in data rate (1.5 MB/s to 1.8 MB/s) in the sub-6 band. With FSS implementation, data rates in the mmWave band increase by 72% (579.9 kB/s to 1.08 MB/s) and throughput increases by 62% (192 MB/s to 305.3 MB/s). There is also a noticeable increase in reference signal strength indicators (RSSI), indicating improvements in signal quality. The results show significant performance improvements, up to 200 % in data rate.