Dual-key slot mmwave antenna array with dual-band performance at 28 GHz and 38 GHz using characteristic mode analysis

In this work, a dual key-shaped antenna for 28/38 GHz mmWave applications is designed, analyzed, and tested using the Theory of Characteristic Modes. The antenna is printed on a 0.254 mm thick substrate and has a compact footprint of 10 × 12 mm², making it suitable for modern space-limited 5G devices. It supports two operating bands centered at 28 GHz and 38 GHz, with measured fractional bandwidths of 12.5% and 21.05%, respectively. At the lower band, the first four characteristic modes dominate the radiation, while Modes 2, 3, 4, 6, and 10 mainly shape the higher-band performance. To further enhance gain and cover wider practical needs, the design is extended into a four-element linear array with an overall size of 19.75 × 26 × 0.254 mm³. The array provides peak gains of 10.5 dBi at 28 GHz and 11 dBi at 38 GHz, while maintaining more than 75% efficiency across both operating bands. A prototype of the antenna and array was fabricated and tested using in-house measurement facilities, showing good agreement with the simulated results. The proposed antenna system meets the key performance requirements for 5G mmWave communication and offers a compact and efficient solution for future 28/38 GHz wireless devices.