A Compact and Low-Profile MIMO Antenna Using a Miniature Circular High-Impedance Surface for Wearable Applications

A new miniature circular high-impedance surface (HIS) is used to design a compact and low-profile multi-in multi-out (MIMO) antenna for wearable applications. The antenna is designed to operate from 2.4 to 2.49 GHz for wireless local area network application. By employing a pair of degenerated characteristic modes of a circular loop antenna, the MIMO antenna can achieve a good port-to-port isolation (>15 dB) without increasing its geometric size. A four-element HIS is chosen to match the antenna profile, and a 2 dBi antenna gain improvement is observed. The design was optimized considering the effect of packaging and then a prototype with the optimal parameters was fabricated and tested. Measurement results are in good agreement with simulation results. Furthermore, the loading effect due to lossy human tissue is also considered and the results show that the antenna has a robust performance against the human phantom and a low specific absorption rate can also be obtained.