Flexible Hybrid-Substrate Dual-Band Dual-Mode Wearable Antenna

A flexible dual-band dual-mode wearable antenna with a hybrid dielectric substrate is proposed for off- and on-body communications. It operates at two industrial, scientific, and medical (ISM) bands, namely, with a broadside radiation at 2.45 GHz and an omnidirectional radiation pattern at 5.8 GHz. A hybrid substrate based on flexible polydimethylsiloxane (PDMS) and PF4-foam materials is introduced to overcome the low radiation efficiency in both modes due to the PDMS substrate. The hybrid substrate is realized by replacing the PDMS substrate areas exhibiting high power loss density with a low-loss PF4-foam material. This reduces the dielectric loss and improves the radiation efficiency by an average value of 17% and 20% in the 2.45- and 5.8-GHz ISM bands, respectively. Such a technique extracts the desirable properties of two dielectric materials and combines them to achieve improved antenna performance. The common properties of both materials include high flexibility, resilience, water resistance, and robustness. Importantly, the hybrid substrate offers an optimal trade-off between antenna size and radiation efficiency. In comparison with a PF4-foam-only counterpart, the proposed hybrid substrate demonstrates an antenna area reduction of 19%, while the PDMS-only substrate design exhibits an antenna area reduction of 37%. In addition, the design methodology of the dual-mode antennas allows for independent control of the resonances, providing a high degree of design flexibility.