Dual-band circular patch antenna working in TM₄₁ and TM₁₁ mode for on-/off-body communications

A capacitive coupling dual-band circular patch antenna for on-/off-body communications is proposed for 3.5 GHz world interoperability for microwave access band and 5.8 GHz industrial scientific medical band. The antenna has a compact structure with a single substrate made of polydimethylsiloxane which is flexible and easy to wear. To realise off-body mode, the antenna adopted bias feeding. The on-body mode is achieved by symmetrically loading four shorting vias on the edge of the patch to stimulate TM₄₁ mode, which tends to bring a high gain of the antenna. The measured operating bandwidths of the antenna for off-body and on-body modes are 120 MHz (3.45–3.57 GHz) and 360 MHz (5.54–5.90 GHz) respectively. The peak gains are 5.99 dBi for off-body mode and 5.46 dBi for on-body mode. Moreover, the antenna displays robust performances when it is bended or closed to human bodies. Meanwhile, low specific absorption rate values are proving that the antenna is safe to wear on human bodies.