Design of compact multi stub resonator based flexible monopole antenna for 5G wearable applications in N77 and N78 bands

In this article, a simply structured small-size multi stub resonator based flexible monopole wearable antenna is proposed for N77 (3.3–4.2 GHz) and N78 (3.3–3.8 GHz) bands of 5G communication that was design on the RT/Duroid 5880 substrate with a thickness of 20 mil (0.508 mm). The presented antenna configuration comprised of a monopole antenna and a vertically aligned symmetrically loaded multi stub resonator which excite resonant mode at 3.525 GHz for N77 and N78 bands of 5G applications. At the outset, it is fabricated, tested and its performance experimentally verified. It has the measured impedance bandwidth of about 1.3 GHz (3.15–4.45 GHz) and peak gain of 2.37 dBi at 3.475 GHz. Afterward, the presented monopole antenna is investigated by utilizing multi-layer tissue model for specific absorption rate (SAR) evaluation. At 3.5 GHz, the 1 g/10 g SAR values are 0.112/0.073 W/Kg, respectively, which is substantially under typical values. Lastly, the measured performance of the presented monopole wearable antenna is assessed at numerous on-body parts (i.e., wrist, chest, and leg) and diverse bending scenarios for flexibility and conformability analysis. With the small antenna footprint of 30 mm × 16 mm × 0.508 mm (0.35λ0 × 0.187λ0 × 0.0059λ0 at 3.5 GHz), wide bandwidth, low SAR values, flexible and conformal in nature makes it is suitable for modern 5G wearable applications.