A DGS-based hexagonal millimetre-wave antenna for 5 G applications using foam substrate

This paper presents a compact hexagonal microstrip antenna of 4.5 mm × 5.5 mm size designed for 28 GHz 5 G millimetre-wave applications. Unlike conventional rectangular patches, the proposed design integrates an L-shaped slot within the hexagonal geometry and employs a defected ground structure (DGS) to enhance impedance bandwidth. The use of a flexible foam substrate (εr = 1.07, h = 2 mm) not only ensures lightweight and conformal characteristics but also enables stable performance under practical conditions. The antenna achieves a bandwidth from 26.96 to 29.07 GHz (7.5% FBW) with a peak gain of 6.8 dBi and an excellent return loss of −36.39 dB. Furthermore, SAR analysis on a compact tissue-equivalent phantom 7 mm × 9 mm × 17 mm confirms radiation exposure levels well below IEEE safety limits for both 1 g and 10 g tissues. A compact footprint, improved return loss, conformal compatibility, and verified SAR compliance, wideband operation along with the comparison of simulated, fabricated and equivalent circuit model performance, making it highly suitable for wearable, handheld, and compact 5 G devices. This work provides a practical and safe mmWave antenna solution that bridges the gap between miniaturisation, high performance and regulatory compliance.