A Compact Ultrawideband Antenna System With Stable Broadside Radiation Patterns for Brain–Machine Interface Applications

In this study, we have developed a compact and ultrathin wideband antenna system with stable broadside radiation patterns for brain-machine interface applications. The antenna system operates in the ultrawideband (UWB) frequency range and employs a deionized (DI) water-infilled superstrate to achieve efficient radiation in the broadside direction. The antenna was constructed using a thin Taconic TRF-43 substrate, which has a relative permittivity ( $\varepsilon _{r}$ ) of 4.3 and a loss tangent (tan $\delta $ ) of 0.0035. By incorporating a modified rectangular slot on the ground plane and a tapered stepped microstrip feedline, we achieved a broad frequency response. The overall system consists of a compact $10\times 9\times 0.7$ mm antenna, along with system dummies such as batteries, sensors, and electronic components, all enclosed in a biocompatible casing manufactured via 3-D printing. The design and analysis of the system were performed using computer simulation technology (CST) and Sim4Life simulation tools. To validate our findings, we built a prototype and conducted measurements using a brain phantom made of semi-solid artificial tissue-emulating (ATE) material. Our results demonstrate that the antenna exhibits a −10-dB bandwidth of 129% from 3 to 14 GHz, with a peak gain of −19 dBi at 3 GHz while maintaining the desired broadside radiation characteristics.