CURRENTLY, A LOT of effort is being devoted to the integration of RF transceiver modules with embedded signal processing and sensor circuitry for small, low-power wireless nodesmostly at 2.45 GHz and below. The antenna presents a significant problem in such miniaturized systems, as the smaller size demands tradeoffs between design parameters like efficiency, bandwidth, and radiation characteristics. In addition, antenna performance is affected by close proximity to the human body. At the School of Electronics, Electrical Engineering, and Computer Science (Belfast, UK), Gareth A. Conway and William G. Scanlon investigated the on-body performance of a range of wearable antennas using both finitedifference- time-domain (FDTD) simulations and physical measurements.
The researchers measured the path gain between two devices mounted on tissue-equivalent numerical and experimental phantoms, which represented human muscle tissue at 2.45 GHz. Their work focused specifically on the performance of a compact higher-mode microstrip patch antenna (HMMPA) with a profile as low as λ/20. The 5- and 10-mmhigh HMMPA prototypes had an impedance bandwidth of 6.7 and 8.6 percent, respectively. Compared to a fundamental-mode microstrip patch antenna, both antennas offered 11 dB higher path gain.
In this work, on-body HMMPA performance was found to be comparable to a quarter-wave monopole antenna on a same-size groundplane and mounted normally to the tissue surface. This finding indicates that the low-profile and more physically robust antenna is a viable solution for body-worn antenna applications. See "Antennas for Over-Body-Surface Communication at 2.45 GHz," IEEE Transactions On Antennas And Propagation, April 2009, p. 844.
