Distributed Antennas for Wearable Applications

The concept of using a distribution of antennas as a wearable antenna to protect the operator's body from electromagnetic radiation is presented here. The main idea is to use the interference produced by antennas to achieve destructive or near-destructive interference at the body's location. This way, the body's exposure to radiation is low. This principle works with any type of antenna, even antennas with no ground plane nor high impedance surface. A practical implementation was carried out with a group of three antennas on a military tactical jacket. The specific absorption rate (SAR) obtained by electromagnetic simulation is 1.31 W/kg for 10 g of tissue, which is below the limit value of 2 W/kg. The efficiency is 74%. For a single dipole placed at the same distance from the body, the efficiency is 54% and the SAR is 3.16 W/kg. Spatial coverage is good, except in the direction of the body. The measured gain is 3.3 dBi. To obtain full coverage, at least two antennas or two groups of antennas must be used. But this time, destructive interference is problematic in some directions. This can be resolved by adding a time-varying phase shift from 0 to π or by using a multiple input multiple output system. By taking the antenna group receiving the most signal, transmission minima are greatly reduced.