A Dual-Band, Dual-Pattern Antenna for Body-Centric Communications

A dual-band, dual-pattern antenna is presented for 1.437 GHz L-band and 2.45 GHz Industrial Scientific and Medical (ISM) band applications. The antenna is based on multilayer circular patches with symmetric slots and two asymmetric cylindrical vias that shorten the multiple layers with the ground plane using Plated Through-Holes (PTHs) to generate the required resonant modes. The first mode is operated at 1.437 GHz, providing an omnidirectional radiation pattern, while the second mode is operated at 2.45 GHz, providing a directional or broadside radiation pattern. The antenna was fabricated to validate the simulation results and excellent agreement was found between the simulation and experimental results. The antenna has a total size of only 6×6×0.443 cm3, which corresponds to an electrical size of 0.5λ0×0.5λ0×0.03λ0 at 2.45 GHz and 0.28λ0×0.28λ0×0.02λ0 at 1.437GHz, thanks to the loading effect of shorting vias. The gain of the antenna is 1.62 dBi at 1.437 GHz and 6.48 dBi at 2.45 GHz, along with quite good radiation efficiencies of 83.4% and 96%, respectively. For body-centric applications, the performance of the antenna was also examined in close proximity to the human body. Nearly stable performance was found in close proximity to the human body, comparable to free space performance in terms of both impedance matching and radiation patterns. The 10g Specific Absorption Rate (SAR) of the antenna was also measured and found to be below the international compliance limits. These characteristics make the antenna a very promising choice for body-centric communications. The antenna also applies to other wireless systems such as MIMO, wireless ad hoc networks, etc. It offers radiation pattern diversity in a single planar package with a highly flexible and adaptable design by providing much more degrees of freedom than classical microstrip antennas.