Abstract

This paper presents an analysis of the input impedance and radiation pattern behavior for a rectangular loop antenna when it is reshaped from a narrow square to wide and flat. The antenna operation is examined by 3D electromagnetic simulations. Parametric simulation results are shown to explain the effect of antenna dimensions on the impedance behavior. Based on the numerical results, an equivalent circuit is developed to model the impedance change due to reshaping the loop antenna. The main observations are that the decreased height and the increased width of the antenna increase the bandwidth potential of the inherently narrowband loop and increase its directivity. These characteristics together with a vertical loop orientation enable a high performance antenna for locations very close to conductive or lossy materials. Based on the presented impedance analysis, an optimized antenna prototype for a wearable use is manufactured and its performance is verified by measurements. Measured radiation efficiency for the antenna in contact with a human tissue phantom is -5.0 dB at 2 GHz and the obtainable bandwidth potential is > 10 %.