Ultra Wide Band CPW-Fed Circularly Polarized Microstrip Antenna for Wearable Applications

A conformal rigid microstrip ultra-wideband (UWB) circularly polarized wearable antenna is proposed to overcome the behavioural irregularities of flexible body-worn antennas. The design demonstrates the inclusion of two L shaped radiators along with an L shape feed and also a vertically protruded stub embedded with the ground plane for achieving the required ultra-wide bandwidth and circular polarization. Coplanar waveguide (CPW) feed is used to overcome the bandwidth limitation of circular polarization. The proposed low profile antenna with dimensions 75 x 63 x 1.52 mm(3) yields a 10 dB impedance bandwidth of 111.4% (1.28-4.5 GHz) and a 3 dB axial ratio bandwidth of 45.61% (2.2-3.5 GHz). On body performance measurement of this planar antenna validates its applicability under body worn condition. Specific absorption rate (SAR) assessment has also been evaluated for this antenna on a hypothetical body model to justify its acceptance for the wearable application. It is observed that the maximum radiation amount absorbed by the body model is restricted to a maximum SAR value of 1.19 W/kg and 1.43 W/kg over 1 g and 10 g average body mass respectively. The time-domain characteristics such as group delay and waveform response, also exhibit satisfactory UWB performance of the proposed antenna. A lumped wideband equivalent circuit model of the antenna is also developed for estimating the broadband matching ability.