Design And Performance Analysis Of Flexible Substrate Antenna

Wireless Body Area Network?WBAN?is a body-centric wireless communication system.The system,collecting useful data and transmitting these signals to hospital or emergency service station,has been serviced for us.Antenna plays an important role while transmitting/receiving signals in the system.Traditional antennas are rigid that cannot conformal well with human body.Fortunately,some flexible materials were found and antennas can be fabricated by them.When human body contacting with these flexible antennas,motions can't be affected.Flexible antennas based on Polyimide are proposed and the deformation of flexible antenna as well as biological electromagnetic characteristics on the surface of human body are discussed.Moreover,mutual influences between antenna and human body are analyzed and artificial magnetic conductor structure is utilized to reduce the mutual influences.The detailed contents of paper is as follows:?1?Two kinds of quasi Yagi-Uda antenna based on Polyimide are designed,measured and analysis.The first quasi Yagi-Uda antenna uses microstrip line feed.It works at2.45GHz frequency band and size is 65mm×56mm×0.71mm.When antenna is under deformation conditions,the changes of return loss and radiation patterns are researched.Results show the more serious deformation,the poorer antenna performance.Second quasi Yagi-Uda antenna uses coplanar waveguide feed.It works at 5.8GHz frequency band and size is 65mm×56mm×0.71mm.S11 parameter is measured.Antenna is bent at x-axis and y-axis directions with radius r=8mm respectively.It can be seen that radiation efficiency is reduced and maximum gain is minimum when y-axis bending.?2?Dual-band antenna based on Polyimide is designed,measured and analysis.It works at 2.4GHz and 5.8GHz frequency while size of antenna is just 30mm×25mm×0.15mm.S11parameter of simulation agrees with measurement.When antenna is placed at human arm distance of 5mm,radiation efficiency and maximum gain reduces and SAR value can't meet regulated standard.Moreover,S11 parameter is measured when antenna is placed on eight different human arms.Result show S₁₁ parameter is affected by body tissues greatly.?3?Artificial magnetic conductor structure of 3×3 elements is utilized to reduced mutual influences between antenna and human body.First of all,square artificial magnetic conductor structure of FR4 substrate is regard as reference,thickness of 1.6 mm.The structure is placed below the antenna,frequency offset and SAR are analysis.In order to comformal well with human body,then flexible artificial conductor structure of Polyimide substrate is simulated and fabricated,thickness of 1mm.Results show the structure enhances radiation efficiency of antenna,maximum gain and reduces frequency offset,SAR.The influences of artificial magnetic conductor's size and distance far away from antenna on resonant frequency are analyzed.