Study of Antenna Concept for Wearable Devices

University essay from KTH/Elektroteknisk teori och konstruktion


SmartWatches are watches with the property that they can connect to internet.The interest and market for smartwatches has increased remarkably over the pastfew years. However, most of today's solutions cover only the frequency bandsBluetooth (BT) and Global Positioning System(GPS). A desired property of thenext generation of smartwatches is to include additional frequency bands suchas Global System for Mobile Communication(GSM) and Third Generation (3G)cellular bands, so that the Smart Watch can become independent of a smartphone.This sets new challenges for antenna design in small regions. The limited sizetogether with the increased bandwidth demand causes the major problem.The purpose of this thesis is to investigate the antenna concept for wrist wear-able devices that has earlier been developed by the RF team at Sunway Commu-nication AB in Stockholm. The main objective of this project is to study howthis antenna concept can be changed to achieve a given set of requirements onfrequency, bandwidth and eciency. Characteristic Mode Analysis and antennaquality factor calculated from the input impedance, are tools used to help under-stand and improve the characteristics of the antenna.A decomposition method and a parametric study were initially applied to theplanar version of the antenna concept. We investigated then the inuence of theposition of the feeds and the slot that separates the two antenna elements. Anoptimised design of the planar antenna was achieved based on the results fromthose studies. Four prototypes of this antenna were built and measured in the RFlaboratory in Kista.The possibility of miniaturization was studied through simulations by analysingthe eect of using a higher dielectric constant material in the antenna. Two dif-ferent arrangements were investigated. The eect of bending the antenna to t ona human wrist was also investigated, where a frequency shift was observed in theresults. The change in bandwidth of the dierent modes is related to the changein the stored energy of the antenna caused by the bending.We made a prototype of the planar antenna that shows a good agreement withsimulation results and fulls the basic requirements on frequency, bandwidth andeciency. We also found that the addition of a shorting pin showed a bandwidthimprovement of the high-band port and we showed through simulation that it ispossible to reduce the size of the antenna by adding a layer of PCABS material.

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