以高阻抗平面設計頻率可調整之穿戴式天線

Abstract

本論文主要提出一種頻率可調整之穿戴式天線，並確保該天線不會朝向人體輻射而對使用者造成影響。首先，我們提出一種頻率可調整之高阻抗平面來抑制主要輻射源/天線的背向輻射，且維持整個天線結構的低姿態與保角特性。我們在週期性排列的塊狀金屬片之間焊上變電容二極體，改變其電容值來調整高阻抗平面的工作頻率。本論文設計了兩支寬頻天線作為主要輻射源，包含一領結型天線以及印刷式偶極天線陣列，將其分別擺放於前述高阻抗平面上，以達到低姿態、頻率可調整且單向輻射之要求。模擬和實驗結果皆證明了頻率可調的特性，背向輻射也有效的被抑制。最後，我們將天線結構彎曲以模擬該天線伏貼在手臂上的情形，發現該天線之效能並沒有因為彎曲而有太大的改變。此外，我們也討論了該天線的特定吸收比率(Specific Absorption Rate，簡稱SAR)，模擬結果證實：由於使用高阻抗面，該天線之SAR 值確實大幅降低。綜合前述，我們相信該天線將可應用在穿戴式無線通訊系統上。

A frequency-agile, wearable antenna is presented in this thesis. To avoid the influences of the electromagnetic fields radiated on the user’s body while keeping the entire structure low-profile and conformal, we propose a frequency-agile high impedance surface (HIS), which is then integrated with the main radiator/antenna to suppress its backward radiation. The frequency agility is achieved by soldering varactor diodes between adjacent metallic patches that are periodically etched on a dielectric substrate with conductor backing. The operating frequency of the HIS can be tuned by changing the capacitance of the varactor diodes. For integration with the HIS, two broadband planar antennas, including a printed bow-tie antenna and a printed dipole array, are also presented in this thesis. By placing the printed antennas on the HIS respectively, two designs of frequency-agile, low-profile antennas with unidirectional radiation pattern are realized. Lastly, we bend the entire antenna conformally to a cylinder to simulate the situation that the antenna is attached onto a user’s arm. It is found that the performances of the antenna remain nearly unchanged. Moreover, the Specification Absorption Rate (SAR) of the antenna is also discussed. According to the simulation results, the SAR value is reduced significantly by using the HIS. Therefore, the proposed antenna may be suitable for use in body-worn wireless communication systems.