本論文中，利用在步階式阻抗共振器(Stepped-impedance resonator, SIR)末端加上二極體負載製作成可開關式的帶通濾波器，並在濾波器輸出端接上寬頻天線(Broadband Antenna),形成可開關之四頻天線。負載的二極體可改變步階式阻抗共振器共振條件。由於散佈式耦合的饋入技術的低負載效應，因此不需要複雜的匹配網路來設計多頻帶的電路。

四頻帶通濾波器電路架構包含二分之一波長步階式阻抗共振器、四分之一波長步階式阻抗共振器。每個通帶皆由一對共振器控制可增加設計自由度，並且使用散佈式耦合技術減少頻帶間的負載效應，即可將四個帶通濾波器整合在一起，並將二極體負載接在共振器末端以設計可獨立開關四個頻帶的可調式裝置。

寬頻天線為微帶線結構，包含單極輻射體，其架構為一半波長步階式阻抗共振器，以拉近倍頻之方式形成超寬頻通帶，並具有線性極化特性。將濾波器輸出端連接於寬頻天線之饋入端，作為通帶選擇器，即可實現多頻天線之架構。

本論文中以兩種不同介電常數跟介質損耗之電路板材進行實驗，並將可開關之天線與純被動天線加以比較，且輔以模擬結果，與設計理論，實測結果相互驗證。

In this thesis, we made switchable bandpass filters by adding diodes to the end of Stepped-impedance resonator (SIR). Then we combined broadband antennas to the output port of bandpass filters to form switchable quad-band antennas. As we switching the loading diodes, the resonance condition of SIRs would be changed. By low loading effect of distributed fed-in technique, there is no need to design complex matching network for multiband circuits.

Quad-band bandpass filters include quarter-wavelength and half-wavelength SIRs. Each passband is controlled by one pair of resonators and it will increase the degree of freedom to design. By the low loading effect of distributed coupling between passbands，four bandpass filters could be combine together, and the diodes at the end of resonators could perfume the switchable independently device.

Broadband antennas were built on microstrip line structure. The monopole radiator is a half-wavelength SIR. It performs a wide passband by pull down the harmonic frequencies, and it has linear polarization characteristics. We can implement multiband antennas by adding bandpass filters on the input port of antennas to make the passband selection.

We will perform experience on two kinds of substrates which have different relative dielectric constants and loss tangent values in this thesis. We will also compare the switchable antennas with passive ones. Finally we will identify our research by performing full-wave EM simulation and implement measurement.

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