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.
