| Summary: | 碩士 === 國立彰化師範大學 === 電信工程研究所 === 99 === This study aims to design and implement balanced wideband (WB) and ultra-wideband (UWB) bandpass filters (BPFs) for application in modern wireless communication systems. The proposed research work of this thesis is divided into three parts with each addressed in a chapter. In the first part, a slotline multi-mode resonator (SLMMR) in conjunction with a microstrip-to-slotline transition (MST) feeding structure was used to construct a balanced WB BPF. The concept of adjustable higher-order-mode resonant frequency of the stepped-impedance structure was adopted to reduce the size of the slotline resonator and thus make the designed BPF a more compact one.
In the second part of this thesis, a UWB BPF was designed using a slotline resonator (SLR) whose differential-mode (DM) half circuit has a uniform width. The SLR is bent at two sides, but with its mid-section left straight along the plane of symmetry (POS). When the BPF is excited differentially, the POS can be replaced with an electric wall, and the SLR half circuit works as a uniform slotline multi-mode resonator (USMMR). To obtain the desired UWB response, the first three resonant modes of the USMMR were located in the DM passband. Then the USMMR was fed with a similar MST structure as that used in the BPF circuit of the first part to achieve strong coupling and UWB response. On the other hand, when the BPF is in CM operation, the POS is virtually open-circuited, and the USMMR is divided into two shorter quarter-wavelength SLRs. In addition, the mid-section of the USMMR is now an incomplete slotline. This renders null magnetic current flow in the mid-section and thereby prevents the CM signal from transmission.
In the third part of the proposed research work, a UWB BPF with a 5-GHz notch band was designed and implemented. The design idea is the same as that employed in the second part except that the SLR is a stepped-impedance one. To avoid the interference with the WLAN system (with frequency ranging from 5.15 GHz to 5.825 GHz), a notch-band centered at 5.5 GHz within the UWB was generated by loading the microstrip feeding lines with a half-wavelength short-circuited stub.
The proposed balanced WB and UWB BPFs in this thesis were simulated and measured for performance verification, and very good agreement between theoretical prediction and measurement was observed. Results obtained in this study reveal that the proposed balance WB and UWB BPFs are feasible for application in MB-OFDM and UWB communication systems. The proposed design technique can serve as a useful reference for researchers and engineers working in this and related fields.
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