Quadruple Band Filter Design with Flexible Band Allocation
Date Issued
2011
Date
2011
Author(s)
Lin, Wei-Chih
Abstract
With different requirements on the band allocations, this thesis proposes two methods for the design of quad-band bandpass filters. Thus the designed filters are fabricated on the printed circuited boards and verified by experiments.
The first part focuses on the design for closely spaced pass-bands. Through a general idea of frequency transformation, the poles and zeros of a single band response are transformed into poles and zeros of a multiband response according to the cutoff frequency of each band. Then, theoretical analysis is made to predict the nth order response and discuss the distribution of the numbers of poles and zeros. Finally, to reduce the number of resonators, a method for extracting the resonant frequency points between multi-mode and single mode resonators is proposed. If the module about resonant frequency points is constructed, the band-pass response of multi-band could be directly realized by designing the fundamental single-band Chebyshev response and achieving the fast and low-cost circuit design.
The second part deals with the case of arbitrarily spaced pass-bands. The design concept is to connect four pass-bands together to form quad-band response by exploiting the frequency orthogonality. Then, to avoid loading effect by tapped line, parallel coupled lines are served as the I/O coupling structure to meet external quality factors for quad-band requirements. Moreover, multi-mode resonators are introduced to replace with many single-mode resonators and utilize the concepts of coupling matrix to explain the location of mode-frequency. By this way, the number of resonators and circuit area can be reduced. Finally, we make improvement for stopband.
The four circuits are fabricated in this thesis, and the simulated results show a good agreement with the measured results. About the first part, the open-loop and net-type resonators are applied. These two quadband filters are designed and fabricated with the areas 1.18λg × 0.144λg ,0.533λg × 0.27λg , the center frequencies at 1.86、1.95、2.04、2.14GHz, 1.82、1.94、2.06、2.18GHz, the fractional bandwidth 1.5%、1.33%、1.33%、1.5%, 2.2%、1.85%、1.75%、1.84%, and the insertion loss 2.2、2.3、1.8、1.3dB, 1.2、1.7、2、1.2dB, respectively. The second part is the combination of coupled lines and net-type resonators. The occupied area is 0.788λg × 0.066λg , the center frequencies at 0.8、1.0、1.4、1.8GHz, the fractional bandwidth about 12.1%、8.3%、5.5%、3.8%, and the insertion loss 1.6、2、2.5、2.7dB.
Subjects
Quad-band filter
Band allocations
Extraction of multi-mode resonators
Frequency transformation
Type
thesis
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