0. 微波工程期中報告 論文研討: Microstrip Dual-band Dual-path Bandpass Filter 報告人:
Z. I. Khan 1, M. K. Mohd Salleh 2, M. A. Abdul Latip
Faculty of Electrical Engineering
Universiti Teknologi MARA (UiTM)
40450 Shah Alam, Malaysia
Proceedings of the Asia-Pacific Microwave Conference 2011
報告人:
碩研電子一甲 MA 郭俊良
Southern Taiwan University
Department of Electronic Engineering

1. 摘要
A dual-mode dual-band bandpass filter topology is proposed by connecting two quarter-wavelength parallel coupled-lines to two half-wavelength lines creating a dual-path structure.
Based on the topology, the characteristics of the filter response such as the bandwidth and the separation between the bands can be controlled by varying the even- and odd-mode impedances of the coupled-lines and the line impedance of the half-wavelength lines. Using microstrip technology, the filter was designed at 2.5 GHz using TRF45 (Taconic) and the results show the filter is suitable in addressing medium band applications.
These concepts are validated through simulations and experiments.
Index Terms — Dual-mode, dual-band, bandpass filter.
Proceedings of the Asia-Pacific Microwave Conference 2011

2. 簡介 Proceedings of the Asia-Pacific Microwave Conference 2011
As wireless systems become more multifunctional, it increases the importance of having multiband operations.
Dual-band filters appear thereby as one of the solutions to optimize the size and cost of such multifunctional system.
The dual-band filters are located at the front ends of the wireless system enabling pre-selection of more than one band at the same time as well as rejection of interferers.
There are numerous methods in producing a dual-band bandpass filter.
It can be observed that by directly cascading two individual filters with two specified single pass-bands will produce the dual-band effect.
However, this approach needs large overall size.
Another method is by cascading a broadband filter with a band-stop structure which separates two passband with central frequency and the bandwidth is arranged appropriately hence producing the dual-band effect.
This concept has a greater potential of having a compact size filter.
Proceedings of the Asia-Pacific Microwave Conference 2011

3. 建議雙波段微帶濾波器
The proposed dual-band filter topology is depicted where two half-wavelength paths are connected to two quarter-wavelength coupled lines. Frequency f0 found at the center of the two passband responses, is the reference frequency at which the quarter-wavelength coupled lines and the half-wavelength lines are defined. The frequencies f1 and f2 are the center frequencies of the first and the second pass-band. Each bandpass response is of a second order, seen by their two poles in the bands. As such, a very compact filter can be designed to produce a second order dual-band response. A total of three transmission zeros are found in the frequency response of the filter that will assure a good level of selectivity.
Proceedings of the Asia-Pacific Microwave Conference 2011

4. 建議雙波段微帶濾波器 Proceedings of the Asia-Pacific Microwave Conference 2011
As the dual-band filter response is symmetrical about f0 which can be arbitrarily chosen, any dual-band filter of any center frequency can be realized, theoretically, using this concept of topology.
The range of realizable coupling level of the coupled-lines will be the main factor that will limit such a topology in terms of the bandwidth and the passbands separation.
A working configuration of the impedances Zoe, Zoo and Zr will exhibit a dual-band bandpass response that is shown in where the reference frequency of the transmission line length is f0.
The frequency separation between the passbands, the passband bandwidth and the in-band ripple level of the passband, can be varied by varying the impedances Zoe, Zoo and Zr. However, the increase of bandwidth will be followed by increase in rejection levels as shown.
One example of working impedance configuration of the filter elements is: Zoe = 100 , Zoo = 62 , and Zr = 43, which will result in a dual-band response centered at f1‘ = 1.77 GHz and f2’ = 2.96 GHz for a chosen reference frequency of 2.5 GHz. The relative bandwidths for the passbands are 29.7% and 17.6% respectively which is equivalent to 526 MHz.
Proceedings of the Asia-Pacific Microwave Conference 2011

5. 建議雙波段微帶濾波器
The proposed topology is tested through the design of microstrip dual-band bandpass filter on TRF45 whose characteristics are: dielectric constant, r = 4.5, substrates thickness, h = 1.6 mm and loss tangent, tan =
The complete layout of the dual-band microstrip filter with the elements’ dimensions is shown.
As mentioned earlier, the bandwidth and the in-band ripple level of the passbands, can be varied by varying the impedance of each of the filter elements (Zoe, Zoo and Zr), hence by adjusting the dimensions of the lines in the filter.
Proceedings of the Asia-Pacific Microwave Conference 2011

6. Proceedings of the Asia-Pacific Microwave Conference 2011

7. 結論
A compact topology of dual-mode dual-band microstrip bandpass filter is proposed by using only two coupled – lines and two half-wavelength lines.
Only three control parameters are used in setting the desired characteristics of the filter response.
The proposed topology has been realized and tested using microstrip technology and results have shown good agreement between measurement and simulation.
Proceedings of the Asia-Pacific Microwave Conference 2011

8. 心得
感覺上無線系統變得更加多功能的，增加了波段與波行操作的重要性，雙波段濾波器從而出現這種多功能系統的雙頻段濾波器位於前端的預選擇多於一個頻帶的無線系統，使在相同的時間，以及拒絕干擾。有許多方法生產的雙帶通濾波器。可以觀察到，通過與兩個指定的單通頻帶直接級聯兩個單個的過濾器會產生雙頻效果。這個概念有一個更大的潛力，具有緊湊的尺寸過濾器。
Proceedings of the Asia-Pacific Microwave Conference 2011

9. 參考文獻
C.W. Tang, W.T. Liu, M. GG. Chen and Y.C. Lin, “Design of Dual-Band Bandpass Filterss with Short-end Coupled Line,” European Microwave Confereence, pp , 2009.
K. Kim, H. S. Pyo, J. M. Ann, and Y. Lim, “Dual-band Filter using Half Wavelength Resonators and Dual-mode Resonators,” /09 IEEE, 2009.
Tsai, L.C, and Hsue, C.W, ““Dual-band Bandpass Filter using equal length coupled-series-sshunted lines and Z-transform technique”, IEEE Trans. Miccrow. Theory Tech., 2004, 52, (4), pp
C. Quendo, E. Rius, and C. PPerson, “An Original Topology of Dual-Band Filter with Trannsmission Zeros,” IEEE MTE-S Digest, WEID
M. L. Chuang, “Concurrent ddual-band filter using single set of microstrip open-loop resonaators”, IEEE Electronics Letters, Vol. 41 , No. 18, September 2005.
S. Sun, and L. Zhu, “ Compa ct Dual-band Microstrip Bandpass Filter without External Feedss” IEEE Microwave and Wireless Components Letters, Vol. 15, No. 10, October 2005.
D. Ahn, J. -S. Kim, Y.-K. Sh in and K. -Y. Kang, “Design of 2pole Band Pass Filters using Closed Loop Resonator and Fig. 6. Simulated and measured results of the duual-band filter. Coupled Lines” , IEEE MT 1646, 1996.
[7] Z. I. Khan, M. K. Mohd Cascaded Rings Dual-band Conference, December 2010.