The advantage of this newly designed filter is its simple abilities to set up and to adjust the resonant frequencies of four bands. In addition, by using the skew-symmetrical 00 feeding structure, the filter quality has been improved.
Trang 1MICROSTRIP QUAD-BAND BANDPASS FILTER USING
A MODIFIED CROSS AND AN OPEN STUB RESONATOR
Nguyen Tran Quang1*, Bui Ngoc My2
Abstract: The four bandpasses are designed and controlled to operate at the
central frequencies 1.8GHz (4G), 2.4GHz (WLAN), 3.5GHz (WiMAX) and 5GHz (WLAN) A microstrip quad-band band-pass filter using a modified cross and an open stub resonator The advantage of this newly designed filter is its simple abilities to set up and to adjust the resonant frequencies of four bands In addition, by using the skew-symmetrical 0 0 feeding structure, the filter quality has been improved
Keywords: Filter, Microwave, Resonator, Microstrip
1 INTRODUCTION
Recently, there have been several studies on the design of microstrip quad-band bandpass filters For the multi-band bandpass filters, selecting and adjusting the resonant frequencies determines the filter's functions, which is more complicated due to the different frequency bands If the band resonant frequencies are interdependent, it will be difficult and complicated to design In this article, a new resonant structure using a microstrip quad-band bandpass filter design, which is a modified cross and an open stub resonator is proposed The new resonant structure creates four bands operating independently at the central frequencies 1.8GHz (2.4GHz), 2.4GHz (WLAN), 3.5GHz (WiMAX) and 5GHz (WLAN) The advantage of this design filter is its simplicity and independence in adjusting, selecting the center resonant frequencies at all bandpasses
2 DESIGNING THE QUAD-BAND FILTER WITH A NEW RESONANT STRUCTURE HAVING AN INDEPENDENT ADJUSTMENT TO THE
RESONANT FREQUENCIES
The proposed resonant structure is the modified cross structure combining with
an open stub resonator which is presented in Figure 1
Figure 1 Analysis of the new resonant structure in the odd and even mode
(a) Basic cross-resonant structure, (b) Odd mode, (c) Even mode
L 3
Z 3 L 3
0
Z 1
Z 2 L 2
L 1
Z 4 L 4
Z 1
L 1 /2
(b) (a)
2Z 3
0
Z 1
2Z 2 L 2
L 1 /2
2Z 4 L 4
(c)
0
0 ’
Trang 2The new resonant structure on the microstrip circuit is symmetric across the 0-0 ’
axis because of using the method of odd-even mode to analyze the structure [1]
The impedance formula for Z in on the microstrip circuit is used to compute the resonant frequencies [2]
l jZ
Z
l jZ
Z Z Z
L
L in
tan
tan 0
0
0 (1)
On the odd mode of Figure 1b is a short circuit with the half-length, replacing in
formula (1) with the values l = L 1 /2; Z 0 = Z 1; ZL = 0 (short circuit), we calculate Z in:
2
tan 1
1
L jZ
Z in (2) The resonance occurs whenZ in , replacing in (2), we calculate:
1
L
(3) According to [3], the coefficient transmission of the propagation constant is
g
2 , replacing in (3) we calculate the guided wavelength of microstrip of the odd mode resonant frequency:
1
g
(4) Basing on the connection between the wavelength transmission and the frequencies on the microstrip
eff g
c f
eff
o L
c f
1 2
(5)
Where is the velocity of light in free space (c = 3.108 m/s); ε eff is the effective dielectric constant of the substrate
On the even mode of Fig 1c, the circuit consists of a short circuit and two open circuits At the short circuit, it is divided into two stages, Figure 2:
Figure 2 The short-circuited transmission in the even mode
Z 1
L 1 /2
Z in
2Z 2
L 2
Z in1
Z L
(stage1) (stage 2)
Trang 3At stage 1, Z in1 is calculated with the values l = L 2 ; Z 0 = 2Z 2 ; Z L = 0 (short
circuit), substituting into formula (1) we have:
2 2
1 j2Z tan L
Z in (6)
At stage 2, Z in is calculated with l = L 1 /2; Z 0 = Z 1 ; Z L = Z in1, replacing in (1) we get:
2 tan tan
2
2 tan tan
2
1 2
2 1
1 1
2 2
L Z
Z
L Z
L Z
jZ
Z in
The resonance occurs whenZ in , substituting in to (7), we calculate:
2
1 1 2
2 2 tan tan
Z
Z L
(8)
If we select Z 1 = 2Z 2, we will have:
1 2 tan tanL2 L1 (9)
Replacing coefficient transmission of the propagation constant β, we calculate the guided wavelength of microstrip λ g and the resonant frequency in the even
mode f e1 in a short circuit, equals to:
) 2 (
2 L1 L2
g
(10)
eff e
L L
c f
) 2 (
2 1 2
1
(11)
The two open circuits in the even mode of Figure 1c also consist of two stages
Figure 3 shows the first open circuit transmission with the impedance branch Z 3,
length L 3:
Figure 3 The open circuit transmission in the even mode, branched Z 3 , L 3
At stage 1, Z in1 is calculated with the values: l = L 3 ; Z 0 = 2Z 3 ; Z L (open circuit), substituting into formula (1):
3
3 1
tan
2
L
Z j
Z in
(12)
At stage 2, replacing l = L 1 /2; Z 0 = Z 1 ; Z L = Z in1 into (1), we get Zin:
Z 1
L 1 /2
L 3
Z in1
Z L
(stage 1) (stage 2)
Trang 42 tan 2 tan
tan 2 tan 2
1 3
3 1
3 1
1 3
Z L Z
L
L Z
Z jZ
Z in
The resonance occurs whenZ in , from (13) we have:
1
3 1
3
2 2 cot tan
Z
Z L
(14)
In special case of selecting Z 1 = 2Z 3:
1 2 cot
(15)
Replacing coefficient transmission of the propagation constant β, we calculate the guided wavelength of microstrip λ g and the resonant frequency in the even
mode f e2 in the first open transmission, equals to:
3
L
g
(16)
eff e
L L
c f
) 2 ( 1 3
2
(17)
Similar to the open transmission, the second branch in the even mode with the
impedance Z 4 , the length L 4 is also calculated the resonant frequency f e3 by:
eff e
L L
c f
) 2 ( 1 4
3
(18)
Thus, there are four resonant frequencies in the new proposed resonant structure
It is reported that the center resonant frequency values of all the bands depend on not
only the velocity of light c and the effective dielectric constant of the substrate ε eff, but also the length of the microstrip segments Table 1 shows the guided wavelength
of microstrip λ g and the resonant frequencies f in the different modes
Table 1 The values λ g and f in different resonance modes
Mode Wavelength transmission (λ g) Resonant frequencies (f)
eff
L
c
1
2
eff
L L
c
) 2 (
2 1 2
eff
L L
c
) 2 ( 1 3
eff
L L
c
) 2 ( 1 4
Trang 5From the above table, we see that the odd-mode resonant frequency f o depends
only on the length L 1 Besides the length of L 1, the resonance frequencies in the
even mode f e1 , f e2 and f e3 depend solely on the lengths L 2 , L 3 and L 4 Thus, the
selected method for the resonant frequency f o is first set by adjusting the value L 1
After fixing the values f o and L 1 , the resonant frequencies in the even mode f e1 , f e2
and f e3 are set up and adjusted completely
When calculating the design and selecting the values L 1 > 2L 3 and L 4 > L 3, we
have four resonant frequencies f e1 < f o < f e3 < f e2 orderly The design of filter uses
the skew-symmetrical 00 feeding structure to create extra transmission zeros at the adjacent three passbands, sharp passband skirts of the filter have been observed This coupling structure makes a very compact circuit [4]
In order to fit with all the bandpasses designed for 1,8GHz (4G), 2.4GHz (WLAN), 3.5GHz (WiMAX) and 5GHz (WLAN), the filter is constructed on a
substrate with relative permittivity of 3.55, thickness of h = 0.813 mm, t =
0.035mm and loss tangent of 0.0027
The quad-band bandpass filter using the new resonance form has the physical structure shown in Figure 4:
Figure 4 The physical model of four-band filter proposed
In the above model (Fig.4), the two ports Input/Output are combined with the impedance 50Ω
The variable cross resonant structure has a main circuit with the length L 1 + L 2 +
L 3 + L 4 , which determines the resonance frequency f o = 2.4GHz
When the frequency f o has been selected, the length of the short circuit in the variable cross resonant structure will determine the resonant frequency value
f e1 = 1.8GHz, the length value L 7 is used for selection and adjustment f e1
The half-length in the variable cross resonant structure is the open circuit and is
equivalent to L 8 + 2L 9 which determines the resonant frequency value f e2 = 5GHz
The length L 9 is used to select and to adjust f e2
The modified open circuit has the length L 5 + L 6 which determines the value of
resonant frequency f e3 = 3.5GHz The length L 5 is used to select and to adjust f e3 With this design, it will be simple and completely independent to select and adjust the resonant frequencies
Output
S 1
W 0
Input
L 1
L 7
L 8
L 5
W 1
W 3
L 6
L 2
L 3
L 4
W 2
S 0
S 2
S 3
S 4
L 9
W 4
Trang 6The values W 0 , W 1 , W 2 , W 3 and W 4 are used to adjust the impedance of the
circuit segments The values S 0 , S 1 , S 2 , S 3 and S 4 are the coefficients which is used
to adjust the characteristics of the filter bands
3 SIMULATION AND EVALUATION
Using the simulation software Ansoft HFSS 13.0.2 to check and adjust the
physical parameters in the structure The main circuit length value L 1 + L 2 + L 3 +
L 4 in the cross resonant structure is used to set up the center resonant frequency
f o = 2.4GHz on the second bandpass After having fixed f o , the length L 7 is adjusted
to select and to adjust the of resonant frequency f e1 = 1.8GHz on the first bandpass
Figure 5 describes the adjustment of the length L 7 to select f e1 on the first
bandpass, the resonant frequencies on the three bandpasses are f o , f e2 , and f e3 which
is not affected The length L 7 is adjusted from 1.5mm to 2.5mm, when L 7 is
increased, f e1 will be decreased and vice versa The resonant frequency value: f e1 =
1.8GHz with L 7 = 2.3mm
Figure 5 Simulation results adjusted the length L 7 to f e1 = 1.8GHz
Figure 6 Simulation results adjusted the
length L 9 to f e2 = 5GHz Figure 7 Simulation results adjusted the length L 5 to f e3 = 3.5GHz
Frequency (GHz)
Frequency (GHz)
Frequency (GHz)
Trang 7The fourth resonant frequency f e2 depends on the length value of a half square
meter The length of a half square meter is adjusted by the value L 9 The length L 9
is adjusted from 3.1mm to 4.1mm, L 9 is also in inverse ratio to f e2 The value f e2 =
5GHz with L 9 = 3.6mm Figure 6 shows the simulation results when changing L 9
The resonant frequency f e3 depends on the length of the modified stub The
length L 5 is used to adjust the third frequency f e3 Adjusting the L 5 length from
5.8mm to 6.8mm, the resonant frequency of the third band f e3 = 3.5GHz with L 5 = 6.3mm, in Figure 7
After being adjusted, the proposed microstrip quad-band bandpass filter has the
physical parameter values shown in Table 2 The diameter of the short circuit d =
0.5mm, the physical size of the filter is 18.56 mm x 22.48 mm
Table 2 The physical parameter values of the proposed microstrip quad-band filter
Parameter Value (mm) Parameter Value (mm) Parameter Value (mm)
The proposed microstrip quad-band bandpass filter has the technical specifications which is suitable for the application 4G, WLAN and WiMAX
Table 3 The technical specifications of filter
Technical specifications Unit 1st band 2nd band 3rd band 4thband
External quality factor (Q e) f 0 /δ f-3dB 16,4 14,3 29,2 41,7
Figure 8 Results of simulating characteristics of the proposed filter
Trang 8Figure 8 describes the characteristics of the microstrip quad-band filter using the proposed resonant structure:
The results of this study are compared with a number of recently published works on microstrip quad-band filters, presented in Table 4
Table 4 Comparing the filter with some published works
Works Passband
(GHz)
Insertion loss (dB)
Return loss (dB)
FBW
[5] 2.4/3.5/
5.2/6.8
0.5/1.3/
1.3/1
13/38/
19/26
6.4/9.4/
3.8/4.9
f 1 and f 3 depend on each
other, f 2 and, f 4 depend
on each other
[6] 1.9/2.8/
4.3/5.2
2.3/3.6/
3.5/3.4 >12
5.3/3.4/
3.5/3
f 1 and f 4 depend on each
other, f 2 and, f 3 depend
on each other
[7] 1.8/2.4/
3.5/5.2
0.8/1.4/
1.7/2
13/33/
f 1 and f 3 depend on each
other, f 2 and , f 4 depend
on each other
[8] 2.44/3,53/
5.18/5.79
0.12/0.12/
0.23/0.25
20/20/
15/16
4.96/ 5.07/
2.32/3.63
f 1, f 2, f 3, f 4 depend on
each other
[9] 2,4/3,5/
5,2/5,8
2/1.9/
1.9/1/96
15.5/14.5/
21/16
6.7/7.2/
6.9/5.3 f 3, f 4 depend on f 1, f 2 [10] 1,8/2,4/
3,5/4,6
0.8/1.1/
1.3/1.5
21/15.5/
14/16.5
7.6/8.4/
3.4/3.2
f 1, f 2 and f 3 depend on each other
Proposed 1,8/2,4/
3,5/5,0
1,39/1,07/
1,71/3,11
30,34/23,75/
21,70/27,67
6,1/7/
3,7/2,4 f 1, f 2, f 3, f 4 independently
The advantage of the proposed filter is that it is simple, independent in setting and adjusting the center resonant frequencies of the quad band
4 CONCLUSION
In the article, the results of research, the proposed new resonant structure on the microstrip using the design of quad-band bandpass filter are presented The new resonant structure is a variable cross resonant structure combining an open added stub The new microstrip quad-band bandpass filters is designed basing on this structure which have the advantage of being independent in setting and adjusting the center quad band resonant frequencies
REFERENCES
[1] I C Hunter, “Theory and design of microwave filters” New York: Artech
House, (2001), pp 41-43
[2] D M Pozar, “Microwave Engineering”, 4rd edition, John Wiley & Sons, (2012), pp 59
[3] J S Hong and M J Lancaster, “Microwave filter for RF/microwave application.”, New York: Wiley, (2001), pp 80
[4] C M Tsai, S Y Lee, and C C Tsai, “Performance of a planar filter using a
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Trang 9[5] Hung-Wei Wu and Ru-Yuan Yang, “A new quad-band bandpass filter using asymmetric steped impedance resonators”, Microwave and Wireless Components Letters, IEEE, Vol 21, No 4, (2011), pp 203-205
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[7] M H Weng, C S Ye, Y K Su and S W Lan, “A new compact quad-band bandpass filter using quad-mode stub loaded resonator”, Mircrow Opt
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[8] Haiwen Liu, Baoping Ren, Xuehui Guan, Pin Wen and Yan Wang, “Quad-band high-temperature superconducting “Quad-bandpass filter using quadruple-mode square ring loaded resonator”, IEEE Transactions on Microwave Theory and Techniques, Vol 62, No 12, (2014), pp 2931-2941
[9] Tengfei Yan, Xiao-Hong and Junfeng Yang, “A novel quad-band bandpass filter using short stub loaded E-shaped resonators”, Microwave and Wireless Components Letters, IEEE, Vol 25, No 8, (2015), pp 508-510
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TÓM TẮT
BỘ LỌC SIÊU CAO TẦN BỐN BĂNG TẦN SỬ DỤNG CỘNG HƯỞNG CHỮ THẬP BIẾN ĐỔI KẾT HỢP MỘT ĐOAN CHÊM HỞ MẠCH
Bốn băng thông được thiết kế và điều khiển để hoạt động tại các tần số trung tâm 1,8 GHz (4G) 2.4GHz (WLAN), 3.5GHz (WiMAX) và 5GHz (WLAN) Bộ lọc 4 băng siêu cao tần mạch dải sử dụng một cấu trúc cộng hưởng biến đổi kết hợp với một đoạn chêm hở mạch Ưu điểm của bộ lọc được thiết kế mới là có khả năng đơn giản trong việc thiết lập và cân chỉnh các tần số cộng hưởng của 4 băng tần Thêm vào đó bằng sử dụng kỹ thuật ghép nghiêng 0 0 , chất lượng của bộ lọc được cải tiến
Từ khóa: Bộ lọc, Siêu cao tần, Bộ cộng hưởng, Mạch dải
Nhận bài ngày 01 tháng 3 năm 2017 Hoàn thiện ngày 04 tháng 4 năm 2017 Chấp nhận đăng ngày 05 tháng 4 năm 2017
Address: 1 Department of Military Science / General Department of Technology;
2 Training Department / Academy of Military Science and Technology
* Email: quangkhqs@gmail.com