Microstrip quad band bandpass 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 00 feeding structure, the filter quality has been improved.

Nghiên cứu khoa học công nghệ MICROSTRIP 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 00 feeding structure, the filter quality has been improved Keywords: Filter, Microwave, Resonator, Microstrip 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 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 0 Z3 L3 2Z3 L3 Z2 L2 Z1 Z1 L1 Z1 L1/2 L1/2 Z4 L4 (b) 0’ (a) 2Z2 L2 2Z4 L4 0’ 0’ (c) Figure Analysis of the new resonant structure in the odd and even mode (a) Basic cross-resonant structure, (b) Odd mode, (c) Even mode Tạp chí Nghiên cứu KH&CN quân sự, Số 48, 04 - 2017 95 Kỹ thuật điều khiển & Điện tử The 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 Zin on the microstrip circuit is used to compute the resonant frequencies [2]  Z  jZ tan l   Z in  Z  L  Z  jZ L tan l  (1) On the odd mode of Figure 1b is a short circuit with the half-length, replacing in formula (1) with the values l = L1/2; Z0 = Z1; ZL = (short circuit), we calculate Zin: Z in  jZ tan  L1 (2) The resonance occurs when Z in   , replacing in (2), we calculate:   (3) L1 According to [3], the coefficient transmission of the propagation constant 2 is   , replacing in (3) we calculate the guided wavelength of microstrip of the g odd mode resonant frequency: g1  2L1 (4) Basing on the connection between the wavelength transmission and the c frequencies on the microstrip f  , we have:  g  eff fo  c (5) L1  eff Where is the velocity of light in free space (c = 3.108 m/s); εeff 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: Zin Z1 2Z2 L1/2 L2 (stage 2) ZL Zin1 (stage1) Figure The short-circuited transmission in the even mode 96 N T Quang, B N My, “Microstrip quad-band bandpass filter… an open stub resonator.” Nghiên cứu khoa học công nghệ At stage 1, Zin1 is calculated with the values l = L2; Z0 = 2Z2; ZL = (short circuit), substituting into formula (1) we have: (6) Z in1  j 2Z tan L2 At stage 2, Zin is calculated with l = L1/2; Z0 = Z1; ZL = Zin1, replacing in (1) we get: L Z tan L2  Z1 tan  Z in  jZ1 (7) L1 Z1  Z tan L2 tan  The resonance occurs when Z in   , substituting in to (7), we calculate: tan L2 tan  L1 Z  2Z (8) If we select Z1 = 2Z2, we will have: L1 (9) 1 Replacing coefficient transmission of the propagation constant β, we calculate the guided wavelength of microstrip λg and the resonant frequency in the even mode fe1 in a short circuit, equals to: (10)  g  2( L1  L2 ) tan L2 tan  f e1  c 2( L1  L2 )  eff (11) The two open circuits in the even mode of Figure 1c also consist of two stages Figure shows the first open circuit transmission with the impedance branch Z3, length L3: Zin Z1 2Z3 L1/2 (stage 2) Zin1 ZL L3 (stage 1) Figure The open circuit transmission in the even mode, branched Z3, L3 At stage 1, Zin1 is calculated with the values: l = L3; Z0 = 2Z3; ZL   (open circuit), substituting into formula (1):  j 2Z (12) Z in1  tan  L3 At stage 2, replacing l = L1/2; Z0 = Z1; ZL = Zin1 into (1), we get Zin: Tạp chí Nghiên cứu KH&CN quân sự, Số 48, 04 - 2017 97 Kỹ thuật điều khiển & Điện tử L1 tan  L3 Z in  jZ1 L Z1 tan L3  2Z tan   2Z  Z1 tan  (13) The resonance occurs when Z in   , from (13) we have: tan L3 cot  L1 2Z  Z1 (14) In special case of selecting Z1 = 2Z3: L1 (15)  1 Replacing coefficient transmission of the propagation constant β, we calculate the guided wavelength of microstrip λg and the resonant frequency in the even mode fe2 in the first open transmission, equals to: (16)  g  L1  2L3 tan  L3 cot  fe2  c ( L1  L3 )  eff (17) Similar to the open transmission, the second branch in the even mode with the impedance Z4, the length L4 is also calculated the resonant frequency fe3 by: c (18) f e3  ( L1  L4 )  eff 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 εeff, but also the length of the microstrip segments Table shows the guided wavelength of microstrip λg and the resonant frequencies f in the different modes Table The values λg and f in different resonance modes 98 Mode Wavelength transmission (λg) Resonant frequencies (f) Odd mode 2L1 Even mode 2( L1  L2 ) c 2( L1  L2 )  eff Even mode L1  2L3 c ( L1  L3 )  eff Even mode L1  2L4 c ( L1  L4 )  eff c L1  eff N T Quang, B N My, “Microstrip quad-band bandpass filter… an open stub resonator.” Nghiên cứu khoa học công nghệ From the above table, we see that the odd-mode resonant frequency fo depends only on the length L1 Besides the length of L1, the resonance frequencies in the even mode fe1, fe2 and fe3 depend solely on the lengths L2, L3 and L4 Thus, the selected method for the resonant frequency fo is first set by adjusting the value L1 After fixing the values fo and L1, the resonant frequencies in the even mode fe1, fe2 and fe3 are set up and adjusted completely When calculating the design and selecting the values L1 > 2L3 and L4 > L3, we have four resonant frequencies fe1 < fo < fe3 < fe2 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: Input W0 S1 L1 S0 L2 W4 L8 L9 L6 W2 L7 L5 L3 S3 W1 L4 S2 Output S4 W3 L10 L0 Figure 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 L1 + L2 + L3 + L4, which determines the resonance frequency fo = 2.4GHz When the frequency fo has been selected, the length of the short circuit in the variable cross resonant structure will determine the resonant frequency value fe1 = 1.8GHz, the length value L7 is used for selection and adjustment fe1 The half-length in the variable cross resonant structure is the open circuit and is equivalent to L8 + 2L9 which determines the resonant frequency value fe2 = 5GHz The length L9 is used to select and to adjust fe2 The modified open circuit has the length L5 + L6 which determines the value of resonant frequency fe3 = 3.5GHz The length L5 is used to select and to adjust fe3 With this design, it will be simple and completely independent to select and adjust the resonant frequencies Tạp chí Nghiên cứu KH&CN quân sự, Số 48, 04 - 2017 99 Kỹ thuật điều khiển & Điện tử The values W0, W1, W2, W3 and W4 are used to adjust the impedance of the circuit segments The values S0, S1, S2, S3 and S4 are the coefficients which is used to adjust the characteristics of the filter bands 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 L1 + L2 + L3 + L4 in the cross resonant structure is used to set up the center resonant frequency fo = 2.4GHz on the second bandpass After having fixed fo, the length L7 is adjusted to select and to adjust the of resonant frequency fe1 = 1.8GHz on the first bandpass Figure describes the adjustment of the length L7 to select fe1 on the first bandpass, the resonant frequencies on the three bandpasses are fo, fe2, and fe3 which is not affected The length L7 is adjusted from 1.5mm to 2.5mm, when L7 is increased, fe1 will be decreased and vice versa The resonant frequency value: fe1 = 1.8GHz with L7 = 2.3mm Frequency (GHz) Figure Simulation results adjusted the length L7 to fe1 = 1.8GHz Frequency (GHz) Figure Simulation results adjusted the length L9 to fe2 = 5GHz Frequency (GHz) Figure Simulation results adjusted the length L5 to fe3 = 3.5GHz 100 N T Quang, B N My, “Microstrip quad-band bandpass filter… an open stub resonator.” Nghiên cứu khoa học công nghệ The fourth resonant frequency fe2 depends on the length value of a half square meter The length of a half square meter is adjusted by the value L9 The length L9 is adjusted from 3.1mm to 4.1mm, L9 is also in inverse ratio to fe2 The value fe2 = 5GHz with L9 = 3.6mm Figure shows the simulation results when changing L9 The resonant frequency fe3 depends on the length of the modified stub The length L5 is used to adjust the third frequency fe3 Adjusting the L5 length from 5.8mm to 6.8mm, the resonant frequency of the third band fe3 = 3.5GHz with L5 = 6.3mm, in Figure After being adjusted, the proposed microstrip quad-band bandpass filter has the physical parameter values shown in Table The diameter of the short circuit d = 0.5mm, the physical size of the filter is 18.56 mm x 22.48 mm Table The physical parameter values of the proposed microstrip quad-band filter Parameter Value (mm) Parameter Value (mm) Parameter Value (mm) L0 8,5 L7 2,3 W3 0,45 L1 13,2 L8 2,1 W4 L2 L9 3,6 S0 0,17 L3 8,5 L10 10,1 S1 0,17 L4 10,7 W0 1,78 S2 0,14 L5 6,3 W1 S3 1,8 L6 5,1 W2 0,75 S4 1,5 The proposed microstrip quad-band bandpass filter has the technical specifications which is suitable for the application 4G, WLAN and WiMAX Table The technical specifications of filter Technical specifications Unit 1st band 2nd band 3rd band 4thband Central resonant frequency (f0) GHz 1,8 2,4 3,5 Insertion loss (IL) -dB 1,39 1,07 1,71 3,11 Return loss (RL) -dB 30,34 23,75 21,70 27,67 Fractional bandwidth (FBW-3dB) % 6,1 3,7 2,4 External quality factor (Qe) f0/δf-3dB 16,4 14,3 29,2 41,7 Figure Results of simulating characteristics of the proposed filter Tạp chí Nghiên cứu KH&CN quân sự, Số 48, 04 - 2017 101 Kỹ thuật điều khiển & Điện tử Figure 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 Table Comparing the filter with some published works Works Passband (GHz) Insertion loss (dB) Return loss (dB) [5] 2.4/3.5/ 5.2/6.8 0.5/1.3/ 1.3/1 13/38/ 19/26 [6] 1.9/2.8/ 4.3/5.2 2.3/3.6/ 3.5/3.4 >12 [7] 1.8/2.4/ 3.5/5.2 0.8/1.4/ 1.7/2 13/33/ 24/26 FBW (%) Features f1 and f3 depend on each other, f2 and, f4 depend on each other 5.3/3.4/ f1 and f4 depend on each other, f2 and, f3 depend 3.5/3 on each other f1 and f3 depend on each other, f2 and, f4 depend on each other 4.96/ 5.07/ f1, f2, f3, f4 depend on 2.32/3.63 each other 6.4/9.4/ 3.8/4.9 2.44/3,53/ 0.12/0.12/ 20/20/ 5.18/5.79 0.23/0.25 15/16 2,4/3,5/ 2/1.9/ 15.5/14.5/ 6.7/7.2/ f3, f4 depend on f1, f2 [9] 5,2/5,8 1.9/1/96 21/16 6.9/5.3 1,8/2,4/ 0.8/1.1/ 21/15.5/ 7.6/8.4/ f1, f2 and f3 depend on [10] 3,5/4,6 1.3/1.5 14/16.5 3.4/3.2 each other 1,8/2,4/ 1,39/1,07/ 30,34/23,75/ 6,1/7/ f1, f2, f3, f4 independently Proposed 3,5/5,0 1,71/3,11 21,70/27,67 3,7/2,4 The advantage of the proposed filter is that it is simple, independent in setting and adjusting the center resonant frequencies of the quad band [8] 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 00 feed structure”, IEEE Trans Microw Theory Tech., Vol 50, No 10, (2002), pp 2362-2367 102 N T Quang, B N My, “Microstrip quad-band bandpass filter… an open stub resonator.” Nghiên cứu khoa học công nghệ [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 [6] J Xu, C Miao, L Cui, Y -X, Ji and W Wu, “Compact high isolation quadband bandpass filter using quad-mode resonator”, Electron lett., vol 48, (2012), pp 28-38 [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 Technol Lett., vol 56, (2014), pp 1630-1632 [8] Haiwen Liu, Baoping Ren, Xuehui Guan, Pin Wen and Yan Wang, “Quadband high-temperature superconducting bandpass filter using quadruplemode 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 10] Van Phuong Do, Duc Uyen Nguyen, Tran Quang Nguyen and Minh Tan Doan, “Quad-Band filter using square ring crossed stub loaded resonators”, IEEE ATC 2016, (2016), pp 468-471 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 thiết kế điều khiển để hoạt động tần số trung tâm 1,8 GHz (4G) 2.4GHz (WLAN), 3.5GHz (WiMAX) 5GHz (WLAN) Bộ lọc băng siêu cao tần mạch dải sử dụng cấu trúc cộng hưởng biến đổi kết hợp với đoạn chêm hở mạch Ưu điểm lọc thiết kế có khả đơn giản việc thiết lập cân chỉnh tần số cộng hưởng băng tần Thêm vào sử dụng kỹ thuật ghép nghiêng 00, chất lượng lọc cải tiến Từ khóa: Bộ lọc, Siêu cao tần, Bộ cộng hưởng, Mạch dải Nhận ngày 01 tháng năm 2017 Hoàn thiện ngày 04 tháng năm 2017 Chấp nhận đăng ngày 05 tháng năm 2017 Address: Department of Military Science / General Department of Technology; Training Department / Academy of Military Science and Technology * Email: quangkhqs@gmail.com Tạp chí Nghiên cứu KH&CN quân sự, Số 48, 04 - 2017 103 ... N T Quang, B N My, Microstrip quad- band bandpass filter an open stub resonator. ” Nghiên cứu khoa học công nghệ [5] Hung-Wei Wu and Ru-Yuan Yang, A new quad- band bandpass filter using asymmetric... 1630-1632 [8] Haiwen Liu, Baoping Ren, Xuehui Guan, Pin Wen and Yan Wang, “Quadband high-temperature superconducting bandpass filter using quadruplemode square ring loaded resonator , IEEE Transactions... microstrip quad- band bandpass filter has the technical specifications which is suitable for the application 4G, WLAN and WiMAX Table The technical specifications of filter Technical specifications