Compact Microstrip UWB Bandpass Filter with Triple-Notched Bands and Wide Upper Stopband

Transcription

1 Progress In Eletromagnetis Researh, Vol. 144, , 214 Compat Mirostrip UWB Bandpass Filter with Triple-Nothed Bands and Wide Upper Stopband Huaxia Peng 1, Junding Zhao 2, *, and Bing Wang 1 Abstrat A novel ompat ultra-wideband (UWB) bandpass filter (BPF) with triple sharply nothed bands and wide upper stopband is proposed. The basi UWB BPF is omposed of two mirostrip interdigital oupled lines and one multiple-mode resonator (MMR). Then, to ahieve triple band-nothed performane, the proposed triple-mode stepped impedane resonator (TMSIR) is studied and oupled to the interdigital oupled lines of the basi UWB BPF. To validate the design theory, a mirostrip UWB BPF with three nothed bands respetively entered at 5.2 GHz, 5.8 GHz, and 6.8 GHz is designed and fabriated. Both simulated and experimental results are provided with good agreement. 1. INTRODUCTION In 22, the U.S. Federal Communiations Commission (FCC) authorized the unliensed use of ultrawideband (UWB, from 3.1 to 1.6 GHz) for a variety of appliations, suh as indoor and hand-held systems [1]. UWB BPFs, as one of the essential omponents of the UWB systems, have gained muh attention in reent years. There are many methods presented to design UWB bandpass filters. For instane, multiple-mode resonator (MMR) [2, 3], defeted mirostrip struture (DMS) [4], defeted ground struture (DGS) [5, 6], multilayer oupled struture [7, 8], and the asaded low-pass/high-pass filters [9, 1] have been widely used to ahieve UWB harateristis. However, the existing wireless networks, suh as WiMAX (i.e., 3.5 GHz bands), WLAN (i.e., 5.2 GHz and 5.8 GHz bands), RFID (i.e., 6.8 GHz bands) and some satellite ommuniation (i.e., 8. GHz bands) signals, an interfere with UWB networks. Therefore, ompat UWB BPFs with multiple nothed bands are emergently needed to rejet these undesired interfering signals [11 23]. To ahieve a nothed band, the radial-uniform impedane resonators (UIR)/stepped impedane resonators (SIR) loaded stub resonator is employed in [11], and the Y-shaped radial stub is used in [12]. On the other hand, one of the two arms in the oupled-line setions is extended and folded in [13], and a stepped impedane resonator (SIR) is embedded in [14] to blok unwanted existing radio signals. However, these methods an only ahieve one nothed band. Then, two embedded open iruited stubs are employed [15], and a oupled simplified omposite right/left-handed resonator is used in [16] to get two nothed bands. In the same way, a novel E-shaped resonator is oupled to the initial UWB BPF to ahieve dual nothed bands [17]. However, the seletivity designed with these methods needs to be improved. Double open-iruit stubs are embedded into broadside-oupled stepped impedane resonators on middle layer in [18], and folded stepped impedane resonators are vertially-oupled to the seond layer in [19]. Two nothed bands an also be introdued into an UWB BPF. However, they are based on a multilayer struture and hardly ompatible with the existing mirowave-integrated iruit. Two L-shaped folded shunt open-iruited stubs are plaed on the feed lines in [2], and two tri-setion stepped impedane resonators and a parallel gap-oupled mirostrip resonator are used in [21] to get triple nothed bands. However, the performane of the filters needs to be improved. Additionally, a Reeived 4 Deember 213, Aepted 7 January 214, Sheduled 17 January 214 * Corresponding author: Junding Zhao (jundingzhao528@gmail.om). 1 Shool of Eletrial and Information Engineering, Hunan University of Tehnology (HUT), Zhuzhou 4127, China. 2 Ministerial Key Laboratory of JGMT, Nanjing University of Siene and Tehnology (NUST), Nanjing 2194, China.

2 186 Peng, Zhao, and Wang triple-mode stepped impedane resonator (SIR) in [22] and a square ring short stub loaded resonator (SRSSLR) in [23] are oupled to the main transmission line of the basi mirostrip UWB BPF to ahieve triple nothed bands. But, the proposed UWB BPFs have a relatively narrow upper stopband, and the seletivity are not ideal. In this paper, we present a novel UWB BPF with triple sharply-nothed bands and wide upper stopband. The design proedures are as following: the basi mirostrip UWB BPF with wide upper stopband is designed using two mirostrip interdigital oupled lines and one multiple-mode resonator (MMR). Then, triple band-nothed harateristis are ahieved by oupling the proposed triple-mode stepped impedane resonator (TMSIR) to the mirostrip interdigital oupled lines of the basi UWB BPF. The triple-nothed bands an be easily generated and realized by ontrolling the loations of evenodd modes resonane frequeny of the triple-mode stepped impedane resonator. Finally, the proposed filter is designed, fabriated and measured. Good agreement between measured and simulated results is ahieved. 2. CHARACTERISTICS OF THE NOTCHED STRUCTURE Figure 1 shows the geometry of the proposed triple-mode stepped impedane resonator (TMSIR). The proposed TMSIR is omposed of a stepped impedane hairpin resonator and two short-ended stubs. Sine the resonator is symmetrial to the A-A and B-B plane, the resonane properties of the TMSIR an be analyzed by the even-odd modes analysis method. Under mode exitation, the resonator eletrial field distribution of the resonator exhibits either an even or odd mode distribution property as shown in Figure 2. For the even mode ondition, the eletrial fields exhibit a symmetri distribution along B-B axis as shown in Figure 2(a). While for the odd mode, the eletrial fields exhibit an anti-symmetri distribution along A-A axis as shown in Figure 2(b) and B-B axis as shown in Figure 2(). Thus, based on the eletrial field distribution property, the even-odd modes resonane frequenies an be dedued as: f noth = (1) λ noth εeff f noth-even1 = 4(L e2 + L e3 + L e4 ) (2) ε eff f noth-odd1 = 2(L e1 + 2L e2 + L e4 ) (3) ε eff f noth-odd2 = 4(L e2 + L e4 ) (4) ε eff where λ noth is the wavelength of the enter frequeny of the nothed band, f noth the enter frequeny of the nothed band, ε eff the effetive dieletri onstant, and the light speed in free spae. A L e4 W e2 W e4 B W e3 R B' L e3 L e2 W e1 L e1 A' Figure 1. Geometry of the proposed TMSIR.

3 Progress In Eletromagnetis Researh, Vol. 144, A B B' B B' A (a) (b) () Figure 2. Eletrial field distribution of the proposed TMSIR: (a) even mode, (b) odd mode, () odd mode. L 2 W 2 D 1 D 2 5Ω J -9 o MMR J -9 o 5Ω L 1 L 3 L 3 D W 1 L 1 L 2 C 3 L1 C 2 C 1 L 2 C 3 C 2 W C 1 (a) Figure 3. Shemati layout and equivalent iruit network of the presented UWB BPF with triplenothed bands: (a) shemati layout, (b) equivalent transmission line network. (b) 3. UWB BPF WITH NOTCHED-BANDS DESIGN Figures 3(a) and 3(b) illustrate the shemati and equivalent transmission line model, respetively. Figure 3(a) omprises one multiple-mode resonator and two mirostrip interdigital oupled lines, whih is oupled to a triple-mode stepped impedane resonator (TMSIR). Herein, the two mirostrip interdigital oupled lines are formed to provide suffiiently strong oupling degree in the desired UWB band. The equivalent transmission-line network of the proposed filter is shown in Figure 3(b). The interdigital oupled lines an be deemed as two single transmission lines at two sides and a J-inverter suseptane in the middle. The TMSIR oupled into the interdigital oupled lines of the basi UWB BPF an be modeled as three shunt series resonant branhes. The initial MMR is first proposed by [24] aiming at alloating its first three resonant modes loated within GHz. However, the out-of-band rejetion and seletivity of the proposed UWB filter are not ideal. Thus, two short open-iruited stubs are shunt-onneted to the initial MMR to ahieve more resonant modes. The simulated S 21 -magnitudes of the basi UWB bandpass filter under weak oupling are plotted in Figure 4(a). Five resonant peaks an be obviously observed in UWB passband, i.e., f 1, f 2, f 3, f 4, and f 5 are used to ononstitute the desired UWB passband. By aneling the other resonant modes, the upper-stopband of the basi UWB bandpass filter an be signifiantly extended. Two transmission zeros are generated by two short open-iruited stubs near the lower and upper ut-off frequenies, leading to a higher rejetion skirt outside the desired passband. As a starting part of this work, a basi mirostrip UWB BPF is designed. The simulated sattering parameters are shown in Figure 4(b). Referring to Figure 4(b), the proposed UWB BPF has an

4 188 Peng, Zhao, and Wang S-parameters (db) f f f f f 4 5 Strong oupling Weak oupling Frequeny (GHz) (a) S-parameters (db) S 11 Sim. S 21 Sim Frequeny (GHz) Figure 4. Simulated S-parameters of the proposed basi UWB BPF: (a) weak oupling, (b) strong oupling. (b) S 21 (db) fnoth-even1 f noth -odd1 fnoth-odd2 S 21 (db) -2 fnoth-even1 f noth- odd 1 fnoth-odd2-3 Le2=5.mm Le2=5.5mm Le2=6.mm -3 Le3=2.3mm Le3=2.5mm Le3=2.7mm Frequeny (GHz) (a) Frequeny (GHz) (b) S 21 (db) -1-2 fnoth-even1 f noth -odd1 fnoth-odd2-3 Le4=2.8mm Le4=3.mm Le4=3.2mm Frequeny (GHz) Figure 5. Simulated S-parameters of the new struture with various dimensions: (a) L e2, (b) L e3, () L e4. () insertion loss better than 3 db over the GHz bandwidth, and the upper-stopband with 15 db attenuation is up to 29.2 GHz. In addition, the return loss is under 2 db over most part of the passband. Then, a triple-mode stepped impedane resonator (TMSIR) is oupled to the two mirostrip interdigital oupled lines of the basi UWB BPF to realize triple band-nothed harateristis. The struture is simple and flexible for bloking unwanted narrow band radio signals that may appear in UWB band. The resonant frequenies of all nothed bands simultaneously move down with inreasing

5 Progress In Eletromagnetis Researh, Vol. 144, L e2. However, to ahieve these noth bands at desired frequenies, f noth-odd2 an be determined by varying the length of L e2, then f noth-even1 an be simply ontrolled by varying the length of L e3. Finally, f noth-odd1 an be simply ontrolled by varying the length of L e4. Thus, by appropriately varying the TMSIR dimensions, three nothed bands an be ahieved at desired frequenies. The transfer harateristis of the proposed TMSIR with various dimensions are studied by HFSS 11., as shown in Figure 5. Thus, by appropriately varying the TMSIR dimensions, triple nothed bands an be adjusted at desired frequenies. 4. EXPERIMENTAL RESULTS The UWB BPF with triple nothed bands and wide upper stopband has been designed on substrate Rogers RT/Duroid 588 with a dieletri onstant of 3.38, thikness of.58 mm, and loss tangent of.27. The strutural parameters for the optimal UWB filter iruit are seleted as follows: (as illustrated in Figures 1 and 3) L 1 = 7.8 mm, L 2 = 11.5 mm, W = 1.1 mm, W 1 =.1 mm, W 2 =.9 mm, D =.1 mm, D 1 = 2.1 mm, D 1 =.7 mm, L e1 = 6.5 mm, l e2 = 5.5 mm, L e3 = 2.8 mm, L e4 = 3. mm, W e1 =.4 mm, W e2 =.3 mm, W e3 =.4 mm, W e4 =.4 mm, and R =.1 mm. Finally, the fabriated UWB filter is measured with an Agilent N5244A vetor network analyzer. Simulated and measured sattering parameters are desribed in Figure 6 with good agreement. Referring to Figure 6, the fabriated UWB filter has a passband from 3. to 1.3 GHz, and the upper-stopband with 15 db attenuation is up to 3 GHz. The return loss is under 15 db over most part of the passband. For the two highly rejeted nothed bands, the measured results show that a better 15 db insertion loss at 5.2 GHz, 5.8 GHz, and 6.8 GHz with the respetive 3 db FBW of 2.%, 2.7% and 3.8% are ahieved. The measured group-delay result exhibits that the UWB BPF obtains a flat group delay response as shown Figure 7. The deviations of the measurements from the simulations are expeted mainly due to the refletions from the onnetors and the finite substrate. Figure 8 shows a photograph of the fabriated UWB BPF. The overall size is only about mm 2. The omparison with other reported UWB BPFs is shown in Table 1 [11 23], whih depits that the proposed filter has good harateristis with ompat size and wide upper stopband. 5-1 S-parameters (db) Sim. S 11 Sim. S 21 Mea. S 11 Mea. S Frequeny (GHz) Group Delay (ns) Simulated Measured Frequeny (GHz) Figure 6. Simulated and measured S-parameters of the designed UWB BPF. Figure 7. Simulated and measured group delay of the designed UWB BPF. Figure 8. Photograph of the fabriated UWB filter.

6 19 Peng, Zhao, and Wang Table 1. Comparisons with other proposed UWB BPFs with nothed band. Ref. Noth 3 db Upper Ciruit size Ciruit Insertion frequeny (GHz) Passband stopband (λg: at 6.85 GHz) dimension loss (db) /attenuation (GHz) (GHz) (db) [11] D /5.5 > [12] D > 2 17 [13] D > [14] D > 2 2 [15] D /8. > 2 25 [16] D /8.1 > [17] D /8. > [18] D /6. > 1 18 [19] D /8. 18 [2] D /6.5/9.1 > [21] D /6.5/8.93 > 1 16 [22] D /5.9/8. > 1 2 [23] D /5.8/8.1 > This work D /5.8/6.8 > CONCLUSION A novel ompat UWB BPF has been proposed and designed. The prototype ahieves a wide passband with triple sharply nothed bands and wide upper stopband by properly tuning the parameters of the new struture. Good agreement between simulation and measurement results demonstrates the validity of the proposed method. Due to its simple topology, ompat size, and exellent performane, the proposed filter is very attrative for use in future UWB wireless tehnologies. ACKNOWLEDGMENT This work was supported by the National Natural Siene Foundation of China under Grant Nos and , Sientifi Researh Fund of Hunan Provinial Eduation Department under Grant No. 13C22, and the Hunan Provine Nature Siene Foundation of China under Grant No. 14JJ2118. REFERENCES 1. FCC, Revision of Part 15, the Commission s Rules Regarding to Ultra-Wide-Band Transmission System, First Note and Order Federal Communiation Commission, ET-Doket , Zhu, H. and Q.-X. Chu, Compat ultra-wideband (UWB) bandpass filter using dual-stub-loaded resonator (DSLR), IEEE Mirow. Wireless Compon. Lett., Vol. 23, No. 1, , Qiang, L., Y.-J. Zhao, Q. Sun, W. Zhao, and B. Liu, A ompat UWB HMSIW bandpass filter based on omplementary split-ring resonators, Progress In Eletromagnetis Researh C, Vol. 11, , Fallahzadeh, S. and M. Tayarani, A new mirostrip UWB bandpass filter using defeted mirostrip strutures, Journal of Eletromagneti Waves and Appliations, Vol. 4, No. 7, , Shobeyri, M. and M.-H. Vadjed-Samiei, Compat ultra-wideband bandpass filter with defeted ground struture, Progress In Eletromagnetis Researh Letters, Vol. 4, 25 31, 28.

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