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1 2017 2nd International Conference on Applied Mechanics and Mechatronics Engineering (AMME 2017) ISBN: A Compact Wide Stopband and Wide Passband Bandpass Filter Fabricated Using an SIR Technique Wen KO 1, Yu-chang LIN 2, *, Ming-wei HSU 3 and Man-long HER 4 1 Department of Electronic Engineering, National Chin-Yi University of Technology, No.57, Sec. 2, Zhongshan Rd., Taiping Dist., Taichung 41170, Taiwan R.O.C. 2 Ph.D. Program in Electrical and Communications Engineering, Feng-Chia University, 100, Wen-Hua Rd., Taichung, 40724, Taiwan R.O.C. 3 Department of Electronics Engineering, Nan Kai University of Technology, No.568, Zhongzheng Rd., Caotun Township, Nantou County 54243, Taiwan R.O.C. 4 Department of Communications Engineering, Feng-Chia University, 100, Wen-Hua Rd., Taichung, 40724, Taiwan R.O.C. *Corresponding author Keywords: Wide stopband passband filter, Wide passband BPF, Stepped impedance resonator. Abstract. The demand for modern multiband and wideband communication systems is increasing. Bandpass filter architecture is widely used, and its reorganization and innovation can produce a new wideband filter. In this paper, two low-impedance stepped impedance resonators (SIRs) are strongly coupled to form an equivalent capacitor. This paper also presents a circuit that can become an inductor, a capacitor, and an inductive series resonant wide stopband bandpass filter. The center frequency of the bandpass filter is 2.3 GHz. The wide stopband frequency of the band is as high as 8.05 GHz. The center frequency can be controlled by a low-impedance capacitor when the same SIR is used in a set of architectures. In this paper, the center frequency is controlled by a 4.1 GHz series-resonant wide-stopband bandpass filter that is connected to the lower half of the transmission line. The overall circuit function becomes a wideband bandpass filter. This wideband circuit can filter up and down for a 3-dB cutoff frequency ranging from 1.9 to 4.5 GHz. The filter bandwidth is 2.6 GHz. The center frequency is 3.2 GHz. Introduction Currently, the demand for high-speed and high-quality wireless communication systems is increasing. The amount of transmitted data is also increasing substantially. Different users require wireless information services with different parameters. To meet the bandwidth and speed needs of all users, the bandwidth of a filter can be increased in an integrated system. Thus, wide passband microwave bandpass filters (BPFs) are becoming increasingly pivotal. Extensive research of the relevant research, design, and production methods has also been conducted. Patch dual-mode BPFs using open stubs for second harmonic suppression have been studied. Novel perturbation elements in a right crossed-slot patch resonator provide two transmission zeros. The second harmonic can be suppressed by T-shape lines [1]. Improved spurious suppression can be provided by adding a few shunt open stubs to a traditional open-loop BPF. A design curve for the shunt open stubs can be obtained by calculating an ABCD matrix [2]. This thesis standardizes these three types of stepped impedance resonators (SIRs) and systematically summarizes their fundamental characteristics, such as resonance conditions, resonator length, harmonic (second harmonic) frequency, and equivalent circuits. Because microwave circuit simulators have become more popular recently and because high-performance computers have made electromagnetic (EM) analysis a usable design tool, SIRs and newly developed resonators based on advanced SIR concepts have been used in various practical applications, including coaxial and microstrip line configurations and planar circuits. In this thesis, an ultra-wideband BPF is developed by cascading a 335

2 wide passband BPF and a wide passband bandstop filter. By properly selecting transmission line impedances, the bandwidths of both wide passband BPFs and bandstop filters can be independently designed [3]. A new broadband microstrip SIR and BPF embedded slot cut band structure can improve the performance of a stopband. The present paper describes a slotted resonator that is interdigitally coupled to the ends of a wire and embedded slot feed. Because of the slotted return line and the resonator, the proposed filter has a wide upper stopband [4]. The proposed device uses four different mechanisms to create five transmission zeros, leading to sharp skirts and a wide stopband [5]. This paper presents a new and simplified wide passband bandpass filter. Its structure consists of two sets of SIRs with different sizes. The resonant frequency of the upper SIR is 2.3 GHz, and the resonant frequency of the lower SIR is 4.1 GHz. The resonators of the upper half and lower half are connected in parallel. The two sets of BPFs have different center frequencies. The entire device, operating as a single wide passband bandpass filter, can exhibit a frequency range from 1.9 to 4.5 GHz. The bandwidth of the wide passband bandpass filter is 2.6 GHz, and its center frequency is 3.2 GHz. The filter circuit is designed with a microstrip line and a coupling principle. The filter circuit controls the upper and lower half frequencies (i.e., 1.9 and 4.5 GHz) by controlling the impedance ratio of the SIRs. Circuit Structure of 2.3 GHz Wide Stopband Bandpass Filter Morikazu Sagawa, Mitsuo Makimoto, and Sadahiko Yamashita analyzed the stepped impedance characteristics of resonators, they discovered how to change the ratio of two types of transmission line impedance to control the location of the second harmonic an showd how to use SIRs to design BPFs [6]. The architecture of an SIR is shown in Figure 1. The SIR shown is composed of two types of characteristic microstrip line impedances, Z1 and Z2. Their structure is symmetrical; the definition of these two types of microstrip line impedance ratio is tan θ1: tan θ2 = Z2/Z1 = R. The electrical lengths of these microstrip lines are 2θ1 and 2θ2, respectively; the total electrical length is 2 (θ1, θ2) = θt. According to the theory of the transmission lines, the impedances ZA and ZB are formalized as (1) and (2) respectively. (1) Figure 1(a) is a schematic of the basic structure of the SIR. Figure 1 indicates the Z2/Z1 impedance ratio regarding the second harmonic of the location point. Figure 1(c) illustrates the SIR major coupled condition and minor coupling conditions. The wide stopband BPF is composed of two sets of high and low impedance ratios Z2/Z1 = R = 0.5 SIR; through the three sections of the transmission line, the BPF receives a series to the I/P and O/P ends. According to Figure 1 [6], when the SIR impedance ratio Z2/Z1 = 1, the second harmonic 2f0 = 4.6 GHz; when the impedance ratio of the SIR Z2/Z1 = 0.5, the second harmonic 3.5f0 = 8.05 GHz. Figure 2(a) illustrates a relevant circuit simulation for 2.3 GHz. In Figure 5.2, the center frequency f0 is 2.3 GHz, the circuit impedance ratio Z2/Z1 = 0.5. The second harmonic in Figure 1 is exactly 3.5f0; therefore, the second harmonic of Figure 2(a) is 8.05 GHz. (2) 336

3 Figure 1. SIR: (a) basic structure of SIR; relationship between impedance ratio and normalized spurious resonance frequency; (c) interstage coupling of λ/4-type SIR. (c) 337

4 Figure 2. Wide stopband BPF with SIR: (a) structure of 2.3 GHz wide stopband BPF; simulated frequency responses by IE3D. In the circuit architecture shown in Figure 2(a), the use of strong coupling is necessary. Strong coupling can be used to improve the Z1 sign compensation of the high impedance of fine copper wire. Figure 3 is an enlarged view of a part of the circuit illustrated in Figure 2(a). Figure 4 depicts the simulated frequency responses, from MWO software. The circuit layout and measured results are illustrated in Figure 5(a) and 5, respectively. Figures 5 and 2 illustrate that the positions of the center frequency and second harmonic frequency are the same (2.3 and 8.05 GHz). 338

5 Figure 3. SIR structure: an enlarged view of a part of Figure 2. Figure GHz wide stopband BPF simulated frequency responses by MWO. (a) Figure GHz wide stopband BPF: (a) photograph of layout; measured results. Circuit Structure of 4.1 GHz Wide Stopband Bandpass Filter Figure 6(a) shown a wide stopband with a center frequency of 4.1 GHz; its circuit architecture is the same as that illustrated in Figure 2(a), but the center frequency is not the same. Figure 6 depicts the responses of the circuit simulation. Figure 7 is the simulated frequency responses from MWO software. The circuit layout and the measured results are depicted in Figure 8(a) and Figure 8, respectively. 339

6 Figure GHz wide stopband BPF with SIR: (a) structure of wide stopband BPF; simulated frequency responses by IE3D. Figure GHz wide stopband BPF simulated frequency responses by MWO. 340

7 Figure GHz wide stopband BPF: (a) photograph of layout; measured results. Circuit Structure of Wide Passband Bandpass Filter In this paper, the wide passband bandpass filter is composed of two wide stopband BPFs with distinct center frequencies. The first circuit is depicted in Figure 2(a) and 2, where f01 is equal to 2.3 GHz; the second circuit is illustrated in Figure 6(a) and 6, where f02 is equal to 4.1 GHz. The SIR that is composed of these two wide stopband BPFs connected in parallel is shown in Figure 9(a); it forms a wide passband bandpass filter. IE3D EM simulation indicates that the BPF depicted in Figure 9(a) provides favorable effects. The simulation results are presented in Figure 9; three negative 30 db transmission zeros exist, of which f01 is equal to 2.3 GHz, f02 is equal to 4.1 GHz, and f03 is equal to 3.2 GHz. Three transmission zeros are generated by the three resonators, the lump equivalent circuits of which are illustrated in Figure 14. The frequency f01 is generated by the series resonance of the two sets, {L1, C7, L1} and {L1, C10, L1}. The frequency f02 is generated by the series resonance of the two sets, {L2, C1, L2} and {L2, C4, L2}. The frequency f03 is the center frequency of the wide passband bandpass filter. The frequency f03 is generated by the parallel connection of f01 and f02. The resonance of these three resonance points forms an effective wide passband bandpass filter. The circuit layout and the measured results are depicted in Figure 10(a) and Figure 10, respectively. Figure 11 and Figure 13 illustrate the effects of suppressing the second harmonic of 8.05 GHz in Figure 2 and o adding two open stubs in the appropriate positions of the I/P and O/P port. (a) Figure 9. Wide passband BPF: (a) structure of Wide passband BPF; simulated frequency responses by IE3D. 341

8 Figure GHz wide passband BPF: (a) photograph of layout; measured results. Figure 12 depicts the simulation frequency responses of the MWO simulation of a wide passband BPF. The circuit layout is illustrated in Figure 13(a). The topology circuit in Figure 12(a) and the lump circuit in Figure 14(a) can be used to strengthen the analysis of Figure 9(a). Figure 15 shows the conditions and basis of the coupled lines and transmission line, which transform the equivalent circuit [7]. 342

9 Figure 11. Wide passband BPF with open stubs: (a) structure of wide passband BPF; simulated frequency responses by IE3D. 343

10 Figure 12. Wide passband BPF simulation frequency responses of MWO. (a) Figure GHz wide passband BPF with open stubs: (a) photograph of layout; measured results. Simulated and Measured Results The circuit structures of the wide stopband BPF, the wide passband BPF, and the IE3D circuit simulation are described in sections 2, 3 and 4. Fabrication measurement results can be taken from the circuit board and form Figure 5, Figure 8 and Figure 10. The topology circuit simulation of sections 2, 3 and 4 are quite representative and accurate. This paper discusses wide stopband BPFs and wide passband BPFs. These circuits were physically implemented in actual circuit layout by using RO4003 printed circuit boards. The plate relative dielectric constant was 3.38, the plate thickness was mm, and the loss tangent was The filter used two types of simulation software, namely MWO and IE3D. The simulation results had only slight error. After repeated fine-tuning of the simulation with several circuit board fabrication measurements, the final apparatus achieved optimal performance. 344

11 Figure 14. Wide passband BPF: (a) lump circuit of microstrip; lump circuit of microstrip (if strong coupling exists then C 10 >> C11 and C 12). 345

12 Figure 15. Condition of transforming with topology and lump circuit: (a) representation of the capacitances of coupled lines and transmission line gap; representation of the capacitances of open stubs; (c) representation of the inductance of TX line. Conclusion In this study, the whole circuit structure was composed of transmission lines and SIR. The SIR was formed by adding high impedance inductance coupling lines and low-impedance capacitive coupling lines. The low-impedance lines of the two SIRs used strong coupling to produce bandpass filtering of the inductor-capacitor-inductor series resonant. The upper half of the SIR controlled the passing of the low-frequency band, namely 2.3 GHz; the lower half of the SIR controlled the passing of the high-frequency band, namely 4.1 GHz. When the upper and the lower halves of the SIR were connected to the three transmission lines, the system formed a new channel, with a bandwidth of 2.6 GHz, and the new wideband bandpass filter center frequency was 3.2 GHz. The circuit characteristics of the SIR are as follows. The high-impedance line width was 0.5 mm for its jagged part, and the low-impedance line width was 4 mm, with a ratio of 1:80. Therefore, the second harmonic shifted to 8.05 GHz, but the higher harmonic, namely 8.05 GHz, was suppressed by the shunt open stubs on the input and output ports. Thus, the proposed structure is simple and elegant and offers useful characteristics for wideband bandpass filter applications. Reference [1] Byung-Kuk Jeon, Hee Nam, Ki-Cheol Yoon, Design of a Patch Dual-Mode Bandpass Filter with Second Harmonic Suppression Using Open Stubs, Asia-Pacific Microwave Conference, December 7-10, [2] Wen-Hua Tu, Huifeng Li, Krzysztof A. Michalski, Microstrip Open-Loop Ring Bandpass Filter Using Open Stubs for Harmonic Suppression, IEEE MTT-S International Microwave Symposium Digest, June 11-16, [3] Ching-Wen Tang, Ming-Guang Chen, A Microstrip Ultra-Wideband Bandpass Filter With Cascaded Wideband Bandpass and Bandstop Filters, IEEE Transactions on Microwave Theory and Technology, Vol. 55, No. 11, November [4] Mongkol Meeloon, Sarawuth Chaimool, Prayoot Akkaraekthalin, A Wideband Bandpass Filter with a Notch-Band Using Step-Impedance Resonator and Embedded Slots, Asia-Pacific Microwave Conference, December 7-10,

13 [5] Amir Torabi, Keyvan Forooraghi, Miniature Harmonic-Suppressed Microstrip Bandpass Filter Using a Triple-Mode Stub-Loaded Resonator and Spur Lines, IEEE Microwave and Wireless Components Letters, Vol. 21, No. 5, May [6] M. Sagawa, M. Makimoto, S. Yamashita, Geometrical Structures and Fundamental Characteristics of Microwave Stepped-Impedance Resonators, IEEE Transactions on Microwave Theory and Technology, Vol. 45, No. 7, pp , July [7] R.K. Mongia, I.J. Bahl, P. Bhartia, RF and microwave coupled-line circuits, second ed., Norwood, MA: Artech House,