AbstractA low pass filter only allows signals below its cut-off frequency to pass while attenuating other signals with frequencies higher than those of the filter. Several interesting techniques were proposed by researchers to design low pass filter. However, majority of those filters present difficulties of integration with other elements of electronics gadgets, high cost, high power consumption, large size and low-frequency application. Consequently, the current study focused on design and simulation of a parallel coupled-line microstrip low pass filter. Computer Simulation Technology (CST) microwave software was used for the design and simulation of the filter. Results Analyses were made and the resulting frequency responses were plotted using a sigma plot. It was concluded that the proposed microstrip filter presents solutions to the issues observed in the former designs.Abstract

A low pass filter only allows signals below its cut-off frequency to pass while attenuating other signals with frequencies higher than those of the filter. Several interesting techniques were proposed by researchers to design low pass filter. However, majority of those filters present difficulties of integration with other elements of electronics gadgets, high cost, high power consumption, large size and low-frequency application. Consequently, the current study focused on design and simulation of a parallel coupled-line microstrip low pass filter. Computer Simulation Technology (CST) microwave software was used for the design and simulation of the filter. Results Analyses were made and the resulting frequency responses were plotted using a sigma plot. It was concluded that the proposed microstrip filter presents solutions to the issues observed in the former designs

Adam, Shuaibu Musa

Afolabi, David

Idris, Adamu

Man, Ka Lok

Nanjappan, Vijayakumar

Yusuf, Shamsuddeen

English

Shamsuddeen Yusuf

Shuaibu Musa Adam

Adamu Idris

David Afolabi

Vijayakumar Nanjappan

Ka Lok Man

Crossref

Design and Simulation of 2.4 GHz Microstrip Parallel Coupled Line Low Pass Filter for Wireless Communication System

imec Publications (Interuniversity Microelectronics Centre)

Design and Simulation of 2.4 GHz Microstrip Parallel Coupled Line Low Pass Filter for Wireless Communication System

Adamu, Idris

Lirias

This work is partially supported by the AI University Research Centre (AIURC) of the Xi'an Jiaotong-Liverpool University (XJTLU), China and Jiangsu (Provincial) Data Science and Cognitive Computational Engineering Research Centre at XJTLU

OuluREPO University of Oulu repository

 1Abstract—A low pass filter only allows signals below its cut-off frequency to pass while attenuating other signals with frequencies higher than those of the filter. Several interesting techniques were proposed by researchers to design low pass filter. However, majority of those filters present difficulties of integration with other elements of electronics gadgets, high cost, high power consumption, large size and low-frequency application. Consequently, the current study focussed on design and simulation of a parallel coupled-line microstrip low pass filter. CST microwave software was used for the design and simulation of the filter. Results Analyses were made and the resulting frequency responses were plotted using a sigma plot. It was concluded that the proposed microstrip filter presents solutions to the issues observed in the former designs.   Index Terms— Microstrip; Coupled line; Low pass filter; Insertion loss, Return loss.  I. INTRODUCTION A microwave low pass filter is a two-port, passive, reciprocal and linear device that shunts unwanted signal frequencies while allowing the desired frequency to pass. In general, the electrical performance of a filter is described in terms of its frequency selectivity, insertion loss, return loss and group delay variation in the passband. Filters are required to have small insertion loss, large return loss for good impedance matching with interconnecting components and high-frequency selectivity to prevent interference [1]. If a filter has  Manuscript received 10 June, 2021; accepted 15 August, 2021.  This research was supported by the Key Programme Special Fund underGrant No. [KSF-P-02]; and Suzhou-Leuven IoT & AI cluster, AI frequency selectivity, and guard band between channels can be determined to be small which indicates that the frequency can be used efficiently. Also, a small group delay and amplitude variation of the filter in the passband is required for minimum signal degradation [2]. Microwave low-pass filters (LPFs) have been widely used as a key building block to suppress all the unwanted high-frequency harmonics and inter-modulation in various wireless communication systems [3]. Due to unexpected frequency-distributed behaviour, the conventional transmission-line based LPFs, such as stepped-impedance and open-stub filters, always suffer from gradual cut-off attenuation skirt and narrow upper-stop bandwidth [4]. To sharpen this roll-off skirt, it is a usual approach to raise the order of a low-pass filter to a great extent. Unfortunately, this enlarges the overall circuit size and accumulates in-band insertion loss. In [5], a microstrip line with extremely high impedance is formed by etching out an aperture on the ground plane underneath the strip conductor. This approach allows effectively widening the upper stopband of stepped-impedance low-pass filters due to an enlarged impedance ratio. But, it still suffers from poor rejection near the cut-off frequency [6]. In recent years, various types of miniaturised and performance-improved low-pass have been explored in [7]-[8] based on the original idea of [9]. These low-pass filters are basically constructed by a hairpin- or C-shaped folded unit in geometry. Because an additional coupling route is created between the two non-adjacent sections, University Research Centre (AI-URC) of the Xi'an Jiaotong-Liverpool University, China.Shamsuddeen Yusuf1, Shuaibu Musa Adam2,3, Adamu Idris2, Vijayakumar Nanjappan4, David Afolabi5, Ka Lok Man6,7,8,9,10* 1Department of Electrical Engineering, Kano University of Science and Technology, Wudil,  Kano, Nigeria  2Department of Physics, Federal University Dutsin-Ma, Dutsin-Ma, Nigeria 3Faculty of Science and Computing, Al-Istiqama University Sumaila, Kano, Nigeria 4Center for Ubiquitous Computing, University of Oulu,  Oulu, Finland 5Design Technology and Computer Science Department, United World College, Changshu, China  6School of Advanced Technology, Xi'an Jiaotong-Liverpool University,  Suzhou 215123, China 7Swinburne University of Technology Sarawak, Malaysia  8imec-DistriNet, KU Leuven, Belgium  9Kazimieras Simonavičius University, Lithuania 10Faculty of Informatics, Vytautas Magnus University, Lithuania sywaliyyi@gmail.com; mashuaibu@fudutsinma.edu.ng; aidris@fudutsinma.edu.ng; vijayakumar.nanjappan@oulu.fi; david.afolabi@live.com; *Ka.Man@xjtlu.edu.cn Design and Simulation of 2.4GHz MicrostripParallel Coupled Line Low pass Filter forWireless Communication System attenuation poles are excited to improve the upper stopband performances. High impedance transmission lines and tightly-coupled twin lines are connected in parallel to generate three attenuation poles in the stopband [10]. A stepped impedance hairpin resonator is presented in [11] to make up a class of elliptic-function LPFs with a wide stopband. By allocating an attenuation pole close to the cut-off frequency, a sharp roll-off skirt was achieved in [12]. However, only one attenuation pole was excited in the stopband [13] all three attenuation poles are  far away from the desired low passband, so the roll-off skirt near the cut-off frequency has not been increased so much [14]. In this letter, for the first time, a class of coupled-line hairpin filters is designed on a microstrip to have a low-pass frequency response with an expanded upper-stopband. It was designed by centrally tap-connecting the two coupled-line strip conductors and adjusting the coupling strength between them, three attenuation poles with controllable spacing can be excited in the first harmonic passband to widen and deepen the upper stopband. In analysis, a set of closed-form design equations are firstly established based on the well-known coupled-line theory [15] to explain the mechanism for exciting and reallocating these attenuation poles. Finally, two LPFs with a single and two asymmetrical units are optimally designed with the 3dB cut-off frequency at 2.5 GHz. Measured results are provided to confirm the predicted ones for the single-unit LPF and experimentally demonstrate a wide upper-stopband in the range 3.2–11.8 GHz with the insertion loss higher than 20 dB for the two-unit LPF [16]. II. MATERIALS AND METHOD  A. Setting of Simulation Parameters  The design specification of the filter is shown in Table I. The specification of the dielectric material was obtained from the Rogers Corporation [16].  TABLE  I. FILTER SPECIFICATION  Microstrip coupled line low pass filter is composed of three basic layers; the ground layer, the substrate and the patch which is the top layer. At each port of the low pass filter, there is a waveguide. As shown in Figure 1, the ground and the upper layers are made up of conducting material. While the middle layer is the substrate, an insulating material, between the parallel-coupled lines forming the capacitor; and vacuum was used as the dielectric material. The filter was designed by following various steps using CST microwave studio. I. Ground layer: It is made up of a conducting material i.e. annealed copper which formed the base of the filter with a very thin thickness typically 0.035mm. The dimension of the ground plane is 90mm by 30mm. The ground layer isshown in Figure 2.  Fig. 1. Proposed microstrip low pass filter   Fig. 2. Ground layer of the filter  II. Substrate layer: The proposed structure is printed over a low-cost FR-4 material which is readily available. The substrate with a dielectric constant of 4.3, loss tangent of 0.016 and thickness of 1.52 mm is considered material forming the substrate. The substrate layer is quite thicker than the ground plane. It has the same dimension as that of the ground plane. The substrate layer is shown in Figure 3.   Fig. 3. Substrate layer of the filter  The specification of dielectric material used as a substrate is given in Table II.  TABLE  II. SPECIFICATION OF DIELECTRIC MATERIAL USED AS A SUBSTRATE  III. Transmission lines:  The transmission lines form the upper layer of the low pass filter. It is also made up of annealed copper of thickness 0.035mm. It consists of a rectangular bar laying horizontally and vertically on top of the substrate. Thehorizontal patch ensures the inductive or resistive effect, while the vertical layer which is space at one point ensuresthe capacitive effect and thus is responsible for rejecting other harmonics above the fundamental cut-off frequency. The horizontal transmission lines run throughout the length of the substrate (i.e. 90mm). They are located 12mm Filter specification Value Cut-off frequency 2.4GHZ Load impedance  50Ω Source impedance 50Ω Insertion loss  -30dB Return loss Greater than -0.5dB Order  3 Parameter Value Dielectric constant ( 4.3 Substrate height 1.52mm loss tangent (δ) 0.016 Copper thickness 0.035mm to 15mm of the substrate width, hence they are 3mm width.The vertical ones which are attached with the horizontal ones are generally of equal length and width i.e. 14mm and 6.66mm respectively. But, to ensure the capacitive effect of the low pass filter the vertical annealed copper was spaced between 4.8mm to 5mm to provide a space of 0.2mm for the vacuum serving dielectric material.  The vertical bars were grounded at 13.5mm below the midpoint of the vertical patch with a cylindrical annealed  copper material with inner and outer radius 0.15mm and 3mm respectively with a thickness that runs to ground layer of the filter. The transmission line layer is shown in Figure 4.  Fig. 4. Transmission line layer of the filter B. Analytical relation for calculating characteristics impedance and effective dielectric constant  If thickness of the copper track ‘t’ and the width ‘W’ ofthe copper track is less than the height ‘h’ of the insulatingmaterial, the effective dielectric constant ‘’ is found to using eqn. 1. Whereas, if the width of the track is greater than the height of the insulator, ‘’ is found using eqn. 2.   = + [√12ℎ+ . −]     (1) Where  is the relative dielectric constant.   = + [√12ℎ]           (2) Thus, the characteristics impedance becomes:  =0[ℎ.90.667 ln(ℎ.444)]         (3) C. Impedance Matching  Impedance matching is necessary especially in communication to minimise loss of signal strength and ensure all the power generated is merely transmitted. The filter is no exception. CST microwave studio has the advantage of its built-in analytical calculator, which is used in determining various design parameters.   I. CST microwave studio calculator method:  The calculator performs several functions but, most important for this design is calculating the wavelength, effective dielectric constant and the input impedance to ensure impedance matching and other important design parameters given in Table III. This calculator is easier to use in calculating the input and output impedance of the filter. The only parameters needed are the height of the substrate (h), the width of the transmission line (w) and lastly the dielectric constant of the substrate (ε_r). In some CST microwave calculatoreven the cut-off frequency may be of utmost importance.The values of Table III were inputted to the calculator in which the input and output impedance of the filter was found to be 49.80ohm. This is displayed in Figure 5. TABLE  III. PROPOSED LOW PASS FILTER DESIGN PARAMETERS Parameter Value Height of the substrate (h) 1.52mm Width of the transmission line (w) 3.00mm Dielectric constant of the substrate ( 4.30 Cut-off frequency 2.4GHz   Fig. 5. CST Microwave studio impedance calculation  II. Analytical method for impedance calculation:  This is given by the relationship shown in eqn. 6. First, we determined the effective dielectric constant from the information given in Table II.  = + [√12ℎ            (4)   =4. +4. [√121.523] = 3.27       (5) The dielectric constant value obtained from eqn. (5) coincides with the value of effective permittivity calculated by the CST microwave calculator.  =0[ℎ.90.667 ln(ℎ.444)]              (6)  =0.7[31.52.90.667 ln(31.52.444)] = 49.80Ω    (7) It can be seen from Figure 5 and eqn. (7) that, the results were found to be almost equal if not exactly equal to the one obtained from the CST microwave studio calculator. Thus, the CST microwave studio calculator and the analytical method proved to be effective. III. SIMULATION RESULTS AND ANALYSES  A. Insertion (S21) and Return (S11) Loss The simulated low-pass filter response is shown in Figure 6. The gain (dB) is plotted on the y-axis against the frequency (GHz) on the x-axis. It is clear that the simulated cut-off frequency was found to be 2.4GHz. The value of the insertion loss (S21) and return loss (S11) at 2.4GHz were found to be -29.941dB and -0.505dB respectively. B. Field Monitors As expected, Figure 7 shows the surface current at different frequency. The field monitors applied at 0.4GHz,0.8GHz and 1.2GHz show all the signal passing through the filter because, they are within the pass band frequency. The cut-off frequency of the filter as already known is 2.4GHz and this correspond to what happened in Figure 7 (d) in which the signal is attenuated. frequency, GHz1.0 1.5 2.0 2.5 3.0 3.5Reflection coefficient, dB-40-30-20-100S 1 1 (R L)S 2 1 (IL) Fig. 6. Frequency response of the low-pass filter   (a) (b) (c) (d)Fig. 7. Surface current at different field monitors IV. CONCLUSIONS Filters are one of the primary and essential parts of the microwave and communication systems. The microstrip low-pass filter was simulated using CST microwave studio software. In order to predict the performance of the filter, few parameters in the structure were analysed and found to have good relationship with the microwave theory. An optimisation process has been introduced along with the simulation procedure, focusing on the filter dimension in order to improve the response of the filter. A. Suggestions for Future Studies Validation of the proposed filter topology via prototype development is beyond the scope of this research study. It is suggested that this should be part of a future study's objectives. CONFLICTS OF INTERESTThe authors declare that they have no conflicts of interest.REFERENCES[1] J. S. Hong and M. J. Lancaster, Microstrip Filters for RF/Microwave Applications. New York: Wiley, 2001. [2]  L. Zhu, H. Bu, and K. Wu, “Unified CADmodel of microstrip linewith back side aperture for multilayer integrated circuit,” in IEEE MTT-S Int. Dig., vol. 2, pp. 981–984, Jun. 2000. [3]  R. J. 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Chang, “Compact elliptic-function low-pass filters using microstrip stepped-impedance hairpin resonators,”IEEE Trans. Microwave. Theory Tech., vol. 51, no. 1, pp. 193–19. [15]  Sourabh Sagar, Sonam Y. C. et al., “Designing and Parametric Extraction of Low Pass Filter Using Metamaterials,” IEEE Students Conference, 2020. [16]    F. Teberio et al., “Chirping techniques to maximize the power-handling capability of harmonic waveguide low-pass filters,” IEEE Trans. Microw. Theory Techn., vol. 64, no. 9, pp. 2814–2823, Sep. 2016. 

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Design and Simulation of 2.4 GHz Microstrip Parallel Coupled Line Low Pass Filter for Wireless Communication System

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imec Publications (Interuniversity Microelectronics Centre)

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imec Publications (Interuniversity Microelectronics Centre)

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