Journal of Multidisciplinary Applied Natural Science ACCEPTED MANUSCRIPT • OPEN ACCESS Impact of Feed Point Position on Patch Antenna’s Return Loss and Bandwidth for UWB Applications To cite this article before publication: M. F. Ahmed, M. H. Kabir, and A. Z. M. T. Islam. (2023). J. Multidiscip. Appl. Nat. Sci. in press. https://doi.org/10.47352/jmans.2774-3047.158. Manuscript version: Accepted Manuscript Accepted Manuscript is “the version of the article accepted for publication including all changes made as a result of the peer review process, and which may also include the addition to the article by Pandawa Institute of a header, an article ID, a cover sheet and/or an ‘Accepted Manuscript’ watermark, but excluding any other editing, typesetting or other changes made by Pandawa Institute and/or its licensors” This Accepted Manuscript is © 2023 The Author(s). 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All third-party content is fully copyright protected and is not published on a gold open access basis under a CC BY license, unless that is specifically stated in the figure caption in the Version of Record. View the article online for updates and enhancements. https://doi.org/10.47352/jmans.2774-3047.158 https://creativecommons.org/licenses/by/4.0/ https://doi.org/10.47352/jmans.2774-3047.158 Impact of Feed Point Position on Patch Antenna’s Return 1 Loss and Bandwidth for UWB Applications 2 3 Md. Firoz Ahmed1,a); Md. Hasnat Kabir1,a*); Abu Zafor Md. Touhidul Islam2,b) 4 5 1Department of Information and Communication Engineering, University of Rajshahi, Rajshahi-6205 6 (Bangladesh) 7 2Department of Electrical and Electronic Engineering, University of Rajshahi, Rajshahi-6205 (Bangladesh) 8 a) Correspondence: hasnatkabir11@gmail.com 9 10 ORCIDs: 11 First AUTHOR : https://orcid.org/0000-0003-2721-0596 12 Second AUTHOR : https://orcid.org/0000-0002-8516-8587 13 Third AUTHOR : https://orcid.org/0000-0002-0613-016X 14 15 AUTHOR CONTIBUTIONS 16 17 Conceptualization, M.FA. and M.HK.; Methodology, M.FA, and M.HK.; Software, 18 M.FA., M.HK., and A.Z.M.TI.; Validation, M.FA., M.HK. and A.Z.M.TI.; formal analysis, 19 M.FA. and M.HK.; Investigation, M.FA.; Resources, M.HK.; Data Curation, M.FA. and 20 M.HK.; Writing—original draft preparation, M.FA.; Writing—review and editing, M.FA., 21 M.HK. and A.Z.M.TI.; Visualization, M.FA. and M.HK.; Supervision, M.HK. and 22 A.Z.M.TI.; Project Administration, M.HK. and A.Z.M.TI.; Funding acquisition, no funding 23 acquisition. 24 25 CONFLICT OF INTEREST 26 27 The authors declare no conflict of interest. 28 29 30 31 32 33 34 35 36 A CC EP TE D M A N U SC RI PT mailto:hasnatkabir11@gmail.com https://orcid.org/0000-0003-2721-0596 https://orcid.org/0000-0002-8516-8587 https://orcid.org/0000-0002-0613-016X Impact of Feed Point Position on Patch Antenna’s Return 1 Loss and Bandwidth for UWB Applications 2 3 Abstract. The demand for compact, lightweight, and high-performance antennas has 4 increased in recent times in the communication industry. Microstrip patch antenna (MPA) 5 becomes a better choice to effectively fulfill these requirements. In this study, hybrid 6 techniques of partial ground plane, slotted patch, and defective ground structure are 7 employed in MPA design to reduce the return loss, good impedance matching, and increased 8 the bandwidth, gain, and efficiency of the antenna. This research demonstrates the impact of 9 altering the feed point position, a crucial phenomenon of antenna design, on the patch 10 antenna and determines the proper feed point location by comparing a minimum return loss 11 (S11) which achieves the highest performance for the designed antenna. High-frequency 12 structure simulator (HFSS) software is used to design and simulate the patch antenna. The 13 operating frequency of the antenna is 6.85 GHz for UWB applications (3.1–10.6 GHz). A 14 FR4 epoxy substrate material with dimensions of 30 mm × 20 mm is used to design the 15 antenna. It has a dielectric constant of 4.4, a thickness of 0.8 mm and a tangent loss of 0.02. 16 Multiple resonant frequencies are observed with different return losses for each feed location. 17 The analysis shows that the finest feeding point is found at the center of the patch (9, 0) with 18 a very low return loss (-28.35 dB), and a high impedance bandwidth (19.7 GHz). The antenna 19 also achieved a gain of 4.46 dB, a directivity of 4.6904 dB, and a radiation efficiency of 20 95.90%. Hence, the location of the feed point can be considered as an influential factor in the 21 antenna design. 22 23 Keywords: patch antenna; return loss; bandwidth; feed point position; HFSS; UWB; FR4; 24 hybrid technique 25 26 1. INTRODUCTION 27 28 The development of wireless communications and information technology has made 29 multiple chances for improving the effectiveness of present signal transmission and 30 processing systems. This development is a key impetus for the creation of innovative 31 technologies and systems. Wireless communication system requires an antenna, which is 32 used to transmit or receive radio waves. Effective and dependable antennas such as parabolic 33 A CC EP TE D M A N U SC RI PT reflectors, patch antennas, slot antennas, and folded dipole antennas are needed for the new 1 generation of wireless systems. Even though each type of antenna has its own benefits and 2 drawbacks, the signal from an RF system cannot be sent or received properly without an 3 appropriate design of the antenna. In many wireless communication systems, low-profile 4 antennas are required [1]. 5 Microstrip patch antenna (MPA) is one kind of low-profile antennas. It has some desired 6 characteristics such as light-weight, ease of fabrication, flexibility to adapt to curved surfaces, 7 cost-effectiveness, and compatibility with integrated circuit technology. These attractive 8 properties of MPAs have increased their popularity and demand, and more study is being 9 done for better understanding to improve their performance. MPAs can be created in a variety 10 of shapes like square, rectangular, circular, triangular, trapezoidal, elliptical, etc [2]. 11 Microstrip patch antennas have various advantages, but they also have some drawbacks, for 12 instance, low efficiency and power, low gain and restricted bandwidth. Numerous strategies 13 have been studied and developed in an attempt to overcome their bandwidth and gain 14 constraints. The feeding method or feeding point can play a significant role in considerably 15 increasing or decreasing the microstrip patch antenna’s functionality [3]. The four feed 16 mechanisms such as microstrip line, coaxial probe, aperture coupling, and proximity coupling 17 are most widely used to feed a microstrip patch antenna [4][5]. Their properties as well as 18 advantages and limitations are described elsewhere [6]-[8]. When these various feeding 19 systems are used to improve impedance matching at different frequency bands, the 20 effectiveness of several characteristic factors such as radiation pattern, gain, and beam width 21 are changed. These factors must be considered whenever a new antenna application needs to 22 be designed [9]. 23 An aperture-coupled feed microstrip patch antenna was developed for the 2.4 GHz 24 frequency band [10][11]. The two feeding methods such as aperture coupled and proximity 25 coupled were used to excite the microstrip patch antenna [12]. Mandal et al. [13] 26 demonstrated that in contrast to aperture-coupled patch antenna, proximity-coupled feed 27 gives considerably greater return loss. It was also studied that the coaxial feedlines provide 28 good impedance matching for designing and analyzing microstrip patch antennas. Matching 29 the impedance between patch and feedline was conducted using coaxial and microstrip line 30 techniques [14]. Several investigations were performed to find the best feed point locations. 31 For instance, the effect of feed location on rectangular microstrip antenna operating at TM11 32 mode was presented in Paul et al [15]. Some investigations were performed to find the proper 33 location for feeding the patch antenna [16]-[18]. A patch antenna made of metamaterials was 34 A CC EP TE D M A N U SC RI PT demonstrated to be influenced by the feed point's position [4]. A study was done to 1 investigate how the feed point position impacts the operating frequency, return loss, and 2 bandwidth of a rectangular microstrip patch antenna and to determine the ideal feed point 3 position [19]-[21]. The effectiveness of a circular patch microstrip antenna was investigated 4 with regard to the impact of feed fluctuation [22]. 5 A T-matching network motivated by metamaterials was directly inserted inside the 6 feedline of a microstrip antenna to accomplish the maximum possible transmission of energy 7 between the front end of an RF wireless transceiver and the antenna [23]. A small, low-8 profile antenna made of metamaterial unit cells was used to demonstrate high-speed 9 effectiveness for wireless devices through the UHF-SHF bands [24]. An innovative 10 composite right/left-handed (CRLH) metamaterial unit cell-based tiny ultra-wideband (UWB) 11 antenna was developed for modern wireless communication applications [25]. A creative and 12 diminutive nine-element antenna array with a shared aperture structure was described in order 13 to provide substantial gain as well as excellent radiation efficiency at the millimeter-wave 5 14 G band [26]. A novel antenna array with high inter-element isolation was suggested for 5G 15 MIMO communication systems operating at sub-6 GHz [27]. It employed a hybrid strategy 16 that included a flawed ground plane, matching stubs, and dot walls. A hybrid right-left-17 handed metamaterial transmission line planar antenna's bandwidth and gain were increased 18 by using a non-Foster impedance matching circuit board [28]. Planar antennas were created 19 with implanted slots to increase their bandwidth for reliable multiband RF communications 20 [29]. A novel drifted line loop-based planar broadband antenna was developed for mobile 21 wireless communication devices [30]. 22 However, the majority of these studies [16][17][19]-[21] focus primarily on identifying 23 the best feed point, but the key deficiencies of their designed antenna are large antenna size, 24 narrow bandwidth, and limited range of applications. Therefore, a compact rectangular patch 25 antenna is developed for UWB (3.1–10.6 GHz) systems by employing hybrid methodologies 26 (partial ground plane, slotted patch, and defective ground structure) in order to get over from 27 these difficulties. This paper explains how shifting the feed point position implicates the 28 operating frequency, return loss, and impedance bandwidth of the designed antenna. It is also 29 determined the finest feed point location by minimizing the return loss (S11) for suitable 30 applications of the UWB band. 31 32 A CC EP TE D M A N U SC RI PT 1 Figure 1. The design of the microstrip line feed 2 3 2. MATERIALS AND METHODS 4 5 FR4 glass epoxy is widely used due to its good strength-to-weight ratios and ability to 6 operate well under both high and low pressure. It has a 4.4 dielectric constant and a 0.02 7 tangent loss. FR4 glass epoxy is commonly employed as an electrical insulator because of its 8 low water absorption rate [31]. 9 In the design of the proposed antenna, several techniques have been applied such as partial 10 ground plane (PGP), slotted patch, and defective ground structure (DGS). The narrow band 11 characteristics of the microstrip patch antenna are converted into wide band characteristics 12 using partial ground plane methodology [32]. PGP reduces the energy stored in the substrate 13 and back lobe radiation [33]. Imperfections or defects or slots on the ground plane are 14 referred to as defective ground structure (DGS) in microwave planar circuits [34]. It is used 15 to boost the bandwidth and gain of microstrip antennas, as well as to diminish cross-16 polarization, dimension, mutual coupling between nearby components and higher mode 17 harmonics [35]. DGS can be a variety of shapes such as concentric ring circles, spirals, 18 dumbbells, elliptical, U and V slots [36]. A patch having slots in the forms of a U, H, T, E, or 19 other shape is known as a slotted patch. The gain, bandwidth, and efficiency of an antenna 20 are increased; while the return loss, VSWR, and antenna size are decreased using this 21 technique. The edge of the microstrip patch is directly connected to a conducting strip in this 22 form of the feed mechanism, as shown in figure 1. The benefit of this type of feeding 23 configuration is that the feed can be engraved on the same substrate to yield a planar 24 structure. The patch is wider than the conducting strip. This method is popular because it is 25 reasonably easy to design, assess, and produce [37]. 26 27 A CC EP TE D M A N U SC RI PT 2.1. Antenna Structure. The proposed rectangular patch antenna uses a microstrip feedline 1 technique which is more consistent and less complicated than coaxial feedline, aperture 2 coupled feedline, and proximity couple feedline approaches. It is powered by a direct 3 connected microstrip feedline with a characteristic impedance of 50 ohms shown in figure 1. 4 The size of the feedline is 2 by 15 mm. FR4-epoxy substrate with dimensions of 30 by 20 5 mm is used to design the antenna. It has a thickness of 0.8 mm, a relative permittivity of 4.4, 6 and a tangent loss of 0.02. Both the patch and the ground are made of copper material. The 7 patch is 14 mm × 18 mm in size. The ground plane is partially employed to increase the 8 impedance bandwidth and to reduce the return loss of the antenna. The size of the PGP is 14 9 mm in length and 20 mm in width. A rectangular slot referred to as a DGS is inserted into the 10 antenna's partial ground plane, as well as 2 different slots (triangular and rectangular) are 11 implanted into the radiating patch, as illustrated in figure 2. These modifications are made to 12 increase the impedance bandwidth of the antenna. The evaluation and optimization of this 13 antenna are performed using High-Frequency Structure Simulator (HFSS) software (v.15). 14 Table 1 shows the different design parameters of the proposed antenna. 15 16 17 Figure 2. Proposed antenna structure 18 19 20 21 22 23 A CC EP TE D M A N U SC RI PT Table 1. Design Parameters of the proposed antenna 1 Parameters Values (mm) Ws = Wg 20.0 Ls 30.0 h 0.80 Wp 18.0 Lp = Lg 14.0 Lf 15.0 Wf = Wg1= Wp1 2.00 Lg1 3.00 Lp1 8.00 Lp5 = Lp6 = Wp2= Wp3 =Wp4 0.50 Lp2=Lp3=Lp4 7.00 Wp5=Wp6 6.50 p = q 6.00 r 8.48 2 2.2. Feed Point Position. Microstrip line feeding position is chosen because it offers the 3 best impedance match between the antenna and the feedline. The impedance matching is 4 required for the maximum power transfer. The feed point needs to be placed at that position 5 on the patch where the input impedance is 50 ohms for the operating frequency. It was done 6 by moving the feed point locations using a trial and error basis. The optimal feed point 7 location was selected by comparing the minimal negative return loss (S11) among other feed 8 point positions. The best feed point can be found along the length of the patch where the S11 9 is minimal [38]. In order to determine the optimal feed point in this design, Z was set to zero 10 and only Y was changed. 11 12 3. RESULTS AND DISCUSSION 13 14 A rectangular patch microstrip antenna using a microstrip feeding line approach has been 15 designed and simulated using finite element method based HFSS v.15 software. The substrate 16 thickness is in the X-direction, and the patch antenna is intended to be positioned in the 17 A CC EP TE D M A N U SC RI PT origin's Y-Z plane. A microstrip feedline is considered in the feeding scheme which 1 drastically impacts on the return loss and bandwidth of the antenna. We have investigated the 2 effect of the feedline's width on the proposed antenna. The width of the feedline varies from 1 3 to 3 mm to determine the appropriate width of the proposed antenna. Table 2 summarizes the 4 outcomes of the simulation. Variation is observed in the antenna properties by changing the 5 width of the feedline. Table 2 shows that the minimum return loss and the maximum 6 bandwidth are achieved with 2 mm width of feedline. This is the justification for choosing 2 7 mm width for the proposed antenna and the rest of the analysis has been carried out by this 8 width. 9 10 Table 2. Effect of feed width changes in the return loss and impedance bandwidth 11 Feed width, Wf (mm) Return loss (S11) (dB) Impedance Bandwidth (GHz) 1.0 -27.76 10.0 (3.67–13.67) 1.5 -27.53 10.5 (3.30–13.80) 2.0 -28.35 19.7 (3.15–22.85) 2.5 -25.83 0.84 (3.09–3.93) 3.0 -16.02 7.52 (4.59–12.11) 12 The investigation and simulation processes have been carried out for each of the Y-Z 13 plane feeding location points. The feed point position has been altered along the patch width 14 from the left to the right edge to achieve the best location. The simulated results are shown in 15 Table 3. The ideal operating frequency can be chosen to get the lowest return loss. The 16 difference between the power that is fed into the system and the power that is reflected is 17 known as the return loss, and it is expressed in decibels (dB). 18 19 A CC EP TE D M A N U SC RI PT 1 Figure 3. Return loss vs. frequency for (7, 0), (8, 0), (9, 0) feed point position 2 3 The least S11 for the axis (9, 0) is found to be - 28.35 dB. The axis (9, 0) is the center of 4 the patch; thus, it can be said that the impedance is perfectly matched at the center of the 5 patch. The values below and above (9, 0) show the worst performance in the return loss and 6 bandwidth of the antenna. 7 8 9 Figure 4. 2D Far-field radiation pattern of the proposed antenna at feed point (9, 0) 10 11 We have carried out the study at 15 different feeding points. Three observations from 12 among 15 feeding point locations are compared in the graph shown in figure 3. According to 13 our analysis, the selected feed point location has the minimum return loss (-28.35 dB). It is 14 calculated using a S11 graph. The bandwidth of an antenna is defined as the frequency range 15 over which S11 is less than -10 dB (-10 dB is an acceptable number that represents a VSWR 16 of 2). The suggested antenna has a bandwidth of 19.7 GHz (calculated using -10 dB return 17 A CC EP TE D M A N U SC RI PT loss) ranging from 3.15 to 22.85 GHz with a working frequency of 7.7 GHz at the feed point 1 position (9, 0). This operating frequency is slightly greater than the designed frequency, 2 which is 6.85 GHz. 3 4 Table 3. Implication of feed position on operating frequency, return loss, and impedance 5 bandwidth 6 7 The radiation pattern, also known as the far-field pattern, describes how the intensity of 8 electromagnetic waves radiating from an antenna or from other sources. The radiation pattern 9 varies depending on their direction. In the current work, it has been utilized to illustrate how 10 the power radiation is distributed around the antenna as a function of direction as indicated by 11 the phi angle at 6.85 GHz. The most effective method for showing radiation pattern is a three-12 dimensional graph. The surface of the patch antenna determines radiation magnitude. It can 13 also be represented using polar or angular coordinates. Figure 4 depicts the 2D far-field 14 radiation pattern of the proposed antenna at the feed point position (9, 0) at phi = 0° and 90° 15 degrees. This pattern closely mimics a dipole antenna and has a maximum radiated power of 16 22.19 dB at phi = 0° and 90° at 6.85 GHz, which represents a substantial benefit in ultra-17 wideband communication technology. 18 19 Feed position (Y, Z) (mm) Operating Frequency (GHz) Minimum Return loss (S11) (dB) Impedance Bandwidth (GHz) (7.00, 0) 5.70 -16.98 1.30 (7.25, 0) 3.20 -25.17 1.00 (7.50, 0) 6.60 -15.24 2.10 (7.75, 0) 5.60 -13.69 1.45 (8.00, 0) 6.30 -18.43 4.20 (8.25, 0) 3.40 -24.80 1.50 (8.50, 0) 7.40 -22.83 9.60 (9.00, 0) 7.70 -28.35 19.7 (9.25, 0) 7.70 -23.60 10.9 (9.50, 0) 6.30 -22.80 9.35 (9.75, 0) 6.35 -21.09 8.30 (10.00, 0) 6.55 -18.23 5.10 (10.25, 0) 6.40 -17.12 3.70 (10.50, 0) 6.55 -18.05 3.05 (10.75, 0) 6.20 -15.38 1.60 A CC EP TE D M A N U SC RI PT 1 Figure 5. Gain (dB) of the proposed antenna at feed point (9, 0) 2 3 The gain of an antenna measures the amount of energy transmitted from an isotropic 4 source in the direction of maximum radiation. The gain of the proposed antenna at feed point 5 (9, 0) is shown in figure 5. The suggested antenna attains a gain of 4.46 dB at 6.85 GHz. 6 Directivity is a simple factor to determine the range of energy transmission in a specific 7 direction. It is one of the factors that affect the gain of the antennas. Figure 6 shows the 8 directivity of the proposed antenna at feed point position (9, 0). The antenna provides a high 9 directivity of 4.6904 dB at feed point location (9, 0). 10 11 12 Figure 6. 3D directivity (dB) of the proposed antenna at feed point (9, 0) 13 14 The output power to input power ratio is used to determine the efficiency of any system, 15 but the radiated power to input power ratio is used to measure the antenna efficiency. The 16 A CC EP TE D M A N U SC RI PT antenna functions similarly to all other components of a microwave circuit. Dielectric losses 1 or mismatches are two factors that can lead to power loss. The radiation efficiency of the 2 planned antenna at feed point (9, 0) is shown in figure 7. The radiation efficiency is found to 3 be 95.90% at the optimal feed point with operating frequency of 6.85 GHz. 4 5 6 Figure 7. Radiation efficiency of the proposed antenna at feed point (9, 0) 7 8 Table 4 compares the performance assessments of the proposed antenna with a few 9 previously developed antennas. It is clear from this table that a significant gain and a narrow 10 bandwidth were achieved using a large antenna size [17]-[21]. However, the suggested 11 antenna is smaller than the observed antennas [17]-[21] and has a wider bandwidth of 19.7 12 GHz (3.15 to 22.85 GHz), which boosts the higher data rates. 13 14 Table 4. Comparisons of the current work with recently published work 15 Patch Size (mm2) Impedance Bandwidth (GHz) Gain (dB) Ref. 21.80 × 30.80 0.01 (10.00 MHz) 3.73 [17] 36.10 × 49.40 - 5.35 [19] 38.00 × 30.00 1.00 - [20] 28.00 × 36.00 0.03 (30.00 MHz) - [21] 14.00 × 18.00 19.70 (3.15–22.85) 4.46 This work - : Not mentioned 16 17 A CC EP TE D M A N U SC RI PT 4. CONCLUSIONS 1 2 The effectiveness of a rectangular patch antenna can be varied by altering the feed point 3 locations. The best outcome of the 15 feeding locations of the proposed antenna on the 4 FR4_epoxy substrate has been investigated. The findings show that the feed point (9, 0) 5 yields superior results. It implies that there is better impedance matching between the feedline 6 and patch at this point. The proposed antenna has a return loss of -28.35 dB, a bandwidth of 7 19.7 GHz from 3.15 to 22.85 GHz, a gain of 4.46 dB, a directivity of 4.6904 dB and a 8 radiation efficiency of 95.90% at the feed point position (9, 0). 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