# An Omni-Directional Wideband Patch Antenna with Parasitic Elements for Sub-6 GHz Band Applications

Authors: Liton Chandra Paul; Himel Kumar Saha; Tithi Rani; Md. Zulfiker Mahmud; Tushar Kanti Roy; Wang-Sang Lee
Journal: International Journal of Antennas and Propagation
 (2022)

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## Abstract

An omni-directional inset fed wideband microstrip patch antenna (MPA) for Sub-6 GHz applications has been presented. Initially, a slotted small patch antenna with a full ground plane is designed and then partial ground plane and electromagnetically coupled parasitic elements have been incorporated and optimized to get desired performance. The volume of the studied antenna is 40 × 40 × 1.575 mm3 having a partial ground plane. Rogers RT 5880 is used as the dielectric substrate tier. The simulated operating band of the MPA ranges from 2.67 GHz to 4.20 GHz, covering the N77 and N78 bands with a centre operating frequency of 3.29 GHz. The antenna can also be used for WiMAX rel 2 (3.4–3.6 GHz) applications. After fabrication and testing, the antenna also shows almost the same working band extending from 2.67 GHz to 4.15 GHz. The use of a partial ground plane plays a vital role in making it an omni-directional antenna, and the existence of a rectangular parasitic element in the ground plane influences the improvement of gain and directivity of the antenna. The designed MPA allows it to run as a wide band antenna with a good reflection coefficient profile, high average efficiency, and 1 < VSWR < 2. At a resonant tip of 3.29 GHz, the simulated gain and directivity are 3.16 dB and 3.38 dBi, respectively. The measured gain is slightly higher than the simulated gain. The computer simulation technology (CST) is used for modelling and exploring all the performance matrices of the antenna. The results of the fabricated prototype present very good similarity with the simulated results and both simulated and measured results also support the Sub-6 GHz band. The antenna prototype shows a very well balanced set of radiation characteristics with a miniaturized volume and high efficiency. Therefore, the inset fed MPA can be contemplated as a candid model for Sub-6 GHz band applications.


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## Body

## 1. Introduction

Industrial revolution in wireless technology has become incontestable by the exponentially increasing number of wireless communication users. To meet the demand of huge data rates in wireless handy applications, technology has jumped from 2G to 3G, 3G to 4G, and 4G to 5G very rapidly and further developing day by day. The wireless communication researchers are also trying to conceptualize 6G technology. The 4th generation technology has evolved into 5G technology to issue a higher data rate, larger bandwidth, and minor delay since 2019 [1]. In packet switched wireless systems, a large bandwidth is used in 5G cell phones today. The 5 G provides data rate bigger than 100 Mbps at ultimate mobility and greater than 1 Gbps at meagre mobility [2]. The data rate varies from 5 Gbps up to 50 Gbps which is promised by 5G technology. To fulfil the criteria towards 2020, ITU provided 5G frequency bands that include N77 (3.3–4.2 GHz), N78 (3.3–3.8 GHz), and N79 (4.4–5.0 GHz) bands [3]. The low cost, low power level, lower consumed battery, and higher data rate motivate the communication engineers to establish the efficient and widespread utilization of 5G technology. Microstrip slotted antennas are broadly used for wireless communications including WiMAX, WLAN, WPAN, LTE, Bluetooth, ISM, WiFi, 3G, 4G, and 5G applications [4–7]. The ITU provides different 5G bands for different countries. In the USA, 3.1–3.55 GHz and 3.7–4.2 GHz are used as the Sub-6 5G band. For Europe, 3.4–3.8 GHz is considered. In China, 3.3–3.6 GHz and 4.8–4.99 GHz bands have been allocated for 5G applications [8]. Microstrip patch antenna (MPA) is more preferable in the spectrum of wireless communication because of their low cost, light weight, stable radiation pattern, and high gain. The inset feeding technique, coplanar waveguide, partial ground plane, defected ground structure, slotted patch, and different shaped patch are applied to improve the performance of an antenna [9, 10]. An ultrawideband antenna is illustrated in Ref. [11]. Though the bandwidth of the antenna is excellent and it ranges from 3.05 GHz to 5.82 GHz, the efficiency and gain are very unstable over the bandwidth. The gain remains negative approximately up to 4.5 GHz and efficiency is also lower than 60% up to 5.5 GHz. In Ref. [12], a slotted antenna is proposed. The wide bandwidth is produced by the antenna having a maximum gain of 2.69 dB. The antenna is capable of serving 5G, WiMAX, WLAN, and 4G applications. A compact monopole patch antenna is described in Ref. [13]. The size of the antenna is 30 × 34 mm2. The antenna has a very good coverage for the Sub-6 band with a reflection coefficient of −50 dB. A rose-like patch antenna (20 × 35 × 0.79 mm 3) with a slotted partial ground plane for Sub-6 GHz is proposed in Ref. [14]. For designing ultrawide band MPA, CST software is used in Ref. [15]. The bandwidth of the proposed RMPA is 2.32 GHz–5.24 GHz. The antenna is suitable for the Chinese 5G operating band. The gains are 2.52 dB at 2.55 GHz, 3.04 dB at 3.5 GHz, and 4.31 dB at 4.75 GHz. The antenna is also applicable for WiFi, Bluetooth, and WLAN communication which is an advantage of the antenna. In Ref. [16], a flexible antenna is proposed. Rogers 5880 is used as a flexible substrate. For 5 G, the MPA resonates at 3.5 GHz with a gain and efficiency of 2.51 dB and 92.7%, respectively. For the ISM band, the antenna resonates at 2.45 GHz with a gain of 1.74 dB and efficiency of 94%. In Ref. [17], a hexagonal-shaped antenna is described. A CPW feeding technique is used in the proposed antenna. The antenna is applicable for both WLAN and Sub-6 GHz applications. The gain of the antenna is poor (>1.5 dB), and the efficiency is greater than 85%. A concept of metamaterial is applied to enhance the performance of antennas [18, 19]. In Ref. [20], a compact MPA is described. The antenna is square shaped, having a bandwidth ranging from 3.4 to 3.6 GHz. The antenna is preferable for only the N78 band and not applicable for the N77 and N79 band. A Rogers RT 5880 based slotted monopole planar array for Sub-6 GHz is described in Ref. [21]. In Ref. [22], a large antenna having size of 40 × 60 × 1.52 mm3 and efficiency of 80% has been discussed for 5G application. A dual band antenna with low bandwidth is described in Ref. [23]. Similarly, many antennas for Sub-6 GHz 5G applications with comparatively higher volume and lower efficiency have been studied in Refs. [24–34].A compact (40 × 40 × 1.575 mm3) antenna with comparatively stable gain (Simulated: 1.95 dB to 3.92 dB and Measured: 2.45 dB to 3.51 dB) and directivity (2.97 dBi to 4.08 dBi) as well as having a high average radiation efficiency over the whole operating frequency range of Sub-6 GHz band application is analyzed briefly. The paper has been organized as follows: Section 2 elucidates the structure of omni-directional inset fed wideband microstrip patch antenna (MPA). All the simulated and measured outcomes are critically analyzed in section 3, and at last, conclusion of the presented work has been drawn at section 4.


## 2. Structure of the Inset Fed MPA

The geometrical formation of the proposed omni-directional inset-fed MPA with a partial ground plane for Sub-6 GHz band application is described in detail in this section. The antenna has three tiers, namely, ground, patch, and substrate. A fragment of Rogers RT 5880 material (2.2, 0.0009) is exercised for the antenna. The copper (annealed) is used for both patch and ground plane of the MPA. The thickness of Rogers RT 5880 and copper are 1.575 mm and 0.035 mm, respectively. Initially the size of the antenna has been estimated by using some fundamental equations (1)–(4) and then the greatness of the MPA is optimized to 40 mm × 40 mm × 1.575 mm by using CST-MWS.(1)Patchwidth,WP=c2fr2εr+1,where c = velocity of light, fr = resonance frequency, and εr = dielectric constant.(2)Length,L=0.412hεreff+0.3Wp/h+0.264εreff−0.258Wp/h+0.8,(3)Effectivelength,Leff=c2frεreff,(4)Patchlength,Lp=Leff−2ΔL.Figures1(a) and 1(b) exhibits the top and back view with necessary labelling. The 3D view and fabricated prototype are presented in Figures 1(c) and 1(d), respectively. The width and length of the patch are Wp = 10 mm and Lp = 9 mm. There is a rectangular slot on the patch having width (Ws) and length (Ls) of 8 mm and 6 mm, respectively. The size of the inset is 1 mm × 2 mm. There are two rectangular shaped parasitic elements besides each side of the patch having a width (x) of 11 mm and length (m) of 22 mm. These parasitic elements influence the reflection coefficient as well as the efficiency of the antenna. The intervening space between two parasitic elements (d) is 12 mm. The width (Wf) and length (Lf) of the feeder are 4.8 mm and 18 mm, respectively. The MPA has a partial ground plane, and the length of the partial ground plane (Lg) is 14 mm and a parasitic element has a length (PL) of 21 mm. Actually, the lower part of the back side of the antenna acts as a partial ground plane and the upper part which is electrically separated but electromagnetically connected acts as a parasitic element. The partial ground plane aids to set the antenna omni-directional and rectangular parasitic elements enhance the directivity of the MPA over the exhaustive working Sub-6 GHz frequency band. The effective impedance of the antenna is completely matched with 50 Ω port impedance. The enumerated extent of excitation coefficient (k) is 4.6 to 8.68, and ultimately the worth of k has been optimized to 4.6 for the proposed MPA. All the designed factors are charted in Table 1.Figure 1
Proposed microstrip patch antenna (MPA). (a) Top view. (b) Back view. (c) 3D view. (d) Fabricated prototype.
(a)(b)(c)(d)Table 1
List of the factors of designed MPA.
Name and symbolWeight (mm)Length (L)40Width (W)40Thickness of Rogers RT 5880 (h)1.575Thickness of copper (t)0.035Patch’s length (Lp)9Patch’s width (Wp)10Length of slot (Ls)6Width of slot (Ws)8Length of the parasitic element on the patch (m)22Width of the parasitic element on the patch (x)11Distance between two parasitic elements of patch (d)12Feeder’s length (Lf)18Feeder’s width (Wf)4.8Length of parasitic element on ground plane (PL)21Ground plane’s length (Lg)14


## 3. Results and Discussion

At first the fabricated MPA is designed and optimized by using CST-MWS and then fabricated and tested in the antenna laboratory. The simulated and measured scattering parameter (S11-parameter) of an omni-directional microstrip patch antenna (MPA) is displayed in Figure 2. The S11 parameter is measured by using a vector network analyzer (VNA). The antenna is resonated at a frequency of 3.29 GHz with a simulated reflection coefficient of −33.69 dB and measured reflection coefficient of −25 dB. The simulated and measured operating frequency coverage ranges of the proposed antenna are 2.67 GHz to 4.20 GHz and 2.67 GHz to 4.15 GHz. Therefore, the measured and simulated bandwidths are 1.48 GHz and 1.53 GHz at the −10 dB point of the scattering parameter curve. The bandwidth is quite good for Sub-6 GHz bands (covering N77 and N78 bands). The antenna can also be useful for WiMAX rel 2 (3.4 GHz–3.6 GHz). Different countries use different Sub-6 GHz 5G bands. The designed antenna covers 5G bands of many countries such as 3.1–3.55 GHz and 3.7–4.2 GHz bands of USA, 3.4–3.8 GHz band of Europe, 3.6–3.8 GHz band of Spain, 3.3–3.6 GHz band of China, 3.4–3.8 GHz band of Ireland, 3.6–4.2 GHz band of Japan, 3.4–3.7 GHz band of Korea, 3.3–3.4 GHz band of India. The variation of the reflection coefficient for different lengths of parasitic element on the ground plane (PL) as well as without parasitic element is shown in Figure 3. The return loss is higher without a parasitic element on the ground plane, and its centre frequency is 4.1 GHz. When the length (PL) is varied from 9 mm to 21 mm with step size of 2 mm, the bandwidth of the antenna is slowly switched to the left side and the return loss is enhanced. The current flow on the surface of the microstrip patch antenna (MPA) at 3.29 GHz is illustrated in Figure 4 and the current is 47.49 A/m. The current distribution is slightly high at both left and right edges of the rectangular parasitic elements, and it is maximum at lower part of the antenna especially near the feeder of the MPA. Figure 5 represents the fabricated antenna setup within the anechoic chamber for radiation characteristics measurement. The polar and 3D representation of both gain and directivity are at 3.296 GHz, and linear gain and directivity graph over the exhaustive operating bandwidth of the inset fed MPA are illustrated in Figures 6(a)–6(f). At 3.29 GHz, the gain and directivity are 3.16 dB and 3.38 dBi. From Figure 6(e), the gain and directivity vary from 1.95 dB to 3.92 dB and 2.97 dBi to 4.08 dBi. The measured and simulated gain of the inset fed MPA are also compared in Figure 6(f). The measured gain also varies from 2.45 dB to 3.51 dB. There is a good compliance between the measured gain and simulated gain of the designed inset fed MPA prototype.Figure 2
S11 curve of the designed MPA.Figure 3
Variation of the reflection coefficient for different length of parasitic element on the ground plane (PL).Figure 4
Surface current of the MPA at 3.296 GHz.Figure 5
Fabricated prototype within the anechoic chamber.Figure 6
Gain and directivity of the inset fed MPA. (a) Gain (polar). (b) Gain (3D). (c) Directivity (polar). (d) Directivity (3D). (e) Simulated gain and directivity. (f) Simulated and measured gain.
(a)(b)(c)(d)(e)(f)The gain of MPA increases by increasing the length (m) and width (x) of the parasitic element on the patch as depicted in Figure 7 and Figure 8, respectively. The gain of the antenna also increases with increasing the length of the parasitic element on the ground plane (PL), as displayed in Figure 9. The MPA shows maximum gain for m = 22 mm, x = 11 mm, and PL = 21 mm.Figure 7
Variation of the gain for different length of parasitic element on patch (m).Figure 8
Variation of the gain for different width of the parasitic element on the patch (x).Figure 9
Variation of the gain for different length of parasitic element on the ground plane (PL).The polar scheme illustrations of the radiation pattern of the fabricated MPA forϕ = 0° and 90° at 3.29 GHz are depicted in Figure 10. From the pattern, the principal lobe is guided at 180° at ϕ = 0° and 178° at ϕ = 90°. For both the electric and magnetic field, half power beam width (HPBW) or 3 dB angular beam width is 171° at ϕ = 0° and 83.4 at ϕ = 90°. The main lobe magnitudes are 17.9 dBV/m at both ϕ = 0° and ϕ = 90° (for E-field); similarly, the main lobe magnitudes are −33.6 dBA/m at both ϕ = 0° and ϕ = 90° (for the H-field). The voltage standing wave ratio (VSWR) of the MPA prototype is displayed in Figure 11. From the figure, both the measured VSWR and simulated VSWR of the fabricated prototype are 1 < VSWR < 2. The simulated and measured values are 1.04 and 1.32, respectively, at resonant points which are near to unity, revealing good port impedance matching property of the proposed MPA. The impact of the length of the parasitic element of the ground plane (PL) on VSWR has been studied in Figure 12. The antenna shows the best VSWR for PL = 21 mm.Figure 10
E-field and H-field of the prototype.Figure 11
VSWR.Figure 12
Variation of the VSWR for different length of parasitic element on the ground plane (PL).For any antenna, efficiency is the ability of being able to emit EM signals successfully. A linear representation of measured and simulated efficiency graph is incorporated in Figure13. The antenna shows good efficiency. There is a slight deviation of measured efficiency from the simulated efficiency which may happen due to the soldering error and port defect. From the graph, the maximum efficiency of the prototype is high (simulated is 95% and measured is 92%) which reveals that the designed MPA emits most of the input signal. The value of simulated efficiency ranges from 93% to 97% and measured efficiency ranges from 78% to 92% over the whole bandwidth. The impedance (real and imaginary part) is demonstrated in Figure 14. The real part and the imaginary part values are 53.35 Ω and −0.28 Ω, respectively, at 3.29 GHz. That means the impedance matching is upright for the fabricated prototype with respect to the reference 50 Ω SMA connector. A comparison Table 2 is incorporated to buttress the strength of the proposed design. Most of the cited designs have higher volume and lower efficiency than our proposed antenna. From Table 2, it can be conferred that the proposed design has a very well balanced set of radiation characteristics with a lower volume for Sub-6 GHz applications.Figure 13
Radiation efficiency of the MPA.Figure 14
Z parameters of the MPA.Table 2
Comparison table.
IndexReference No.This work[22][23][24][25][26][27][28][29][30][31][32][33][34]Physical size (L × W × h) mm340 × 60 × 1.5246 × 46 × 3.17535×35×∗78 × 58 × 0.940 × 30 × 1.6130×130×∗22.5 × 10.7 × 1.645 × 45 × 1.048 × 35 × 1.6236 × 36 × 434 × 34 × 3.2150 × 80 × 0.890×90×∗40 × 40 × 1.575Electrical size0.27λ × 0.4λ0.37λ × 0.37λ0.39λ × 0.39λ0.99λ × 0.73 λ0.44λ × 0.33λ1.19λ × 1.19λ0.26λ × 0.12λ0.27λ × 0.27 λ0.3λ × 0.22λ0.34λ × 0.34λ0.35λ × 0.35λ0.64λ × 0.34λ0.97λ × 0.97λ0.36λ × 0.36λSubstrate materialRogers RO4350 B (εr=3.48)Rogers RT (εr=2.2)ECCOSTOCK HIK (εr=10)PETεr=3.2)FR-4FR-4FR-4εr=4.3)FR-4εr=4.4)FR-4εr=4.3)FR-4εr=4.4)FR-4εr=4.3)FR-4εr=4.5)Rogers RO4003Cεr=3.38), Taconic TLX-9εr=2.5)Rogers RT 5880 (εr=2.2)Operating frequency range (GHz)2–52.44–2.54, 3.19–3.553.30–4.383.89–5.93.28–4.02.75–5.453.4–4.21.82–2.92, 3.15–4.751.85–3.82.8–3.81∼3.1–3.75∼1.27–1.5, ∼2.2–2.5, ∼3.5–4.23.24–3.82.67–4.20Maximum gain (dB)7.14∼4632.58.42.37.54.0444.083.8510.433.92BW (GHz)30.1, 0.361.082.010.722.70.80.1, 1.61.951.010.650.23, 0.3, 0.70.561.53Radiation efficiency (%)80——∼80—∼8073—92——80—95Applied methodsMetamaterial, slotENGTL metamaterialsDRA, parasiticCPW fedPartial groundBalunLog-periodic patchNon-centred L-shapedMetamaterialAperture coupledSlot, PIN diodeStub, open slotMetasurfaceParasitic, partial ground∗Not mentioned.


## 4. Conclusion

The fabricated omni-directional MPA has the ability to cover the Sub-6 GHz (N77 and N78) band for 5G applications and WiMAX rel 2 applications. The volume of the antenna is 40 × 40 × 1.575 = 2520 mm3 which is made by Rogers RT 5880 and simulated by the CST-MWS suite. The simulated bandwidth and measured bandwidth of the MPA are 1.53 GHz (2.67 GHz–4.20 GHz) and 1.48 GHz (2.67 GHz–4.15 GHz) with a suitable return loss profile. The antenna has a good far field radiation pattern with good gain and directivity. Over the exhaustive bandwidth, the VSWR satisfies 1 < VSWR < 2. The simulated and measured VSWR are 1.04 and 1.32 at the resonance point. The inset feeding technique, partial ground plane, and parasitic elements make the antenna more suitable for Sub-6 GHz application. It can also be used for WiMAX rel 2. The average radiation efficiencies of the proposed MPA are approximately 95% (simulated) and 92% (measured) over the working band. Due to the good agreement between simulated and measured results as well as wide range of frequency coverage, the designed omni-directional inset fed MPA may be taken into account as an excellent model for Sub-6 GHz applications.



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*Source: 9645280-2022-10-04.xml*