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

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 mm 3 having a partial ground plane. Rogers RT 5880 is used as the dielectric substrate tier. The simulated operating band of the MPA ranges from 2.67GHz to 4.20GHz, covering the N77 and N78 bands with a centre operating frequency of 3.29GHz. The antenna can also be used for WiMAX rel 2 (3.4–3.6GHz) applications. After fabrication and testing, the antenna also shows almost the same working band extending from 2.67 GHz to 4.15GHz. 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 3.29GHz, the simulated gain and directivity are 3.16dB 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-6GHz band applications.


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. e wireless communication researchers are also trying to conceptualize 6G technology. e 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. e 5 G provides data rate bigger than 100 Mbps at ultimate mobility and greater than 1 Gbps at meagre mobility [2]. e data rate varies from 5 Gbps up to 50 Gbps which is promised by 5G technology. To ful l 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]. e 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][5][6][7].
e 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. e 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]. ough 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. e 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. e wide bandwidth is produced by the antenna having a maximum gain of 2.69 dB. e antenna is capable of serving 5G, WiMAX, WLAN, and 4G applications. A compact monopole patch antenna is described in Ref. [13]. e size of the antenna is 30 × 34 mm 2 . e 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]. e bandwidth of the proposed RMPA is 2.32  GHz. e antenna is suitable for the Chinese 5G operating band. e gains are 2.52 dB at 2.55 GHz, 3.04 dB at 3.5 GHz, and 4.31 dB at 4.75 GHz. e 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. e antenna is applicable for both WLAN and Sub-6 GHz applications. e 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. e antenna is square shaped, having a bandwidth ranging from 3.4 to 3.6 GHz. e 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 mm 3 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][25][26][27][28][29][30][31][32][33][34].
A compact (40 × 40 × 1.575 mm 3 ) 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. e 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.

Structure of the Inset Fed MPA
e 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. e 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. e copper (annealed) is used for both patch and ground plane of the MPA. e 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.
where c = velocity of light, f r = resonance frequency, and ε r = dielectric constant.
Patch length, International Journal of Antennas and Propagation ground plane, and the length of the partial ground plane (L g ) is 14 mm and a parasitic element has a length (P L ) 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. e 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. e effective impedance of the antenna is completely matched with 50 Ω port impedance. e 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.

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. e simulated and measured scattering parameter (S 11 -parameter) of an omni-directional microstrip patch antenna (MPA) is displayed in Figure 2. e S 11 parameter is measured by using a vector network analyzer (VNA). e antenna is resonated at a frequency of 3.  Figure 3. e return loss is higher without a parasitic element on the ground plane, and its      Figure 6(f ). e measured gain also varies from 2.45 dB to 3.51 dB. ere is a good compliance between the measured gain and simulated gain of the designed inset fed MPA prototype. e 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. e gain of the antenna also increases with increasing the length of the parasitic element on the ground plane (P L ), as displayed in Figure 9. e MPA shows maximum gain for m � 22 mm, x � 11 mm, and P L � 21 mm. e polar scheme illustrations of the radiation pattern of the fabricated MPA for ϕ � 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°. e 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). e 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. e 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. e impact of the length of the parasitic element of the ground plane (P L ) on VSWR has been studied in Figure 12. e antenna shows the best VSWR for P L � 21 mm.
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 Figure 13. e antenna shows good efficiency. ere 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. e value of simulated efficiency ranges from 93% to 97% and measured efficiency ranges from 78% to 92% over the whole bandwidth. e impedance (real and imaginary part) is demonstrated in Figure 14. e real part and the imaginary part values are 53.35 Ω and −0.28 Ω, respectively, at 3.29 GHz. at 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  International Journal of Antennas and Propagation International Journal of Antennas and Propagation the proposed design has a very well balanced set of radiation characteristics with a lower volume for Sub-6 GHz applications.

Conclusion
e 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. e volume of the antenna is 40 × 40 × 1.575 = 2520 mm 3 which is made by Rogers RT 5880 and simulated by the CST-MWS suite. e 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. e antenna has a good far field radiation pattern with good gain and directivity. Over the exhaustive bandwidth, the VSWR satisfies 1 < VSWR < 2. e simulated and measured VSWR are 1.04 and 1.32 at the resonance point. e 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. e 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.

Data Availability
e data used to support the findings of this study are included within the article.

Conflicts of Interest
e authors declare that they have no conflicts of interest.