Design and analysis of an inset-fed circle patch microstrip antenna operated at 28 GHz for 5G application

Trường Đại học Vinh Tạp chí khoa học, Tập 49 - Số 2A/2020, tr. 57-63 
 DESIGN AND ANALYSIS OF AN INSET-FED CIRCLE 
 PATCH MICROSTRIP ANTENNA OPERATED 
 AT 28 GHZ FOR 5G APPLICATION 
 Nguyen Thi Kim Thu, Cao Thanh Nghia, 
 Le Anh Duc, Nguyen Thi Quynh Hoa 
 School of Engineering and Technology, Vinh University 
 Received on 30/12/2019, accepted for publication on 23/3/2020 
 Abstract: This paper presents a microstrip antenna design which it's radiating 
 element is circular and applied to 5G systems. The model and parameters of the 
 antenna were simulated and analyzed by High-Frequency Structure Simulator (HFSS) 
 computer code on FR4-epoxy laminate microwave. The simulation results of the 
 antenna show that it operates at 28 GHz with return loss S11= -40 dB, bandwidth 
 BW=2 GHz, power gain greater than 5 dB, radiation efficiency greater than 87% and 
 Voltage Standing Wave Ratio (VSWR) is less than 2 in the operating band from 26.8 
 to 28.8 GHz, respectively. From the results achieved, the designed antenna is suitable 
 to be used in devices using 5G technology. 
 Keywords: Microstrip antenna; inset-fed; circular patch; 5G technology. 
 1. Introduction 
 In the context of information and communication systems are running out of 
resources, 5G technology is an effective solution to meet current development and 
communication needs. Compared to 4G technology, 5G antennas work at higher resonant 
frequencies, thus allowing their devices to achieve a higher data rate. For high-mobility 
users, the expected rate of 5G technology is 5.0 Gbps while for low-mobility users it is 
50.0 Gbps. Besides, the goal of the International Telecommunication Union on 5G is 3 
times more spectrally effective than Long-Term Evolution (LTE). Researchers find a 
way to deal with this problem in the 5th generation of communication by providing a 
higher data rate, using an extremely high-frequency band (EHF) as around frequency 
bands 28 GHz, 38 GHz, and 68 GHz [1 - 9]. Federal communication commission (FCC) 
proposed the band spectrum of 27.5 to 28.25 GHz for 28 GHz band spectrum application 
while the ETSI proposed that for 5G communication antenna must have a bandwidth of 
1GHz for S11 less than -10 dB [1], [2]. 
 Moreover, modern wireless communication systems required low cost, 
lightweight, low profile, high-gain and simple to manufacture to ensure reliability, 
mobility, and high efficiency leads to innovations in designing antennas for 5G [3], [4]. 
Currently, there are many techniques used in the design of antennas, one of the most 
commonly applied methods is microstrip technology, which has outstanding advantages 
compared to other technologies such as compact, low profile, easy for feeding, easy to 
etch on any PCB should be convenient in integration on modern equipment, low 
production costs. Besides, microstrip technology can use many shapes to design radiation 
surfaces for antennas such as rectangles, squares, circles, triangles... This makes it easier 
to choose the shape of the antenna to suit the shape of each type of device [5],[6]. 
Email: ntqhoa@vinhuni.edu.vn (N. T. Q. Hoa) 
 57 
 N. T. K. Thu, C. T. Nghĩa, L. A. Đức, N. T. Q. Hoa / Design and analysis of an inset-fed circle patch 
 For the 28 GHz band, Park et al. have proposed an 8-element array antenna with a 
bandwidth of 2.3 GHz but its structure is complex especially [7], [8]. Abbas Awan et al. 
have proposed a patch antenna with improved performance using DGS, however, it has a 
quite narrow bandwidth of 1.38 GHz [11]. A simple microstrip based structure has also 
been reported such as that by Khalily et al. providing a gain of 15.6 dBi within around 20 
× 20 mm size, its bandwidth also only achieved from 27.3 to 29 GHz [9], [10], [11]. 
 In this paper, we propose a microstrip antenna design with a circular radiation 
element, which operates at the 28 GHz band for 5G systems. The antenna is fed by a 
compact inset-fed, the overall dimensions of the antenna are 5.6 mm x 5.6 mm x 0.8 mm. 
The antenna operating frequency range is from 26.8 to 28.8 GHz, which is suitable for 
application in 5G communication. The antenna is designed and investigated based on the 
HFSS full-wave simulation software. 
 2. Structural Design and Simulations 
 The proposed circle patch antenna using a microstrip line for feeding is given in 
Fig 1. The dimension of the overall antenna structure is 5.6 mm x 5.6 mm fabricated on 
an FR-4 substrate with a dielectric constant of 4.4, a substrate thickness of 0.8 mm, and a 
loss tangent of 0.02. The radiating and ground layers are made from copper, with 
thickness t of 0.035 mm and electric conductivity σ of 5.96×107 S/m. The radius of the 
patch, designed to operate at 28 GHz, the standard frequency for 5G communication 
antenna, is calculated using the formulas given in [12]. 
 (1) 
 ⁄ 
 , * ( ) +-
 where (2) 
 √ 
 (3) 
r is the radius of the circular patch, fr is the operating frequency, h and r are the 
thickness and the dielectric constant of substrate. 
 Apply the formulas (1), (2) and (3) to calculate the circular radius of the patch 
r=1.5 mm, L=6 mm. To achieve the desired results, the designers used the PSO algorithm 
(Particle Swarm Optimization) used in familiar Ansoft HFSS software for antenna 
dimensions. 
 The optimization process is carried out by investigating the effect of the return 
loss S11 versus changes in the dimension of the radiation element's radius. Because the 
original antenna (r = 1.5 mm) operates at frequencies lower than 28 GHz, so the size of 
the antenna must be reduced in order for it to operate at higher frequencies. Initial 
initialization parameters are r from 1 to 1.5 mm, with step = 0.1 mm and the optimum 
results are calculated and displayed at 28 GHz. After optimization, the most suitable 
result is selected corresponding to r = 1.3 mm. 
 Two symmetrical rectangular notches of dimensions m x g are etched in radiating 
circular patch with the 0.5 mm length (m) and 0.15 mm width (g). To obtain a 
characteristic impedance of 50 Ω, the feedline width (w) and length (k) are determined 
0.3 mm and 1.8 mm respectively. The detailed dimensions of the proposed circular patch 
antenna are shown in Tab 1 and simulated by HFSS software. 
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Trường Đại học Vinh Tạp chí khoa học, Tập 49 - Số 2A/2020, tr. 57-63 
 Fig. 1: Schematic of proposed circle patch 
 microstrip antenna (a) 3D view and (b)Top view 
 Tab. 1: Dimensions of proposed patch antenna 
 Parameters Value (mm) 
 L 5.6 
 h 0.8 
 t 0.035 
 D 2.6 
 k 1.8 
 w 0.3 
 g 0.15 
 m 0.5 
 3. Results and Discussion 
 3.1. Return Loss Parameter 
 The simulated S-parameter shown in Fig. 2 indicates that the value of return loss 
(S11) is -40 dB at 28 GHz with bandwidth ranging from 26.8 GHz to 28.8 GHz, which 
entirely covers 5G frequency band allocated from GHz 27.5 to 28.25 GHz. 
 Fig. 2: Simulated S-parameter of circular patch microstrip antenna 
 59 
 N. T. K. Thu, C. T. Nghĩa, L. A. Đức, N. T. Q. Hoa / Design and analysis of an inset-fed circle patch 
 3.2. Voltage Standing Wave Ratio 
 Voltage Standing Wave Ratio (VSWR) of the proposed circle patch antenna is 
shown in Fig. 3. The value of VSWR at 28 GHz is reported to be 1.25 which value is less 
than 2 indicating improved matching conditions. 
 Fig. 3: VSWR of circular patch microstrip antenna 
 3.3. Smith Chart 
 The Fig. 4 shown the scattering parameter S11 for the proposed circular patch 
microstrip antenna at the range of frequency 20 GHz -30 GHz on the Smith chart exhibits 
a good impedance matching of approximately 50 Ω at the resonate frequency. 
 Fig. 4: Smith chart of circular patch microstrip antenna 
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Trường Đại học Vinh Tạp chí khoa học, Tập 49 - Số 2A/2020, tr. 57-63 
 3.4. Gain and Radiation Efficiency 
 The gains of the proposed antenna were given in Fig. 5. As shown in Fig. 5, the 
proposed antenna provides a total maximum gain of 5.44 dB and the gains stay above 5 
dB throughout the band. 
 Fig. 5: Power gain 3D (a) and 2D versus frequency (b) 
 of circular patch microstrip antenna 
 The radiation efficiency and patterns of the proposed antenna are provided in Fig. 
6 and Fig. 7. As shown in Fig. 6, the radiation efficiency of antenna obtains above 87% 
in the bandwidth ranging from 26.7 GHz to 28.25 GHz. The 3-D total gain confirms that 
the maximum power of the antenna could be achieved along the z-axis. In YOZ-plane 
and XOZ-plane, the radiation patterns of the designed antenna are quite similar to the 
directional radiation patterns with maximum power along the Z-axis, while it exhibits an 
omnidirectional radiation pattern in the XOY-plane 
 Fig. 6: Radiation Efficiency of circular patch microstrip antenna 
 61 
 N. T. K. Thu, C. T. Nghĩa, L. A. Đức, N. T. Q. Hoa / Design and analysis of an inset-fed circle patch 
 Fig. 7: (a) Radiation pattern in XOY plane, (b) XOZ plane, and YOZ plane 
 4. Conclusion 
 This paper presents an antenna design on the FR4-epoxy substrate for 5G 
technology. The radiation element of the antenna is circular and fed by a microstrip line. 
The model and parameters of the antenna are simulated and extracted by HFSS 13.0. The 
simulated results show that the proposed antenna achieves the resonate frequency at 28 
GHz, the total gain of 5.4 dB, the impedance of 50 Ω, the bandwidth of 2 GHz, the 
radiation efficiency of more than 87% through the whole the frequency band. Compared 
to the before microstrip antennas for 5G communication, the ones that have used 
different shapes to design. This our design, the total dimension is smaller, the bandwidth 
is wider, and the power gain is improved. The obtained results prove that the proposed 
antenna is suitable for 5G standard from 27.5 to 28.25 GHz. 
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[6] W. Roh et al., “Millimeter-wave beamforming as an enabling technology for 5G 
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 TÓM TẮT 
 PHÂN TÍCH VÀ THIẾT KẾ ĂNG-TEN VI DẢI HÌNH TRÒN 
 HOẠT ĐỘNG Ở TẦN SỐ TRUNG TÂM 28 GHZ CHO ỨNG DỤNG 5G 
 Bài báo này trình bày một thiết kế ăng-ten vi dải áp dụng cho các hệ thống 5G với 
phần tử bức xạ hình tròn. Các thông số của ăng-ten được mô phỏng và phân tích bằng 
phần mềm HFSS trên vật liệu điện môi FR4-epoxy. Kết quả mô phỏng cho thấy ăng-ten 
hoạt động ở băng tần 28 GHz với mức suy hao bằng -40 dB, băng thông 2 GHz, độ lợi 
công suất lớn hơn 5 dB, hiệu suất bức xạ lớn hơn 87% và tỷ lệ sóng điện áp đứng nhỏ 
hơn 2 trong băng tần hoạt động tương ứng từ 26,8 đến 28,8 GHz. Từ kết quả đạt được, 
ăng-ten được thiết kế phù hợp để sử dụng trong các thiết bị sử dụng công nghệ 5G. 
 Keyword: Ăng-ten vi dải; phần tử bức xạ hình tròn; công nghệ 5G. 
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