Design of MIMO Antenna for 5G-NR Midbands (N77/ N78/ N79)

Abstract

This present study offers to design and simulate a compact 2×2 MIMO T-slotted composite-shaped microstrip patch antenna for 5G New Radio (5G- NR) midband applications, specifically targeting bands N77, N78, and N79, operating from 3.3 GHz to 5 GHz. Using Ansys High-Frequency Structure Simulator (HFSS). The antenna was designed on an FR4 epoxy substrate with a dielectric constant (?r) of 4.4, thickness of 1.6 mm, and overall dimensions of 22.5 × 32 mm. The two-element antenna with no load lines achieves S?? = ?17.29 dB at 4.16 GHz and S?? = ?21.17 dB at 4.12 GHz, isolation (S??/S??) of ?31.33 dB at 4.68 GHz, VSWRs of 1.32 and 1.19, radiation efficiency up to 91.59%, and bandwidths of 520 MHz (S??) and 720 MHz (S??). Diversity performance of the final design was evaluated and shows excellent values: Envelope Correlation Coefficient (ECC) < 0.1 across 3.3–5 GHz, Diversity Gain (DG) near 10 dB, Channel Capacity Loss (CCL) < 0.4 bits/s/Hz, Mean Effective Gain (MEG) < ?3 dB, and Total Active Reflection Coefficient (TARC) < ?10 dB between 4.78 GHz and 4.91 GHz.

Introduction

The evolution of 5G wireless communication has increased the demand for high-performance MIMO (Multiple-Input Multiple-Output) antennas that can deliver high data rates, reliable signal transmission, and efficient spectrum use, especially in the 3.3–5.0 GHz midband spectrum (N77, N78, N79 bands). These bands offer a good balance between coverage and speed, making them vital for 5G base stations, IoT, and high-speed networks.

Challenges and Innovations in MIMO Antenna Design

Designing effective MIMO antennas faces challenges like:

• Impedance mismatch

• Mutual coupling

• Low isolation

• Reduced radiation efficiency

To overcome these, researchers use techniques like:

• Slot-loading

• Defected Ground Structures (DGS)

• Decoupling networks

• Machine learning (e.g., Random Forest, XGBoost) for return loss optimization

Performance metrics include:

• Return Loss (S11, S22)

• Envelope Correlation Coefficient (ECC)

• Diversity Gain (DG)

• Channel Capacity Loss (CCL)

• Mean Effective Gain (MEG)

• Total Active Reflection Coefficient (TARC)

Proposed Antenna Design: 2×2 MIMO Without Load Line

• Configuration: Two patch antennas on FR-4 substrate; one rotated 180° for improved isolation and reduced mutual coupling.

• Size: 22.5 × 32 mm, thickness: 1.6 mm, dielectric constant: 4.4

• Ports: Two, for independent feeding and radiation

Performance Highlights:

• Resonant frequencies: 4.16 GHz (Port 1), 4.12 GHz (Port 2)

• Return Loss: –17.29 dB and –21.17 dB → Good impedance matching

• Bandwidth: 520 MHz (Port 1), 720 MHz (Port 2)

• Isolation: –31.33 dB at 4.68 GHz → Excellent mutual coupling reduction

• VSWR: ~1.19–1.31 → Efficient power transfer

• Radiation Efficiency:

  • 91.59% at 3.68 GHz

  • 80.46% at 4.12 GHz

  • 78.91% at 4.16 GHz

  • 89.63% at 4.88 GHz

• 3D Gain Pattern: Directional radiation suitable for focused high-gain applications

• Impedance (Smith Chart): Near 50Ω match → Minimal reflection, high signal transfer

Conclusion

In this paper successfully presents the design, simulation of a compact 2×2 MIMO T-slotted composite-shaped microstrip patch antenna for 5G mid-band applications covering N77, N78, and N79 bands (3.3 GHz to 5 GHz). The S-parameters (S11, S22, S12, S21), VSWR, return loss, radiation efficiency, gain, smith chart, electric field (E-field) and current density (J-field) distributions were evaluated for the designed antenna. The paper demonstrates the viability of compact, efficient, and low-profile antennas suitable for integration into 5G wireless communication systems. In the future, this antenna design can be expanded into higher-order MIMO systems such as 4×4 or 8×8 arrays to meet the increasing demand for higher data rates and enhanced spatial diversity in advanced wireless applications. These larger MIMO configurations can significantly boost signal reliability and system capacity, particularly in dense urban environments and next-generation smart communication systems. Furthermore, optimization in terms of physical structure like reducing the antenna\'s size without compromising performance can be achieved by adopting novel feeding mechanisms, superior substrate materials, and structural innovations. Such enhancements aim to deliver better impedance matching, higher gain, and improved isolation, ensuring the antenna remains efficient, compact, and suitable for mid-band 5G MIMO applications.

References

[1] T. Addepalli, T. Vidyavathi, K. Neelima, M. Sharma, and D. Kumar, “Asymmetrical fed Calendula flower-shaped four-port 5G-NR band (n77, n78, and n79) MIMO antenna with high diversity performance,” Int. J. Microw. Wirel. Technol., vol. 15, no. 4, pp. 683–697, 2023, doi: 10.1017/S1759078722000800. [2] N. S and V. Seethalakshmi, “MIMO Antenna with Isolation Enrichment for 5G Mobile Information,” Mob. Inf. Syst., vol. 2022, no. 1, p. 1802352, 2022, doi: https://doi.org/10.1155/2022/1802352. [3] N. Bujjibabu and S. Varadarajan, “High isolated Psi-Shaped 4x4 MIMO UWB antenna for RF energy harvesting applications,” Mater. Today Proc., 2023, doi: https://doi.org/10.1016/j.matpr.2023.03.798. [4] P. K. S. Rachit Jain, Vandana Vikas Thakery, “Employing Machine Learning Models to Predict Return Loss Precisely in 5G Antenna,” Prog. Electromagn. Res. M, vol. 118, pp. 151–161, 2023, doi: 10.2528/PIERM23062505. [5] B. Nannepaga and S. Varadarajan, “Enhancing RF energy harvesting in smart cities with two port MIMO-UWB antenna design using machine learning algorithms,” Frequenz, vol. 78, no. 9–10, pp. 413–431, 2024, doi: doi:10.1515/freq-2023-0386. [6] M. A. Haque et al., “Broadband high gain performance MIMO antenna array for 5 G mm-wave applications-based gain prediction using machine learning approach,” AlexandriaEng. J., vol. 104, pp. 665–679, 2024, doi: https://doi.org/10.1016 /j.aej. 2024.08.025. [7] A. Es-saleh, M. Bendaoued, S. Lakrit, S. Das, and A. Faize, “Design aspects of MIMO antennas and its applications: A comprehensive review,” Results Eng., vol. 25, p. 103797, 2025, doi: https://doi.org/10.1016/j.rineng.2024.103797. [8] Balanis, C. A. (2016). Antenna theory: Analysis and design (4th ed.). Wiley.

Copyright

Copyright © 2025 Bujjibabu Nannepaga, Gondru Sandeep, Boddu Nikitha, Nagireddy Deepthi, Mangineedu Sravani Krishna, Surasani Bharath Kumar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.