High-Performance Circularly Polarized MIMO Antenna for 5G mmWave n261 Band Using Asymmetric Stubs

Abstract

This research presents the design and analysis of a circularly polarized MIMO antenna employing an inset-fed rectangular patch integrated with asymmetric stubs and slots. The antenna is specifically optimized for 5G millimeter-wave (mmWave) applications targeting the n261 band (27.50–28.35 GHz), with a center frequency of 28 GHz.The structure is fabricated on a Rogers RT/duroid 5880 substrate, characterized by a compact footprint of 19.64 × 30.25 × 0.79 mm³. The proposed design achieves operating bandwidth of 27.44 - 28.79 (1.36) GHz.based on the 2:1 VSWR and operating bandwidth of 1.28 GHz (27.46–28.74 GHz) based on the –10 dB return loss criterion.

Introduction

The paper presents the design and analysis of a compact circularly polarized (CP) MIMO antenna for 28 GHz 5G millimeter-wave (mmWave) applications. With the increasing demand for high-speed, low-latency 5G communications, MIMO architectures combined with CP antennas are essential for improving spectral efficiency, reducing signal fading, and enhancing polarization diversity.

The proposed antenna uses asymmetrically loaded stubs and tilted slots to achieve circular polarization and high port isolation. It is fabricated on a Rogers RT/Duroid 5880 substrate with dimensions 19.64 × 30.25 × 0.79 mm³. The design process involves five steps, evolving from a single SISO element to a mirrored dual-port MIMO structure.

Key Results:

• Impedance Bandwidth: 1.36 GHz (27.44–28.79 GHz)

• Axial Ratio Bandwidth: 0.4 GHz (AR ≤ 3 dB for CP)

• Peak Gain: 8.09 dBi

• Radiation Efficiency: 92.87%

• ECC (Envelope Correlation Coefficient): 0.0022 → indicates excellent isolation

• VSWR: ≤ 2 across the operating band

A comparative analysis shows that this antenna achieves competitive performance in terms of size, gain, isolation, and CP bandwidth, making it well-suited for 5G mmWave applications, especially in urban and mobile environments.

Conclusion

A compact circularly polarized MIMO antenna integrating asymmetric stubs and tilted slots has been developed, operating within a –10 dB impedance bandwidth of 1.28 GHz (27.46–28.74 GHz). The antenna achieves a circular polarization (CP) axial ratio bandwidth of 0.4 GHz (27.8–28.2 GHz). Simulated performance shows high radiation efficiency ranging from 92.87% to 94.23% and total efficiency between 83.9% and 92.93%. The realized gain spans from 6.04 to 8.09 dBi across the band. The design also demonstrates strong isolation of 22 dB at the 28 GHz resonant frequency and maintains a low ECC, with a peak value of only 0.035, indicating excellent diversity performance. These results confirm that the proposed asymmetrically loaded and slotted MIMO antenna delivers efficient performance with a compact footprint. The design approach also offers potential for future extensions to multiband or reconfigurable circularly polarized antenna systems.

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Copyright

Copyright © 2025 Sandesh Bhandari, Neha Sharma, R. B. Gaikwad. 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.