Quad-Port Circularly Polarized MIMO Antenna with Wide Axial Ratio

Area of Science:

• Electromagnetics
• Antenna Theory
• Wireless Communications

Background:

• Multi-input-multi-output (MIMO) antennas are crucial for enhancing wireless communication capacity.
• Circularly polarized (CP) antennas are advantageous for mitigating polarization mismatch losses.
• Achieving high isolation in compact MIMO antenna designs remains a significant challenge.

Purpose of the Study:

• To design and analyze a quad-port circularly polarized MIMO antenna with inherent high isolation.
• To investigate the modal behavior of an asymmetric square slot with an inverted L-strip for CP radiation using Characteristic Mode Analysis (CMA).
• To achieve broadband CP performance and evaluate the diversity characteristics of the proposed MIMO antenna.

Main Methods:

• Characteristic Mode Analysis (CMA) was employed to analyze the modes of the asymmetric square slot with an inverted L-strip.
• Modal parameter extraction was performed for circular polarization (CP) radiation.
• A microstrip feed was utilized for broadband CP, and the unit was replicated orthogonally to form the quad-port MIMO antenna.

Main Results:

• The proposed quad-port CP-MIMO antenna achieved port isolation greater than 21 dB without additional decoupling structures.
• The antenna exhibited impedance matching (S11 < -10 dB) from 5.37 GHz to over 11 GHz.
• A wide axial ratio bandwidth (ARBW) of 4.65 GHz (5.61 GHz to 10.26 GHz) and a peak realized gain of 5.69 dBi at 8.4 GHz were achieved.

Conclusions:

• The study successfully demonstrated a compact quad-port CP-MIMO antenna with excellent isolation and broadband CP performance.
• CMA proved effective in guiding the design for modal parameter extraction and achieving CP radiation.
• The proposed antenna design offers advantages over existing MIMO structures and shows good agreement between simulation and measurement.