Why MIMO Antennas Require the Same Grounding

 

Reasons for Shared Grounding in MIMO:

MIMO antennas utilize multiple transmitting and receiving antenna elements to simultaneously send and receive multiple signals, thereby enabling spatial channel multiplexing. This technology significantly improves the throughput and spectral efficiency of communication systems.

However, to achieve efficient MIMO communication, the signals between antenna elements need to remain relatively independent to reduce interference and coupling.

With the advancement of communication technology, the miniaturization of MIMO antennas has become a key trend in modern communication system design. However, this trend of miniaturization results in reduced distances between antenna elements, increasing coupling between them.

As seen, many MIMO antenna designs require the use of a common ground, which is based on several considerations:

Reducing the Impact of Ground Waves:

In operation, MIMO antennas are affected not only by space waves but also by ground waves. If each antenna element uses a separate ground plane, complex reflections and diffraction may occur between the planes, which increases coupling and interference between antenna elements. Using a common ground plane helps mitigate the impact of ground waves by creating a unified ground potential, thus reducing interference between antenna elements.

Creating an Equal Potential Surface:

In MIMO antenna design, a common ground is typically used to connect the ground planes of individual antenna elements in order to construct an equal potential surface. This helps minimize potential differences between antenna elements, reducing interference and coupling further.

Practical Application Requirements:

In real-world applications, MIMO antennas are often installed in constrained spaces, such as in mobile phones or base stations. These devices have strict requirements for antenna size and layout. Shared grounding can make better use of available space, making MIMO antenna designs more compact and efficient.

Optimizing Antenna Performance:

By using a common ground, MIMO antennas can more easily achieve impedance matching, directional control, and polarization diversity. These functions help optimize antenna performance, improving communication quality and efficiency.

Decoupling Methods for MIMO Antennas:

In simple terms, to reduce coupling effects between MIMO antenna elements, decoupling strategies typically involve the following methods:

Diversity Techniques: By placing antenna elements orthogonally or designing special antenna structures, the isolation between elements can be significantly increased.

Neutralization Line Technology: Metal lines are connected between antenna elements to introduce new current coupling paths. These new paths have currents that flow in the opposite direction to those in the original coupling paths, neutralizing radiation fields and reducing mutual coupling.

Electromagnetic Bandgap (EBG) Structures: By arranging EBG structures between antenna elements in a specific pattern, a bandgap for electromagnetic waves is created, reducing coupling between antenna elements.

Defective Ground Structures: By etching slots or gaps corresponding to the decoupling frequency range on the ground plane, or extending current coupling paths, the coupling between antenna elements can be reduced.

Parasitic Branches: These are added as reflectors between radiating elements. They generate new current paths in the existing coupling paths, and the radiation fields produced by these paths cancel each other out, improving isolation between antenna elements.

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