Compact and low mutual coupling 4 × 4 wideband MIMO antenna design for 5G millimeter-wave applications

Why this tiny hardware matters for your phone

As our phones and connected gadgets stream ever more video, games, and sensor data, today’s wireless networks are being pushed to their limits. Fifth‑generation (5G) systems promise multi‑gigabit speeds by using millimeter‑wave signals, but this only works if we can squeeze many efficient, cooperating antennas into a very small space—like the corner of a smartphone—without them interfering with each other. This paper reports a compact antenna design that does exactly that, opening the door to slimmer devices that still enjoy ultra‑fast, reliable 5G links.

Building blocks for faster wireless links

The authors focus on a technology called multiple‑input multiple‑output (MIMO), where several antennas transmit and receive in parallel to boost data rates and reliability. At 5G millimeter‑wave frequencies around 24–32 GHz, wavelengths are only a few millimeters long, so many antennas can, in principle, fit inside a phone. The catch is that when antennas sit too close together they “talk” to each other instead of the network, wasting power and muddying the signal. The team set out to create a four‑antenna module that is small enough for handheld devices yet keeps this unwanted interaction extremely low across a broad slice of the 5G spectrum.

Shaping the antenna for wideband performance

The design starts from a single tiny metal patch on a flat circuit board. Through step‑by‑step refinements, the researchers turn this into a wideband radiator. They carve a Greek cross–shaped slot into the patch and add rounded edges, while cutting a carefully sized quadrilateral opening in the metal layer on the board’s underside. These features lengthen and redistribute the electric currents in ways that let the antenna operate efficiently from 24 to 32 GHz rather than at a narrow single frequency. Tests of this one element show a peak gain of about 6 dBi—respectable for such a compact part—and high radiation efficiency, meaning most of the power fed into it is actually radiated into space.

Arranging four antennas without crosstalk

To build the full module, four of these elements are placed on a board only 40 by 40 millimeters in size, roughly the footprint of a small watch face. Crucially, the elements are arranged at right angles to one another, so their preferred directions of radiation and current flow differ. This simple geometric trick dramatically reduces the tendency of one antenna to pick up energy from its neighbors. Simulations and measurements show that signals leaking between ports are about 25 to 30 decibels weaker than the intended signals—far better isolation than many earlier designs, and achieved without extra “decoupling” structures that add bulk and loss. Across the band, the array maintains strong, well‑shaped beams pointing away from the phone, suitable for linking to 5G base stations.

Proving reliability, capacity, and safety

Beyond raw gain and isolation, the team evaluates a suite of MIMO quality indicators that translate more directly into user experience. They find that the antennas’ signals are essentially uncorrelated, which maximizes the independent data streams that can be sent—a key to higher throughput. Diversity gain values are close to the theoretical ideal, and estimated channel capacity remains high over the operating band, indicating robust performance even in environments with reflections and fading. Importantly for handheld use, the authors also model how much of the radiated energy would be absorbed by a nearby human hand. The specific absorption rate stays below international safety limits, suggesting that the design can deliver high data rates without overheating tissue.

What this means for everyday devices

In plain terms, the work demonstrates that it is possible to pack four powerful millimeter‑wave antennas into a space small enough for a smartphone or wearable, while keeping them from interfering with each other and while staying within safety guidelines. The carefully shaped cross‑slot elements and their orthogonal layout together provide wide frequency coverage, strong isolation, and efficient radiation. If adopted in commercial products, such antenna modules could help future phones, vehicles, and Internet‑of‑Things gadgets maintain stable multi‑gigabit 5G connections in crowded cities and indoors, bringing the promised high‑speed, low‑latency wireless experience closer to everyday reality.

Citation: Edries, M., Mohamed, H.A., Elsheakh, D.N. et al. Compact and low mutual coupling 4 × 4 wideband MIMO antenna design for 5G millimeter-wave applications. Sci Rep 16, 9804 (2026). https://doi.org/10.1038/s41598-026-39770-3

Keywords: 5G millimeter wave, MIMO antenna, smartphone antennas, wireless capacity, compact antenna design