When you hear about 5G’s revolutionary speed and capacity, you’re hearing about millimeter waves—a type of electromagnetic radiation that’s fundamentally different from anything previous wireless generations have used. Understanding these high-frequency waves is essential for grasping both what makes 5G special and what makes it controversial.
Let’s dive deep into the science of millimeter waves.
What Are Millimeter Waves?
The Basic Definition
Extremely high frequency (EHF) is the International Telecommunication Union (ITU) designation for the band in the electromagnetic spectrum from 30 to 300 gigahertz (GHz). Radio waves in this band have wavelengths from ten to one millimeter, so it is also called the millimeter band and radiation in this band is called millimeter waves, sometimes abbreviated MMW or mmWave Wikipedia.
However, some define mmWaves as starting at 24 GHz, thus covering the entire FR2 band (24.25 to 71 GHz) Wikipedia, which is the practical definition used in 5G technology.
The 5G Frequency Range
5G mmWave refers to the portion of the 5G spectrum that operates in the 24 GHz to 100 GHz frequency range. These frequencies are much higher than traditional cellular bands (which typically fall below 6 GHz) Techloy.
The millimeter wave band extends to 300 GHz, but 5G is expected to use the 24 GHz to 100 GHz band STL Tech.
To put this in perspective:
- 1G-4G: 300 MHz to 6 GHz
- WiFi: 2.4 GHz and 5 GHz
- 5G mmWave: 24 GHz to 100 GHz
That’s a jump of at least four times the highest frequency used in previous consumer wireless technology.
Why “Millimeter” Waves?
They are called millimeter waves, as their wavelength varies from 1 to 10mm. The millimeter wavelength is less than the tens of centimeter wavelengths of conventional radio frequency communications Cadence.
The relationship between frequency and wavelength is inversely proportional: higher frequencies mean shorter wavelengths. At 30 GHz, the wavelength is exactly 10 millimeters. At 100 GHz, it’s just 3 millimeters.
This tiny wavelength gives millimeter waves their unique properties—both advantageous and challenging.
Why Use Millimeter Waves for 5G?
The Bandwidth Advantage
The 5G spectrum utilizing millimeter-wave frequency bands starting at 24 GHz up to 100 GHz gives ultra high speed, increased traffic, high capacity, with more connected devices in the cellular network Cadence.
Millimeter-wave bands up to 100GHz can support bandwidths up to 2GHz without combining bands to improve data throughput STL Tech.
Think of frequency spectrum like real estate: lower frequencies are crowded with decades of radio, TV, cellular, and WiFi signals. Mobile data traffic is projected to rise 53% each year into the foreseeable future, and we need higher frequency spectrum to accommodate the increases in data usage RCR Wireless News.
The Capacity Solution
The high-frequency bands in the spectrum above 24 GHz were targeted as having the potential to support large bandwidths and high data rates, ideal for increasing the capacity of wireless networks Accton Technology.
5G mmWave can deliver data at speeds over 1 Gbps and latency under one millisecond, built to handle massive data throughput in places where demand is high—stadiums, dense city centers, airports, and factories Techloy.
The Unique Properties of Millimeter Waves
1. Extremely Short Range
Due to the high frequency of millimeter waves, the range is limited to 300-500 feet, making it difficult to penetrate buildings. In contrast, 3G and 4G networks can move further and penetrate better into building materials STL Tech.
A single mmWave transceiver isn’t likely to provide solid coverage for anything much larger than a city block Digital Trends.
Why? As frequency increases, signals lose strength more rapidly with distance—a phenomenon called “path loss.”
2. Line-of-Sight Propagation
Millimeter waves propagate solely by line-of-sight paths. They are not refracted by the ionosphere nor do they travel along the Earth as ground waves as lower frequency radio waves do Wikipedia.
This means:
- They travel in straight lines
- They can’t bend around obstacles
- They don’t bounce off the atmosphere
- They require clear paths between transmitter and receiver
3. Easily Blocked by Objects
At typical power densities they are blocked by building walls and suffer significant attenuation passing through foliage Wikipedia.
These signals travel only short distances and are easily blocked by walls, windows, and vegetation, so FR2 is mainly used in dense urban areas such as stadiums and city centers Wikipedia.
Even your hand can block a millimeter wave signal!
4. Atmospheric Absorption
Absorption by atmospheric gases is a significant factor throughout the band and increases with frequency. However, this absorption is maximum at a few specific absorption lines, mainly those of oxygen at 60 GHz and water vapor at 24 GHz and 184 GHz Wikipedia.
When it rains, the millimeter-wave signal strength drops slightly, first at a slightly slower speed, and then connection problems can occur. How bad it gets depends on how hard it rains and other factors, such as the distance from the cell tower STL Tech.
How Millimeter Waves Interact with the Human Body
This is where things get particularly important from a health perspective.
Shallow Penetration Depth
Millimeter waves penetrate into the human skin deep enough (delta = 0.65 mm at 42 GHz) to affect most skin structures located in the epidermis and dermis PubMed.
The penetration depth at 30 GHz is approximately 1 mm, decreasing to about 0.3 mm at 100 GHz. At the dermis layer of the skin, penetration depth decreases from 8.1 mm at 6 GHz to 0.92 mm at 30 GHz MDPI.
To put this in context:
- 4G (2 GHz): Penetrates several centimeters into the body
- 5G mmWave (30 GHz): Penetrates less than 1 millimeter—barely past the skin surface
- 5G mmWave (100 GHz): Penetrates only 0.3 millimeters—just the outermost skin layers
Surface Absorption
Ninety to ninety-five percent of the incident energy may be absorbed in the skin. On account of the submillimeter depths of penetration in the skin, superficial SAR’s as high as 65-357 W/Kg have been calculated for power density of incident radiation IEEE Xplore.
At mmWave frequencies (approximately 60 GHz), approximately 30-40% of incident electromagnetic wave power is reflected from the skin surface under normal incidence. Of the remaining transmitted power, a large fraction is absorbed in the epidermis and dermis, with penetration depths typically in the sub-millimeter range RF Page.
The Primary Target: Skin
The primary biological targets of 60-GHz radiations are the skin and eyes Cambridge Core.
Millimeter waves are absorbed by the skin’s surface and do not penetrate deeply, which minimizes potential risks to internal organs but concentrates energy in surface tissues Hualianxingtong.
Thermal Effects
Shallow penetration depth of 60-GHz radiations in the skin (typically 0.5 mm) results in SAR levels that are significantly higher than those obtained at microwaves for identical power density values. This may lead to significant heating, even for low-power exposures Cambridge Core.
Because most of the millimeter-wave absorption is in the region of the cutaneous thermal receptors (0.1 – 1.0 mm), the sensations of absorbed energy are likely to be similar to those of infrared radiation IEEE Xplore.
The Infrastructure Challenge
Small Cell Density
It is projected that outdoor cell sizes will be typically 100m to 200m and indoor high-density deployments might be as small as 10m Accton Technology.
Compare this to 4G towers that can cover several kilometers!
Massive MIMO Technology
Great advancements have been made in RF silicon that allow a large number of RF chains to be supported in large antenna arrays. The computational and switching capacity available enables “massive multiple-input-multiple-output (massive MIMO)” antennas to create highly directional beams that focus transmitted energy in ways that can overcome path losses Accton Technology.
A fundamental characteristic of mmWave, the short wavelengths, means that even massive MIMO antennas can be relatively compact and small effective antennas can be easily integrated into user devices. Whereas MIMO antennas for under 6 GHz wireless may support eight elements, at mmWave frequencies the number can be much larger Accton Technology.
The Three Tiers of 5G Spectrum
Understanding where millimeter waves fit in the overall 5G picture:
Low-Band (Below 1 GHz)
Great for wide area coverage and indoor penetration, providing nationwide connectivity with coverage similar to 4G Telecom Trainer
Mid-Band (1-6 GHz)
Strikes a balance between coverage and speed, making them suitable for urban and suburban areas—the “sweet spot” of 5G SoftHandTech
High-Band / mmWave (24-100 GHz)
Provides ultra-fast data speeds over short distances, ideal for dense urban environments and high-capacity applications SoftHandTech
Millimeter waves deliver the largest available spectrum for 5G, with speeds surpassing 10 Gbps and latencies under 1 millisecond. But due to its limited range, it’s best used in localized settings Telecom Trainer.
Where You’ll Find mmWave 5G
In the U.S., Verizon has already deployed more than 40,000 mmWave cell sites in dense urban areas to handle high demand. While most smartphones and carriers still rely on sub-6 GHz 5G for everyday use, mmWave is slowly finding its niche where speed and responsiveness are mission-critical Techloy.
Typical deployment locations:
- Stadiums and arenas: Handling thousands of simultaneous connections
- Urban centers: Supporting high-density usage
- Airports: Managing passenger and operational traffic
- Convention centers: Supporting business connectivity
- Smart factories: Enabling industrial IoT applications
- Fixed wireless access: Providing home internet in urban areas
Previous Uses of Millimeter Waves
Until recently, millimeter waves were used only in satellite and radar systems and were typically operated in the military and aerospace industries STL Tech.
Usually, you’ll find the EHF spectrum used by satellite weather systems, military weapons radar, police speed radar, and security screening systems at airport checkpoints Digital Trends.
With Raytheon, the U.S. Air Force has developed a nonlethal antipersonnel weapon system called Active Denial System (ADS) which emits a beam of millimeter radio waves. The weapon causes a person in the beam to feel an intense burning pain, as if their skin is going to catch fire Wikipedia.
Safety Standards and Millimeter Waves
International organizations like the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the World Health Organization (WHO) have set safety guidelines for EMF exposure. These guidelines ensure that 5G emissions fall within acceptable levels Hualianxingtong.
As long as 5G follows national guidelines for exposure, 5G has no significant impact on the human body according to regulatory standards. Device manufacturers and service providers make sure their products and services meet all regulations and guidelines RF Page.
However, the biological effects of RF radiation over a long period of time on the human body at different frequency ranges have never been fully studied, particularly at millimeter wave frequencies RF Page.
The Research Gap
The current scientific evidence regarding mmWaves’ effects on the skin and skin cells is limited to approximately 99 studies. This indicates a significant gap in our understanding, making it challenging to establish evidence-based exposure limits MDPI.
Advantages and Disadvantages Summary
Advantages:
- Enormous bandwidth: Supports multi-gigabit speeds
- Low latency: Response times under 1 millisecond
- Spectrum availability: Vast, underutilized frequency space
- Small antennas: Short wavelengths allow compact designs
- Reduced interference: Short range limits cross-cell interference
- Shallow penetration: Doesn’t reach deep into the body
Disadvantages:
- Very short range: 300-500 feet maximum
- Line-of-sight required: Easily blocked by obstacles
- Weather sensitive: Rain and humidity cause attenuation
- Building penetration: Cannot pass through walls effectively
- Dense infrastructure needed: Requires many small cells
- High deployment cost: Expensive to build out
- Concentrated skin absorption: Higher surface SAR values
The Bottom Line
Millimeter waves represent a radical departure from traditional cellular technology. Their extreme frequencies give 5G its revolutionary speed and capacity, but also create unique challenges and exposure patterns.
Key takeaways:
- They’re much higher frequency than any previous consumer wireless technology (24-100 GHz vs. <6 GHz)
- They have tiny wavelengths measured in millimeters, giving them unique propagation characteristics
- They can’t travel far and are easily blocked, requiring dense networks of small cells
- They’re absorbed at the skin surface with penetration depths of less than 1 millimeter
- They require new technologies like massive MIMO and beamforming to be practical
- They’re best suited for hotspots rather than wide-area coverage
- Research on long-term health effects is limited, particularly for chronic, low-level exposure scenarios
Understanding millimeter waves helps demystify both 5G’s incredible capabilities and the legitimate questions about this new technology. As with any emerging technology, informed awareness beats both blind enthusiasm and unfounded fear.
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Disclaimer: This article provides educational information about millimeter wave technology. It should not replace professional health, safety, or technical advice. Consult qualified experts for specific concerns.
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