4.5 GHz Band
Understanding the 4.5 GHz Band (n79)
In the global race for 5G dominance, spectrum is the ultimate currency. While the majority of the world focused entirely on the 3.5 GHz C-Band, several massive telecom markets (like China and Japan) aggressively expanded their 5G footprint much higher into the spectrum, targeting the 4.5 GHz Band.
The Power of Band n79
In the 3GPP specifications, the massive block from 4.4 to 5.0 GHz is defined as Band n79.
- Because very few legacy technologies operate in this block, the band is virtually empty.
- This allows telecom operators like China Mobile to deploy massive 100 MHz or 200 MHz super-channels.
- When combined with 64T64R Massive MIMO active antennas, Band n79 acts as a massive "capacity umbrella" over dense urban environments, absorbing the massive data load of millions of 5G smartphones to prevent the lower 3.5 GHz band from collapsing.
The Physics of 6.6 Centimeters
At 4.5 GHz, the physical wavelength is roughly 6.6 centimeters. This sits dangerously close to the limits of mid-band physics.
| The Limitation | The Engineering Reality |
|---|---|
| Indoor Penetration | A 4.5 GHz wave struggles significantly to penetrate modern buildings. While it can pass through a single wooden wall, it is violently reflected by Low-E window glass and concrete, forcing carriers to rely on lower bands (like 700 MHz) for deep indoor coverage. |
| Foliage Attenuation | The 6.6 cm wavelength is the exact size of a mature tree leaf. During the summer, an oak tree will violently scatter and absorb a 4.5 GHz signal. Towers must be built below the canopy or placed in areas with clear line-of-sight to the street. |
Key Equations
The 4.5 GHz Band (encompassing the 4400 to 5000 MHz spectrum block) is an emerging upper mid-band frequency heavily targeted by Asian telecommunications operators (specifically...
Key specifications:
4.5 GHz | 5000 MHz | 3.5 GHz | 5.0 GHz
Power: P(dBm) = 10log(PmW), 0dBm = 1mW
Comparison
| Band | Range | Wavelength | Application | Standard |
|---|---|---|---|---|
| 4.5 GHz Band | 4.5 GHz region | 66.7 mm | Primary use | ITU allocation |
| Adjacent lower | 4.0 GHz | 74.1 mm | Related band | Shared spectrum |
| Adjacent upper | 5.0 GHz | 60.6 mm | Related band | Guard band |
| Harmonic 2f | 9.0 GHz | 33.3 mm | Spurious | Filter required |
| Sub-harmonic | 2.3 GHz | 133.3 mm | LO option | Mixer design |
Frequently Asked Questions
Is the 4.5 GHz band used in the United States?
For commercial 5G, no. The 4.4 to 4.9 GHz block in the US is strictly reserved for the military (Navy and Air Force) and highly specialized aeronautical telemetry (like tracking a test missile in flight). Because the military vehemently refuses to share this critical spectrum, US cellular carriers are forced to rely entirely on the 3.7 GHz C-Band instead.
Does my iPhone support Band n79?
Yes. Even though Band n79 is not used in the United States or Europe, companies like Apple and Samsung build universal world-phones. They include the necessary Band n79 RF filters in the hardware so that if an American travels to Tokyo or Beijing, their phone will seamlessly connect to the local high-speed 5G network.
Is this the same as 5 GHz Wi-Fi?
No. Standard 5 GHz Wi-Fi operates in the unlicensed 5.1 to 5.8 GHz range. The 4.5 GHz band sits strictly below the Wi-Fi frequencies and requires a multi-billion dollar government license to legally transmit.