120.0 GHz Band
Understanding the 120.0 GHz Band
If you need to wirelessly transmit 100 Gigabits per second across a city street, you cannot use 5G. The sub-6 GHz bands don't have enough bandwidth, and the 28 GHz mmWave bands are too crowded. You must ascend into the Terahertz gap.
The 120 GHz Band provides a pristine, empty superhighway for data.
The Physics of the 2.5mm Wave
Because the wavelength is 2.5 millimeters, the physical properties of the RF signal change drastically compared to lower frequencies.
- Extreme Free-Space Path Loss (FSPL): Even in a pure vacuum, the 120 GHz signal spreads out and weakens incredibly fast.
- Atmospheric Attenuation: In addition to FSPL, the signal is physically absorbed by water vapor and oxygen molecules in the air. A 120 GHz link is practically limited to distances of less than 1 kilometer (roughly 3,000 feet).
- Zero Penetration: A 120 GHz wave cannot penetrate a piece of paper, let alone a brick wall or a window. It is strictly a Line-of-Sight (LOS) technology. If a pigeon flies through the beam, the link will drop.
The Massive Antenna Gain Advantage
The saving grace of 120 GHz is the physics of antenna gain. The gain of a dish antenna is directly proportional to how many wavelengths can fit across its surface.
A standard 1-foot (30 cm) dish at 5 GHz provides a weak 15 dBi of gain. However, because the 120 GHz wavelength is so microscopic, that exact same 1-foot dish provides an unbelievable 45+ dBi of gain. The dish focuses the 120 GHz energy into an ultra-intense, pencil-thin laser beam, allowing it to punch through the atmospheric attenuation and establish a link.
Hardware Challenges
You cannot generate 120 GHz using standard silicon CMOS transistors; they simply cannot switch fast enough. To build a 120 GHz radio, engineers must use exotic semiconductor compounds like Indium Phosphide (InP) or Silicon Germanium (SiGe). Furthermore, coaxial cables are physically impossible at this frequency; the entire internal radio architecture must be routed using microscopic gold-plated waveguides.
Key Equations
The 120.0 GHz Band represents the bleeding edge of the D-Band (110 GHz to 170 GHz) sub-millimeter wave spectrum. Operating at a microscopic wavelength of...
Key specifications:
120.0 GHz | 110 GHz | 170 GHz | 2.5 m | 120 GHz | 100 Gbps
Power: P(dBm) = 10log(PmW), 0dBm = 1mW
Comparison
| Band | Range | Wavelength | Application | Standard |
|---|---|---|---|---|
| 120.0 GHz Band | 120 GHz region | 2.5 mm | Primary use | ITU allocation |
| Adjacent lower | 108.0 GHz | 2.8 mm | Related band | Shared spectrum |
| Adjacent upper | 132.0 GHz | 2.3 mm | Related band | Guard band |
| Harmonic 2f | 240.0 GHz | 1.3 mm | Spurious | Filter required |
| Sub-harmonic | 60.0 GHz | 5.0 mm | LO option | Mixer design |
Frequently Asked Questions
Is 120 GHz considered Terahertz (THz)?
Technically, Terahertz begins at 300 GHz (0.3 THz). However, the industry loosely refers to anything above 100 GHz as the 'sub-Terahertz' or 'Terahertz Gap' region, because the engineering techniques required to operate here are completely different from traditional microwave engineering.
Could 120 GHz be used for Wi-Fi?
Yes, but strictly for 'in-room' applications. The IEEE 802.15.3d standard was developed to push 100 Gbps speeds using the lower THz bands. It would be used for wireless server racks in a data center, or instantaneous wireless VR headset connections, but the signal would never leave the room.
How do you align a 120 GHz dish?
With excruciating difficulty. Because the antenna gain is so high, the physical beam is less than 0.5 degrees wide. If the tower sways in the wind by a fraction of a degree, the beam will miss the receiving dish entirely. Engineers are forced to use motorized, auto-tracking gimbals to keep the dishes perfectly aligned in real-time.