What Are Millimeter Wavebands?

Millimeter wavebands are the segments of the electromagnetic spectrum spanning frequencies from 30 GHz to 300 GHz, corresponding to free-space wavelengths of ten millimeters down to one millimeter. The ITU designates this range as the Extremely High Frequency (EHF) band, and within it, engineers and spectrum regulators have identified a set of sub-bands differentiated by their propagation characteristics, atmospheric absorption windows, and allocated services. These sub-bands provide the radio spectrum supporting millimeter wave radar, short-range wireless links, satellite communications, and emerging 5G and beyond-5G cellular access.

The characteristics that define each waveband within this range are shaped by atmospheric physics. Absorption peaks from oxygen and water vapor divide the 30 to 300 GHz range into windows of low loss separated by zones of high attenuation, and these windows largely determine which frequencies are commercially and militarily useful.

Atmospheric Windows and Absorption Bands

The millimeter wave range contains several distinct propagation windows. Near 35 GHz (Ka-band lower edge), 77 GHz (W-band lower edge), and 94 GHz, attenuation from dry air and water vapor is relatively low, making these frequencies practical for long-range radar and satellite communication. An oxygen absorption peak near 60 GHz produces attenuation rates exceeding 15 dB per kilometer, making that region unsuitable for beyond-line-of-sight links but useful for short-range secure communications and unlicensed 60 GHz Wi-Fi, where the atmospheric loss provides inherent spatial isolation. The FCC millimeter wave spectrum management bulletin provides a detailed accounting of these absorption features and their implications for spectrum management, noting that the wide bandwidths available across these windows support high data-rate applications impractical at lower frequencies.

Designated Sub-Bands and Naming Conventions

The millimeter wave range overlaps with several IEEE radar letter-band designations. Ka-band covers 26.5 to 40 GHz, V-band covers 40 to 75 GHz, W-band spans 75 to 110 GHz, and the G, Y, and J sub-millimeter bands extend beyond. The ITU Radiocommunication Sector further divides the spectrum through the Radio Regulations, allocating specific windows to fixed, mobile, satellite, and radio astronomy services. The bands around 26 GHz, 28 GHz, 38 GHz, 39 GHz, and 66 to 71 GHz have been identified internationally as candidates for IMT-2020 (5G) deployments, as described in ITU-D documentation on future millimeter wave use for 5G. National regulators, including the FCC in the United States and Ofcom in the United Kingdom, have licensed spectrum in these bands for commercial mobile broadband.

Channel and Link Budget Characteristics

Each millimeter waveband carries distinct path loss and multipath characteristics that must be accounted for in link budget calculations. Compared to sub-6 GHz bands, path loss at millimeter wave frequencies is higher per unit distance, rain attenuation becomes a significant margin consumer above 10 GHz, and building penetration is severely reduced. Antenna gains achievable with physically small apertures compensate partly for path loss, and beamforming with large antenna arrays is standard practice. Capacity studies that modeled urban millimeter wave channel measurements at 28 and 38 GHz, such as millimeter wave channel modeling and cellular capacity evaluation, showed that spatial multiplexing combined with densely deployed small cells can yield per-user throughput far exceeding that of legacy cellular networks, provided sufficient scattering exists to sustain multiple spatial streams.

Applications

Millimeter wavebands have applications in a wide range of fields, including:

• 5G and beyond-5G dense urban small-cell networks
• Fixed wireless access for last-mile broadband delivery
• Automotive radar at 77 GHz for safety and autonomous driving
• Satellite communication feeder links and inter-satellite links
• Passive millimeter wave imaging for security and remote sensing
• Radio astronomy and atmospheric science observation