What Are Microwave Frequencies?

Microwave frequencies are the portion of the electromagnetic spectrum spanning approximately 300 MHz to 300 GHz, corresponding to free-space wavelengths from one meter down to one millimeter. This range sits between conventional radio frequencies and the far-infrared band, inheriting some properties of both. The microwave region is home to a large share of the world's wireless infrastructure: point-to-point links, radar systems, satellite communications, and consumer technologies such as Wi-Fi and Bluetooth all operate within it. Engineers often further subdivide the range into the microwave proper (300 MHz to 30 GHz) and the millimeter-wave band (30 GHz to 300 GHz), the latter attracting growing interest for its wide available bandwidth.

The boundaries are not universally fixed. The ITU Radio Regulations define the range from 300 MHz to 300 GHz as "Super High Frequency" and "Extremely High Frequency" bands, while the FCC and IEEE use slightly different segment definitions depending on context. The OSHA overview of radiofrequency and microwave radiation places the boundary at 300 MHz on the low end and notes that practical microwave engineering concerns generally begin around 1 GHz, where wavelengths become short enough that lumped-circuit approximations break down and distributed transmission-line analysis becomes necessary.

Frequency Band Designations

The microwave spectrum is divided into letter-designated bands whose names were assigned by the military during World War II and subsequently formalized in IEEE Standard 521. L-band spans 1 to 2 GHz and is used in GPS receivers and long-range air-traffic-control radar. S-band (2 to 4 GHz) covers weather-surveillance radar and several 2.4 GHz Wi-Fi channels. C-band (4 to 8 GHz) hosts satellite video distribution and fixed-service terrestrial links. X-band (8 to 12 GHz) is widely used in shipborne and airborne radar as well as some satellite imaging. Ku-band (12 to 18 GHz) and Ka-band (26.5 to 40 GHz) carry the bulk of modern satellite broadband service. The millimeter-wave bands above 57 GHz are being allocated for short-range communication including the IEEE 802.11ad/ay Wi-Fi standards and 5G NR FR2 channels at 24 to 52 GHz. A concise summary of letter-band assignments and their primary services appears in the frequency band reference from everythingRF.

Propagation Characteristics

Microwave propagation differs from both lower-frequency radio waves and optical signals. Below roughly 10 GHz, atmospheric and rain attenuation are small enough that line-of-sight distances of tens of kilometers are practical for point-to-point links with modest antenna gain. Above 10 GHz, oxygen absorption produces a broad attenuation window near 60 GHz (roughly 15 dB/km) that is actually useful for unlicensed short-range links because it limits co-channel interference at distance. Water-vapor absorption near 22 GHz and oxygen absorption near 118 GHz create additional windows and peaks that system designers must account for in link budgets. Diffraction around terrain features is limited at microwave frequencies, so communication links are engineered for unobstructed paths with Fresnel-zone clearance criteria.

Spectrum Management and Allocation

The International Telecommunication Union (ITU) allocates microwave frequencies globally through the Radio Regulations, partitioning the spectrum among fixed, mobile, satellite, radiolocation, and other service categories. National regulators implement these allocations, assigning licenses or designating bands for unlicensed operation. The 5.8 GHz industrial, scientific, and medical (ISM) band and the 60 GHz band are among the unlicensed allocations that have enabled high-throughput consumer products. In the United States, the FCC's RF safety FAQ describes the safety exposure limits that apply to transmitters across the microwave spectrum, reflecting the thermal interaction mechanism that governs biological effects at these frequencies.

Applications

Microwave frequencies support a wide range of systems and services, including:

• Radar for weather, air traffic control, and maritime navigation
• Satellite communications and direct broadcast television
• Wi-Fi and Bluetooth short-range wireless networks
• Cellular telephony and 5G millimeter-wave broadband
• Microwave backhaul links connecting mobile base stations