What frequency range is considered RF?

The RF spectrum spans from 3 kHz to 300 GHz, divided into bands by the ITU: VLF (3 to 30 kHz, submarine communication), LF (30 to 300 kHz, navigation beacons), MF (300 kHz to 3 MHz, AM radio), HF (3 to 30 MHz, shortwave), VHF (30 to 300 MHz, FM radio, TV), UHF (300 MHz to 3 GHz, cellular, GPS, WiFi 2.4 GHz), SHF (3 to 30 GHz, satellite, radar, WiFi 5/6 GHz, 5G sub-6), and EHF (30 to 300 GHz, 5G mmWave, automotive radar, radio astronomy). The term microwave generally covers 300 MHz to 300 GHz, and millimeter wave covers 30 to 300 GHz where wavelengths are 1 to 10 mm.

What are the fundamental RF equations?

Wavelength-frequency: lambda = c/f, where c = 2.998 times 10 to the 8 m/s. At 1 GHz: lambda = 30 cm. At 28 GHz: lambda = 10.7 mm. Free-space path loss: FSPL(dB) = 32.4 plus 20 log(f in MHz) plus 20 log(d in km). Link budget: P_received = P_TX plus G_TX minus L_TX minus FSPL plus G_RX minus L_RX. Friis transmission: P_r/P_t = G_t times G_r times (lambda/(4 pi d))^2. Noise floor: N = kTB = minus 174 plus 10 log(BW in Hz) dBm. These equations form the foundation of all RF system design.

Why is RF engineering important?

RF engineering enables all wireless technology: cellular networks serving 5 billion subscribers, WiFi connecting 18 billion devices, GPS navigation, satellite communications, automotive radar, medical imaging (MRI), industrial heating, and scientific research (radio astronomy, particle accelerators). The global wireless infrastructure market exceeds 200 billion dollars annually. RF engineers design the components (antennas, amplifiers, filters, mixers, oscillators) and systems (transceivers, radar, satellite payloads) that make wireless communication possible. As spectrum becomes increasingly congested and new applications demand higher data rates, the importance of RF engineering only grows.

Electromagnetic Spectrum

Radio Frequency

/ray-dee-oh free-kwen-see/ — RF

EM waves from 3 kHz to 300 GHz. λ = c/f (1 GHz = 30 cm, 28 GHz = 10.7 mm). Bands: VHF (30-300 MHz, FM/TV), UHF (300 MHz-3 GHz, cellular/WiFi/GPS), SHF (3-30 GHz, satellite/radar/5G), EHF (30-300 GHz, mmWave). Governed by Maxwell's equations. Noise floor: −174 + 10log(BW) dBm/Hz. FSPL = 32.4 + 20log(f) + 20log(d). 5B+ cellular subscribers, 18B+ WiFi devices worldwide.

Range: 3 kHz-300 GHz

c: 3×10⁸ m/s

λ = c/f

Understanding RF

Radio frequency is the foundation of wireless communication. From the first spark-gap transmitters of the late 1800s to today's 5G millimeter-wave phased arrays, RF engineering has enabled humanity to communicate without wires across rooms, cities, continents, and even interplanetary distances. Every wireless device, from a Bluetooth earphone to a deep-space probe, operates on the same electromagnetic principles described by Maxwell's equations.

RF engineering sits at the intersection of physics, electrical engineering, and materials science. It requires understanding of electromagnetic wave propagation, circuit design at high frequencies where wavelength effects dominate, antenna theory, signal processing, and the interaction of EM waves with materials and the environment. The discipline becomes increasingly challenging as frequencies rise into the millimeter-wave and sub-THz ranges.

Fundamental RF Equations

Wavelength-frequency:
λ = c/f = 3×10⁸/f (m)
1 GHz: 30 cm, 5 GHz: 6 cm
28 GHz: 10.7 mm, 77 GHz: 3.9 mm

Free-space path loss:
FSPL = 32.4 + 20log(f_MHz) + 20log(d_km)
2.4 GHz, 100 m: 80 dB
28 GHz, 100 m: 101 dB

Thermal noise floor:
N = kTB = −174 + 10log(BW) dBm
BW = 100 MHz: N = −94 dBm

Friis transmission:
P_r/P_t = G_tG_r(λ/4πd)²

RF Spectrum Band Allocation

Band	Frequency	Wavelength	Application	Example
VHF	30-300 MHz	1-10 m	Broadcast, aviation	FM radio, ATC
UHF	300 MHz-3 GHz	10-100 cm	Cellular, WiFi, GPS	LTE, 802.11
SHF	3-30 GHz	1-10 cm	Satellite, 5G, radar	5G NR, VSAT
EHF	30-300 GHz	1-10 mm	5G mmWave, radar	n258, auto radar
Sub-THz	100-1000 GHz	0.3-3 mm	6G research, imaging	D-band backhaul

Common Questions

Frequently Asked Questions

What frequency range?

3 kHz to 300 GHz (ITU). VLF (3-30 kHz): submarine. LF (30-300 kHz): navigation. MF (0.3-3 MHz): AM radio. HF (3-30 MHz): shortwave. VHF (30-300 MHz): FM/TV. UHF (0.3-3 GHz): cellular/WiFi/GPS. SHF (3-30 GHz): satellite/radar/5G. EHF (30-300 GHz): mmWave. "Microwave" = 300 MHz-300 GHz. "mmWave" = 30-300 GHz.

Fundamental equations?

λ=c/f (1 GHz=30 cm). FSPL=32.4+20logf+20logd. Friis: Pr/Pt=GtGr(λ/4πd)². Noise: N=kTB=−174+10log(BW). Link budget: P_RX = P_TX+G_TX−L_TX−FSPL+G_RX−L_RX. These equations form the foundation of all RF system design.

Why important?

Enables all wireless: 5B cellular subscribers, 18B WiFi devices, GPS, satellite, automotive radar, MRI, industrial heating. $200B+ wireless infrastructure market annually. RF engineers design antennas, amplifiers, filters, mixers, oscillators, and complete transceiver systems. Growing importance as spectrum becomes congested and 6G/sub-THz emerge.

Related Terms

← RFID S-Parameters →

RF Engineering

Request a Quote

Need RF system design, spectrum analysis, or wireless consultation? Contact our team.

Get in Touch