Lesson 5/1050%
MODULE 05 — STANDARDS

Frequency Ranges & RE Standards

This is the most reference-heavy lesson in the course: which frequency range maps to which standard and antenna, which of the nine major RE standards applies to your product category, how each emission source actually radiates energy, and what real limit lines, test setups, and lab equipment look like. Use it as a lookup reference throughout the rest of the course.

Each frequency band used in RE testing is associated with a typical governing standard and a specific antenna type best suited to measuring it. The chart below visualizes the same data as the table so you can see the bands span the spectrum without gaps.

Frequency Range Typical Standard Antenna
9 kHz – 30 MHz CISPR Loop
30 MHz – 300 MHz CISPR 32 Biconical
300 MHz – 1 GHz CISPR Log Periodic
1 GHz – 6 GHz FCC Horn
6 GHz – 18 GHz Automotive Horn
18 GHz – 40 GHz Radar Horn
Frequency Band Coverage (log scale)

Real antennas used to cover these bands — note how antenna geometry scales with wavelength: longer elements for lower frequencies, compact horns for the microwave bands.

IEC loop antenna diagram used for 9 kHz to 30 MHz radiated emission measurements
Loop Antenna (9 kHz–30 MHz) Shielded loop, sensitive to the magnetic field component — used for low-frequency RE per CISPR/IEC.
Wikimedia Commons
Rotatable log-periodic dipole array antenna used for 300 MHz to 1 GHz radiated emission testing
Log-Periodic Dipole Array (300 MHz–1 GHz) Wideband directional array — the standard antenna for the upper VHF / UHF CISPR 32 band.
Wikimedia Commons
Diagram of pyramidal, conical and sectoral horn antenna types used above 1 GHz
Horn Antenna (1 GHz–40 GHz) Compact, high-gain waveguide horn — used for microwave-band RE (automotive radar, 5G, aerospace).
Wikimedia Commons

Nine major standards cover the vast majority of commercial, industrial, medical, automotive, military, and aerospace products:

FCC Part 15

Region: USA

Consumer electronics, computers, IoT, wireless products.

CISPR 11

Applies to: Industrial, Scientific and Medical (ISM) equipment

Industrial heaters, medical RF devices, laboratory equipment.

CISPR 14

Applies to: Household appliances

Washing machines, refrigerators, vacuum cleaners.

CISPR 15

Applies to: Lighting equipment

LED drivers, street lights, ballasts.

CISPR 25

Applies to: Automotive

ECU, infotainment, Battery Management Systems, ADAS, radar, cameras.

CISPR 32

Applies to: Multimedia Equipment

Laptop, TV, printer, network switch, monitor.

IEC 60601-1-2

Applies to: Medical Devices

ECG, ventilator, MRI subsystem, ultrasound, patient monitors.

MIL-STD-461

Applies to: Military equipment

Radar, missile systems, naval electronics, tactical radios.

RTCA DO-160

Applies to: Avionics

Flight computers, cockpit displays, navigation equipment.

Reference tip: When in doubt about which standard applies, start from the product category (consumer, medical, automotive, military, avionics, industrial/ISM, household, lighting, or multimedia) rather than the frequency range — the category determines the standard, and the standard then specifies the frequency ranges and limits to test against.

Standards don't just define a frequency range — they define a limit line: the maximum field strength (in dBµV/m) allowed at each frequency. Here is a real, representative comparison of two widely used Class B (residential/light industrial) quasi-peak limit lines:

FCC Part 15 vs. CISPR 32 Class B — Radiated Emission Limits

Representative quasi-peak limit lines at their respective standard test distances (FCC: 3 m; CISPR 32 Class B: 10 m). Always confirm exact limits, distances, and detector requirements against the current published standard — these values are for teaching purposes only.

Every RE failure traces back to a physical mechanism: a changing current or voltage creating a time-varying field that couples onto a structure large enough to radiate efficiently. The animations below illustrate the three most common sources.

⏲ Digital Clocks & Harmonics

A square wave clock is not a single tone — by Fourier analysis it is a fundamental plus an infinite series of odd harmonics (3f, 5f, 7f…). Fast edges push energy into higher harmonics, and any trace, cable, or ground bounce that resonates near one of those harmonics becomes an unintentional antenna.

⚡ Switch-Mode Power Supplies

The transformer and switching node in an SMPS carry high dI/dt and dV/dt at the switching frequency and its harmonics. The loop formed by the primary switch, transformer, and return path radiates a pulsing magnetic field that a loop or biconical antenna will pick up directly.

🔌 Cables as Unintentional Antennas

Common-mode current on an I/O or power cable turns the entire cable length into a monopole-like radiator. Even a few microamps of common-mode current on a 1 m cable can produce field strengths that exceed Class B limits, because cable lengths are frequently a significant fraction of a wavelength at the harmonics of interest.

RE testing is performed in a controlled environment that removes reflections and ambient RF so the only signal measured is the one radiated by the Equipment Under Test (EUT).

Semi-anechoic chamber used for EMC radiated emission testing at Nemko, Norway, showing RF absorber cones lining the walls and ceiling
Semi-Anechoic Chamber (SAC) Absorber-lined walls/ceiling eliminate reflections; a conductive floor simulates the ground plane of an open area test site.
Wikimedia Commons
Modern real-time spectrum analyzer used as an EMI test receiver for radiated emission measurements
EMI Test Receiver / Spectrum Analyzer Sweeps the required frequency range with quasi-peak, peak, and average detectors to compare measured field strength against the limit line.
Wikimedia Commons

EUT Test Setup Diagram — the standard geometry used across CISPR/FCC radiated emission test methods:

EUT sits on a non-conductive turntable (rotated 0–360°) atop the ground plane; the receive antenna sweeps 1–4 m in height while the turntable rotates, to find the worst-case azimuth and antenna height for each frequency.

Typical Test Equipment

📡
EMI Receiver / Spectrum Analyzer

CISPR 16-1-1 compliant receiver with peak, quasi-peak, and average detectors.

📶
Loop, Biconical, LPDA & Horn Antennas

Cover 9 kHz–40 GHz in overlapping bands with calibrated antenna factors.

🔌
Low-Noise Preamplifier

Boosts weak signals above the receiver noise floor, especially above 1 GHz.

🔄
Turntable & Antenna Mast

Automated 0–360° rotation and 1–4 m antenna height scan to find worst case.

🏠
Semi-Anechoic Chamber / OATS

Absorber-lined chamber or open-area test site with a conductive ground plane.

📊
Site Validation / Calibration Kit

Reference antennas and site attenuation measurements used to qualify the test site.

KNOWLEDGE CHECK

Module 5 Quiz

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