Radiated emissions are unintentional emissions/noise generated by electronic devices. Radiated emissions can be caused due to factors like leakage currents from high voltage circuits, switching currents in digital circuits, arcing/sparking, antennas etc. Some of the other causes of radiated emissions include the allocation of multiple devices to the same frequency band or spectrum of operation, the use of miniaturized and compact electronic circuit designs, Insufficient reflection loss and absorption loss in the shielding or enclosure utilized or issues in the circuit design itself.

When it comes to signal propagation through cables, reflections can be minimized when the cable length is shorter than the signal wavelength at low frequencies. However, at high frequencies, successful propagation without reflections depends on maintaining impedance matching along the signal path. Real-world systems often utilize conductors that are not designed as transmission lines for high frequencies, behaving more like antennas and radiating signals as electromagnetic fields. This antenna-like behavior is precisely why radiated emissions become a significant concern in high-frequency scenarios.

For example, radiated emissions, occurring at high frequencies, significantly impact the EMI signature of a power converter. The upper limit for the test frequency in radiated tests can reach 1GHz or even higher, depending on the specification. Performing radiated EMI measurements are essential for compliance testing. However, it can pose challenges and potentially create bottlenecks in the product development cycle.

EMC Standards for radiated emissions:

EMC standards and regulations define limits for radiated emissions to ensure that electronic devices and systems do not cause harmful interference to other devices and can coexist in the electromagnetic environment. These standards vary depending on the specific application and region, but there are some widely recognized international standards that provide guidelines for radiated emission limits. Here are a few examples:

FCC Part 15: The Federal Communications Commission (FCC) in the United States sets limits for radiated emissions from electronic devices under Part 15 of its regulations. These limits are specified for different frequency ranges and depend on the class of the device.

CISPR 22: The International Special Committee on Radio Interference (CISPR) publishes CISPR 22, which sets limits and measurement methods for radiated emissions from information technology equipment (ITE). CISPR 22 is widely used as a reference standard in many countries.

EN 55032: The European Union's EMC directive sets requirements for radiated emissions in Europe. EN 55032 is the harmonized standard that specifies limits and measurement methods for radiated emissions from multimedia equipment.

Methods to reduce radiated emissions:

There are several methods to reduce radiated emissions, some of the important ones are as follows:

Shielding: Enclosing sensitive components or circuits within shielding materials can help contain and minimize the radiation of electromagnetic fields. This shielding can be achieved through metal enclosures, conductive coatings, or shielding fabrics.

EMI Filtering: Implementing filters in the circuitry can attenuate unwanted noise and harmonics, reducing the radiated emissions. Filters can be used to suppress specific frequencies or frequency ranges.

Proper Cabling and Wiring: Careful selection and routing of cables and wiring can minimize emissions. Using shielded cables and maintaining proper separation between signal and power lines can reduce electromagnetic coupling.

Grounding and Bonding: Proper grounding and bonding techniques can help reduce the propagation of unwanted electromagnetic fields. By providing a low-impedance path to the ground, excess energy can be safely dissipated, minimizing radiated emissions.

Layout and Component Placement: Thoughtful design of the circuit layout and placement of components can help minimize the loop area and optimize signal paths. This can reduce the antenna-like behavior of conductors and mitigate radiated emissions.

EMC Testing and Compliance: Conducting EMC testing during the development and certification process can help identify and address radiated emissions issues. Compliance with relevant EMC standards ensures that radiated emissions are within acceptable limits.

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