What To Ask When Selecting Antennas For EMC Testing

By John Oncea, Editor

Choosing the right antennas for EMC testing is crucial. Different antennas have different radiation patterns, frequency ranges, and polarization characteristics. Selecting antennas that accurately represent the intended operational environment of the DUT is essential for accurate testing results.

An EMC antenna is a set of specialized antennas that measure radiated emissions and radiated immunity during Electromagnetic Compatibility (EMC) testing to ensure that electronic devices don’t emit a large amount of electromagnetic interference (EMI). The antennas receive electromagnetic energy from the equipment under test (EUT) and produce data that can be compared to specified limit values thereby ensuring that a device can function properly in its intended electromagnetic environment without interfering with other devices or equipment nearby.

EMC testing also confirms that a device meets test standards such as IEC, MIL-STD, and DO-160. These EMC standards and norms define terms, rules, and test methods for EMC, according to the Academy of EMC. In addition, they specify limits and minimum test levels for electric and electromagnetic emissions and immunity of electromechanical and electronic products.

“EMC standards help to make measurements comparable and repeatable by defining the test methods, the test equipment, and the test environment,” writes the Academy of EMC. “And an important point about EMC standards: they have the purpose of bringing harmonization to EMC testing, in the best case: a global harmonization.”

EMC standards are established by international, national, or regional organizations and committees authorized by administrative entities. For instance, the EU delegates the wording of EMC standards to CENELEC. Alternatively, administrative and regulatory bodies may also create EMC standards and regulations themselves.

​You May Ask Yourself …

Antennas play a crucial role in both transmitting and receiving electromagnetic signals, converting electrical signals into electromagnetic waves (transmitting) or vice versa (receiving). Antennas are used in various applications, such as communication systems (like radio, TV, and wireless networks), radar systems, satellite communication, and more.

EMC testing, on the other hand, refers to the process of evaluating and ensuring that electronic devices and systems can function properly in their intended electromagnetic environment without causing interference to other devices or being susceptible to interference from external sources. When it comes to EMC testing, antennas are used in various ways to simulate real-world scenarios and to measure electromagnetic emissions and susceptibility.

There’s a lot to consider when selecting an emissions antenna for EMC testing, notes In Compliance. What is the frequency range you need to cover? What type of antenna is required by the test standard? Does the antenna need to illuminate the test area?

Consideration also has to be given to whether the antenna needs to produce an RF field and if it needs to sit at a distance from the test. Don’t forget to ask yourself if it needs to handle an input signal from a high-power amplifier source, as well as what the parameters listed in antenna specifications are and how to interpret them.

When selecting an antenna for EMC testing, you can consider factors such as:

• Antenna length: Ideally, the antenna length should be equal to the wavelength of the signal. However, an antenna that is 1⁄2 or 1⁄4 of the wavelength also will produce good results.
• Antenna type: Some common antenna types for short-range devices include PCB, chip, and wire antennas. Biconical antennas are often used to measure radiated emissions. Horn antennas are directional and can pick up weak signals, making them a good choice for both immunity and emission testing.
• Power handling: For most applications, an antenna that can handle 5-10 watts is sufficient.
• Voltage Standing Wave Ratio (VSWR): This measurement indicates how well the antenna matches the impedance of 50 Ohms. A value closest to 1 is best.
• Measured field strength: This is the electric field strength produced by a given input power. This information is useful for determining amp/antenna combinations.
• Frequency range: The antenna must cover a specific frequency range.

Other factors to consider include Antenna factor, Polarization, and Antenna gain.

Some Solutions And Approaches To Consider

As noted, antennas are used in various ways to simulate real-world scenarios and to measure electromagnetic emissions and susceptibility when it comes to EMC testing. Some solutions and approaches involving antennas in EMC testing include:

• Radiated Emissions Testing: In this type of testing, antennas are used to measure the electromagnetic radiation emitted by electronic devices. The DUT is placed within an anechoic chamber or an open-area test site. The emissions are then measured using specialized antennas designed for specific frequency ranges. These antennas are placed at defined distances and orientations relative to the DUT to measure radiated emissions.
• Radiated Susceptibility Testing: This involves subjecting the DUT to electromagnetic fields to see if it can operate without any issues. The DUT is exposed to controlled electromagnetic fields generated by antennas. The antennas used in this case are designed to generate specific field strengths and frequencies. The DUT's performance is then evaluated to determine if it's susceptible to electromagnetic interference.
• Transient Emission and Susceptibility Testing: Antennas also can be used to inject transient signals (such as fast electrical pulses) into a DUT to assess its susceptibility to such disturbances or to measure its emissions during transient events.
• Conducted Emissions and Susceptibility Testing: While conducted emissions and susceptibility primarily involve direct electrical connections, antennas can still play a role in capturing radiated emissions generated by conducted signals in cables and wires.
• Near-Field Scanning: Near-field scanning involves moving a specialized antenna near the DUT to map out its electromagnetic field distribution. This can provide insights into potential EMC issues and aid in optimizing the design to mitigate these issues.
• EMC Chamber Design: In anechoic chambers used for EMC testing, the layout and arrangement of absorber materials and antennas are designed to create a controlled environment with minimal external interference, ensuring accurate measurements.

Choosing the right antennas for EMC testing is crucial as they help simulate real-world scenarios and measure electromagnetic emissions and susceptibilities. Different antennas have different radiation patterns, frequency ranges, and polarization characteristics. Selecting antennas that accurately represent the intended operational environment of the DUT is essential for accurate testing results.

Accurate testing requires careful selection and calibration of antennas, proper chamber design, and adherence to established testing standards to ensure the reliability and compliance of electronic devices in their electromagnetic environments.