IEC 61000-4-3: Radiated Immunity Testing

Radiated Immunity (RI) testing involves subjecting the electronic products to strong radiated electromagnetic (EM) fields. The idea behind the radiated immunity test is that your product will see various types of electric field disturbances in real-world usage. Real-world EM disturbance sources come from a wide range of sources, including cell phones, microwaves, computers, and motors to name a few. The RI test is intended to see how well your product performs when it’s subjected to an electric field of a specified amplitude (measured in volts/meter) across a range of frequencies. The product must continue to operate normally and cannot show any signs of susceptibility when subjected to these electromagnetic fields.

A typical Radiated Immunity test setup and the equipment involved during RI testing are shown in the figure below.

The following are the necessary test equipment to perform Radiated Immunity calibration and testing:

• Semi-anechoic chamber (SAC) (or GTEM-Cells according to IEC 61000-4-20)
• RF absorbers
• Signal generator(s) (depending on the test frequency range)
• Broadband RF amplifier(s) (depending on the required test levels and frequency range) 
• 3-channel RF Power meter
• Antenna(s) (depending on the frequency range and power levels) 
• Electric Field probe(s) (depending on the test frequency range) 
• Attenuators and RF Co-axial cables 
• Test Automation software

Before starting the actual RI test, the SAC/GTEM must be calibrated to ensure the uniformity of the field over the Equipment Under Test (EUT). IEC 61000-4-3 uses the concept of a Uniform Field Area (UFA, see below), which is a hypothetical vertical plane of the field in which field variations are very minimal.

The field calibration should be performed without an EUT inside the chamber.

The calibration should always be performed using an unmodulated carrier signal for both horizontal and vertical antenna polarizations. IEC 61000-4-3 recommends a test distance of 3 m (or at least at 1 m) between the antenna and the UFA. Also, the field probe sensor should be at least 1 m from the antenna tip. During the calibration process, the correlation between field within the UFA and forward power (FWD PWR) applied to the antenna is determined and recorded through test automation software.

There are two different calibration methods that can be used to achieve the same field uniformity:

1. Constant field strength calibration: Constant field strength used to establish the required forward power
2. Constant power calibration: Constant power used to establish the required forward power

In both methods, the uniform field should be recorded using a calibrated field probe sensor at each particular frequency and each of the 16-points one after the other using the step size not greater than 1% of preceding frequency value. The forward power required to establish the target field strength should be recorded for all the 16-points for both vertical and horizontal antenna polarization.

The calibration is valid as long as the test setup used for it remains unchanged for the actual testing, therefore the calibration setup (Sig gen, amplifier, attenuators, antenna, additional absorber, cables, etc.) shall be maintained in the same form and locations. Even small changes may significantly affect the target field inside the chamber.

Normally, the 16-point chamber calibration would take up to 2-3 days, assuming there will not be any technical issues such as chamber leaks, ground reflections, amplifier saturation, cable losses, and antenna spot-size to name a few. To save both time and money, HVT offers an automated Field Probe Positioner FSM2315 from INNCO which helps to automate the entire 16-point chamber calibration process with high accuracy and no test setup errors (without having to go in and out of the chamber for changing the field probe for every gridpoint position.) The Field Probe Positioner FSM2315 is designed according to IEC 61000-4-3. The automated system provides X and Y axis positions for both continuous and step by step movement for the filed probe from 0.8 m above the ground floor and also covers UFA of 1.5 m x 1.5 m.

After the calibration procedure, the 16 forward power/field strength readings are sorted into ascending order. Starting from the top, if at least 12 readings are within ±6 dB tolerance, then the maximum forward power level out of these readings is recorded. The recorded maximum forward level will be replayed during the actual testing to achieve the target field strength (V/m).

During the actual test, the EUT will be exposed to a uniform electric field. The EUT should be placed on a non-conductive test table at 0.8 m high from the ground plane/turntable. The target RF field is propagated in this way: Signal generator feeds a modulated sine wave to a broadband RF power amplifier. The output of the amplifier is connected to the transmitting antenna, which turns the varying conducted voltage into a varying radiated electric field. The field is usually amplitude modulated (AM) at 80% with a 1 kHz sine wave. For some test standards, the depth of modulation and frequency are different.

The transmitting antenna should be placed at a distance that sufficiently covers the UFA and the EUT. While testing, if the EUT is not fully illuminated or exposed to an antenna beam then multiple antenna positions shall be performed to expose/cover the entire EUT to verify its immunity. 

In a nutshell, immunity testing is just the application of some electromagnetic phenomena to verify your product immunity or susceptibility. So, you can think of it as the opposite of emissions testing (which we’ll cover in another post). Instead of measuring what’s coming from your product, immunity testing involves subjecting your product to EM field.

HV TECHNOLOGIES, Inc. knows how hard it is to get a product to market on time and within budget. Many of our customers tell us that EMC compliance testing can be a real bottleneck in their new product development process. Therefore, testing your products early in the cycle to make sure they are safe and compliant is just as important as designing them.

Historically, radiated immunity test equipment (chamber, amplifier, antenna, field probe, cables, etc.) selection was based mainly on knowledge and information from EMC industry experts. However, proper RI test equipment selection is an important step in achieving the required test levels (V/m). Considerations are numerous, but HVT’s selection of EMC test and measurement equipment have become industry standards and products of choice for achieving reliable and comprehensive solutions for radiated immunity as well as for all other EMC testing.

Radiated immunity test systems can be configured in many ways. HVT and its partners are specialized and have all the expertise in providing complete turnkey solutions with various flexible and easy-to-use configurations. HVT offers turn-key radiated immunity test systems through their European partner Frankonia that are fully compliant to test standards like IEC 61000-4-3, ISO 11452-2, DO-160 Section 20, MIL-STD-461 RS103, etc. The below pictures are some of the examples of recently completed turn-key RI test systems according to IEC 61000-4-3 and IEC 61000-4-20 EMC test requirements.

Frankonia’s one-rack turn-key test systems help to develop simple test setups and produce repeatable test results by eliminating guesswork, required many different test equipment, and possible test setup errors. If you would like to learn more, feel free to contact one of our sales managers at +1 (703) 365-2330 or emcsales@hvtechnologies.com.