EMC Basics: What is Radiated Emissions & Immunity Testing?

Blog Post created by nickben Employee on Jul 20, 2018

After reading my last blog you’ve been given a brief intro on What are EMC & EMI Measurements and why it is important to measure for to ensure your device is pre-compliant.


In this blog we’ll discuss 2 of the 4 EMC pre-compliance tests – radiated tests, emissions and immunity – in more detail.


Radiated Testing

Radiated tests, as mentioned in the previous EMC basics blog, entail characterizing unintentional electromagnetic energy release from an electronic device. Radiated tests are the most common EMC test done around the world.


Many regulatory bodies across the globe set emission limit standards that all electronic products must meet. Looking at Figure 1 below we see a setup that is commonly seen at a test house, where your product will eventually have to acquire certification from. Your product is placed in a semi-anechoic chamber with an antenna directed at it to capture any phenomena radiating from the device.


However, before even sending your device to a test house, it’s important to first do pre-compliance tests of your own. This will not only save you money, but also avoid throwing off your schedule if your device fails at a test house and redesign work is needed. Before we get into how the tests are made, let’s get a better idea of the different kind of radiated tests.


Figure 1: Semi-Anechoic chamber where an EMC/EMI test is being conducted with dual antennas. The material of the chamber does not allow signals to leave or enter the room to ensure accurate measurements are made.


Radiated Testing - Emissions

Radiated emissions testing can be a bit more complicated than say, conducted emissions testing. This is because radiated tests entail through the air testing, which adds some complexity in how we can accurately measure emissions from a device (Figure 2). The complexity is attributed to the ambient environment, which can interfere with your device under test’s (DUT’s) emissions measurement. So, as part of emissions test, it is important to be able to identify what signals are coming from your device versus the ones coming from the environment. The topic of conflicting ambient signals will be discussed in more detail in a later blog.


When testing for radiated emissions, your intention is to determine the electromagnetic energy strength of the emissions that are being output by your device. Most devices usually have some sort of emission, but it is a question of whether those emissions from your device are compliant with the standards set by the regulatory body of your respective region. Pre-compliance testing is done to answer this very question.


Figure 2: An example of what emissions and immunity testing entail.


Radiated Testing – Immunity

Radiated tests for immunity entail testing the susceptibility of your device to emissions from other surrounding devices (Figure 2). Let’s say you work in a company that designs and manufactures phones. At some point you must determine what these phones’ susceptibility are to the emissions that, let’s say, a nearby laptop may have. Immunity is important to test for because you do not want your device to be accidentally influenced by a neighboring device.



Now that you have a better understanding of the types of radiated tests that exist and what they are, knowing how to test for them is the next step. Furthermore, let’s not forget that radiated tests only give you half of the story of EMC pre-compliance testing, as you should also have a good grasp on what conducted tests are – radiated and immunity. This will be discussed in a later blog here on the RF Test blog.


For an even more expansive and detailed look into EMC tests, check out the Making Conducted and Radiated Emissions Measurements for more information. Finally, if you enjoyed the blog make sure to give it a like, comment or share! Thanks for reading, and I look forward to seeing you in the next one.