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22.01.2019
| News
| Connectivity Testing
| IoT, laboratory, testing, safety, wireless

SAR and OTA: a difficult relationship

If you haven’t heard of SAR and OTA yet, chances are you won’t forget about them after reading this article. They have to do with that computer in your pocket you won’t stop looking at. OTA, or over-the-air, and SAR, specific absorption rate, are all about the signals and of radiation in your smartphone.

OTA EMC test

When you make a phone call, the battery, antenna, chips and other parts in your phone emit a certain amount of radiation. That’s an inevitable by-product of making your phone call technically possible.

At the same time, your phone should be built in such a way that it doesn’t emit too much radiation to make sure you can use your phone in a safe way. That’s where OTA and SAR play an important role.

Can you hear me?

Through OTA testing, you can check whether devices that are ready to be sold on the market meet the minimum radio frequency (or RF) performance operator requirements. The RF performance of your smartphone should be good enough to ensure your phone works well under most circumstances.

OTA testing consists of the measurement of the maximum transmission power of the device as well as its maximum sensitivity or, in other words, the minimum signal level that the device can receive and understand. The two combined allow the tester to assess the radiation pattern of the device for both the transmission and reception and see if it’s adequate in all possible directions using fake heads, hands and wrists to simulate real conditions.

All in an effort to make sure you can hear the person on the other side well.

OTA testing is not mandatory, at least not for European Conformity (CE) or the Federal Communications Commission (FCC), for example. However, most network operators will ask manufacturers to perform independent OTA testing.

So what’s that difficult relationship we were talking about earlier? There are two sides to this story; it’s great to have a powerful device that receives and transmits information well. However, with that comes radiation. And as mentioned earlier, radiation emitted by your smart device needs to stay within certain safe limits. That’s where specific absorption rate (SAR) testing comes in, which you could say does the opposite of OTA testing.

Sugar, salt and water

And in come the fake heads and bodies as well. SAR testing is done by using fake body parts composed of specific materials that simulate the dielectric properties of our body.

Basically, the conductivity and permittivity of the human body is mimicked with a liquid solution of, among others, sugar, salt, water and other ingredients. Different compositions of the solution are used for different frequencies, simulating, for example 1800 MHz, Wi-Fi or 5G.

What that looks like? See the image below for an idea.

You can imagine that if a device performs really well during an OTA test, this might not benefit its SAR rating. It’s up to the manufacturer to find the perfect balance. It’s good to note that SAR testing is always required, for CE and also by the FCC in the US, while OTA testing isn’t. For any other questions about SAR and OTA testing, feel free to reach out to one of our experts at www.dekra-product-safety.com/wireless

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