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DEVICES
ISSUE 03 2014
SAR regulations and requirements vary from country to country, but generally limit the amount of absorption in a ‘head phantom’ test set-up
costly. But that’s the same now as it has been for 2G and 3G devices. Taoglas has a range of antenna designs that can work for pretty much every position on the board; we’ve spent years of research in this area.
Explain LTE device antenna testing for performance and quality? EMSS: With the growth in complexity of design and integration aspects we have seen an increase in use of simulation from concept prototype stage, right through to compliance estimation studies.
Taoglas: In terms of LTE device antennas, there’s testing of the device – the superset - and then there’s testing the antenna – a subset of these tests. The way you test the antenna is to do passive mode efficiency testing. You passively test such things as the efficiency and radiation pattern, and polarisation. We do these tests in our CTIA-approved anechoic chamber in one of three antenna design locations globally, depending on where the customer is. We do passive antenna testing in situ in the device. We are not testing the radio, we are testing the antenna, but we are testing it in the enclosure with battery and display and exactly how the product would be used. The way to test the device is you do a TRP test; antenna performance is reflected by TRP.
Has the industry largely sidelined SAR issues in recent years in relation to latest devices or is it still as important as ever? Can you explain the SAR test process? EMSS: This depends on what you define as the ‘SAR issues’. Device manufacturers are only required to be compliant with the relevant standards, rather than determining whether the values that are required by the standards are actually safe. SAR is definitely still important and there might still be some market benefit to developing devices with SAR that is much lower than the required value. However, public concern has diminished compared to earlier years.
SAR regulations and requirements vary from country to country, but generally limit the amount of absorption in a ‘head phantom’ test set-up. Newer standards also address issues related to multiple transmitters, MIMO configurations,
body and hand SAR and different device types, e.g. mobile, tablet, laptop. One of the challenges with integrated antenna design is optimising the performance envelope: maximising TRP while minimising SAR. This process can be facilitated by simulating different geometric configurations using automated optimisation. This process allows multiple parameters (e.g. dimensions or position of the antennas) to be automatically changed while targeting multiple performance goals, such as matching, TRP and SAR.
Taoglas: SAR is something you are required to do in certain circumstances depending on how your transmitter works – you are required to do it by the FCC in US and Industry Canada in Canada and ETSI in Europe. It’s not voluntary and it’s not optional. For LTE, there’s absolutely no difference to any other device. SAR guidelines are not specific to the type of radio; they are simply the amount of energy delivered into human tissue at a certain distance. The nature of the transmitter is not relevant. There are no SAR guidelines specific to LTE versus 3G/2G. LTE puts out 23dbm of transmit power – significantly less than 2G devices – making it easier to pass SAR requirements than a GPRS/GSM device, which put out 33dbm at a maximum. CDMA devices top out at 24dbm, similar in power levels to modern LTE devices. You don’t impact SAR with the antenna – you impact SAR with the mechanical design. You have to do your best to move the antenna away from the body in your design. LTE
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