EMC pre-certification test using the intelligent amplifiers of iAMP-Series

EMC is a large technical testing domain applying RF technology. The major two classes of tests performed are emission tests and immunity tests. While emission tests focus on the radiated electromagnetic fields of the device under test (DUT), and therefore is mainly about receiver technology of the measuring devices, immunity testing verifies that the DUT does not show any behavior outside its specification and function when it is subjected to an externally generated electro-magnetic field. 

Becker Nachrichtentechnik focuses on the immunity testing application. With in this field, there are two typical test setups: 

• Large devices under test and an optimally controlled environment requires the use of anechoic chambers. Within these chambers a transmitting antenna creates the electromagnetic field that propagates to the DUT.  Such a test setup is inherently expensive, not only because of the typically large anechoic chamber, but also due to the high power level of the RF signal that drives the antenna. Only a tiny part of the transmitted RF power actually reaches the DUT and most power is absorbed by the chamber itself.
• For smaller devices and mostly used in pre-certification tests, the DUT is placed in a so called TEM cell (Transverse Electromagnetic Cell) or its extension to GHz frequencies, the GTEM cell (Gigahertz Transverse Electomagnetic Cell). Such a cell can be placed in a normal laboratory and all kind of sizes are available.

The typical RF power level needed to drive an antenna in an anechoic chamber ranges from 100 W to kWs of power. In a (G)TEM cell, only 10 to 50 W of RF power are required to reach a sufficiently intense electromagnetic field at the location of the DUT. This is the power range of Becker Nachrichtentechnik EMC products. 

As the upper frequency limit is expected to increase further in the future as new communication systems are added in higher bands, the latest version of the EMC immunity standard DIN EN 55035 requires testing up to 6 GHz and will take full effect in the coming months.

In order to save expensive test time in certification labs, many manufacturers are conducting EMC pre-certification tests in their own laboratories, thus reducing the risk of failing the final certification test. Of course, the cost of the equipment plays a bigger role in this use case than for certification testing bodies.

For this reason, Becker Nachrichtentechnik has developed the iAMP line of intelligent amplifiers that simplify the test setup prior to certification and allow customers to focus primarily on the test execution. Carrying out the test is also complex, since the decisive question for a manufacturer is how the correct behavior of the test object can be monitored during the immission test.

Before performing the actual test, the field strength at the DUT location must be calibrated over the entire frequency range used. For this purpose, a field sensor replaces the DUT in the (G)TEM cell and the relationship between RF power and field strength is measured and documented (sometimes for several positions of the field sensor). In case of the actual test, the calibration of the power generator is configured based on these measured values. In order to guarantee a precise field strength, the RF power entering the cell is monitored during the test, not the actual field strength at the DUT.

The products of the iAMP line from Becker Nachrichtentechnik carry out the calibration cycle autonomously. During the test execution, the operator's control computer simply requests the appropriate field strength at the appropriate frequency and concentrates on monitoring the behavior of the DUT. This means that reproducible test conditions and more efficient measurements can be implemented in order to develop the product in short iterations in accordance with EMC.