GTEM cell in EMC Testing: operation, applications, and NMR-CUBE

We live surrounded by electromagnetic waves. From smartphones to microwave ovens, from networking devices to industrial plants, we are constantly exposed to electromagnetic fields of varying intensity and frequency. But what happens when these waves interfere with the operation of our electronic devices?

Every day, we use tools that must guarantee absolute reliability: an emergency button, an industrial control system, a medical device. If these devices were to experience electromagnetic interference, they might stop functioning correctly, leading to potentially dangerous consequences. How can we ensure they are immune to such disturbances? The answer lies in electromagnetic compatibility (EMC) testing, and one of the most widely used tools for conducting these tests is the GTEM cell (Fig.1), valued for its versatility and effectiveness

GTEM cell and TEM Cell: what are they?

The GTEM cell (Gigahertz Transverse Electromagnetic Mode Cell) is an evolution of the traditional TEM cell (Transverse Electromagnetic Mode Cell) (Fig.2). While the TEM cell was one of the first solutions adopted for EMC testing, with a parallelepiped-shaped structure and limited to lower frequencies (up to 1 GHz), the GTEM cell was designed to handle a broader frequency range, reaching several tens of gigahertz. This makes it ideal for modern devices such as smartphones, wireless devices, and applications in the medical or aerospace sectors.

The GTEM cell offers numerous advantages over the TEM cell: thanks to its tapered structure and internal septum that stabilizes the electromagnetic field, the GTEM can perform immunity and radiated emission tests with significant time and cost savings. Additionally, its compact shape allows testing in confined spaces, reducing the need for large anechoic chambers.

How does the GTEM cell work?

Inside the GTEM cell, electromagnetic fields can be generated with a high level of uniformity, allowing devices to be tested under controlled electromagnetic waves (Fig.3). The tests can be of two types:

1. Measurement of electromagnetic emissions: to verify how much a device emits electromagnetic fields.
2. Immunity testing: to assess the device's resistance to external interference.

Thanks to its efficiency, ability to operate at frequencies up to gigahertz, compactness, and versatility, the GTEM cell is a valid alternative to an anechoic chamber.

The importance of proper positioning in EMC testing

A fundamental aspect of test reliability is the correct positioning of the device under test (EUT) inside the cell. To ensure precise measurements, it’s crucial to prevent the support from interfering with the generated electromagnetic field. This need led to the development of the NMR-CUBE, a non-magnetic support designed to eliminate positioning issues in EMC testing. Thanks to its structure, it significantly reduces reflections, allowing for more accurate and reliable results.

Reference standards and EMC compliance

The use of GTEM cells in EMC testing is regulated by international standards, including CEI EN 61000-4-3, which establishes test methods for immunity to radiated electromagnetic fields. This is one of the most relevant standards for tests performed with GTEM Cells, as it defines how devices must withstand high-frequency electromagnetic field interference. Manufacturers looking to certify their devices for compliance and safety must subject them to rigorous testing according to these standards, which also include others related to immunity to electrostatic disturbances and conducted signals, such as CEI EN 61000-4-2 and CEI EN 61000-4-6.

In conclusion, GTEM cells are an excellent tool for EMC testing, thanks to their wide frequency range and relatively small size. Moreover, their combined use with innovative tools like the NMR-CUBE significantly improves the reliability and quality of tests.