{"id":4296,"date":"2026-08-24T12:02:45","date_gmt":"2026-08-24T12:02:45","guid":{"rendered":"https:\/\/theemcnews.co.uk\/?page_id=4296"},"modified":"2026-08-24T12:09:18","modified_gmt":"2026-08-24T12:09:18","slug":"five-new-emc-articles-one-practical-website-tip-and-useful-engineering-support-gathered-into-this-weeks-edition-of-the-weekly-signal","status":"publish","type":"page","link":"https:\/\/theemcnews.co.uk\/index.php\/five-new-emc-articles-one-practical-website-tip-and-useful-engineering-support-gathered-into-this-weeks-edition-of-the-weekly-signal\/","title":{"rendered":"Five new EMC articles, one practical website tip and useful engineering support – gathered into this week’s edition of The Weekly Signal."},"content":{"rendered":"\t\t
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# GTEM Cells: What They Measure and When to Use Them<\/p>

A GTEM cell can expose an emissions problem within minutes, but only if the EUT, cabling and measurement method fit the cell. Put an electrically large or poorly controlled installation inside it and the clean-looking plot may be misleading.<\/p>

-What is a GTEM cell?<\/p>

A gigahertz transverse electromagnetic, or GTEM, cell is a tapered, shielded transmission structure designed to support a predominantly transverse electromagnetic mode over a broad frequency range.<\/p>

A central septum forms one conductor, while the enclosure acts as the return path. Absorbing material and resistive loading at the tapered end reduce reflections and help suppress unwanted modes.<\/p>

For radiated emissions work, energy produced by the equipment under test, or EUT, couples into the cell and is measured at the RF port using a suitable receiver or spectrum analyser.<\/p>

Measurements are normally taken with the EUT in multiple orthogonal orientations because a single position cannot adequately represent every polarisation and radiation direction.<\/p>

-What does a GTEM cell actually tell you?<\/p>

The measurement provides an indication of the electromagnetic energy radiated by the EUT within a controlled environment. This makes the GTEM cell particularly useful during product development, troubleshooting and pre-compliance work.<\/p>

However, the resulting data is not automatically equivalent to a measurement from an open-area test site, semi-anechoic chamber or fully anechoic room.<\/p>

A conversion or correlation method is needed, together with knowledge of the cell geometry, validation data and applicable test procedure.<\/p>

IEC 61000-4-20 describes emissions and immunity testing in transverse electromagnetic waveguides, including TEM and GTEM structures. The current edition, relevant product standard and any customer-specific test plan should always be checked before deciding whether the method is acceptable.<\/p>

A GTEM cell is therefore best understood as a controlled electromagnetic environment rather than a small chamber with interchangeable results.<\/p>

-Where does a GTEM cell make engineering sense?<\/p>

GTEM cells are particularly useful for compact EUTs such as:<\/p>

* Embedded controllers
* Sensor modules
* Small power converters
* Communications products
* Populated circuit assemblies
* Electronic control units<\/p>

The EUT must fit within the cell’s usable test volume without approaching the septum, floor or side walls too closely.<\/p>

Physical fit alone is not enough. The product and its representative cable arrangement must remain electrically suitable for the intended method and frequency range.<\/p>

A small enclosure with a two-metre unscreened cable is no longer simply a compact radiating system. The cable may become the dominant radiation source and interact with the cell boundaries.<\/p>

-Why GTEM cells are valuable during development<\/p>

One of the biggest advantages of a GTEM cell is speed.<\/p>

Engineers can compare:<\/p>

* PCB revisions
* Clock settings
* Filter components
* Enclosure treatments
* Cable terminations
* Grounding changes
* Shielding improvements<\/p>

without waiting for access to a formal chamber.<\/p>

The shielded enclosure also reduces ambient RF signals, making small changes easier to identify than measurements made with an improvised antenna in an ordinary workshop.<\/p>

Relative measurements can often be more useful than premature pass\/fail declarations.<\/p>

For example, if a revised common-mode choke reduces a repeatable spectral feature in all relevant EUT orientations, that provides useful development evidence.<\/p>

If the apparent improvement only occurs after the cable has been moved, however, the change may belong to the test setup rather than the product.<\/p>

-GTEM testing and compliance<\/p>

For products intended for CE or UKCA marking, early calibrated measurements can support design decisions and the technical file.<\/p>

They do not, by themselves, establish conformity.<\/p>

The manufacturer or responsible economic operator still needs to identify the applicable legislation, product or product-family standard, limits, operating modes, conformity assessment route and documentation requirements.<\/p>

For more information on the wider EMC requirements associated with CE marking, see **EMC Hire’s EMC testing for CE marking** guidance.<\/p>

-When should you consider a GTEM cell?<\/p>

A GTEM cell is a strong option when:<\/p>

* The EUT is relatively compact
* Cable arrangements can be controlled
* Rapid development feedback is required
* Laboratory space is limited
* Shielded measurements are needed
* The objective is pre-compliance or troubleshooting
* The test method is compatible with the cell<\/p>

It becomes less attractive when the EUT is electrically large, cables dominate the radiation behaviour or the final product standard specifically requires another test environment.<\/p>

The key is to select the test method before selecting the equipment.<\/p>

A GTEM cell can provide fast and repeatable engineering information, but only when the EUT, cabling, cell and measurement procedure are considered as one system.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"

# GTEM Cells: What They Measure and When to Use Them A GTEM cell can expose an emissions problem within minutes, but only if the EUT, cabling and measurement method fit the cell. Put an electrically large or poorly controlled installation inside it and the clean-looking plot may be misleading.… <\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"elementor_header_footer","meta":{"footnotes":""},"class_list":["post-4296","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/pages\/4296","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/comments?post=4296"}],"version-history":[{"count":4,"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/pages\/4296\/revisions"}],"predecessor-version":[{"id":4304,"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/pages\/4296\/revisions\/4304"}],"wp:attachment":[{"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/media?parent=4296"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}