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Taking a look at every kind of EMI antenna

Posted: 06 Aug 2015 ?? ?Print Version ?Bookmark and Share

Keywords:ETS-Lindgren? EMI? antenna? testing? hybrid?

Almost all every electronic device, system and subsystem must go through EMI testing, which includes radiated emissions and immunity. Nearly all EMI chambers or open-area test sites (OATS) will have more than one type of antenna to handle a wide range of frequencies. For temporary precompliance tests, you might set up an antenna in a basement or conference room. Precompliance tests help you troubleshoot and correct EMI problems before going to a full-compliance lab.

EMI antennas come in several forms. The types shown in this pictorial (one type per page) are: biconical; log-periodic; horn; bi-log, biconilog, hybrid-a combination of log-periodic and biconical; and specialty antennas.

Which antenna you use depends on several factors. For example: radiated emissions, radiated immunity, precompliance, full compliance, frequency range, power (for immunity only) and size.

Hybrid EMI antenna

A hybrid EMI antenna measures emissions in a makeshift lab in a conference room. (Photo by Kenneth Wyatt.

The most common EMI test you'll perform in your facility is radiated emissions. Which antenna you use depends on frequency, size, antenna gain, and your budget. The most popular antenna for precompliance tests is the hybrid, also called Bi-log, Biconilog, Combilog or other names. Hybrids have a wide frequency range, typically from 30 MHz to 2 GHz, 3 GHz, or 7 GHz, depending on model. That wide range makes hybrid antennas desirable because you don't need to change antennas, which you'd have to do with biconical and log-periodic. The advantage of using multiple antennas comes in performance. For example, a lab might use a biconical antenna for frequencies below 200 MHz, a log-periodic antenna up to 1 GHz, and a horn antenna above 1 GHz. But you can often use a single hybrid antenna. "Even some compliance test labs use Bi-log antennas now," said Doug Kramer, who manages the calibration, EMC, and wireless labs at ETS-Lindgren.

The size of antenna is another consideration, for the amount of space you have in a chamber or other room can limit size. Larger antennas have a wider frequency range and better sensitivity than smaller antennas. Some hybrid antennas have bent elements to conserve space.

Many antennas can be used for both radiated emissions and radiated immunity tests. But, you must pay attention to how much power you need to drive an antenna to get the required field strength for an immunity test. "If you're performing immunity tests, you'll typically need a larger antenna than if you're performing emissions measurement only" said Greg Senko, vice president at Teseq. In addition, hybrid antennas typically require more space than more dedicated antennas, Senko noted.

The following pages take you through some of the EMI antennas used for testing commercial products.

Biconical antennas

Biconical antennas cover the low end of the frequency range. They can be used for radiated emissions or immunity tests.

SAS-544 biconical antenna

The SAS-544 biconical antenna from AH Systems has a frequency range of 20MHz to 300MHz.

AB-900 biconical antenna

The AB-900 biconical antenna from Com-Power covers 30MHz to 300MHz.

VBA-6106

Covering 30MHz to 300MHz, the VBA-6106 from Teseq can handle op to 10W when used as a transmit antenna for radiated immunity tests.

3110C Biconical antenna

Also covering 30 MHz to 300 MHz, the 3110C Biconical antenna from ETS-Lindgren measures 79cm x 52cm x 131cm.


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