E-field measurement - Page 1
Forum section: electronics / rf-microwave

author: jashugan
author_rank: Regular Contributor
timestamp: August 28, 2020, 09:19:07 am
content: Hello,I've built an open Gtem following the tutorial in Internet, and it works pretty good, both S11 and S21 parameters seem quite good. However, what I'd like to do is to calibrate the E-field inside of it, to be able to have some quantitative measurements during EMC tests.Do you have an idea of how to calibrate the GTEM?Thanks in advance!

author: JoeyG
author_rank: Regular Contributor
timestamp: August 28, 2020, 10:59:10 am
content: (I don't have more info than what is below)We assume you have all the RF absorbent material inside also.I would suggest a OATs highly calibrated comb generator , where all the peak frequencies have been recorded.I believe this is how OATs site are calibrated , with a know reference (or calibrated transmitter across different frequencies)Then it's a relative comparison of the measurements in the GTEM for the device under test and the comb generator (trasnmitter).You will need to see how the RF reflections bounce of the walls at minute distances at every space in the GTEM and calibrate these out for he DUT and antenna etcreferenceshttp://www.compliance-club.com/archive/old_archive/020312.htmhttp://www.nict.go.jp/publication/shuppan/kihou-journal/journal-vol63no1/journal-vol63no1-02-06.pdfhttps://www.dare.eu/calibration/emcrf-calibrationsMore secrets in these standards - but they may need to be purchased.StandardsANSCI 63.4 Methods of measurement of radio-noise emissions from lowvoltage electrical and electronic equipment in the range of 9khz to 40 ghzAS/NZS 61000.4.3 Electromagnetic compatibility (EMC) Testing andmeasurement techniques - Radiated radiofrequency electromagnetic field immunity testAS/NZS 61000.4.6 Electromagnetic compatibility (EMC) Testing andmeasurement techniques - Immunity to conducteddisturbances, induced by radiofrequency fieldsAS/NZS CISPR 16-1 Specification for radio disturbance and immunity measuringapparatusCISPR 22 Compliance Test of Power-Line Transmission SystemsISO/IEC 17025 General requirements for the competence of testing andcalibration laboratories

author: JoeyG
author_rank: Regular Contributor
timestamp: August 28, 2020, 11:00:39 am
content: Perhaps this one as wellhttps://www.armms.org/media/uploads/anechoicchamberarmms.pdf

author: jashugan
author_rank: Regular Contributor
timestamp: August 28, 2020, 12:10:36 pm
content: Thanks JoeyG.I didn't put any RF absorbent, I did a quite straight copy of thishttp://eagle.chaosproject.com/sandbox/acstrial/newsletters/summer08/pp2.pdfHow can I put RF absorbent in such a small space? Are they necessary?Regarding the methods, I thought of something easier, if possible, like for example a simple antenna placed inside the GTEM with known irradiated power (i.e., the source power + the antenna gain @ frequency). However at the moment I don't have an RF generator, even if I need to buy it ASAP.Thank you again

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 28, 2020, 12:57:37 pm
content: Hi,I too have built a modified version of the open TEM cell described in the paper by Sandeep M. Satav and Vivek Agarwal.Here is a picture of mine:The paper describes how to calculate the E field:andSince CEdepends on the EUT, the calibration depends on the EUT.d = distance from the septum to the walld is based on physical measurement.If you assume CE= 1You don't need to calibrate the open TEM cell.I use mine in arelativefashion. If you get a 10dB improvement in a TEM cell you will get a 10 dB improvement in OATS.Regards,Jay_Diddy_B

author: coppercone2
author_rank: Super Contributor
timestamp: August 30, 2020, 08:44:32 am
content: what is that copper mesh doing ?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 30, 2020, 02:32:06 pm
content: Quote from: coppercone2 on August 30, 2020, 08:44:32 amDo you mean this?It is not mesh, It is 3M copper foil tape. I made the TEM cell from copper clad FR4. It was used to connect the copper foil together.Jay_Diddy_B

author: coppercone2
author_rank: Super Contributor
timestamp: August 30, 2020, 08:48:42 pm
content: looks dimpled.https://www.digikey.com/product-detail/en/3m/1182-1%2F2%2522X18YD/3M157269-ND/3863737?utm_adgroup=RF%2FIF%20and%20RFID&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_3M_0019_Co-op&utm_term=&utm_content=RF%2FIF%20and%20RFID&gclid=CjwKCAjwnK36BRBVEiwAsMT8WFR3GcAweffSZpGZkw8bUT9x_0NfbHjGEw5Iohtwfmrbs2sHtnnWJBoCzmMQAvD_BwEThis type?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 30, 2020, 09:45:58 pm
content: Coppercone2,I can't be 100% certain but I think it is 3M 1245 1 inch wide.This is soft copper tape that is embossed to provide a metal to metal contact. It cuts through the adhesive.Link:https://www.digikey.com/product-detail/en/3m/1245-X-1/3M1245C-ND/1630183It was something I had on hand when I built the open TEM cell. I soldered the tape every few inches.Jay_Diddy_B

author: coppercone2
author_rank: Super Contributor
timestamp: August 30, 2020, 10:32:38 pm
content: thats an interesting product, never saw it embossed, I thought it had a conductive adhesive