how to measure dielectric permittivity
how to measure dielectric permittivity
(OP)
hi, i need to design an UHF RFID tag antenna on 0.45mm thick Maylar the substrate is 450 micron Polyester, dose any one know how can i measure its dielectric permittivity at UHF (869mhz).
thanks
thanks





RE: how to measure dielectric permittivity
How accurate do you need the data? 1% or 10%?
Does dielectric value affect a super small (electrically speaking) antenna? Have you alot of experience in RFiD design?
kch
RE: how to measure dielectric permittivity
i am designing ultra thin platform independent antenna and accurate value of permittivity is important at UHF. i have been working on these antennas for about a year now.
do you know how to measure the permitivity for this material with 0.45mm thickness.
ali
RE: how to measure dielectric permittivity
The basic method uses the dielectric material between parallel plates to create a capacitor, which then can be analyzed. Additional software extracts the parameters of the material being tested from the data and corrects for the presence of the fixture.
RE: how to measure dielectric permittivity
Guess the value, build a prototype antenna, measure the prototype antenna, and then adjust accordingly.
RE: how to measure dielectric permittivity
If you have money, you can send it to Damaskos, they do an assortment of measurement techniques.
Resonator techniques are simplest. you make a transmission line with small cuts or breaks in the transmission line at spacing 1/4 lambda and another transmission line with cuts 3/4 lambda and measure S21. With accurate mechanical knowledge you have highest transmission at your proper wavelength. Since there is 1/2 lambda delta line length between the two samples, and the cuts are the same, you find the dielectric constant accurately. A coworker used this at my former workplace and got the answer that was higher than what Rogers corp. specified. I thought he was wrong until we made a microwave lens and proved he was right.
Rogers is now changing how they specify dielectric on many of their products from the "this is what we measured using a standard IPC measurement tehcnique" to "use this dielectric value for circuits"
kch
RE: how to measure dielectric permittivity