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resistance and reluctance of a capacitance in high frequency

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payam_p

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Hello everyone

I've designed a broadband CMMA (composed meta-material absorber) an used capacitors with 2.2 pf and 2.7 pf capacitances on it's surface, which has shown about 8 GHz B.W. (bandwidth) higher than 90% absorption.
We know that in reality a capacitor show resistance and reluctance from itself when it's used on high frequency. Here are my two questions first "how can I calculate the resistance and reluctance of a capacitor working in x-band" AND second "what's it's equivalent circuit"?

Thanks in advance.
 

kobeismygod

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there are my thoughts about you question,hope it can helps you

1,if you want to calculate the equivalent resisrance brings by parastics inductor,you need to know how much inductance there are,but that hard to be confirmed ,so the best way to find the result is checking the table which caps vendor provides.
2,for the componets with pakage,they will bring some paratics elements like inductance,resistance or capacitance unavidable,so if you want to understand affect by these elements,you will need add these elements in the model of components and form the equivalent circuit.
 
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srizbf

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calculation of capacitive reactance and resistance is based on basic equations taking into permittance of the materials.

if it is a manufactured one , the supplier will have the data.
if it is to be designed then the designer should have all values.

apart from that , the values at x-band calculation is not as easy ,as i think not much info on charecteristics at that freq will be available.( as all the contacts(terminals) are also included).

the eq circuit is a parallel combination of cap and resistance , representing the loss factor.
you may be aware that there are measuring instruments for finding the eq circuit .

agilent(formerly HP , now has new name?) site can be checked for the instruments.

other forum experts may give more info on this.
 
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payam_p

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thanks for your helps so far guys.
kobeismygod so you're saying that we can calculate equivalent resistance from parastice inductance, where can i find the table you're suggesting?
and second i've surely used the capacitor on my modeling, which is on CST, the point is that CST, as far as know, look at the capacitor as an ideal capacitor, so in order to have the best out put we'll have to calculate the equivalent and then enter it.
srizbf yeah i know the calculation and the basic equations that's all right but it's not a simple structure which will make the calculation like a night mare that way and some software helps will be needed, it is indeed supposed to be a manufactured on and they have it (a capacitor with the characteristics needed which is 0402 size 1 mm*0.5 mm), which is all true, but i couldn't find one single table on which i can find some useful information about the high frequency or even as high as x-band!
so the equivalent is parallel good to know that.
and what are the measuring instruments you're indicating, would you be exact?
 

kobeismygod

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i mean you can find the Res/Freq curve from vendor's spec,not parastics inductance.because that curve will cover the frequency you interst in general.
 
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payam_p

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Hi again
let's see.
using the LCR meter is a really good way but this one is to be used from 1 MHz to 3 GHz and though it's the best i found myself (the second bests maximum frequency was 2 GHz), it's not good enough! cause it's maximum frequency is 3 GHz but my structure is working at x-band.
 

SunnySkyguy

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Are you using an SA or a Network Analyzer with Smith Charts and all s parameters?

The latter is better, since you need the vector response and not just the scalar absorption.

You can rent or might find an old 9 GHz Anritsu cheap for <10k$ (<10%)
 
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payam_p

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thanks sunny
I think that's the easiest and fastest way i can find it out. :-D
I hope the university has one which works on the x-band or i'll be damned. :smile:
kobeismygod thank you again but that was the very first thing i did, of course i looked in any datasheet i could lay my hand on and i had found no useful curve on x-band, there were some curves on that frequency for sure but they had no data on what i was looking for, so i thought of other ways to gather that info, Spectrum Analyzer is the best way so far and i'll appreciate any other suggestions.
thanks in advance.
 

payam_p

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I thought and re-thought about it so many times and i'm wondering if there is any theoretical way to calculate it.
it's mostly because, while seeing it on SA or NA is enough for calculating, one can't be sure that the SA or NA is wholesome (no one can't guaranty s.th. in a university lab! it might be broken and it happens a lot that it's not known) or that it works sufficiently! so it'll be grate to know the range, at least, and the worth problem is that i can't visit my university any sooner than 3 days later which is a lot of wasted time.
so I'd thank anyone giving me any answers whether it's a PDF or book giving some clue on a way to calculate it or even if someone has a SA or NA and can check a 1 mm*0.5 mm 22 pf capacitor on it and calculate it's resistance and inductance and capacitance on x-band.

p.s. (for those who hadn't read the whole thread) SA=Spectrum analyzer and NA=Network analyzer.
thanks a bunch guys
 

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