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[SOLVED] RFID read range distance calculation

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Hanaf

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Hi.

I have problem to prove the read range distance of my rfid is increase if i increase the gain. here, i use friss equation to prove if the gain is increased, the read range also increase. i dont know whether i should assume the Pt of reader or not. i think i should check with the rfid reader that have in the market, but i dont know the pt of the reader and the gain of the reader. does anyone here can help me?
 

Hello,

What frequency, Radiation field or inductive?
 

the freq is 2.45ghz. my gain is 3.5dbi. i try to google the rfid reader in the market but i cant find the Pt and Gain of the reader.
 

Hello Hanaf,

What you miss to use the Friis formula, is the gain and sensitivity of the chip. Mostly complete tags are specified with sensitivity in V/m.

You can use E = 5.5*sqrt(Gi*Pt) / r, r is not in the sqrt function.

Gi = gain of antenna (not in dB's) and r = distance. 3.5 dBi -> Gi = 2.2.

Note that this simple formula doesn't take into account destructive and constructive interference due to multipath effects.

If your TX antenna is circular polarized, and the tag is linear (very likely), you need to reduce the gain with factor two (or reduce with 3 dB).
 

TQ, actually i'm not familiar with the equation u gave above. but TQ very much.
 

What tag data do you have with regards to sensitivity.

Regarding the formula, do you mean that you don't know how to read the formula, or that you can't find it elsewhere?
 

What tag data do you have with regards to sensitivity.

Regarding the formula, do you mean that you don't know how to read the formula, or that you can't find it elsewhere?


actually, i know how to read. the friss formula have the Pt, Gt, Pr right? The Pt and Gt is from the reader. but my project is about transponder. So, i dont know the value of Pt and Gt. Hope u can understand since my english a lil bit weak.
 

Hello,

If you don't know the Pt*Gt product, make yourself a dipole, and check the VSWR to make sure that matching is OK. In that case Gi = 2.1 dBi. You can also use another antenna, but you should be confident about the gain (standard gain horn?).

The power received by an antenna: PRX = PFD*Ae, PFD = power flux density in W/m^2. PRX is received power in W.

Ae = effective aperture of antenna = Gi*lambda^2/(4*pi). Gi not in dBs

E field PFD relation: E = sqrt(PFD*377) in V/m

So based on the power reading from, for example, a spectrum analyser, you can determine the E-field at your target.

Make sure you check for uniformity of the field close to the target as too strong reflections will make your results useless. Also don't forget to correct for cable loss as this can be significant at 2.45 GHz.
 

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