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Loop Antenna for chipless RFID tag

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AiosZios

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Hi all,

I try to design a loop antenna to read my chipless RFID tag. The frequency range is from 150MHz to 280MHz. After using the formula of loop antenna, i get a loop antenna circumference at 1.61m, radius of loop at 0.256m, radius of the wire at 4mm and single turn.

The loop antenna is very big compare to my tag which dimension is 48 x 47 mm. Is that mean antenna is too big to read my tag?

Besides that, does anyone know how to calculate the bandwidth of loop antenna above ?

Thanks!
 

After using the formula of loop antenna
Which "formula"?

The frequency range is uncommon for RFID, because there are no free frequency bands. I'm also not aware of chipless RFID systems.
EAS (electronic article surveillance) is usually based on simpled resonant circuits, but in a lower frequency range. UHF RFID systems are
mostly using circular polarized dipole pairs or patch antennas.

In the near field range, an inductive coupler can for VHF as well, if the dimensions are small related to the wavelength.
 

There is no RFID tag without a chip. If a tag is without chip it may not be RFID tag. Guess you are refreing to a EAS tag as "Frank" has mentioned.
Cheers
 

Which "formula"?

The frequency range is uncommon for RFID, because there are no free frequency bands. I'm also not aware of chipless RFID systems.
EAS (electronic article surveillance) is usually based on simpled resonant circuits, but in a lower frequency range. UHF RFID systems are
mostly using circular polarized dipole pairs or patch antennas.

In the near field range, an inductive coupler can for VHF as well, if the dimensions are small related to the wavelength.

hello sir
thnx to guide
but we use hard tags then how it oscillates with doors and how its frequency make differnce .
so please guide me about this technology
 

As far as I know, there is no special loop antenna formula. Each application requires its own fresh approach. Is this a frequency swept system (like many 8 MHz EAS) or does it use a wide band pulse? What is the expected reading range?

If you want inductive behavior (near field communication), you need to get as uniform as possible current through your loop (to reduce far field radiation), and the loop must be small w.r.t. wavelength. Common mode current should be very low.

Making a loop with the required bandwidth needs a lot of resistive loading. You can increase the bandwidth by making a 2 or more resonator design (you will get more then twice the bandwidth for a single tuned circuit).

You can make the current more uniform by dividing the tuning capacitance across the circumference of the loop.

If the response time isn't too demanding, you may change the tuning frequency of the antenna. This allows you to select higher Q factor, hence getting more field given certain available power.

Regarding the tags, how do you avoid shift in tuning frequency due to vicinity of other objects?

Regarding chipless tags; yes they do exist: backscatter tags where the backscatter is delayed with a SAW resonating structure (yes, they can store data).

Regarding frequency range; very strange, I hope it is used in a fully shielded building only to avoid visits from your telecom administration.
 

There's no response from the original poster since more than a year, I think the VHF RFID plans are gone.
 

FvM, I didn't notice the date of the original posting, I just saw "today".
 

Hi AiosZios,

I am also designing chipless rfid tag but in UHF range, and may i know why u have choosen the loop antenna as reader Tx or Rx antenna??u can also use LPDA antenna??
 

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