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Rfid near field antenna

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venkatasuresh

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haii ..i want to design rfid near field rectangular array antenna...plz suggest me how to design the antenna..basic requirements.. and which software is suitable for this....plz suggest me because i dont have more knowledge in this.. i want to do this as my thesis work.
 

WimRFP

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You may tell us the frequency band (I assume 13.56 MHz). Before diverting to simulation, try to understand the matter. Based on the coil current, you can use magnetostatics to calculate the field (A/m) at certain distance from the rectangular or round loop antenna. You can calculate the inductance based on standard formulas. As you may know, thick inductors result in less inductance.

To have sufficient bandwidth for the tag signal to get back to the reader, the Q factor of the coil has to be reduced mostly. Value depends on data rate (or subcarrier frequency). Values around 30 are used. Q-factor reduction can be done by placing a resistor in parallel with the coil.

You have to tune the coil with a capacitor and use L network (or inductive coupling) to transform the impedance of the LCR circuit to 50 Ohms. Some antennas require a balancing circuit to avoid common mode current on the feed cable. Common mode current on feed cables should be avoided as this may lead to interference and/or undesired far field radiation.

You also should know (or measure) the minimum required field strength for the tag to respond.

You may read: "RFID Handbook, Fundamentals and Applications in Contactless Smart Cards and Identification"
 

venkatasuresh

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thanks for u r information.. i will refer to handbook.. frequency band is above uhf..i.e 2.8 or 2 GHz. etc
 

WimRFP

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Are your sure you are in the near field as "near field" for 2 GHz is just a few cm. If so, same theory applies as for near field 13.56 MHz RFID, except for the size of the antennas.
 

venkatasuresh

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small mistake in befor thread.. its 3 GHz.. i.e above the UHf range...my reference paper is design of rfid near field circular antenna at 2.4 GHz..now..here is there any possibility to design rectangular array antenna for rfid above the 2.4 GHz
 

WimRFP

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3 GHz doesn't change, near field distance is about 1cm. Maybe you should give some more details about what you want to avoid confusion.
 

venkatasuresh

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Design of RFID Near-Field Focusing Circular Patch
Array Antenna at 2.4GHz with Applications. this the base paper.. can u plz explain briefly about that topic..
 

TomTang

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it's very difficuit to design RF antenna, i am worriing now for one wifi antenna for small tag.
 

venkatasuresh

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is it very difficult..then how can i design..plz suggest me how to desgin an Rf antenna...its my thesis work
 

WimRFP

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The path to antenna design is
- knowing LCR circuits
- knowing basic field properties, material properties (E, H, B, D, potentials, etc) and their relation to lumped components.
- to have excellent understanding of transmission line theory.
- knowing how fields and radiation do originate from current segments and how the form the radiated power.
- knowing about constructive and destructive interference and radiation patterns (for your case also near or transition field patterns, they are more elaborate).
- knowing behavior of structures no longer small w.r.t. wavelength (reflection, refraction, fresnel theory).
- knowing properties of existing antenna types to enable you to make a first selection.
- knowing how to use a suitable software package for your challenge.

It is not easy but when you really want it, are willing to put lots of effort in it, you can master it.
 

TomTang

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Hi WimRFP,
Thank you very much!
below is two board i designed, but the round board is much better than square board, i think it's because the eeprom is nearer to the antenna, is it?


---------- Post added at 15:04 ---------- Previous post was at 15:02 ----------

let's explain the boards: the solution is sensor tag, wifi + g-sensor tag, chip set is g2
 

venkatasuresh

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okkkk thanku for u r information

---------- Post added at 22:23 ---------- Previous post was at 22:13 ----------

suggest any one of the suitable software for this
 

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