Design a log periodic loop antenna for UHF RFID reader

[long88]

Hi all,
I am a newbie on antenna design. I am currently having a project which wanna do design an antenna with log periodic structure and for RFID applications. This antenna will cover UHF RFID band of 860-940Mhz. The dimension shall be small and suitable for handheld RFID reader.

I am planing to design a helix antenna with log periodic structure. The spacing and diameter of each turn will vary with a spacing factor. But i don't know how to calculate the parameters of antenna. eg. spacing, turn, gain.Anyone know how to calcuate? I am confuse because am i able to used the helix antenna formula to calculate?

Anyone have related journals or information please share with me! If there is other antenna structure suitable for this application, please share with me!Thank you

Best regard,
Long88

 

[FvM]

Logper is for wideband, it's of no use for 860 to 940 MHz.

 

[long88]

Thank for FvM reply.
But i did find some research on using helix antenna for UHF compact handheld RFID reader antenna. I wanna to design an antenna for universal uhf RFID bands. Is there any suitable antenna structure?

best regards,
long88

 

[Libor124]

Hi,

My recomendation is the book The RF in RFID , Daniel M.Dobkin page 241-283 , (special 282-283). I have done some antennas for readers, all depend what do you expect from the antenna (suitable is for an example dipol+ one element if you need the size the small asap)

Here is one solution , please see the picture

 

[long88]

Hi Libor124,
Thank for comment. Where can i download the content u share? it seem like got many interesting knowledge about antenna!
Currently i am doing some simulation by using CST, i am now searching proper materials that use to fabricate antenna.
Any type of wire is suitable for helix winding ?

 

[Libor124]

Hi,

I have attached the datasheet .
"Which type of wire for helix winding ?" It is the right question. I can only say please try Cu dia 0.5-1.2mm or Cu band.

 

[FvM]

It's not clear to me, why you want to use a helix antenna and which kind of helix antenna you're referring to. The shown picture is rather suggesting a simple λ/2 dipole. If you intend higher directivity respectively gain, a yagi antenna would be first choice.

 

[Libor124]

Hi FvM,

My reply has two separate parts as I understand long88's question

1) you are right the picture is a simple λ/2 dipole

I fully agree with you that a yagi antenna is good solution for some (special) UHF RFID applications, this solution need only a little bit space around a yagi antenna

2) "micro helix antenna" - we have used it with very a good result for UHF RFID semi-passive tags

Note:
According to our experiences a helix antenna is sometimes a good solution for "RFID unfriendly enviroment", but it is not as easy.

 

[FvM]

I agree, that the type of helix antenna you're referring to, "coiling up" a dipole antenna to shorten it, can be useful for tags. Also high Er patch antennas are a common solution to build small tags. But I won't suggest it for a reader, unless a small form factor is absolutely required. I think, that a standard dipole gain is suitable for most applications.

 

[long88]

Thank for Libor and Fvm reply.
I use the helix structure because i would like to generate circular polarization. Since most of tags are linearly polarized therefore a rfid reader with CP is better right? The helix will be operate in axial mode and i intend to reduce the spacing between each turns. I am using the concept of log periodic to reduce the spacing between each loop. Do u all think is practical?
I did a rough simulation by use CST. I only draw helix winding,ground plane and the coaxial feed.The materials of helix winding ,ground plane and coaxial feed are PEC (Perfect electric conductor) and coaxial's dielectric is use the teflon.The reduce space antenna have lower gain compare to helix axial mode but with compact dimension.

Currently I am try to simulate the antenna with proper materials and more details on the dimension of antenna.eg draw the complete coaxial connector, ground plane materials and the conductor wire confined with insulator wire. But CST transient solver always stop due to less mesh plane along the direction of propagation. I still able to simulate the result by reduce the mesh limit or PBA but the result tends to not stable. Any idea to solve this problem?

 

[FvM]

Crossed dipols with 90° feed or a patch with circular polarization are more compact solutions, I think.

 

[long88]

Thank for reply. do u know any materials that suitable for helix winding?

 

[FvM]

Helical antennas are e.g. discussed in Balanis' antenna textbook. I still don't see their advantage for UHF RFID. They are dedicated broadband antennas, but you don't need broadband.

 

[long88]

Hi FVM,
I think u are right. I am going to design a cross dipole or dipole antenna with CST. How to design the balun and feader? do u have the simulation file?can send to me for reference ?thx

 

[kap5051]

please help me;

i am doing a project of UHF rfid reader.....

and i don't know, which antenna i need....

and also how will passive tags will get powered by this..???