50ohm UHF antenna for handheld device

[Jenya86]

50ohm uhf antenna

I have to design a 50 ohm UHF antenna for RFID reader module that will be imbedded in hand held device. This antenna need to be as small as it is possible.
So, could you help me, what should i pay attention for? What to start with?

Thanks a lot)

 

[RF-OM]

uhf 50 ohm antenna

It depends on what you already know. You need to be familiar with electrical theory and RF basics. Then you need to have some understanding what is antenna and how it works. For this I can recommend you a book Antenna for all applications (if I remember the title right, but it should be very close). There you will find good explanation for antenna basics, what is antenna, the radiation resistance and radiation efficiency. There are also good chapters on different kinds of antennas. All this valuable information was written for general antennas, whereas RFID may require different conditions, namely near field when the distance between antenna and RFID tag is smaller than near field zone. Depending on application, antenna directivity may be very important for RFID. There is no one recipe for all situations.

You also may try to do search for RFID antennas and applications. There are some companies who make RFICs and even antennas for RFID. Many of them have application notes and other helpful information.

 

[Abhishekabs]

rfid antenna theory uhf

Hi Jenya86
RFID reader mostly uses loop antennas.
check this site for detail information.
http://rfid-handbook.de/forum/list.php?4
Also find IEEE papers, it is good thing to start when you are new, since you come to know how people do it.
I hope this helps you.
Abhishkabs

 

[Jenya86]

download antenna theory and design 2nd

Thanks very much for being so helpful and responsive. i will search and study information from the links you gave me)

Added after 18 minutes:

and one general question: what are the common sizes of such antennas?? how small it can be?

Thanks.

 

[FvM]

50 ohm uhf dipole

I guess, you are referring to a ISO 18000-6 appplicaton. Generally circular polarized dipole pairs or patch antennas are preferred. λ/2 (ca. 15 cm) is a natural dimension for these antennas, but you can build smaller patch antennas with high Er substrates. I've recently seen a around 4 or 5 cm diameter patch antenna developed at a university.

 

[zirtapoz]

handheld device antenna

Refer this

it ll be usefull for all..

 

[RF-OM]

antena uhf back to back

To Jenya86,

Size may differ a lot. From full size which is usually a bit less than half of the wavelength to hundreds times smaller. For example for some medical transceivers that designed to go through your body tracts it is actually hundreds times less then normal antenna size, but this cases are not typical. Usually you have some MRD driven limitations and must design something that will be the best possible approximation to these requirements.

 

[Jenya86]

antenna theory 50 ohm

Could somebody help me please! I need this book,but that i found is only to buy it! maybe someone know,where i can download it to read online free!))

Antenna Theory and Design, 2nd Edition,

by Warren L. Stutzman, Gary A. Thiele.

 

[RF-OM]

build handheld antenna

I checked my library. Unfortunately there is no this book. Did you searched Book Upload/Download part of this site?