what type of antenna did you recomended for me.

[antenna9071]

I want to build a antenna of this condition. what type of antenna did you recomended

*much metal in the environment
*will sit on vehicle for hight speed max 200km/h
*dual band 868Mhz( Rfid),2,25GHz
*smal max (w*L*H) 5cm*10cm*2cm
*range max 15-20m
*circular polarized

 

[VEBill]

You have provided a lot of information, but still not enough to fully understand the application. Is this an RFID on cars application?

 

[antenna9071]

The antenna are going to sit on a train, It will comunicate with a RFID tag beside the rail and a gateway on the train

 

[VEBill]

Is the RFID tag going to be one of those 'no battery' types that requires a fairly high field strength from the reader? If so, then I believe you have a set of requirements that are impossible.

 

[IRstuff]

200km/hr = 55 m/s. Even with the receiver right against the train, the specified range is met for less than 1 second. Supposedly, there are few tags that have low-latency wake-up.

Have you looked at ZigBee Pro as a possible alternative? Outdoor range with even rather puny antennas can be in excess of 100 m. Additionally, the systems are already configured for low-latency wake-up (~30ms).

TTFN

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[antenna9071]

I have look at some design of zigbee.

 

[Higgler]

I'd suggest a dual band patch antenna. The bandwidth at 868 and 2250 Mhz will set the thickness of the antenna. You only need circular polarization if the range is not far enough with Linear polarization. Linear polarization is an easier, less expensive antenna design.

Expect the patch antenna size to be relatively small 8"x3"x(0.5"thick) with zero dBic peak gain. You position the probe so that you'd get H pole at the low frequency and V pole at the high frequency.

 

[biff44]

you want an antenna that is flat (air resistance at that high speed) and has a natural ground plane on its backside.

Path antenna, annular ring antenna, etc.

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[biff44]

cavity backed cross slot...

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting