Hi,
What RFid tag unit are you using with the arduino?
Have you attached a UHF aerial to the reader?
If so is the reader designed for an aerial?
What aerial are you using?
Have you got any RFid tags and reader to work, before you added an aerial?
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Not a picture/image like this;
Use proper circuit symbols please.
Thanks.. Tom.. 