In what orientations do antennas cancel each other out? 1

[kirr45]

Hi everyone.

I am curious to know more about antenna orientation. For example. I had an RFID reader hooked up with two antennas. One antenna was horizontal on the side of a doorway. The second antenna was attached above the door pointing down. I noticed when I was trying to read a tag, the top antenna could read it even though i was holding the tag closer to the antenna on the side of the doorway. Does this make sense? How can I figure this out? It doesn't make sense. I want to learn more about antenna configuration and how to maximize the antenna wave propogation efficiency.

Thanks guys

 

[VEBill]

RFID technology is a poor domain to be trying to learn the basics of RF. There are too many potential complications. Based on your description, it seems likely that you've stumbled into one of the complications.

Try swapping the two antenna connections on the Reader (I'm assuming that they're interchangable). See if the preference follows the antenna, or the Reader's port.

 

[kirr45]

It's crazy. With RFID I've noticed the biggest problem comes from antenna placement and configuration. Any ideas on how I could learn more or experiment to gain experience?

 

[VEBill]

In the long term, nothing like Amateur ('Ham') Radio as a hobby to learn about radio.

 

[Higgler]

Google Poincare Sphere. That'll help. Shows the loss from one polarization to another on a pair of antennas. Here is one reference, plenty more out there

http://spie.org/x32375.xml

 

[VEBill]

Beware that practical antennas often have physical matching networks (e.g. gamma match) that tend to ruin the perfect nulls (because they contain bits of metal not perfectly parallel with the element). So instead of getting 'infinity dB' loss at the null, one might get just -30dB or so.

Obviously this doesn't apply to all types of antennas/feeds; some may provide higher cross polarization isolation.