Here are some ways to prevent antennas from interfering when placed nearby.
- Increase the distance between them
- Orient for inefficient signal transfer (loops at 45 degrees from each other)
- Connect the loops to the tuner box with opposite winding directions
- Metal or ferrite shields to block or direct magnetic fields
- Lower the power levels
- Use the Multiple Antenna Reader which charges and listens to one antenna at a time
- Synchronize multiple Single Antenna Readers
The Multiple Antenna Reader slows the scan rate per antenna. With four antennas each loop is scanned at one quarter the speed of the reader. This may not be a problem depending on the velocity of the tag and the size of the scan zone.
Full speed scanning can be achieved by synchronizing multiple Single Antenna Readers so they all charge and listen at the same time. If the antennas are very close then the 134.2 kHz carriers may need to be synchronized by driving all readers from one oscillator.
The minimum separation between antennas before needing synchronization depends on many factors. The simplest way to find out is to build the system without synchronization and measure the read range at each antenna by turning them on one at a time. Then tune them all on. If the read range is the same you don't need to bother synchronizing.