HF RFID Reader Antenna Producing Uniform Horizontal Magnetic Fields Over a Plane

A planar loop antenna producing uniform horizontal magnetic fields over its plane is presented. The antenna consists of a pair of two-turn spiral coils that are excited alternately. To avoid the bad effect of magnetic coupling between the coils, one of them is made up of a series combination of two spiral coils wound in opposite directions, and a good isolation of more than 32 dB is achieved. The antenna is suitable for a high-frequency radio frequency identification reader antenna that is installed under a chip tray to monitor gaming chips in electronic table game systems.