What is the difference between Monostatic and Bistatic RFID?
Monostatic RFID Antennas & Readers
Typically, RFID readers are monostatic. Monostatic systems use the same antenna for both receiving and transmitting purposes. As shown in the figure below (Figure 1), both antennas in the system first transmit and then switch modes and start receiving RF energy. This system is usually much cheaper than a bistatic system because it requires less antennas and RF cables, but it is also slower than standard bistatic systems because the reader has to switch between transmitting and receiving modes.
Bistatic RFID Antennas & Readers
Bistatic systems use separate antennas for either transmitting or receiving RF energy. In order to have a bistatic system, you must have a bistatic reader. A bistatic reader has two separate RF channels for transmitting and receiving RF energy for every port (see figure 2 below). Each individual antenna port only has one job in a bistatic system, which means bistatic systems read RFID tags faster than monostatic systems.
Circularly polarized antennas are recommended for use in bistatic systems as linear antennas can couple with each other leading to mutual interference. Even while using circularly polarized antennas in a bistatic system, the transmit and receive antennas should have opposite polarization senses. A bistatic system will perform better when a right-hand circularly polarized antenna is paired with a left-hand circularly polarized antenna. The two different senses mitigate antenna coupling and multipath reflections, thus improving the performance of the RFID system.