Comparing Active and Passive UHF transponders

Electric field transponder systems are grouped as either active or passive. The active versions have their own batteries on board for powering up the transponders, while the passive versions are usually very energy efficient and can operate on the energy received from the reader field. At frequencies above 2.4Ghz transponders would usually be active due to problems in energising transponders which have a very high operating frequency. From 400Mhz to 2.45Ghz transponders would usually be passive in contruction.