A phase-modulating RF tag

A new form of RFID tag based on the concept of a phase-modulating surface is presented. The tag consists of a two by two array of pin diode controlled dipole elements. By applying individual d.c. control signals to each of the diodes, it is possible modulate RF energy scattered from the tag. An experimental system is described and measurements made at 10GHz are presented to show that the tag can impart binary phase modulation onto interrogating signals.