PAPER- A Phase modulated RF tag

Introduction

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 to 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.

Experimental system

The RF tag consists of an active surface placed in front of a conducting back-plane. The active surface is a 2 by 2 grid of pin-diode loaded dipoles and is separated from an Aluminium back-plane by a quarter-wavelength thick Rhoacell 51 foam spacer.

Independent switching of each element of the array provides a total of 16 possible scattering states. However if we consider normal incidence illumination of the tag and the mono-static scattered field, then the number of scattering state combinations reduces to five (Fig.4) .

Measurements

The experimental PMRF tag was tested in a NRL arch configured to measure mono-static back-scatter reflectivity using a Hewlett-Packard 8720B network analyser.

Conclusion

An experimental RF tag designed to operate at 10GHz has been designed and tested. Measured data shows that the tag behaves in a similar manner to that predicted by a simplified model, and that the tag can impart BPSK modulation onto a continuous wave incident signal.

This contribution has been published on Loughborough Antenna and Propagation Conference 2011. For further information, please contact elq10yw@sheffield.ac.uk 


Other authors are Dr. A. Tennant and Prof. R.J. Langley;


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