Radar Transponders

Radar Communications Techniques - Passive Transponders

Simple retro-reflecting structures based on corner reflectors are often employed as a means of increasing radar cross section (RCS) and hence target detectability. Retro-reflectors return incident radiation back in the direction of the source. However, if the reflected radiation is also modulated with a code unique to the target, many such targets may be identified by the interrogating source. To this end, modulated retro-reflectors have been developed at Oxford. The initial aims included terrestrial and marine traffic control where there is a need to detect and identify small craft, while a number of other applications include telemetry and high resolution range finding

The technique adopted is the modulated antenna retro-array, whereby antenna pairs in a two-dimensional array are joined by transmission lines and RF switches to achieve the twin aims of retro-reflectivity and modulation of the scattered signal. This novel combination of RF techniques is now protected by a patent (application no. 9720219.6, inventors are J.Thornton and D.J.Edwards) and prototypes have been constructed at 2.5 GHz and 9.4 GHz operating frequencies.

An advantage of the technique is the establishment of a passive communications link - the retro-reflector transmits no RF radiation and hence has low power requirements and does not pollute the local radio environment. Also, by employing planar antennas based on microstrip circuits, the antenna elements and RF modulation circuits may be combined on simple, cheap, lightweight laminates which are well suited to large scale economic production.

For more details contact Prof. David Edwards.