Enhanced Discrimination Techniques for Radar-Based On-Metal Identification Tags.

Abstract

The standoff detection and tracking of metallic targets in highly cluttered environments often poses a difficult engineering challenge. This work introduces a new radar-based approach to overcome these limitations. Novel planar retro-reflective array architectures are presented that, in conjunction with a low-cost, pulsed, Ku-band radar used as the reader, will aide in the standoff detection and tracking of large metallic objects in a highly cluttered environment.

In general, traditional methods to improve performance of such retro-reflective structures involve an increase in gain of the array. In this work, a passive Van Atta array is first presented that achieves 0dBsm of RCS from a retro-reflective tag with 10cm X 15cm footprint that makes use of linear series patch antenna arrays implemented in grounded coplanar waveguide (GCPW) architecture. Modulation is introduced into this structure to provide unique identification and, in conjunction with background subtraction, additionally yields a significant increase in the detectability of the tag without requiring additional gain. This work continues by addressing the narrow field of view in elevation plane that is the consequence of RCS enhancement techniques by developing a new retro-reflective feed architecture. A 300% increase in breadth of the vertical plane beam is demonstrated by feeding the linear series arrays from both terminal ends.

This work concludes with a novel cross-polarized retro-reflective array that utilizes polarization properties to further distinguish itself from surrounding clutter. This array achieves -15dBsm of cross-polarized RCS from an 8.5cm X 5cm footprint. Detectability is enhanced considering the reduced clutter backscatter in cross-polarization configuration at the frequency of operation. This tag configuration also allows ease of integration of amplifiers into the feed network without requiring circulator pairs or lossy two-port 3-dB hybrid junctions. A salient feature of this improved tag is an entirely non-reciprocal target whose unique polarization properties further distinguish it from the surrounding, reciprocal clutter. System techniques are demonstrated that exploit this unique response.

These novel planar retro-reflective array structures are designed and implemented at 26GHz, allowing for a small retro-reflective array footprint. Design details and measurement results for the various improved detection topologies are presented and performance enhancements quantified.