Ground Penetrating Radar (GPR) are widely used to probe the sub-surface. Recently, various time-frequency analyses has been proposed to discriminate buried land mines from other clutter objects and thus reduce GPR false alarm rates. This paper examines the possibility for discrimination and assesses it experimentally. The approach uses the Choi-Williams timefrequency transform to analyse ultra-wideband signal returns from a range of shallow buried objects. Single Value Decomposition is performed on isolated object time-frequency signatures. The signatures are evaluated using a set of waveform norms that discriminate in time, frequency and energy content. The results indicate that this approach could improve land mine detection rates and reduce false alarms.

A novel near-field microwave imaging system was designed and fabricated using the three-dimensional (3D) printing technique to manufacture X-band Pyramidal horn antennas and planar graded-index (GRIN) lenses. The flat lens focusing profile is synthesised by varying the refractive index radially in incremental steps that adjust the air-dielectric mixture. The lens is designed for direct attachment to the antenna aperture and transforms spherical waves emanating from antenna phase center into plane radiating waves. Measurement results show the antenna lens system input impedance is ≤-10 dB, radiation pattern gain is between 10-16 dBi over the 8-12 GHz frequency band and when arrayed for polarimetry sensing has a polarisation cross-talk of ≤-35 dB. The antenna lens system is suitable for ground penetrating radar applications.

This paper presents the design, fabrication and performance of fusion deposition modeled 3D printed X-band horn antennas. The WR90 waveguide feed and pyramidal horn flare are printed as one piece from Acrylonitrile Butadiene Styrene (ABS). Different metallisation techniques are assessed to provide a uniform 40 micron coat on the ABS surfaces. Uniquely, the coaxial waveguide launcher is integrated with the waveguide section in a single interference fit operation. The measured and simulated radiation patterns showed good correlation and the antenna return loss was ≤-10dB over the 8.2-12.4GHz operating range. The measured and simulated antenna gain was in good agreement and increased monotonically from 10 − 17 ± 1.0dBi across the operating frequency. (a) (b) Figure 1. Geometry and finite element model for the 3D printed Pyramidal horn antenna (a) end view (b) side view.

A novel near-field microwave imaging system was designed and fabricated using the three-dimensional (3D) printing technique to manufacture X-band Pyramidal horn antennas and planar graded-index (GRIN) lenses. The flat lens focusing profile is synthesised by varying the refractive index radially in incremental steps that adjust the air-dielectric mixture. The lens is designed for direct attachment to the antenna aperture and transforms spherical waves emanating from antenna phase center into plane radiating waves. Simulated and measurement results show the antenna lens system input impedance is ≤ -10 dB, radiation pattern gain is between 17-20dBi over the 8.2-12.4GHz frequency band and when arrayed for polarimetry sensing has a polarisation cross-talk of ≤-50 dB. A ground penetrating radar system using the nearfield array was scanned over buried targets. The SAR results demonstrated high resolution and polarisation discrimination imagery capable of detecting subsurface objects.

The effect of different decomposition techniques on the imaging and detection accuracy for polarimetric surface penetrating radar data is studied. We derive the general expressions for coherent polarimetric decomposition using the model based polarimetric decomposition of Yamaguchi technique and compare these with some Stokes and Pauli coherent polarisation decomposition parameters. These mathematical treatments are then applied to laboratory based X-band (8.2-12.4GHz) full polarimetry near-field radar measurements taken of shallow buried reference and calibration objects and different landmine types. The Yamaguchi polarimetry filters demonstated significant surface and sub-surface clutter reduction and contrast in subsurface imagery, with some loss in signal power. The Stokes and Pauli parameters demonstrated similar clutter reduction in subsurface imagery providing additional beneficial information on the targets scattering mechanism. Combining these techniques contributes to an improvement of subsurface radar discrimination and understanding of the target type.