Implementation of HEMP waveforms for time-domain modeling

This paper presents recent advances in the development of HEMP waveforms with causal responses suitable for implementation in Finite Difference Time Domain models. New time-domain implementations of the HEMP environment are proposed using direct and indirect employment of the HEMP waveform. Numerical instabilities of the waveform are addressed and a new stable waveform matched to the IEC standard has been evaluated. It is concluded that the implementation of the quotient exponential model provides a stable and accurate waveform for time-domain modelling

Near-field microwave sensor composed of 3D printed antennas and lenses

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

Microwave phase contrast imaging of the subsurface using variation in soil moisture level

A new microwave subsurface imaging product is described which is evolved via time lapsed microwave measurements, over several days, of the soil subsurface. The technique exploits changes in soil moisture levels that occur naturally due to evaporative and percolation processes. A novel technique is investigated for detecting and discriminating buried targets; it provides a scaled phase weighting procedure to form a cumulative B-scan image of the subsurface. The algorithm is demonstrated on ground penetrating radar measurements acquired in the XBand spectrum over soil where reference targets and other buried artefacts are placed. Early stage experimental results suggest the approach shows promise to provide enhanced subsurface imagery with reduced clutter and noise levels

Discrimination of buried objects using time-frequency analysis and waveform norms

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 time-frequency 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

Imaging SAR phenomenology of concealed vibrating targets

This paper describes the novel imaging of SAR phenomena produced from vibrating targets with multipath effects. It has been established, through numerical SAR experiments, that different physical mechanisms interact to produce new artefacts. The computations demonstrated that the edges of a dielectric medium can act as a source for multipath effects to emanate from, leading to the hypothesis that SAR artefacts can arise from through-wall SAR imagery. This deduction and mechanism of origin were validated through several experimental measurements, undertaken at Cranfield University’s Antennas and Ground-based SAR laboratory, yielding results that closely match those predicted

Correlation of specific absorption rates in the human head due to multiple independent sources

This paper examines how the SAR in the head is combined when exposed to the field due to multiple sources. The mechanisms when the sources have the same and different frequencies are discussed. FDTD simulation results are included when an anatomically realistic head is excited by various sources including: plane waves, vertically and horizontally orientated dipoles positioned in front and by the side of the head. Results are presented for two sources over the frequency range 0.5 to 4GHz

Fabrication procedure and performance of 3D printed X-band horn antenna

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 8.212.4GHz operating range. The measured and simulated antenna gain was in good agreement and increased monotonically from 10–17 ± 1.0dBi across the operating frequency

Near-field microwave imaging using a polarimetric array of 3D printed antennas and lenses

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

Correlation of specific absorption rates in the human head due to multiple independent sources

This is a conference paper [© IEEE]. It is also available at: http://ieeexplore.ieee.org/ Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.This paper examines how the SAR in the head is combined when exposed to the field due to multiple sources. The mechanisms when the sources have the same and different frequencies are discussed. FDTD simulation results are included when an anatomically realistic head is excited by various sources including: plane waves, vertically and horizontally orientated dipoles positioned in front and by the side of the head. Results are presented for two sources over the frequency range 0.5 to 4GHz

Comparison of performance of polarimetric decomposition techniques to suppress subsurface clutter in GPR applications

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