Browsing by Author "Morrow, Ivor L."

Now showing 1 - 15 of 15
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    Behaviour of characteristic modes on patch antennas in multilayered media
    (ARMMS: Automated Radio Frequency and Microwave Measurement Society, 2022-04-26) Adamson, Michael F.; Morrow, Ivor L.; James, David
    A design methodology is described supported by Characteristic Mode Analysis (CMA) to enhance the radiation gain from a patch antenna using multiple dielectric superstrates. Analytic expressions for the radiation field patterns and impedance match are derived for the patch eigenmodes. An equivalent commercial simulation model is used to determine the associated characteristic modes. Eigenmode and CMA behaviour are studied as low cost planar dielectric sheets are stacked above the antenna to affect an increase in the radiated field gain. Numerical results are compared with laboratory measurements made on several prototype dielectric radome antenna configurations and demonstrate an impedance bandwidth of 3.6% and radiated field pattern gain of 11.5dBi for a double layer superstrate antenna.
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    Comparison of performance of polarimetric decomposition techniques to suppress subsurface clutter in GPR applications
    (IET, 2019-02-18) Wirth, Sebastian G.; Morrow, Ivor L.
    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.
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    Correlation of specific absorption rates in the human head due to multiple independent sources, Loughborough Antennas & Propagation Conference, Loughborough, 16th - 17th November 2009
    (2009-11-19T13:19:41Z) Whittow, W.; Panagamuwa, C.; Derat, B.; Morrow, Ivor L.
    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.
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    Discrimination of buried objects using time-frequency analysis and waveform norms
    (IEEE, 2017-01-09) Morrow, Ivor L.; Wirth, Sebastian G.; Finnis, Mark V.
    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.
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    Effective polarization filtering techniques for ground penetrating radar applications
    (IEEE, 2019-01-10) Morrow, Ivor L.; Wirth, Sebastian G.
    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 Stokes parameters and model based polarimetric decomposition using the Yamaguchi technique. These techniques are applied to multi-frequency (0.4-4.8GHz) full polarimetric near-field radar measurements of scattering from surface laid calibration objects and shallow buried landmine types and show in detail how the decomposition results provide effective surface and sub-surface clutter reduction and guide the interpretation of scattering from subsurface objects. Data processing methods assume cross-polar symmetry and a novel bistatic calibration procedure was developed to enforce this condition. The Yamaguchi polarimetric decomposition provides significant clutter reduction and image contrast with some loss in signal power; while Stokes parameters also provide imagery localising targets, complementary information on the scattering mechanism is also obtained. Finally a third novel polarimetric filter was formulated based on differential interferometric polarimetric decomposition. The three combined techniques contribute to a significant improvement of subsurface radar performance and detection image contrast.
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    Enhanced Microwave Imaging of the Subsurface for Humanitarian Demining Applications
    (2020-07) Wirth, Sebastian G.; Morrow, Ivor L.
    This thesis presents a theoretical analysis and applied evaluation deploying ground penetrat ing radar (GPR) for landmine detection. An original contribution has been made in designing and manufacturing a light-weight, low-cost, fully polarimetric antenna system for GPR, enabling easy transportation and as sembly. This facilitates extensive use by various smaller communities in remote areas. By achieving the goal of supplying various smaller communities with advanced ground pene trating radar technology the technological standard of landmine detection can be improved beyond existing solutions such as metal detection or manual probing. The novel radar system itself allows detection of various subsurface targets of different shapes and sizes, metallic and non-metallic, in a number of different soils, such as sand, loam or gravel and therefore can be used in versatile environments. The GPR system has been realised by designing novel light-weight, 3D printed X-band horn antennas, manufactured from single piece plastic then copper electroplated. These an tennas are 50% lighter than their commercial equivalents. They are incorporated in an an tenna array as a group of four to allow full-polarimetric imaging of the subsurface. High resolution images of landmines and calibration targets were performed in the subsurface over an experimental sand test bed. For performing subsurface measurements in the near-field, four novel gradient-index (GRIN) lenses were designed and 3D printed to be incorporated in the apertures of the X band antennas. The improved target detection from these lenses was proven by scanning the test bed and comparing the imaging data of the antenna array with and without lenses attached. A rigorous theoretical study of different decomposition techniques and their effect on the imaging and detection accuracy for polarimetric surface penetrating data was performed and applied to the gathered imaging data to reliably isolate and detect subsurface targets. Studied decomposition techniques were Pauli decomposition parameters and Yamaguchi polarime try decomposition. It was found that it is paramount to use both algorithms on one set of subsurface data to detect all features of a buried target. A novel temporal imaging technique was developed for exploiting natural occurring changes in soil moisture level, and hence its dielectric properties. Contrary to the previously intro duced imaging techniques this moisture change detection (MCD) mechanism does not rely on knowledge of the used measurement setup or deploying clutter suppression techniques. This time averaged technique uses several images of a moist subsurface taken over a period while the moisture evaporates from the soil. Each image pixel is weighted by the phase change occurring over the evaporation period and a resulting B-scan image reveals the subsurface targets without surrounding clutter. Finally, a multi-static antenna set-up is examined on its capability for suppressing sur face clutter and its limitations are verified by introducing artificial surface clutter in form of pebbles to the scene. The resulting technique was found to suppress up to 30 The GPR antenna system developed in this thesis and the corresponding imaging tech niques have contributed to a significant improvement in subsurface radar imaging perfor mance and target discrimination capabilities. This work will contribute to more efficient landmine clearance in some of the most challenged parts of the world.
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    ESA measurements using the hybrid fibre-optic reflection measurement system
    (2009-11-19T16:41:30Z) Morrow, Ivor L.; Clow, N.
    Since the introduction of the Wheeler Cap method to measure the radiation efficiency of an Electrically Small Antenna (ESA), there have been several techniques presented in literature that have either enhanced on the method or provided an alternative technique. This paper presents measurements of the radiation efficiency of an electrically small monopole using the Hybrid Fibre-Optic RF Reflection Measurement System (HRS) integrated into the Wheeler Cap. The HRS isolates the ESA from the measurement system [1]. The ESA’s reflection coefficient can then be measured with the isolated ESA inside the Wheeler Cap and in freespace to determine its efficiency. The HRS is also integrated into a far-field measurement range to measure the far-field radiation pattern of the ESA.
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    Fabrication procedure and performance of 3D printed X-band horn antenna
    (IET, 2019-02-18) Wirth, Sebastian G.; Morrow, Ivor L.; Horsfall, Ian
    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.
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    Imaging SAR phenomenology of concealed vibrating targets
    (IEEE, 2018-08-16) Corbett, Brandon; Andre, Daniel; Muff, Darren; Morrow, Ivor L.; Finnis, Mark V.
    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.
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    Implementation of HEMP waveforms for time-domain modeling
    (IEEE, 2018-10-25) Mallinson, Derek; Morrow, Ivor L.
    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.
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    Microstrip antennas utilizing MEMS for reconfigurable polarisation states
    (2009-11-19T16:50:15Z) Morrow, Ivor L.; Clow, N.; Schaubert, D. H.
    A modern approach to an established technique is investigated for the electronic control of polarisation of microstrip patch antennas. The control is achieved by placing micro-electromechanical switches (MEMS) at appropriate locations in a patch antenna. The microwave MEMS are used to switch between open and short circuit conditions that allow reconfiguration of the modal fields. Changing the number and location of short circuit field regions changes the radiated field polarisation from linear horizontal to vertical, right hand circular or left hand polarisation. All of the polarisation states are obtained without changing the frequency of operation, input impedance or radiation pattern of the patch an
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    Microwave phase contrast imaging of the subsurface using variation in soil moisture level
    (IEEE, 2018-10-25) Wirth, Sebastian G.; Morrow, Ivor L.; Andre, Daniel
    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.
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    Near-field microwave imaging using a polarimetric array of 3D printed antennas and lenses
    (IET, 2019-02-18) Wirth, Sebastian G.; Morrow, Ivor L.; Horsfall, Ian
    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.
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    Near-field microwave sensor composed of 3D printed antennas and lenses
    (IEEE, 2018-10-25) Wirth, Sebastian G.; Morrow, Ivor L.
    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.
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    Wideband blade monopole antenna with sleeved coaxial feed
    (2009-11-19T15:46:13Z) Morrow, Ivor L.; Dingley, G.; Cooper, A. (Dstl)
    A wideband planar monopole antenna requiring a small ground plane is described. Numerical and measured results confirms the antenna has good radiation efficiency and stable omni-directional radiation patterns over an impedance bandwidth of 4.1:1 covering the 200-850 MHz frequency spectrum.