Browsing by Author "Wirth, Sebastian"

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    Designing 3D Printed Horn Antennas for Landmine Detection
    (Cranfield University, 2018-01-03 15:24) Wirth, Sebastian
    3MT presented at the 2017 Defence and Security Doctoral Symposium.This work presents the novel design and manufacture of a 3D-printed X-band horn antenna as a single part . This design considerably reduces manufacturing and assembly costs, is sixty percent lighter than an equivalent commercial antennas and offers similar performance. The antennas are particularly suitable for operational scenarios were weight is a key system requirement such as UAVs or as intended in this research for near field ground penetrating radar applications.
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    Effective Polarization Filtering Techniques for Ground Penetrating Radar Applications
    (Cranfield University, 2018-11-23 09:27) Wirth, Sebastian
    Poster presented at the 2018 Defence and Security Doctoral Symposium.Ground penetrating radar (GPR) is increasingly being used for landmine detection. In contrast to metal detecting, GPR can be used for detection of low-metal content or non-metal content targets. Subsurface radar still suffers from two typical problems, a strong clutter response from the surface and high signal to clutter levels in the underground. This paper addresses these problems through the use of a novel near-field full-polarimetric (0.4-5.0GHz) SFCW GPR system that measures the polarimetric microwave backscatter response and synthesises an equivalent complex clutter scattering matrix that suppresses subsurface clutter in the co-pol and cross-pol channels. The technique is compared to Stokes parameter analysis of the polarimtric response and found to offer comparable or better clutter suppression imagery. Results for these techniques are presented for raw B-scan GPR images and synthetic aperture radar imagery. Significant signal features for various buried objects are also characterised. These include GPR near-field radar cross sections for some landmines and common clutter targets and the unique polarization signatures of these objects that can be used to both discriminate and potentially identify unknown landmines. The paper also describes the polarisation channel equalisation and quasi-bistatic antenna calibration procedure undertaken to acquire accurate imagery and absolute RCS values. The presented GPR system uses a linear polarised TEM horn as transmit antenna and two near-field probe (loop) antennas, arranged orthogonally and in front of the TEM horn, to collect the co- and cross-polar response. The loop antennas are placed just outside the near-field of the TEM horn at 11 cm in front of the aperture at 400 MHz. The antenna configuration is moved over a 3m sandpit mechanically. The sandpit is comprised of three bays that each are filled with different soil types (sand, sand/gravel mix and loam) and the presented clutter suppression techniques are tested for targets buried in these different soils with different moisture levels.
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    Giving an Antenna a Pair of Glasses
    (Cranfield University, 2017-11-15 12:02) Wirth, Sebastian
    Digital image presented at the 2017 Defence and Security Doctoral Symposium.This shows a close up image of a novel 3D printed flat microwave lens. The lens synthesises a conventional hyperbolic profile by digitally adjusting the air/ABS plastic density in the radial direction. The resultant synthetic lens is light and compact and offers a performance enhancement component to many antennas and arrays.
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    Light Weight Low Cost X-Band Antennas and Waveguide Components Using Electroplated 3D Printed Plastics
    (Cranfield University, 2017-11-15 12:05) Wirth, Sebastian; Morrow, Ivor; Andre, Daniel; Finnis, Mark
    Poster presented at the 2017 Defence and Security Doctoral Symposium.Low weight and low cost are attractive features in many antenna and waveguide applications including mobile communication, remote sensing and medical scenarios. Electroplating shaped three-dimensional printed plastic components to produce highly conductive surfaces is one advantageous approach. This research contributes to the newly developed design procedure, manufacture and measurements of a 3D printed microwave pyramidal horn antenna electoplated with a 40 um copper coating and a novel flat 3D printed Graded Refractive Index (GRIN) lens. The antenna, waveguide and lens are printed in two pieces, the lens is then attached to the horn antenna aperture to provide a highly collimated radiated beam. Measurements conducted at Cranfield University Antennas and Ground Based SAR (AGBSAR) laboratory on the antenna matching radiated fields and gain demonstrate the performance meets, and in some cases exceeds, that of a standard X-band milled aluminium horn antenna and waveguide but with significantly reduced weight and cost. When the lens is attached to the horn antenna aperture an increase in antenna radiated gain of 5dBi over a 200 MHz bandwidth at 10 GHz is demonstrated. The hybrid antenna-lens sensor is highly suitable for near-field ground penetrating radar imaging of buried landmines. We acknowledge the financial support of the Sir Bobby Charlton Charity "Find A Better Way".
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    Near-Field Virtual Bandwidth Synthetic Aperture Radar Processing for Humanitarian Landmine Detection
    (Cranfield University, 2017-11-15 11:56) Wirth, Sebastian; Morrow, Ivor; Andre, Daniel; Finnis, Mark
    Poster presented at the 2017 Defence and Security Doctoral Symposium.This research presents the first experimental demonstration of the Near-Field Virtual Bandwidth SAR (NFVB-SAR) imaging technique. NFVB-SAR is a newly developed sub-surface imaging technique which in contrast to traditional imaging techniques promises subsurface imaging of soils at ultra-high, centimetre-scale resolution using narrow bandwidth. We specifically exploit the differential interferometric SAR phase history of an electromagnetic wave within a drying soil volume to generate high resolution sub-surface mapping from the returned wave through the soil volume. Experiments were conducted at the Cranfield University Antennas and Ground Based SAR (AGBSAR) laboratory using a near-field full polarimetric data acquisition ground penetrating radar. Measurements were taken over a sandy soil containing a buried landmine while the moisture level was varied. - firstly during controlled water addition and then during an extended natural drying out period. As the sand volume dries, the real radar frequency is sequentially transported across a virtual bandwidth of virtual frequencies. The preliminary results demonstrate that even a moderate soil moisture change (SMC) can produce large virtual bandwidths; for e.g. an SMC change of 10% can provide 6cm vertical resolution at X-band. We acknowledge the financial support of the Sir Bobby Charlton Charity "Find A Better Way",10.17862/cranfield.rd.5585245.v1.