Browsing by Author "Alabaster, Clive M."

Now showing 1 - 7 of 7
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    The dependence of radar target detectability on array weighting function
    (2009-07-14T14:40:00Z) Alabaster, Clive M.; Hughes, Evan J.
    This paper describes simulation work to assess the detectability of targets by an airborne fire control radar (FCR) operating in a medium pulse repetition frequency (PRF) mode in the presence of strong ground clutter as a function of transmitting and receiving array weighting functions.
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    The Design of medium PRF radar schedules for optimum detectability in diverse clutter scenes
    (2009-04-22T14:28:48Z) Alabaster, Clive M.; Hughes, Evan J.
    Airborne fire control radars using medium pulse repetition frequency (PRF) waveforms are required to maintain good target detectability in various clutter scenes. This paper describes work to optimise PRF values of 3 of 8 medium PRF schedules in varying clutter scenes in order to achieve optimal target detectability. To this end, the detectability map is introduced as a means of illustrating and quantifying target detectability over the full Range/Doppler space of interest. The paper concludes that optimised PRF sets achieve similar detectability performances irrespective of the clutter scene.
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    Examination of the effect of array weighting function on radar target detectability
    (2010-07-01) Alabaster, Clive M.; Hughes, Evan J.
    This paper describes a methodology to assess the detectability of targets by anairborne fire control radar operating in a medium PRF mode in the presence of strongground clutter as a function of the transmitting and receiving antenna array weightingfunctions and proportion of failed array elements. It describes the radar, antenna andclutter modelling processes and the method by which target detectability is quantified.The detectability of targets in clutter is described using a detectability map, whichprovides a useful means of comparing target detectability as clutter conditions change.It concludes that the best target detectability is to be achieved using those weightingfunctions on transmit and receive which result in the lowest average sidelobe levelsbut that the margins between the more highly tapered weighting functions were small.Furthermore, it concludes that target detectability degrades as the proportion of failedelements increases. A failure of 5% of the elements gave modest, though meaningful,degradations in target detectability and would therefore form a suitable upper limit.
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    The Measurement of the Reflection and Transmission Properties of Conducting Fabrics to Milli-Metric Wave Frequencies
    (2007-01-01T00:00:00Z) Alabaster, Clive M.; Oxley, C.; Williams, J.; Hopper, R.; Flora, H.; Eibeck, H.
    There is increasing interest in conducting fabrics and their uses at RF and microwave frequencies. This paper for the first time looks at the reflection and transmission measurements of bobbinet and knitted materials from around 8GHz into the milli-metric frequency range 110GHz, where the material geometry is comparable to the wavelength of the wave. Bobbinet materials were found to behave like lossy dielectrics and may be useful in the construction of thin light-weight screening and absorption planes. While the knitted materials, with very small mesh geometry, gave a reflection coefficient which was comparable to a metal foil.
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    Medium PRF Schedules for Airborne Fire Control Radar
    (2009-04-22T14:23:36Z) Alabaster, Clive M.; Hughes, Evan J.; Parry, S. M.; Wiley, D. A.; Matthew, J. H.; Davies, P. G.
    Many modern radar systems use medium pulse repetition frequency (PRF) waveforms to measure target range and velocity in the presence of clutter. Medium PRF waveforms offer excellent clutter rejection characteristics which render them an attractive proposition for airborne fire control radar plus a variety of other military radar applications. This paper describes work to optimise the selection of precise values of PRF for a variety of medium PRF schedules and to rate the quality of the solutions found.
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    The Microwave properties of tissue and other lossy dielectrics
    (Cranfield University, 2004-03) Alabaster, Clive M.; Dahele, J S
    This thesis describes work on the theoretical modelling and experimental measurement of the complex permittivity of dielectrics. The main focus of research has been into the characterisation of permittivity of planar and layered samples within the millimetre wave band. The measurement method is based on the free-space measurement of the transmission and reflection coefficients of samples. A novel analytical method of determining the transmission and reflection coefficients as functions of frequency arising from a generalised structure of planar dielectric layers is also described and validated. The analytical method is based on signal flow techniques. The measurement and analytical techniques have been applied in two main areas: firstly, the acquisition of new data on human skin in the band 57 to 100GHz and secondly, the detection and location of defects in composite materials for which a band of 90 to 100GHz was used. Measurements have been made on the complex permittivity of a single sample of excised human skin fixed in formaldehyde. The experimental results have been corrected to account for the fixing process in formaldehyde and are projected to body temperature. This data is, to the best of the author’s knowledge, the first of its kind to be published. Predicted skin permittivity based on various relaxation models varies widely and only partially fits the measured data. The experimental results have been used to determine the parameters of a Cole-Cole function which gives the best fit to the measured data. The measured skin data has also been used to calculate power deposition in skin exposed to millimetre wave radiation. This work concludes that a skin surface temperature rise of only 0.20C results from a thirty second exposure to signals of 100W/m2. Experimental work with fibreglass composite samples has shown that defects such as delaminations, voids, matrix cracks and improper cure result in resolvable differences in the dielectric properties of the samples at 90 – 100GHz. The measurement technique is particularly sensitive to the detection of cracks and its spatial resolution is 20mm or better. Whilst confirming the general conclusions of previously published work, the specific findings of this study are novel.
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    Microwave radar imaging of inhomogeneous breast phantoms using circular holography
    (2012-07-12) Flores-Tapia, Daniel; Maizlish, Oleksandr; Alabaster, Clive M.; Pistorius, Stephen
    Circular holography is a novel reconstruction technique for Breast Microwave Radar (BMR) imaging. Compared to current state of the art BMR image formation methods, this reconstruction approach yields spatially accurate images with higher signal to noise ratios and no artifacts. Nevertheless, a preclinical study is required to assess the feasibility of this technique in realistic breast imaging scenarios. In this paper, a series of preliminary results showing the performance of circular holography on preclinical datasets are presented. These datasets were recorded from inhomogeneous breast phantoms that mimic the dielectric properties and the anatomy of the different breast tissues. These phantoms were fabricated using Magnetic Resonance (MR) images a base model to emulate the shape and volumes of dense tissue regions. The reconstructed BMR images show that tumor and fibroglandular tissue responses can be effectively distinguished, suggesting that circular holography can be used as BMR reconstruction approach in clinical scenarios.