| 1. |
- Aldhubaib, F., et al.
(författare)
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Aspect segmentation and feature selection of radar targets based on average probability of error
- 2010
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Ingår i: IET Microwaves, Antennas and Propagation. - : Institution of Engineering and Technology (IET). - 1751-8725 .- 1751-8733. ; 4:10, s. 1654-1664
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Tidskriftsartikel (refereegranskat)abstract
- Through statistical estimation by a non-parametric model, a fused polarimetric and resonant return from the radar target is modelled as a function of the target aspect angle. The outcome of this type of modelling is a set of non-parametric density estimates, which are then used to represent this target in a multi-dimensional probability space. These densities within this probability space can be well separated and therefore utilised to make decision rules to identify targets of interest. The return set to be modelled is the average power set associated with spectral bands centred on the target natural resonant frequencies. This return set is mapped into density set using a Gaussian kernel function; subsequently, the density set will be considered as the target radar feature set of interest. To decrease density overlapping between respective densities of different targets, a criterion based on the Bayesian error is employed; first, to bisect the aspect global range into smaller sectors, and second, to select discriminative features that can minimise the average probability of error between the targets respective features. The results show that two targets with similar resonant frequencies can be separated by the Bayesian error criterion based on the proposed features. A simple likelihood ratio test had more than 80% success down to 20 dB of signal-to-noise ratio.
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| 2. |
- Dobsicek Trefna, Hana, 1979, et al.
(författare)
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Evolution of an UWB antenna for hyperthermia array applicator
- 2012
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Ingår i: Proceedings of 6th European Conference on Antennas and Propagation, EuCAP 2012. Prague, 26-30 March 2012.. - 9781457709180 ; , s. 1046 - 1048
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Konferensbidrag (refereegranskat)abstract
- Designs of three UWB antennas and their suitability to be used as a basis antenna element in the hyperthermia applicator for the treatment of tumors in head and neck region are considered. The antennas with reflection coefficient less than -10 dB at frequency range 350 MHz to 1 GHz are immersed in water bolus. The evaluation of the SAR distributions was carried out by comparing the different cross-sections of muscle equivalent phantom. Numerical simulations were performed in CST Microwave studio and verified experimentally via measurements of S-parameters and SAR distributions in phantoms.
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| 3. |
- Fayazi, Seyedeh Shaghayegh, et al.
(författare)
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Microwave imaging of near-field object using ultra-wideband synthetic aperture radar algorithm
- 2012
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Ingår i: 2012 IEEE ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM (APSURSI). - 1522-3965. - 9781467304627
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Konferensbidrag (refereegranskat)abstract
- A simple procedure that suppresses artefact from ultra-wideband (UWB) synthetic aperture radar (SAR) images is proposed and verified using experimental data. The proposed imaging solution is useful for imaging small objects located in the near-field region with less ambiguity.
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| 4. |
- Fayazi, Seyedeh Shaghayegh, et al.
(författare)
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UWB SAR Imaging of Near-Field Object for Industrial Process Applications
- 2013
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Ingår i: 7th European Conference on Antennas and Propagation, EuCAP 2013, Gothenburg, Sweden, 8-12 April 2013. - 2164-3342. - 9781467321877 ; , s. 2245-2248
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Konferensbidrag (refereegranskat)abstract
- Ultra wideband technology becomes more widely used for near-field object detection. We present an aperture synthetic radar (SAR) system using ultra-wideband (UWB) signals for such applications. One of the problems with UWB time-domain SAR imaging algorithm is the artefact originated from scattered field of adjacent objects. In this paper an algorithm based on the Range Point Migration (RPM) method is used to alleviate this problem. This method estimates a possibility distribution of the optimal Direction of Arrival (DOA) of the scattered field from objects. A weighting factor based on this possibility is used to suppress the effect of artifact scattered fields. The results in the paper show that the UWB SAR accompanied with RPM can produce an image of an object with a significant suppression of undesired artifact from scattered field of adjacent objects.
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| 5. |
- Johansson, Markus, 1978, et al.
(författare)
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Comparison between Two Phase Retrieval Methods for Electromagnetic Source Modeling
- 2011
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Ingår i: Progress in Electromagnetics Research B. - 1937-6472. ; 30, s. 239-253
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Tidskriftsartikel (refereegranskat)abstract
- Phase-retrieval from measured phaseless field data is of interest for various applications including electromagnetic dosimetry, electromagnetic compatibility investigations, near-field to far-field transformations and antenna diagnostics. In this study two phaseretrieval methods are compared. The first method, the adjoint field method, employs a gradient-based optimization algorithm based on the adjoint fields. The second method, the phase angle gradient method, uses an optimization algorithm based on the phase angle gradients of a functional. The methods are tested with numerical test cases and the phase angle gradient method is found to retrieve the phase with the best accuracy. Moreover it gives results that agree well with correct phase.
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| 6. |
- Johansson, Markus, 1978, et al.
(författare)
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Electromagnetic Source Modeling using Phase Retrieval Methods
- 2011
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Ingår i: 30th URSI General Assembly and Scientific Symposium, URSIGASS 2011, Istanbul, 13-20 August 2011. - 9781424451173 ; , s. 1-2
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Konferensbidrag (refereegranskat)abstract
- Modeling of the field distributions from electromagnetic sources is of interest for various applications for example electromagnetic compatibility investigations, near-field to far-field transformations, antenna diagnostics and electromagnetic dosimetry. In order to determine whether exposure safety guidelines, such as the EU directive 2004/40/EC, are complied with, source modeling methods are important. Two methods for determining the total field, including phase information, when only field amplitudes have been measured on a set of planes in front of an electromagnetic source have been developed. The first method, the adjoint field method, is a gradient based optimization algorithm based on the adjoint fields. The second method, the phase angle gradient method, employs an optimization algorithm based on the phase angle gradients of a functional. Promising results have been obtained both for numerical test cases and for measured field.
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| 7. |
- Johansson, Markus, 1978, et al.
(författare)
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Performance Evaluation of Phase-Angle Gradient Method for Phase Retrieval based on Low-Frequency amplitude-Only Near-Field Data
- 2010
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Ingår i: Progress in Electromagnetics Research B. - 1937-6472. ; 25:25, s. 113-130
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Tidskriftsartikel (refereegranskat)abstract
- The Phase Angle Gradient Method (PAGM) is a recent technique developed for phase retrieval based on amplitude-only measurement data. Preliminary results have shown that the PAGM is able to perform phase retrieval at 100MHz with accurate phase information based on measured fIeld components on three planar surfaces. In this paper, a performance evaluation of the PAGM under different conFigurations is conducted. Phase retrieval based on field measurements for different plane sizes and separations between the planes are studied rigorously. In addition, the PAGM is tested for different initial phase distributions. The results show that the PAGM is capable of retrieving phase information even if the separation between the measurement planes is small in terms of wavelengths.
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| 8. |
- Johansson, Markus, 1978, et al.
(författare)
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Source Modeling using Phaseless Low-Frequency Near-Field Measurements
- 2012
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Ingår i: IEEE Transactions on Electromagnetic Compatibility. - 0018-9375 .- 1558-187X. ; 54:3, s. 613-624
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Tidskriftsartikel (refereegranskat)abstract
- Field measurements of both amplitude and phase generally are more complicated and require more expensive equipment than amplitude-only measurements. Phase retrieval from measured phaseless field data is, therefore, of interest for source modeling in dosimetry applications, electromagnetic compatibility investigations, near-field to far-field transformations and antenna diagnostics. We here present a phase-retrieval method that uses an optimization algorithm based on the phase angle gradients of a functional. Numerical test cases have shown that the method is working for different initial phase distributions as well as different placements of the source. The method also works well for a test case with measured 50 Hz magnetic flux density from a transformer. The obtained phase angles on a measurement plane in front of the transformer gave calculated field amplitudes on other measurement planes that agree well with measured field. The ratios between the largest amplitude difference and the largest measured amplitude for the three Cartesian magnetic flux density components, for one of the planes, are for example 6.62%, 9.51% and 6.40%.
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| 9. |
- Lui, Hoi-Shun, 1980, et al.
(författare)
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A Novel, Fast, Approximate Target Detection Technique for Metallic Target Below a Frequency Dependant Lossy Halfspace
- 2010
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 58:5, s. 1699-1710
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Tidskriftsartikel (refereegranskat)abstract
- The extinction pulse (E-Pulse) technique has been widely applied to problems involving radar target identification. In this paper a fast approximate target detection and recognition scheme based on the E-Pulse technique is proposed and applied to a subsurface target detection and recognition scenario. Previous studies have demonstrated that the target resonances for subsurface targets are closely related to the target resonances for a target within a homogenous environment. In the proposed method, the target resonance for the target in the homogenous medium will be used to construct the E-Pulse for target detection and recognition purposes. The details of the proposed method will be described in this paper. The obvious example of a target below a dielectric halfspace is the use of ground penetrating radar (GPR) for detecting and recognizing unexploded ordnance (UXO). However, instead of a GPR related scenario, a numerical example of a biomedically related problem, of a hip prosthesis model sited within a halfspace of homogenous human tissue model with realistic dielectric properties will be used to demonstrate the feasibilities of the proposed technique for target detection and recognition. The reasons for the choice of this particular example will also be explained in the paper.
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| 10. |
- Lui, Hoi-Shun, 1980, et al.
(författare)
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Analysis of Forward Scattering Data for Microwave Breast Imaging
- 2011
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Ingår i: Asia Pacific Microwave Conference. - 9781457720345 ; , s. 195-198
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Konferensbidrag (refereegranskat)abstract
- Microwave imaging for breast cancer detection has been of significant interest for the last two decades. Recent studies focus on solving the imaging problem using an inverse scattering approach. Success of these methods relies on the quality of the forward data such that the tumor inside the breast volume is well illuminated. In this paper, a numerical study of the forward scattering data is conducted and the potential use of full polarimetric data is investigated.
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