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Online ISSN 1751-8792 Print ISSN 1751-8784

IET Radar, Sonar & Navigation

Volume 2, Issue 6, December 2008

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Volume 2, Issue 6

December 2008

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    • Inverse synthetic aperture radar imaging of ship target with complex motion
      • Author(s): Y. Li ; R. Wu ; M. Xing ; Z. Bao
      • Source: IET Radar, Sonar & Navigation, Volume 2, Issue 6, p. 395 –403
      • DOI:  10.1049/iet-rsn:20070101
      • Type: Article
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      • p. 395 –403 (9)
        High-resolution inverse synthetic aperture radar (ISAR) imaging and recognition of ship target is very important for many applications. Although the principle of ISAR imaging of ship target on the sea is the same as that of flying target in the sky, the former usually has more complex motion (fluctuation with the oceanic waves) than the latter, which makes the motion compensation very difficult. However, the change in phase chirp rate caused by the complex motion of ships will deteriorate the azimuth focusing quality. In this paper, we first model the complex motion of ship target with cubic phase terms (parameterised on chirp rate and its change rate), then a new ISAR imaging method, referred to as TC-DechirpClean, is proposed, which estimates the chirp rate and the change rate of chirp rate of all scatters in the time–chirp distribution plane. Both numerical and experimental results are provided to demonstrate the performance of the proposed method.
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      Degradation in performance of active radar absorbent material due to cumulative element failure
      • Author(s): B. Chambers
      • Source: IET Radar, Sonar & Navigation, Volume 2, Issue 6, p. 404 –409
      • DOI:  10.1049/iet-rsn:20070118
      • Type: Article
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      • p. 404 –409 (6)
        There is continuing interest in the development of large-area active microwave panels for use as switchable windows, ‘wallpaper’, reflectors or radar-absorbent materials. The density of active devices on such panels may range from a few hundred to tens of thousands per square metre but there is no published information about the reliability of such panels in practice and the effects on their performance of cumulative device failure. A preliminary analysis of such effects in terms of panel radar cross-section and power consumption is provided.
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      Multi-range-resolution radar using inverse filters
      • Author(s): M. Shinriki  and  K. Hamada
      • Source: IET Radar, Sonar & Navigation, Volume 2, Issue 6, p. 410 –418
      • DOI:  10.1049/iet-rsn:20070186
      • Type: Article
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      • p. 410 –418 (9)
        The resolution of a radar range is generally fixed regardless of the detection range. The proposed receiving system for radars is configured with multiple inverse filters so that it has different range resolutions depending on the detection range, and the signal is compressed to a narrow arbitrary pulse width of less than or equal to the reciprocal of the spectrum bandwidth of the transmitted signal. Then the proposed receiving system may be able to have no sidelobes. The frequency response function of each inverse filter used in the receiver is expressed as D(f)/S(f), where D(f) is the Fourier transform of the desired output waveform d(t) and S(f) is the Fourier transform of the transmitted waveform s(t). Specific signal examples are used to clarify what sort of D(f) and S(f) are suitable for preventing D(f)/S(f) from diverging. With regard to this proposed receiving system, a theoretical improvement factor is indicated for the signal-to-noise ratio, and simulations and experiments are conducted to confirm the validity of the proposed receiving system.
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      Urban RF multipath mitigation
      • Author(s): B.D. Rigling
      • Source: IET Radar, Sonar & Navigation, Volume 2, Issue 6, p. 419 –425
      • DOI:  10.1049/iet-rsn:20080040
      • Type: Article
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      • p. 419 –425 (7)
        Sensing in urban environments is of growing interest to the surveillance community, as is observation of targets with micro-Doppler features – elements of the target structure with independent range–Doppler behaviour about some target centroid. Multipath effects unique in character to urban sensing can conceal important features in the range–Doppler response of a target with micro-Doppler behaviour. The range-Doppler smearing because of multipath is analysed, and this analysis serves as the basis for a prominent point multipath mitigation algorithm. The effectiveness of this technique is evaluated with simulated micro-Doppler data with artificial multipath effects.
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      Experimental investigation of selective localisation by decomposition of the time reversal operator and subspace-based technique
      • Author(s): J.-L. Li ; H.-F. Zhao ; W. Fang
      • Source: IET Radar, Sonar & Navigation, Volume 2, Issue 6, p. 426 –434
      • DOI:  10.1049/iet-rsn:20070110
      • Type: Article
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      • p. 426 –434 (9)
        The approaches of the active time reversal (TR) selective localisation based on the decomposition of the time reversal operator (DORT) and the TR multiple signal classification (MUSIC) location are presented. The waveguide experiment describes in detail the procedure of active TR location and shows that (i) the extended target could have multiple distinguishable eigenstates, unlike point-like targets in which one target corresponds to one eigenstate; (ii) the selective location can be achieved by means of the standard TR location in the presence of the suspended and bottom objects; (iii) compared with the standard TR location, TR MUSIC location based on signal subspaces performs better in locating non-resolved targets and has lower sidelobe levels to locate the extended target. Finally, the approach of acquiring the TR operator via array probing by weighting Hadamard–Walsh functions (to produce orthogonal beams) is discussed. The experimental result shows that the ambiguity surfaces of the standard TR location and the TR MUSIC location are greatly improved with this approach.
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      Theoretical limits on SAR imposed by the ionosphere
      • Author(s): D.P. Belcher
      • Source: IET Radar, Sonar & Navigation, Volume 2, Issue 6, p. 435 –448
      • DOI:  10.1049/iet-rsn:20070188
      • Type: Article
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      • p. 435 –448 (14)
        The ultimate theoretical limitations on space-based synthetic aperture radar (SAR) image formation that are imposed by the ionosphere are examined. The effects on the SAR image are derived from first principles, and it is shown that the ionosphere will cause defocusing in both the range and along track directions. The performance of an autofocus procedure is then examined, and it is shown that the range defocusing can always be removed, but the range time delay can only be determined for high percentage bandwidths and high signal-to-noise plus clutter ratios. It is also shown that the performance limits of autofocus are not determined by the absolute total electron content, but are given by the amount of ionospheric turbulence, which limits the along track resolution. The relationship between the requirement for a focussed SAR image and the S4 index and the integrated strength of turbulence CkL is derived.
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      Linearly constrained minimum-‘normalised variance’ beamforming against heavy-tailed impulsive noise of unknown statistics
      • Author(s): J. He  and  Z. Liu
      • Source: IET Radar, Sonar & Navigation, Volume 2, Issue 6, p. 449 –457
      • DOI:  10.1049/iet-rsn:20080035
      • Type: Article
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      • p. 449 –457 (9)
        A new beamforming approach to combat the arbitrary unknown heavy-tailed impulsive noises including all α-stable noises with infinite variance or infinite mean is presented. The new approach, termed as linearly constrained minimum-‘normalized variance’ beamformer (LCMNV), is formulated as one to minimise the normalised variance of the beamformer's output, subject to a pre-specified set of linear constraints. The normalised variance is defined as a pseudo-correlation function of the instantaneously adaptive, infinity-norm snapshot-normalised data, as an alternative to the customary ‘fractional lower-order moments’ (FLOM) for heavy-tailed impulsive noise environments. The proposed beamformer is in essence second-order statistics based, and produces an instantaneously scaled beamformer output. The LCMNV beamformer outperforms the FLOM beamformer with the following advantages: (i) computationally simpler with a closed-form solution, (ii) requiring no prior information or estimation of the effective characteristic exponents of the impulsive noises, (iii) applicable to a wider class of heavy-tailed impulsive noises and (iv) offering better interference-rejection ability.
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      Radar detection based on Bayesian estimation of target amplitude
      • Author(s): M.F. Sabahi ; M. Modarres Hashemi ; A. Sheikhi
      • Source: IET Radar, Sonar & Navigation, Volume 2, Issue 6, p. 458 –467
      • DOI:  10.1049/iet-rsn:20070108
      • Type: Article
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      • p. 458 –467 (10)
        A new approach to detect a target with an unknown amplitude in clutter is proposed. The received signal models under two hypotheses, H0 and H1, are assumed to be the same, except that the target amplitude is zero under H0. Using the Bayesian approach, it is shown that the likelihood ratio can be calculated as the ratio of the prior to posterior probabilities of the target amplitude. Based on this relation, a new method for target detection in Gaussian clutter is presented. This method is applied to cases with both known and unknown clutter statistics and in each case, white and coloured clutters are considered. Simulation results show that the proposed detector has a much better performance compared with conventional generalised likelihood ratio test detectors.
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