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Radar, Sonar and Navigation, IEE Proceedings -

Issue 6 • Date Dec 2001

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Displaying Results 1 - 10 of 10
  • Ambiguities in the harmonic retrieval problem using non-uniform sampling

    Page(s): 325 - 329
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (455 KB)  

    Harmonic retrieval is an important problem in signal processing and has received a lot of attention. However, solutions to the problem are generally based on uniform sampling with a rate equal to or greater than the Nyquist rate, in order to avoid certain overlapping (ambiguities) of the spectrum. An investigation is carried out for the detection and estimation of ambiguities in the harmonic retrieval problem, in the case of non-uniform sampling at a rate lower than the Nyquist rate, using differential geometry. An approach for the calculation of the maximum number of ambiguous generator sets of frequencies, associated with a given non-uniform sampling, is also presented and it is then used for identifying unambiguous groups of irregular samples View full abstract»

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  • Random wave methods for the prediction of the RCS of homogeneous chaotic straight ducts

    Page(s): 331 - 337
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    It is now fairly well established that convergence of shooting-and-bouncing ray methods is not feasible for the determination of the radar cross-section (RCS) of most realistic engine ducts. This is a consequence of classical chaos theory which was not recognised by radar engineers until quite recently (Mackay, 1998). However, at the time no solution to the problem was offered. A random wave method is described for the determination of representative RCS distributions of chaotic straight ducts, under two assumptions: first, that there is local field homogeneity, and secondly, that a Kirchhoff approximation is valid. Typical duct field magnitudes are illustrated for a stadium cross-section duct and the RCS is predicted as a function of scatter angle. A comparison is also made with an accurate modal solution View full abstract»

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  • Time-delay estimation for sinusoidal signals

    Page(s): 318 - 324
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (502 KB)  

    The problem of estimating the difference in arrival times of a complex sinusoid received at two spatially separated sensors is considered. Given the sinusoidal frequency, a simple delay estimator using the phase difference of the discrete-time Fourier transforms of the received signals is devised. Using the periodogram, the algorithm is extended to estimate the delay when the frequency is unknown. The minimum achievable delay variances for the cases of known/unknown frequencies and constant/rectangular envelopes are also derived. Extension to time-delay estimation using real sinusoids is also investigated. The effectiveness of the method is demonstrated by comparing it with the performance bounds for different frequencies, envelopes and noise conditions View full abstract»

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  • Analysis of distortion in the high range resolution profile from a perturbed target

    Page(s): 353 - 362
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (846 KB)  

    Experimental results have demonstrated that even when a target possesses very small perturbed rotational motion, its high range resolution (HRR) radar image profile can be severely distorted. A numerical model has been developed and is able to accurately simulate the observed distorting effects. The well known range-Doppler coupling effect offers a partial explanation for the distortion of a target's HRR profile when the perturbing rotational motion is constant in time during radar interrogation. A more interesting and much more dramatic situation arises when the perturbing motion is time-varying; severe distortion in the target's HRR profile can occur due to the excitation of higher-order sidebands in the phase of the target echo View full abstract»

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  • New approach for hybrid strip-map/spotlight SAR data focusing

    Page(s): 363 - 372
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (754 KB)  

    A new algorithm is presented for processing SAR data acquired in the hybrid strip-map/spotlight SAR configuration whose acquisition mode allows the generation of microwave images with an azimuth resolution better than that obtained in the strip-map case and with an imaged area larger than that achieved in the spotlight operation. The algorithm extends the focusing capability of conventional strip-map processing techniques to the hybrid SAR data; this result is achieved by generalising a previously proposed two-step focusing technique for spotlight SAR data processing, the spotlight mode being a particular case of the more general hybrid one. The key point of the procedure is the first filtering step which implements an azimuth convolution between the raw data and a chirp signal whose rate is selected, in the generalised approach, depending on the characteristics of the hybrid acquisition mode. Following this stage, standard strip-map processing procedures can be used to implement the second processing step, leading to fully focused SAR images. The algorithm, mainly oriented to spaceborne systems, is simple and efficient and allows the design of a generalised processing code suitable for data acquired in the hybrid strip-map/spotlight SAR configuration including the strip-map and spotlight modes as special cases. Experiments carried out on simulated data clarify the rationale of the method and confirm its validity View full abstract»

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  • Low-complexity estimator for four-dimensional parameters under a reparameterised distributed source model

    Page(s): 313 - 317
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (362 KB)  

    The spatial character of a parametric model of a coherently distributed source signal (DSS) can be determined by four parameters: the two-dimensional direction of arrival (DOA) and the corresponding two-dimensional angular spread, associated with azimuth and elevation, respectively. The authors consider the problem of estimating these four parameters using a uniform circular array. A low-complexity estimator is proposed to alleviate the burden of calculation based on a reparameterised model of the DSS. Using the property of the reparameterised model, a two-dimensional searching method is proposed to estimate the generalised steering vectors (GSVs) of the DSS. The nominal DOA and the angular spread can be estimated using the estimated value of the GSV. The method is illustrated by some numerical examples View full abstract»

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  • Parameter estimation for the K-distribution based on [z log(z)]

    Page(s): 309 - 312
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    A new method for estimating the order parameter of a K-distribution is presented which exploits the accuracy of log-based estimators while having a computationally efficient functional form which allows rapid calculation. The estimation accuracy of this new estimator is compared with previous estimators using an analysis technique based on asymptotic expansion of the estimator moments. The new estimator is found to have comparable accuracy to the normalised log estimator while having a much simpler implementation. SAR imaging is discussed as an example View full abstract»

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  • Probabilistic modelling of bistatic Doppler shift

    Page(s): 348 - 352
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (491 KB)  

    The bistatic Doppler shift depends irreducibly on target position and velocity. This fact renders intractable an analytical assessment of the radar's global ability to counter stationary clutter. To avoid lengthy simulations, an easily applicable numerical solution for the cumulative distribution function of the Doppler shift is provided corresponding to plausible assumptions concerning the underlying probability distribution of the target position and velocity View full abstract»

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  • Multipath scattering from complex targets

    Page(s): 343 - 347
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    Identifying interference patterns originating from particular scatterers on complex objects above an electromagnetic smooth surface can be difficult, especially if the scatterers are not dominant. The author shows the existence of an incoherent scattering space where the relative positions of the scatterers in either height or range are irrelevant and where the backscattered power is the result of an incoherent summation of the reflected fields comprising the target. The incoherent scattering space is defined as that space where the maximum multipath phase shift between the scatterers is smaller than π/2. Owing to the small relative phase shift between the scatterers within this space, the fluctuations of the reflected signal are small and a point reflector may hence substitute the complex target. The existence of the space is determined by the height of the radar antenna, the relative height of the scatterers, the range and the electromagnetic frequency View full abstract»

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  • Random wave and Schell model for the mean RCS of bent chaotic ducts with a homogeneous scattered aperture field distribution

    Page(s): 338 - 342
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (437 KB)  

    It is shown how a Schell model can be constructed to estimate the mean radar cross-section (RCS) of long bent engine ducts. A consistent random wave model is also provided to determine representative RCS distributions of such ducts. In both cases it is assumed that the duct has an aperture which is approximately normal to the duct axis and a scattered field distribution which is homogeneous across the aperture. It is believed that such a model is often valid for long chaotic bent ducts when most rays (in a ray representation) undergo many reflections before escaping the duct. A comparison is made with a nonconvergent shooting-and-bouncing prediction of a complex duct View full abstract»

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Aims & Scope

IEE Proceedings Radar, Sonar and Navigation covers the theory and practice of systems involving the processing of signals for radar, radio location, radio navigation and surveillance purposes.

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