Airborne and spaceborne optical remote sensing is an important means formonitoring oil slicks on ocean surface. However, it is still a major challenge to determine both the category (related to a specific value of reflective index) and thickness of the marine oil slick with existing methods, particularly when the oil slick is too thin to obtain significant fluorescence signal with a laser induced fluorescence method. Sun-glint is usually harmful to optical remote sensing of an ocean target. In this work we utilize the polarized sun-glint reflection to monitor oil slicks on a rough ocean surface.The degree of linear polarization (DOLP) of the sun-glint reflection contains the characteristics information of the oil slick with different physical properties. Combiningthe polarized optical remote sensing and the inversion theory based on a thin-film optical model, weanalyze the variation trend of the DOLP with the parameters of solar zenith angle, sensor zenith angle, relative azimuth angle, refractive index and thickness of the oil slick. Different types and thicknesses of the oil slicksgive different Fresnel's reflection coefficients of polarized sun-glint reflections and consequently different Stokes parameters, which lead to different DOLP. We analyze the DOLP of the sun-glint reflection at the wavelength of 532 nm,and determine simultaneously the refractive index and thickness of marineoil slick from the DOLP values measured by a remote detector at two different zenith angles.
The scattering center extraction algorithm is a method to estimate the scattering center from the backscattered field. Superior scattering center extraction algorithms should be robust to noise, independent of the model order, and automatically and quickly operated. In this paper, we propose a novel super resolution scattering center extraction algorithm that satisfies the conditions mentioned above, which has been named the dimension reduced optimization problem (DROP). Using DROP, we determined a one-dimensional scattering center from a high resolution range profile and a two-dimensional scattering center from an inverse synthetic aperture radar image.
This paper presents the design and realization of a 4 × 4 broadband circularly polarized microstrip antenna as subarray element for airborne C-band circularly polarized synthetic aperture radar (CP-SAR). The main objective of this work is to optimize impedance bandwidth, axial-ratio bandwidth, gain, and radiation pattern of a CP-SAR array antenna due to the limitation in the available space for a large array antenna installation on airborne platform. Various patch separations in uniformly 2 × 2 subarray configuration have been simulated to investigate characteristics of impedance bandwidth, axial-ratio bandwidth, gain, and radiation pattern. In order to broaden the impedance bandwidth, the proposed antenna is constructed by stacking two thick substrates with low dielectric constant and dissipation factor. The measured 10-dB impedance bandwidth is 0.91 GHz (17.2%), spanning from 4.83 GHz to 6.01 GHz. A simple square patch with curve corner-truncation is applied as the main radiating patch for circularly-polarized wave generation. The radiating patch is excited by single-fed proximity coupled strip-line feeding. The improvement of axial-ratio bandwidth in 2 × 2 and 4 × 4 subarray is employed by a feeding network with serial-sequential-rotation configuration. Experimental result shows the 3-dB axial-ratio bandwidth achieved 1.18 GHz (22.17%) from 4.8 GHz to 5.71 GHz. Other characteristic parameters such as gain and radiation pattern of the 4 × 4 subarray antenna are also presented and discussed.
Synthetic Aperture Radar (SAR) image registration is to establish reliable correspondences among the images of the same scene. It is a challenging problem to register the airborne SAR images for the instability of airborne SAR systems and the lack of appropriate geo-reference data. Besides, techniques for registering satellite-based SAR images relying on rigorous SAR geocoding cannot be directly applied to airborne SAR images. To address this problem, we present a coarse-to-fine registration method for airborne SAR images by combining SAR-FAST (Features from Accelerated Segment Test) feature detector and DSP-LATCH (Domain-Size Pooling of Learned Arrangements of Three patCH) feature descriptor, which only relies on the gray level intensity of SAR data. More precisely, we first apply SAR-FAST, which is an adapted version of FAST for analyzing SAR images, to detect corners with high accuracy and low computational complexity. To reduce the disturbance of speckle noise as well as to achieve efficient and discriminative feature description, we further propose an improved descriptor named DSP-LATCH to describe the features, which combines the Domain-size Pooling scheme of DSP-SIFT (Scale-Invariant Feature Transform) and the idea of comparing triplets of patches rather than individual pixel values of LATCH. Finally, we conduct a coarse-to-fine strategy for SAR image registration by employing binary feature matching and the Powell algorithm. Compared with the existing feature based SAR image registration methods, e.g., SIFT and its variants, our method yields more reliable matched feature points and achieves higher registration accuracy. The experimental results on different scenes of airborne SAR images demonstrate the superiority of the proposed method in terms of robustness and accuracy.
Two different designs of orthomode transducers for the coming Ku-band receiver of the Italian radio telescope in Medicina are presented and compared, showing design details, describing numerical simulations and discussing manufacturing and test results. Such orthomode transducers provide a tradeoff between low-loss and phase-matching, according to different initial requirements where the final receiver architecture has to be frozen. Both designs show high performance over the operative 13.5-18.1 GHz Ku-band. One of the OMT designs has been fabricated and tested, showing results in very good agreement with simulations.
In this paper we calculate Green's function of a single point source in a one-dimensional infinite periodic lossless medium. The method is based on Broadband Green's Functions with Low Wavenumber Extractions (BBGFL) that express the Green's functions in terms of band solutions that are wavenumber independent. The converegnce of the band expansions are accelerated by a low wavenumber extraction with the wavenumber chosen at the mid-bandgap. The choice of mid-bandgap means that the extracted low wavenumber Green's function can be calculated with very few number of layers. The broadband Green's functions are illustrated for stopband, passband and close to the bandedge. For the case of passband and close to band edge, a modal method is used with first order and second order pole extractions respectively. The modal terms are extracted and integrated analytically. The calculated solutions of single point source Green's functions are compared with the scattering solutions of multilayers using as many as 200,000 layers for the case of passband and near bandedge. The BBGFL computed solutions are in good agreement with those of scattering solutions for stopband, passband, and close to the bandedge.
Minimum variance distortionless response (MVDR) beamformer is an adaptive beamforming technique that provides a method for separating the desired signal from interfering signals. Unfortunately, the MVDR beamformer may have unacceptably low nulling level and high sidelobes, which may lead to significant performance degradation in the case of unexpected interfering signals such as the rapidly moving jammer environments. Via support vector machine regression (SVR), a novel beamforming algorithm (named as SVR-CMT algorithm) is presented for controlling the sidelobes and the nullling level. In the proposed method, firstly, the covariance matrix is tapered based on Mailloux covariance matrix taper (CMT) procedure to broaden the width of nulls for interference signals. Secondly, the equality constraints are modified into inequality constraints to control the sidelobe level. By the ε-insensitive loss function for the sidelobe controller, the modified beamforming optimization problem is formulated as a standard SVR problem so that the weight vector can be obtained effectively. Compared with the previous works, the proposed SVR-CMT method provides better beamforming performance. For instance, (1) it can effectively control the sidelobe and nullling level. (2) it can improve the output signal-to-interference-and-noise ratio (SINR) performance even if the direction-of-arrival (DOA) errors exist. Simulation results demonstrate the efficiency of the presented approach.
A three-dimensional fully interlaced woven microstrip-fed substrate integrated waveguide has been designed, manufactured and experimentally validated. The waveguide has been conceived based on the conventional substrate integrated waveguide (SIW) technology and works in a range of frequencies between 7.5 GHz and 12 GHz. The SIW structure is suitable to be translated into different equivalent woven structures depending on the characteristics of the employed threads, as it has been presented in previous works. In this work, a structure based on rigid weft threads has been employed with the aim of translating both the waveguide and the corresponding SIW to microstrip transitions, into woven patterns and, therefore, achieving the main purpose of a complete integration of the circuit into the textile, avoiding the use of external transitions for its validation. Consequently, three prototypes, using three different lengths, have been manufactured and experimentally characterised, and the theoretically predicted behaviour of the prototypes has been experimentally verified.
In this paper, three viable multilayer rectangular coil structures, namely the spiral, concentrated and uneven compound types, are proposed and analyzed. In the multiple-receiver multiple-frequency wireless power transfer system, the compact coil topologies are particularly preferable and should fulfill the required performance of magnetic field with the compact size design. In order to minimize the variation of magnetic fields that can be picked up by multiple receivers, the uneven compound type is newly derived by combining the merits of both the spiral and concentrated types. Because of providing more uniform magnetic flux density distribution, the uneven compound type can achieve better tolerance of misalignment. Without any misalignment, its transmission efficiency can reach up to 92%. Moreover, their electric potential distributions are analyzed to provide guidance for the maximum input current at the desired operation frequency. Both finite element analysis and experimental results are given to verify the validity of the proposed coil structures.
This paper proposes a new design of reconfigurable three-sector dual-mode dual-polarized antenna for use primarily in mobile communication base stations. The design offers the flexibility to be used as a sectorial (directive) or omnidirectional base station antenna whenever required. The two different radiating modes (omnidirectional and sectorial) depend only on the excitation scenario. The proposed antenna has the advantages of offering broadband, stable radiation pattern and high polarization purity within the desired frequency band, and a simple feeding structure with a remarkable compact size (less than 800 cm3) and low profile. The achieved fractional bandwidth is 55.3% (1.7-3 GHz). The antenna design principle is validated by constructing and testing a prototype with the two modes of operation. An eight-element linear array is then constructed and synthesized as a reconfigurable base station. Results demonstrate how the design may be packaged in a compact size to offer excellent omnidirectional or sectorial performance which makes this new design an ideal candidate for reconfigurable dual-mode mobile base stations.