Yan-Wei Zhao

SAR IMAGING SIMULATION FOR COMPOSITE MODEL OF SHIP ON DYNAMIC OCEAN SCENE

An e-cient double superimposition model (DSM) is proposed to generate two-dimensional (2-D) ocean surface waves. On the basis of this e-cient model, a modulated slope-deterministic facet model (MSDFM) is developed to compute the radar cross section (RCS) of synthetic aperture radar (SAR) for the generated ocean surface. Then, the properties of the SAR imaging mechanism for wind seas are discussed from a combination of SAR and ocean wave parameters. Furthermore, a hybrid facet scheme, which is the combination of physical theory of difiraction equivalent edge currents (PTDEEC) and physical optics (PO) method, is introduced to analyze the high frequency scattering characteristics of large ship target. Finally, this hybrid facet scheme combines with the four-path model and MSDFM to investigate SAR imaging for the composite model of ship on dynamic ocean scene. The resolution degradation of ship-ocean model arising from difierent facet velocities within a SAR resolution cell and the range migration caused by coupling scattering are investigated in this paper. SAR imagery simulations of marine scene are illustrated, proving the validity and practicability of the presented algorithms.

An Efficient Ocean SAR Raw Signal Simulation by Employing Fast Fourier Transform

Synthetic aperture radar (SAR) raw signal simulations for dynamic ocean scene are presented in this paper. In order to improve the computation efficiency of time domain SAR raw signal simulation method, a proper analytical reformulation is made to the time domain expression. This reformulation allows us to design a very efficient simulation scheme by employing fast Fourier transform (FFT) codes. Accordingly, the computational load is dramatically reduced with respect to a time-domain (TD) simulation method, and this makes SAR raw signal simulation of dynamic ocean scene feasible. The SAR images of ocean scene are illustrated, proving the validity and practicability of the presented algorithms.

A Novel Triple-Band Monopole Antenna with Double Coupled C-Shaped Strips for WLAN/WiMAX Applications

In this paper, a novel triple-band monopole antenna with double coupled C-shaped strips for WLAN/WiMAX applications is presented. By adjusting the dimensions of the outer and inner C-shaped strips, three separated impedance bandwidths of 20% (2.28 ∼ 2.78 GHz), 14% (3.33 ∼ 3.83 GHz) and 19% (4.86 ∼ 5.86 GHz) can be obtained. Especially, the asymmetry inner C-shaped strip can be used to adjust the middle and high band characteristics. With these double coupled C-shaped strips, the proposed antenna shows a good triple-band property to satisfy the requirements of 2.4/5.2/5.8 GHz WLAN bands and 2.5/3.5/5.5 GHz WiMAX bands.

An Efficient Slope-Deterministic Facet Model for SAR Imagery Simulation of Marine Scene

An efficient slope-deterministic facet model for the computation of the radar scattering cross section from electrically large sea surface is presented. As a facet-based theory, it is a more comprehensive model which can adequately reflect the specular and diffuse configurations, as well as the mono- and bistatic features. Significant computational efficiency and good agreement with experimental data are observed, which make the proposed facet model well suitable for fast simulation on ocean synthetic aperture radar (SAR) imagery. Base on the facet model, a hybrid scheme is developed to analyze the high frequency composite scattering from the model of a ship at sea, in which the method of equivalent currents (MEC) and a hybrid frame which combines the four path model with the quasi-image method are employed to investigate the scattering characteristics of large ship-like target and its interactions with sea surface respectively. Finally, applications to SAR imagery simulation of marine scene are discussed with the help of the proposed sea and ship-sea scattering mechanism in detail.

A Comprehensive Facet Model for Bistatic SAR Imagery of Dynamic Ocean Scene

A comprehensive facet model for bistatic synthetic aperture radar (Bis-SAR) imagery of dynamic ocean scene is presented in this paper. An e-cient facet scattering model is developed to calculate the radar cross section (RCS) of the ocean surface for Bis- SAR flrstly. Further more, this facet model is combined with a bistatic velocity bunching (V B) modulation of long ocean waves to obtain the Bis-SAR intensity expression in image plane of ocean scene. The displacement of the scatter elements in the image plane and the degradation of radar resolution in azimuth direction are quantiflcationally analyzed. Finally, Bis-SAR imagery simulations of ocean surface are illustrated, proving the validity and practicability of the presented algorithms.

Compact Octagonal Monopole Antenna Employing T-Shaped Quasi-Self-Complimentary Resonators for Tri-Band Operation

A novel tri-band monopole antenna design employing Tshaped quasi-self-complimentary (QSC) resonators is presented. The proposed antenna is composed of a pair of symmetrical QSC resonators, an octagonal monopole radiator and two L-shaped slots. By utilizing these structures, the antenna can yield different resonances to cover the desired bands while maintaining small size and simple structure. Based on this concept, a prototype of tri-band antenna is designed, fabricated and tested. The experimental results show that the antenna has the impedance bandwidths of 190 MHz (2.36–2.55 GHz), 680 MHz (3.37–4.05 GHz) and 1760 MHz (5.12–6.88 GHz), which can cover both WLAN in the 2.4/5.2/5.8 GHz bands and WiMAX in the 3.5 GHz band.

An Efficient Hybrid High-Frequency Solution for the Composite Scattering of the Ship on Very Large Two-Dimensional Sea Surface

A hybrid high-frequency solution is proposed to analyze the bistatic electromagnetic scattering of the ship target on very large two-dimensional randomly rough sea surface in this paper. The comprehensive geometrical model of the ship and sea surface is designed by CAD tools and the sea power spectrum, and its electromagnetic scattering characteristic is evaluated with the method of equivalent currents (MEC). Since the electromagnetic interaction between the ship hull and the sea surface in the vicinity of the broadside is similar to the scattering mechanism of the dihedral re∞ector, the iterative physical optics method (IPO) is utilized to study the electromagnetic coupling efiects. The shadowing correction based on the Z-Bufier technology is introduced to eliminate the efiects of the irrelevant scattering resources. At last, the validity of the hybrid method is conflrmed by the SAR image of the ship on the very large two-dimensional sea surface, and the numerical results are presented to analyze the composite scattering characteristics of the ship on the sea surface.

A compact dual-band antenna with a C-shaped ground plane for WLAN applications

A compact antenna for dual-band operation is presented. The proposed antenna consists of a C-shaped ground plane and an L-shaped monopole radiator. The Γ-shaped stub extending from the ground can achieve a resonance covering the lower band, whereas the L-shaped monopole operates at the upper band. The antenna prototype is designed, fabricated and tested. The experimental results show the antenna covers 2.37–2.53 GHz and 5–6.37 GHz with 10-dB return loss, satisfying the desired standards of WLAN applications. Besides, good radiation patterns and antenna gains over the operating bands have been obtained.

A Bistatic SAR Image Intensity Model for the Composite Ship–Ocean Scene

Based on the scattering mechanisms of multipath, a bistatic synthetic aperture radar (Bis-SAR) image intensity model for the composite ship-ocean (or other metallic targets with ocean) scene is developed in this paper through reasonably dealing with the path lengths of transmitter and receiver to the ship target. To get a Bis-SAR image intensity model for the composite ship-ocean scene, the Bis-SAR image intensity distribution for the ocean surface is analyzed, and the facet scattering model is used to give the individual returns from separate facets. In addition, the influence of velocity bunching (VB) modulation of long ocean waves on the distribution of radar cross section is also discussed. Finally, Bis-SAR imagery simulations of ocean wave and the composite ship-ocean scene are illustrated, and the results show that the proposed Bis-SAR image intensity model can be reasonable and the interaction effects between the ship and sea surface can make significant contributions to the Bis-SAR intensity.

A Bistatic Synthetic Aperture Radar Imagery Simulation of Maritime Scene Using the Extended Nonlinear Chirp Scaling Algorithm

A bistatic synthetic aperture radar (Bis-SAR) imagery simulation of an extended maritime scene is presented. An efficient facet scattering model is developed to collect the raw coupling scattering data from a ship located on sea surface. Then, to avoid the inefficiency of time-domain algorithms and the azimuth-invariant limit of conventional frequency-domain (FD) methods in the bistatic case, an extended nonlinear chirp scaling (NLCS) algorithm is proposed to handle the bistatic data collected from this facet scattering model. The perfect Bis-SAR simulation results of the ship located on the sea surface could prove the validity of the proposed algorithms as well as the practicability of the model for the Bis-SAR imagery with large squint angle in the FD approach.