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For the synthetic aperture radar (SAR) systems, there is an increasing demand for achieving resolutions of 0.2 m times 0.2 m. As the range resolution and system bandwidth are inversely proportional, the system bandwidth are expected to be larger than 1 GHz. Thus an antenna with wider band must be developed. Waveguide slot antenna has been implemented on several SAR satellites due to its inherent advantages...
This paper reports the miniaturization of a microstrip 90 degree coupler by substituting the quarter wave transmission lines employed in conventional 90 degree coupler with its equal circuits consisting of two oblique stubs and an inductor and capacitors. Reduction of the coupler to 27% its size is reported here. This coupler is designed at 1070MHz for using in even harmonic mixers of 3G mobile receivers...
In this paper, based upon the equivalent principle and surface integral equations, the exact model of an antenna and dielectric radome structure is established by using method of moments (MoM). The equivalent strip-model is used for the thin wire antenna, in order to alleviate the singularities in the meshing process. The ill-conditioned MoM matrix is improved by the preconditioning technique. The...
Based on the WINDOWS system, the fast parallel MATLAB algorithm is used in calculating the RCS pattern of perfect electric conductor (PEC) with the method of moments (MoM). The computation of the impedance matrix and its inverse matrix is divided to the parallel computers. Each computer will finish its tasks. Meanwhile the necessary data are exchanged in the sharing space built at the basis of local...
For high frequency wave(2~30 MHz),calculating the current distribute and radiation pattern for antennas is a complex problem because of the interaction between the antenna, the ground, and any buried wire net. Typically, the finite-difference time-domain (FDTD) technique is well suited for modeling fields in heterogeneous media; the method of moments (MoM) is well suited for modeling complex antennas...
The focusing characteristics of ellipsoidal antenna in the millimeter-wave imaging system are analyzed in this paper, which is used for detecting objects hidden in people's body. And it is points out that the advantages of the ellipsoidal antenna having double focusing points, comparing to parabolic antenna in the condition of imaging in near-field. Through the analysis of axial focusing characteristics...
A. new method of simulating polarimetric scatter coefficient of sea rough surface is given. Based on normal line matrix of scattering facets which is derived from a three dimensional sea model, an expression of scattered field with elliptic polarized incidence wave is deduced in Cartesian coordinate system. Finally fully polarized RCS are numerically calculated and compared in different conditions.
Synthetic aperture radiometer has the potential to meet the spatial resolution requirement of passive microwave remote sensing from space. A one-dimensional prototype of aperture synthesis radiometer at millimeter wave band is introduced in this paper. It contains 16 antenna elements, 16 receiving channels, 16 ADCs, and image reconstruction part. Error correction is made in the image reconstruction...
The mono-static stepped-frequency ground penetrating radar (GPR) with a Vivaldi ultra-wide band (UWB) antenna was used to non-destructive estimate the parameters (permittivity, conductivity and thickness) of each layer of a stratified subsurface medium. In this realization, a calibration procedure is necessary. This paper introduces the principle and the implementation of this calibration. The non-directive...
Miniaturization is very important for modern communication systems. This paper presents new bandpass filters with low insertion loss and multi-band as well as wide stopband properties, and new bandstop filters with dual-rejectband and sharp attenuation to get nicer frequency selectivity by using miniature microstrip isosceles triangular resonator, and filter coupling schemes are given and discussed...
Fractal-shaped microwave passive circuits attract much attention recently, but dominantly applied in antennas. In this report, new fractal bandpass filters using equilateral triangular patch resonator are presented to implement high performances of multi-transmission zeros, wide passband and stopband, and low passband insertion loss as well as miniaturization. Using fractal defection in patch, multi...
In this work, a 2-D subaperture polar format algorithm (PFA) based on stepped-chirp signal is proposed. Instead of traditional pulse synthesis preprocessing, the presented method integrates the pulse synthesis process into the range subaperture processing. Meanwhile, due to the multi-resolution property of subaperture processing, this algorithm is able to compensate the space-variant phase error caused...
In this paper two novel cylindrical dielectric resonator antennas (CDRAs) providing circular polarization (CP) using a single probe feed are proposed. By splitting the fundamental mode of cylindrical DR into two near-degenerate orthogonal resonant modes, CP is obtained. The proposed antennas are numerically investigated using High Frequency Structure Simulator (HFSS) based on Finite Element Method...
In this paper, a multilevel coded modulation scheme in adaptive OFDM system is presented. Set partitioning-based on the asymmetric constellation has been used in this scheme to meet unequal error protection. The combination between multilevel coded modulation and adaptive technique can greatly improve the performance of the system. Simulation results have demonstrated the good performance of this...
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