Xu Jiadong

High Efficiency Synchronous DRAM Controller for H.264 HDTV Encoder

A high efficiency memory controller of Synchronous DRAM is proposed to improve memory bandwidth in H.264 HDTV encoder. The feature of SDRAM and memory access pattern of H. 264/AVC encoder is analyzed for suitable controller architecture designing. A new data arrangement in SDRAM has been used to improve bus efficiency by reducing the overhead cycle of page-activation. Experiment results show that the proposed architecture has improved 40% performance of SDRAM bus efficiency.

Signal processing techniques in high-resolution RCS measurement system

Comparing with traditional way of continue-wave RCS measurement system, high-resolution information is gained in stepped-frequency system. Using inverse fast Fourier transform, the frequency-domain data of the whole chamber obtained by testing is interpreted into high-resolution time-domain response, and the unwanted signals can be removed by adding a gating function. The measurement of finite frequency spectrum makes a cut of data; the use of windows reduces the effect of side lobe. Some experiments show that the accuracy will be improved after the signal processing techniques are used.

Microwave propagation in charged sand particles

Based on the forward scattering amplitude function for charged sand particle under the Rayleigh approximation, the calculation model of microwave attenuation due to charged sand particles is given in terms of equisized distribution and exponential distribution. The attenuation is calculated and analyzed. The results show that the attenuation with charged sand is larger than without regard to charges on the sand surface, and the more concentrative the surface charges on sand particles are, the greater are the influence on microwave attenuation. The attenuation due to the sand particles following exponential distribution is greater than that due to the sand particles for the equisized distribution.

Hard-in-loop polarization linear SAR imaging system

A hard-in-loop polarization Synthetic Aperture Radar (SAR) system was constructed in an anechoic chamber. The operation track of SAR was simulated by lateral movement of a scanner. As the core hardware of system, a vector network analyzer was set in the scanner and moved together. Two measured channels were connected with four vertical or horizontal antennas by the expand ports. Then the full-polarization scattering matrixes were collected with the scanner moving. An improved back-projection algorithm was adapted to process the echoes, and four different polarization images were gained. The experiments were carried out on L-band. The measured scene consisted of three fir trees. The images are coincident with the physical characteristic of scene.

Research on Mechanism of Mobile Agent for Wireless Sensor Networks

Computing model of nodes has an important effect on the network performance and the mobile agent computing model for the next generation network has attracted more and more attentions. The background of mobile agent applied in the wireless sensor network is first analyzed. Then a framework based on mobile agent is proposed from two levels, namely network and nodes. After introducing the basic elements, functional definitions and interfaces of the framework, an implementation mechanism based on directed diffusion for mobile agent is presented in detail.

Computer-aided design of octo-filar helix antennas with fixed arm length

An octo-filar helix antenna that can form a backfire or endfire conical beam by changing its pitch angle and feeding modes with its arm length invariable is researched by the Nakano integral equation and the method of moments. A shaped-conical radiation pattern with good circular polarization performance and the best beam conformity can be obtained for almost all the hemisphere. Comparison of the radiation properties, including the beam direction, maximum power gain and 3-dB axial ratio angle coverage under different feeding modes is conducted. The relationship between the pitch angle and the height of the satellite orbit is also presented, which provides theoretical references for the design of the antenna.

New Algorithm of Automatic FEM Mesh Generation for Electromagnetic Scattering Calculation

Automatic mesh generation for finite element method (FEM) plays an important role in electromagnetic scattering calculation. A new algorithm for the automatic generation of finite element meshes is presented. The methodology is a grid-based approach type. Take advantage of it, the algorithm improve the traditional mesh generation scheme thanks to the integration of simple and flexible density control and the rationalization of boundary discretization. In two dimensional cases, the original domain is separated into squares, and then all interior squares are split into isosceles right triangle, which results in uniform meshes with excellent internal triangles like the Almost Regular Triangulations. According to different condition, the squares which intersect the boundary of the domain are adjusted to triangles. A new algorithm is presented for improving the quality of the meshes near to the boundary. In three dimensional cases, its similar. Compared with other methods, its capable of automatically and adaptively generating meshes with reasonable quality, and is easy to implement in program. Also it achieves good quality of mesh. These characteristics have been demonstrated by the examples in the paper.

Design of an imaging chamber for biomedical applications using bowtie antennas

A microwave imaging system for breast cancers using a miniaturized bowtie patch antenna array is presented in this paper. The antenna element was designed with resonant frequency of 2.57 GHz and return loss less than -15 dB. Thirty-six antennas were installed on the walls of the chamber. The back propagation method is used as the imaging algorithm. We demonstrate the capability of the proposed antenna array for imaging biocompatible immersion medium.

A Kind of Discrete Variable Structure UCAV Guidance Law Restrict by the Entering Angle

To solve the problem that the UCAV load data link make analog signals guidance law cannot be used directly, a kind of new discrete variable structure guidance law arithmetic is brought out, which takes the restriction of entry angle into consideration, and conquers the buffeting phenomenon when the tradition discrete variable structure control arithmetic get into sliding mode. The simulation results show that the discrete signal guidance law can meet the tactical UCAV indicator.

Application of particle swarm optimization for the design of a broadband microstrip antenna

The discrete binary particle swarm optimization (PSO) is an extension of standard PSO on binary system. As a time-domain method, finite different time domain (FDTD) can obtain the required broadband frequency information through once time-domain calculation. Therefore, PSOs fitness function can choose multi-point in frequency, that is, the design of fitness function is more flexible when PSO is combining with FDTD. In this paper, discrete binary PSO combined with FDTD method is applied to design a broadband microstrip antenna. Test results show the bandwidth of the optimized antenna at -10dB is expanded significantly compared with the original antenna.