FDTD analysis of ground-penetrating radar antennas with shields and absorbers

One of the most critical hardware components of a ground-penetrating radar (GPR) is the antenna system. Important parameters of antennas, such as antenna bandwidth, radiation waveform and cross coupling determine the GPR system performance. The modified TEM horn antenna with distributed resistor load is presented in this paper, and the radiation properties of the antenna with the shields and absorbers are studied through the three-dimensional finite-difference time-domain (FDTD) scheme. Simulations show that the direct signal coupled from the transmitter is decreased by means of the shields and absorbers. Therefore, using the antenna in the GPR system can improve the signal-to-clutter ratio and the dynamic range of the system. __________ Translated from Chinese Journal of Radio Science, 2006, 21(3): 422–427 [译自: 电波科学学报]     

Analysis on two novel spherical helical antennas

Two novel spherical helical antennas are designed by projecting the planar equiangular spiral antenna onto hemisphere and partial sphere surfaces. Their radiation properties are analyzed by the moment method with curved basis and test function, and the curves of the voltage standing wave ratio (VSWR), gain, polarization and pattern that change with frequency are also given, respectively. It can be seen that the circular polarization band of the novel hemispherical helical antenna is broader. The gain curve of the partial spherical helical antenna is flatter and the structure is simpler. __________ Translated from Journal of Xidian University, 2008, 35(1): 144–147 [译自: 西安电子科技大学学报 (自然科学版)]     

Design and study of a compact planar ultra-wideband antenna

In this paper, a novel, small, and compact planar antenna for ultra-wideband (UWB) applications is proposed. The antenna is an extension of microstrip slot antenna technology. To achieve ultra-wideband characteristics, a tapered microstrip fork-shaped stub has been employed. A symmetric polygon wide slot has been placed on the antenna ground. The design was investigated numerically to obtain proper dimensions for the antenna and a prototype was constructed. The return loss, pattern and gain of the prototype antenna have been measured. The transient pulse signal fidelity has also been investigated by finite-difference time-domain (FDTD) method. Experimental results show that the proposed antenna design has promising characteristics for UWB applications. __________ Translated from Chinese Journal of Radio Science, 2006, 21(4): 582–585 [译自: 电波科学学报]     

A novel auto-reference ultra-wideband receiver scheme

A new auto-reference (AR) transmit-receive scheme and a corresponding group decision algorithm on the generalized likelihood ratio testing (GLRT) principle is proposed in this paper to overcome the drawbacks of the power inefficiency and the high noise vulnerability in transmitted-reference (TR) ultra-wideband (UWB) systems. A partly overlapped detection window structure is introduced in which the decided data frames are regarded as the reference signal so that energy and time resources in the reference frame are saved and full-rate data transmission is achieved. Differential coding was utilized to solve the error propagation problem introduced by the overlapped detection windows. The group decision algorithm on the GLRT principle was utilized to estimate the correlation template through all data frames in detection windows and could offer better noise suppression. Simulation results reveal that the AR scheme with its decision algorithm outperforms the conventional and other modified TR schemes in generalized signal-to-noise ratio (SNR). Translated from Journal Xi’an Jiaotong University, 2006, 40(8): 932–935 [译自: 西安交通大学学报]     

Estimation method of DOA for DS-UWB signal

Direction of arrival (DOA) estimation is one of the key technologies in smart antennas in the direct sequence ultra wideband (DS-UWB) system. Traditional DOA estimation methods based on narrow-band signals are not suitable for such system. Therefore, a fourth-order cumulant-based estimation method ofDOA for DS-UWB signal is proposed. This method is set on the frequency domain model of DS-UWB array signal. Simulation results show that the algorithm is effective and can guarantee adequate estimation accuracy. __________ Translated from Journal of University of Electronic Science and Technology of China, 2007, 36(2): 190–192 [译自: 电子科技大学学报]     

Positioning models and systems based on digital television broadcasting signals

The requirement and feasibility of the positioning system using digital television (DTV) broadcasting signals are analyzed. The principle of DTV positioning on the basis of frame synchronization is brought forward and the ranging characteristic is studied that the observables are asynchronously measured during the same epoch interval. The models of the pseudo-range observation and Doppler carrier phase integral are researched. The system observation and state equations are presented on the basis of the above models. The simulation results showed that DTV positioning technology could remarkably improve the precision of system state estimates using smoothing methods for positioning systems or integrated navigation systems. The DTV positioning that has a sub-meter level ranging error and meter level positioning accuracy can parallel with and even taken as a beneficial substitute for the tradition positioning technology. __________ Translated from Journal of Southeast University (Natural Science Edition), 2006, 36(5): 690–694 [译 自: 东南大学学报(自然科学版)]     

Design and implementation of a multi-axis precision movement machine based on MAS theory

A model construction of a multi-agent system (MAS) and the basic function of the agent are described. The precision control method using the multi-CPU of a programmable logic controller (PLC) is introduced, and a distributed method using multiple CPUs to control different motion machines is given. The test results indicate that in industrial control fields, the combination of using the credible PLC to control the motion machine and multi-CPU task distributing methods can solve multiaxis machine linkage and implication, providing a more credible method for multi-axis motion units. __________ Translated from Journal of North University of China (Natural Science Edition), 2007, 28(1): 32–37 [译自:中北大学学报(自然科学版)]     

Medical image lossless compression based on combining an integer wavelet transform with DPCM

To improve the classical lossless compression of low efficiency, a method of image lossless compression with high efficiency is presented. Its theory and the algorithm implementation are introduced. The basic approach of medical image lossless compression is then briefly described. After analyzing and implementing differential plus code modulation (DPCM) in lossless compression, a new method of combining an integer wavelet transform with DPCM to compress medical images is discussed. The analysis and simulation results show that this new method is simpler and useful. Moreover, it has high compression ratio in medical image lossless compression. __________ Translated from Journal of Northeastern University (Natural Science), 2007, 28(10): 1454–1457 [译自 : 东北大学学报 (自然科学版)]     

Loaded-frequency selective surface

A new frequency-selective surface (FSS) with loadings is introduced in this paper and analyzed by way of period moment methods (PMMs). The simulated results show that FSS may operate in different bands and especially generate a large reduction in the resonant frequency for a fixed unit cell size through different loadings. This provides a new orientation in the development for FSS. Practical circuits are fabricated, and the measured results agree well with the simulated results. __________ Translated from Chinese Journal of Radio Science, 2006, 21(3): 441–444 [译自: 电波科学学报]     

Characteristics of high frequency radio wave propagated in heated ionospheric regions

A two-dimensional Ohm heating theoretic model in the magnetizing ionosphere and a ray-tracing model in a discrete ionosphere background are used to analyze quantitatively the characteristics (mainly the Doppler shift and the phase shift) of the over-the-horizon radar (OTHR) wave, which propagates through the ionospheric region heated by high frequency radio wave. The simulation results about the Doppler and the phase shift are obtained within two minutes after the heater is on. Preliminary conclusions are given by comparing the numerical results with experimental data. __________ Translated from Chinese Journal of Radio Science, 2008, 23(3): 466–470 [译自: 电波科学学报]     

Common-mode radiation characteristic analysis of connections between cables and metal cases

In this paper, the common-mode radiation characteristic of the connection between a cable and a conductor is analyzed by the electric field integral function (EFIF) and the method of moment (MoM). The RWG basis function is adopted as the conductor basis function, the pulse basis function as the wire basis function and the juncture employs Costa basis function. A scheme of singular region separation is proposed to overcome the integration singularity of juncture matrix elements. Some new conclusions of the common-mode radiation characteristics with the metal case are obtained by numeration. __________ Translated from Chinese Journal of Radio Science, 2007, 22(3): 375–379 [译自: 电波科学学报]     

Using Petri nets to verify acyclic rule-based system

A series of Petri net-based definitions were formulated for describing four types of structural errors in a rule-based system (RBS), including inconsistency, incompleteness, redundancy and circularity. A marked ω-Petri net model of acyclic RBS was constructed. Then, its reachability tree was generated to record all reachable relations between propositions in RBS. Moreover, a backward reasoning forest of a reachable marking was generated for explicitly representing reachable paths in RBS. Finally, a set of theorems and algorithms were provided to analyze and check structural errors. The usability of the research results presented in this paper was illustrated by an example. __________ Translated from Journal of Tongji University (Natural Science), 2007, 35(2): 232–238 [译自: 同济大学学报(自然科学版)]     

Droplets actuating chip based on electrowetting-on-dielectric

A droplet-based actuating chip by using the method of electrowetting-on-dielectric (EWOD) was developed to manipulate the microfluidics. Here, the actuation mechanism of the sandwiched-configuration EWOD chips was carefully studied, and the movement of droplets was numerically analyzed by using the computational fluidic software, CFD-ACE+. The fabrication of the chip, including a heavily phosphorus-doped poly-silicon micro-electrode array and a thermally grown SiO₂ dielectric layer, was exploited to improve the chip stability and decrease the actuation voltage. In experiments, the transportation of a deionized droplet of about 0.5 μL is successfully achieved in air by applying the low voltage of 45 V. Translated from Journal of Tsinghua University (Science and Technology), 2006, 46(7): 1 341–1 344 [译自: 清华大学学报 (自然科学版)]     

Diversity analysis of space-time-frequency coded broadband MIMO-OFDM system with correlation across space time and frequency

For the frequency selective and time variant multiple-input multiple-output (MIMO) channel model taking into account transmitting and receiving antenna correlation, the diversity of space-time-frequency coded broadband orthogonal frequency division multiplexing (MIMO-OFDM) system is analyzed. Based on the average pairwise error probability (PEP), the design criterion of space-time-frequency code (STFC) is expanded. For a given STFC, it is found that the achievable diversity order is related to the transmitter and the receiver correlation matrix as well as the time correlation and frequency correlation matrix. The maximum available diversity of STFC over the correlation channel is Lrank(P)rank(Q)rank(R _T). The space-time code and space-frequency code are special cases in our approach. Simulation results validate the findings. __________ Translated from Journal of Southeast University (Natural Science Edition), 2007, 37(4): 549–553 [译自: 东南大学学报(自然科学版)]     

Planar antennas

This article reviews the state of the art in broadband antennas for emerging UWB applications and addresses the important issues of the broadband antenna design for UWB applications. First, a variety of planar monopoles with finite ground planes are reviewed. Next, the roll antennas with enhanced radiation performance are outlined. After that, the planar antennas printed on PCBs are described. A directional antipodal Vivaldi antenna is also presented for UWB applications. Last, a UWB antenna for wearable applications is exemplified     

Analytical design of PI controller for AQM with robustness adjustability

Based on a linearized TCP/AQMmodel, a new proportional integral (PI) controller design approach is proposed. This analytical approach applies H _∞ optimization and internal model control (IMC) theory to design active queue management (AQM) routers that support transmission control protocol (TCP) flows. The most important feature of the proposed scheme lies in that it can be explicitly tuned with a single parameter for the trade-off between performance and stability of the AQM control system. It is thus flexible and easy to use in design. The proposed method and the designed PI controller are verified and compared with other existing AQM schemes using ns-2 simulator. The results show the advantages of the new PI controller design approach for AQM routers supporting TCP flows. __________ Translated from Journal of Shanghai Jiaotong University, 2007, 41(5): 788–791 [译自: 上海交通大学学报]     

Indoor and outdoor people detection and shadow suppression by exploiting HSV color information

An adaptive background model based on maximum statistical probability and a shadow suppression scheme for indoor and outdoor people detection by exploiting hue saturation value (HSV) color information is proposed. To obtain the initial background scene, the frequency of R, G, and B component values for each pixel at the same position in the learning sequence are respectively calculated; the R, G, and B component values with the biggest ratios are incorporated to model the initial background. The background maintenance, or the socalled background re-initiation, is also proposed to adapt to scene changes such as illumination changes and scene geometry changes. Moving cast shadows generally exhibit a challenge for accurate moving target detection. Based on the observation that a shadow cast on a background region lowers its brightness but does not change its chromaticity significantly, we address this problem in the article by exploiting HSV color information. In addition, quantitative metrics is introduced to evaluate the algorithm on a benchmark suite of indoor and outdoor video sequences. The experimental results are given to show the performance of the algorithm. __________ Translated from Journal of Huaqiao University (Natural Science), 2007, 28(1): 30–33 [译自: 华侨大学学报 (自然科学版)]     

Robust adaptive beamforming algorithm based on Bayesian approach

The performance of adaptive array beamforming algorithms substantially degrades in practice because of a slight mismatch between actual and presumed array responses to the desired signal. A novel robust adaptive beamforming algorithm based on Bayesian approach is therefore proposed. The algorithm responds to the current environment by estimating the direction of arrival (DOA) of the actual signal from observations. Computational complexity of the proposed algorithm can thus be reduced compared with other algorithms since the recursive method is used to obtain inverse matrix. In addition, it has strong robustness to the uncertainty of actual signal DOA and makes the mean output array signal-to-interference-plus-noise ratio (SINR) consistently approach the optimum. Simulation results show that the proposed algorithm is better in performance than conventional adaptive beamforming algorithms. __________ Translated from Journal of Northeastern University (Natural Science), 2007, 28(6): 793–796 [译自: 东北大学学报 (自然科学版)]     

Pattern synthesis of antennas based on a modified particle swarm optimization algorithm

In order to overcome the drawbacks of standard particle swarm optimization (PSO) algorithm, such as prematurity and easily trapping in local optimum, a modified PSO algorithm is proposed, in which special techniques, as global best perturbation and inertia weight jump threshold are adopted. The convergence speed and accuracy of the algorithm are improved. The test by some benchmark problems shows that the proposed algorithm achieves relatively higher performance. Thereafter, the applications of the modified PSO in the radiation pattern synthesis of antenna arrays are presented. __________ Translated from Chinese Journal of Radio Science, 2006, 21(6): 873–878 [译自: 电波科学学报]     

High-speed ground moving target detection research using triangular modulation FMCW

The frequency modulated continuous wave (FMCW) radar has the characteristics of low probability of interception, good hidden property and the ability to counter anti-radiation missiles. This paper proposes a new method for high-speed ground moving target detection (GMTD) using triangular modulation FMCW. According to the characteristic of the opposite range shift induced by the upslope and downslope modulation FMCW, the upslope and downslope are imaged, respectively. After compensation of continuous motion of the platform and time difference between upslope and downslope signals for imaging, the moving target can be detected through displaced phase center antenna (DPCA) technology. When the moving target is detected, the moving target image is extracted, and correlation processing is used to obtain the range shift, which can be used to estimate the target radial velocity, and further to find the real position of the target. The effectiveness of this method is verified by the result of computer simulation. __________ Translated from Journal of Xidian University, 2008, 35(4): 586–591 [译自: 西安电子科技大学学报(自然科学版)]