Bing-Zhong Wang

Two Novel Band-Notched UWB Slot Antennas Fed by Microstrip Line

Two kinds of band-notched ultra wide-band slot antennas are proposed. Printed on a dielectric substrate of FR4with relative permittivity of 4.4 and fed by a 50 Ω microstrip line, the proposed antennas introduce semicircular annular strips to reject the frequency band (5.15-5.85 GHz) limited by IEEE802.11a. The parameters which affect the performance of the antennas in terms of its frequency domain characteristics are investigated in this paper.

A NUMERICAL STUDY ON TIME-REVERSAL ELECTROMAGNETIC WAVE FOR INDOOR ULTRA-WIDEBAND SIGNAL TRANSMISSION

In this paper, the propagation of ultra-wideband (UWB) pulse based on time reversal (TR) technique is studied by finite- different time-domain method in indoor environment. Time compression and spatial focusing of TR waveform are simulated and the propagation of multi-waveform string is analyzed. Then UWB wireless signal transmission based on TR concept is studied numerically. The studied results indicate that the UWB communication based on TR technique can obtain better Inter-Symbol Interference (ISI) and Co- Channel Interference (CCI) performance than traditional one because of its unique property.

A hybrid 2-D ADI-FDTD subgridding scheme for modeling on-chip interconnects

The finite-difference time-domain (FDTD) method gives accurate results but uses a large amount of computer memory and time, which can be reduced by applying higher resolution only around critical areas in the problem domain. In this paper, a new subgridding scheme have been proposed which based on the hybridization of the alterative-direction implicit FDTD (ADI-FDTD) and FDTD algorithms. The field components in fine local grids are updated using the ADI-FDTD method, and in the coarse main grids conventional FDTD method is utilized. The technique achieves the same time marching step in the whole domain as employed in the coarse FDTD scheme, and the need for the temporal interpolation of the fields in the fine grids is obviated since the ADI-FDTD scheme is unconditionally stable. Hence, the hybrid ADI-FDTD subgridding scheme is less time consuming and easy to implement. Practical applications of the algorithm in the simulations of the scattering of conducting cylinder and dielectric square cylinder are reported.

Switched Band-Notched UWB/Dual-Band WLAN Slot Antenna With Inverted S-Shaped Slots

A switched antenna that has a capability to operate in the dual-band WLAN frequency bands (2.4-2.485, 5.15-5.35, and 5.725-5.825 GHz) and the band-notched ultrawideband (UWB) frequency band (the stopband covers the frequency band ranging from 5.15 to 5.825 GHz) is presented. The proposed antenna is composed of a rectangular ring slot, four switches, a coplanar waveguide (CPW) feeding line, a T-shaped stub, and two inverted S-shaped slots. The function of the two inverted S-shaped slots can be changed by tuning status of the switches that make the operating bands of the proposed antenna various. To the authors knowledge, a feature that the antenna is able to cover two complementary bands is unique to this letter.

Novel design for low-RCS screens using a combination of dual-AMC

Before closing we point out that realizing a phase difference of 180° between the two different types of patches—be they PEC or AMC is difficult over a wide frequency band. Also, for the fan-type of design, the geometry is necessarily aperiodic, and hence the phase behavior predicted for ideal doubly-periodic screens do not apply very well for the center zone of the fan-type screen. It is indeed satisfying to know that despite this flaw, the fan design performs quite well, even without losses in the screen, though there is obviously room for improvement. Finally, the lossy case is currently under investigation for wideband application, and the results will be reported in a future publication.

Efficient compact 2-D time-domain method with weighted Laguerre polynomials

An efficient time-domain method based on a compact two-dimensional (2-D) finite-difference time-domain (FDTD) method combined with weighted Laguerre polynomials has been proposed to analyze the propagation properties of uniform transmission lines. Starting from Maxwells differential equations corresponding to the compact 2-D FDTD method, we use the orthonormality of weighted Laguerre polynomials and Galerkins testing procedure to eliminate the time variable. Thus, an implicit relation, which results in a marching-on-in-degree scheme, can be obtained. To verify the accuracy and efficiency of the hybrid method, we compare the results with those from the conventional compact 2-D FDTD and compact 2-D alternating-direction-implicit (ADI) FDTD methods. The hybrid method improves the computational efficiency notably, especially for complex problems with fine structure details that are restricted by stability constrains in the FDTD method

A Domain Decomposition Finite-Difference Method Utilizing Characteristic Basis Functions for Solving Electrostatic Problems

This paper presents an efficient approach for solving a linear system of equations arising in the domain decomposition finite-difference (DDFD) method, employed for electrostatic problems. This novel approach is based on utilizing characteristic basis functions (CBFs)-special functions defined on macrodomains, or blocks in which the computational domain is discretized by using the DDFD method. The use of the CBFs leads to a significant reduction in the number of unknowns, and results in a substantial size reduction of the DDFD system; this, in turn, enables us to handle the reduced matrix by using an iteration-free direct solver. The reduced sparse matrix system is solved via the Schur complement approach, which reduces the system into many independent smaller subsystems. Two electrostatic problems are used as examples to illustrate the application of the proposed approach. Numerical results that demonstrate the accuracy and efficiency of the method are included.

RADIATION PATTERNS SYNTHESIS FOR A CONFORMAL DIPOLE ANTENNA ARRAY

A conformal cylindrical dipole array is developed in this paper. Because the conformal dipole array is curved, new far field pattern behaviors emerge. In this paper, we start to analyse the equations for the far field of the conformal dipole array by using the method of moments (MoM) with a dyadic Greens function, and then validate the accuracy of the far field expressions. Next, a novel Gauss amplitude distribution, which is capable to yield a desired far field radiation pattern when the array structure has a relative small cylindrical radius, is proposed. The advantage of the proposed method is that it can provide good aperture distributions to obtain low sidelobe level.

Modeling stripline discontinuities by neural network with knowledge-based neurons

A three-layer neural network with knowledge-based neurons in the hidden layer (NNKBN) is presented for modeling stripline discontinuities. In NNKBN, prior knowledge for stripline discontinuity is incorporated into each hidden neuron. With knowledge-based neurons, the learning ability and generalization of the neural network are improved. Compared with conventional multi-layer perceptron neural network, the NNKBN can map the input-output relationships with fewer hidden neurons and has higher reliability for extrapolation beyond training data range. Two examples are given to illustrate the potential power of this approach.

2-D FDTD method for exact attenuation constant extraction of lossy transmission lines

The two-dimensional finite-difference time-domain (2-D FDTD) method is undeniably efficient for full-wave analysis of uniform transmission lines. However, conventional 2-D FDTD method ignores the spatial attenuation along the propagation direction and yields approximate results. We propose a new 2-D FDTD method for extracting exact attenuation constants of lossy transmission lines. In the proposed method, we take the variation of field components with the propagation direction into consideration and describe an iterative process for finding exact attenuation constants. Numerical experiments show that, compared with the conventional 2-D FDTD method, results given by the iterative process agree much better with analytical solutions or measured data.