One of most difficult challenges in simulating hybrid RF systems by finite-difference time-domain (FDTD) method is to construct the models for active and lumped elements. In this article, by combining the circuit equations with an integral transform, an enhanced FDTD method is proposed to model the hybrid lumped network which consists of nonlinear and high order linear elements with arbitrary connections. Based on this model, an active radiation system is analyzed. And it shows the application extension of the traditional FDTD method.
A triple-band omni-directional antenna which comprises three pairs of dipoles placed back to back and printed on a dielectric substrate is presented. A prototype is constructed and tested. The experimental results show that the 10 dB return loss bandwidth (VSWR < 2.0) in 2.4 GHz, 5.2 GHz and 5.8 GHz reaches as much as 130 MHz, 500MHz and 200 MHz, respectively. Moreover, the radiation patterns are almost omni-directional in the azimuthal plane. Peak antenna gain is 1.63 dBi, 2.36 dBi and 1.54 dBi, which indicate that the proposed antenna can be used as a triple-band antenna for the WLAN application.
The characteristics of the guided electromagnetic wave propagation through a slab waveguide of uniaxially anisotropic dispersive metamaterial are investigated. Taking the cold plasma media model with ωmpz < ωmp⊥ < ωep⊥ as an example,the mode classification established in terms of the operating angular frequency ω0 of the slab waveguide. The results indicate that the mode properties are closely dependent on the frequency. When ω2 mpz < ω20 < ω2mp⊥ there are infinite guided modes. It is also found that when ω2em < ω20 < ω2mpz,there may be multiple solutions of the propagating mode with imaginary transverse wave number in a slab waveguide with thickness less than a certain value.
The propagation properties of surface plasmon polaritons (SPP) modes in nanoscale narrow metallic structures: gap, channel, and rectangular-hole waveguides, are analyzed by the complex effective dielectric constant approximation. The results show that all the SPP modes exist below the critical frequency where the real part of metal permittivity is negative unity. It is found that both cutoff frequency and cutoff height exist in channel waveguide and rectangularhole waveguide. The channel and rectangular-hole waveguides have different propagation properties at cutoffs due to their different cutoff conditions. Compared with the gap waveguide, the channel waveguide has shorter propagation length and better confinement when the operation frequency is near the critical frequency, but has longer propagation length and worse confinement when the operation frequency is far from the critical frequency. Among the three waveguides, the rectangular-hole waveguide has the best confinement factor and the shortest propagation length. The comprehensive analysis for the gap, channel, and rectangular-hole waveguides can provide some guidelines in the design of subwavelength optical devices.
The suitable use of an array antenna at the base station of a wireless communication system can result in improvement in signalto- interference ratio (SIR). In the present work, we consider circular array (CA) and concentric circular antenna array (CCAA) that are used for smart antenna systems. The performance criteria for SIR improvement is employed in this paper, is the spatial interference suppression coefficient. We first develop the expression of this figure of merit for CCAA and then analyze and compare the SIR performance for various configurations of eight and nine elements of CA and CCAA, with and without the element in the center by using circular patch antenna are provided. In addition, the effect of mutual coupling (MC) is taken into account.
Multimode fibers are characterized by multipath propagation of optical signals and this leads to severe intersymbol interference at the output of the fiber. In this work an approach based on the Rake receiver is proposed to overcome this drawback. An optimization algorithm was developed and appropriate software was employed to apply the proposed methodology on specific multimode fiber. Extensive simulation results were produced and are presented herein. The numerical results have shown that the order of magnitude of the maximum data rate, R, supported at different CDMA gains, in order to achieve a Bit Error Rate value smaller or equal to a convergent point, is related to the length of the multimode fiber, L, by the expression R = dL−1 with d increasing from 106 to 107 (Kbps. m) when CDMA gain increases from 50 to 500.
In this paper, a generalized photon wave function (PWF) which is applicable to electromagnetic problems is introduced. The formulation treats the electromagnetics fields as quantum mechanical entities. The introduced PWF is especially useful for boundaryvalue problems. For instance,the reflection coefficient at a dielectric half space is calculated based on the concepts of PWF and quantum mechanics. With the proposed method, inhomogeneous media, both isotropic and anisotropic, can also be analyzed. It is shown that by defining certain new variables, such as effective charges and effective currents, we will be able to describe the behavior of electromagnetic fields by the proposed photon wave function. At the end of this paper, a new FDTD method based on the notion of photon wave function is introduced and the resonance frequencies of a cubic cavity are obtained.
Vector wave three-dimensional (3-D) conducting rough surface scattering problem solved by a UV method with multilevel partitioning (UV-MLP) is developed in this paper. For a 3-D conducting rough surface scattering problem, the scattering structure is partitioned into multilevel block. By looking up the rank in the static problem, the impedance matrix for a given transmitting and receiving block is expressed into a product of U and V matrix. The UV method is illustrated by applying to a 3D scattering problem of random conducting rough surface in this paper. Numerical simulation results are illustrated.
A Ku band six-bit phase shifter is presented in this work. The developed phase shifter consists of four bits realized as periodically loaded-line and two bits based on novel switched-line with loaded-line. A 71Ω line impedance is chosen for the main transmission line in order to reduce the diode loss. Every bit has special tuning elements for the fine tuning of the required phase shift. The phase error for the 64 phase states is not greater than 3.4 degrees at the designed center frequency of 15 GHz, and the insertion loss for the 64 phase states is 5.2 dB±1.1 dB over the operating bandwidth of 14.9-15.1 GHz.
The aim of this work is to introduce the application of wavelet in Electromagnetic Scattering and making improvement in the moment method development. The conventional moment method basis and testing functions are used to digitalize the integral equations of the electric or magnetic field, resulting in dense matrix impedance. By using the wavelet expansion, wavelets as basis and testing functions, a sparse matrix is generated from the previous moment method dense matrix, which may save computational cost. Here application has been made upon two types of two dimensional antennas, which are circular cylindrical antennas and parabolic reflector antennas. Results are compared to the previous work done and published, excellent results are obtained.
This paper describes a steerable broadband dielectric antenna with 30% fractional bandwidth, operating at 11 GHz. The structure consists of a hollow cylindrical dielectric pellet of permittivity 6 fed by four probes. Two methods are described for beam forming: 1- Beam forming has been achieved by individually switching between excited probes. The switched excitation mechanism provides the antenna with a reconfigurable radiation beam that can be moved in the azimuth plane. 2- Variable phase excitation of several probes. Complete azimuth sweep was demonstrated by both methods, allowing any desired angle of beam directions. Simulation and experimental results are presented to illustrate the advantages of both designs.
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 Green's 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.
This paper is concerned with the analysis of the currents induced on a 2D infinite perfectly conducting plane illuminated by a complex beam obtained from the analytical continuation of the real location of a unit impulse source into a complex one. The main goal considering this well-known problem is to understand the meaning of the analytical continuation and the physical information underlying the complex quantities arising from it,and to investigate the capabilities of operating in complex spaces instead of the original real ones through a simple example. Several complex quantities directly related to this problem are analysed and translated into the real domain,leading to a clear and general description of all the possible behaviours of the currents. These results will provide some new insight to extend the complex analysis methodology to more complicated scattering problems. As expected,complex analysis appears to be a full-meaning tool to obtain parameterizations of EM problems,leading to more general solutions and their physical descriptions.
In this study, we address the problem of detecting bodyworn improvised explosive devices (IEDs) from a safe distance using radar. We have used a finite difference frequency domain (FDFD) model to simulate the radar signature of a typical scenario for bodyworn IEDs, and have analyzed wrinkled clothing as a possible source of clutter, as well as the possibility for uniform versus nonuniform array spacing of explosive-filled metal pipes. Our analysis shows distinct characteristics of the pipe backscattered farfield signal for uniformly spaced pipes, with no significant clutter added when the metallic pipe is covered with wrinkled clothing.
A time-domain hybrid approach that combines the Finite- Difference Time-Domain (FDTD) method with Time Domain Physical Optics (TDPO) is presented. The approach can be applied to the analysis of the backscattering of combinative objects including a Small- Size structure (SS) and a Large-Size structure (LS) with respect to the wavelength of interest. When dealing with the coupling of SS to LS, the near-to-near field extrapolation technique based on Kirchhoff's surface integral representation is used and a sequential transfer method is developed. According to the time domain calculation sequence in FDTD, the contribution of SS to LS is transferred directly to far zone observation point. The sequential transfer method has some advantages in high efficiency and small amounts of computer memory. For far zone back scattering, the influence of LS onto SS can be obtained by using the reciprocity theorem. Finally, the validation and application examples are presented, demonstrating the accuracy and effectiveness of this approach.
A hybrid approach of the forward-backward method (FBM) with spectral accelerate algorithm (SAA) and Monte Carlo method is developed in this paper. It is applied to numerical simulation of bistatic scattering from one-dimensional arbitrary dielectric constant soil surface with a conducting object with arbitrary closed contour partially buried under both the horizontal and vertical polarization tapered wave incidence at low grazing angle. The energy conservation has been checked for the FBM/SAA. Numerical simulations of bistatic scattering at low grazing angle have been discussed in this paper.
A novel planar six-way power divider is proposed. Based on the conventional planar microstrip coupled line technology, the proposed compact six-way power divider is comprised of two stages coupled transmission lines, which is different to the conventional multistage power divider using the same expanded structure, one stage folded two-coupled line, and the other hybrid-expanded symmetrical three-coupled line. Therefore, the proposed power divider is size reduction, and has a broad-band property, which is better than 40% of fractional bandwidth. Furthermore, compared to a traditional six-way power divider, it is designed and fabricated easily. From the simulated and measured results, the six-way planar power divider shows a good specifications, which are insert loss 8.1±0.2 dB from 2 GHz to 3 GHz, and return loss less than −18 dB, isolation less than −19.5dB at 2.5 GHz, respectively.
A novel broadband design of a coplanar waveguide (CPW) fed T-shape slot antenna is proposed and experimentally studied. The size of the proposed antenna is reduced by over 26% compared to the reported wide slot antenna. The obtained results show that the impedance bandwidth, determined by 10-dB return loss, of the proposed slot antenna can be as large as 5690MHz or about 121% centered at about 4.695 GHz. The design considerations for achieving broadband operation of the proposed slot antenna are described, and experimental results are presented.
In this paper,a new monopole with G type structure is proposed,consisting of two wires rectangle rings with radius of 2 mm. The software Numerical Electromagnetic Code (NEC) is used to analyze the proposed antenna and a prototype is designed. The experimental and numerical results of the designed wideband antenna are presented and analyzed,and a 510MHz bandwidth from 0.86 GHz to 1.37 GHz is demonstrated. The experimental and numerical results fit well.
A microstrip bandpass filter with a new type of capacitive coupled resonator is presented. The filter is designed to be smaller compared to the same type of parallel-coupled bandpass filter. The filter is designed for a centre frequency of 2.5 GHz that lies in the S-band frequency range. The insertion loss at ƒo is 2.4 dB and the measured 3 dB bandwidth is 8.6%. The agreement between the predicted and measured results is excellent, and even the circuit simulator gives a very good prediction for the filter characteristics.
This paper presents a synthetic concept on eliminating crosstalk within multiconductor transmission lines (MTLs). Firstly, the method of moments (MoM) is used to calculate the per-unitlength (PUL) parameters of transmission lines. Secondly, the crosstalk is predicted using SPICE circuit simulator. Finally, three methods eliminating crosstalk are used synthetically to design the structure of MTLs. According to the results simulated with software, the effect on eliminating crosstalk by the synthetic design is quite satisfactory. Therefore, the concept may be implimented in practical engineering.
Experimental study on a cylindrical Dielectric Resonator Antenna (DRA) using barium titanate (BaTiO3) is presented in this paper. The antenna is fed with a 50Ω microstrip transmission line at frequency around 2.5 GHz. High dielectric constant (εr = 1000) resonator samples with different thickness are employed. The return loss, input impedance and radiation patterns are studied. Design simulation results using CST software also presented.
Communication systems operating at frequencies above 10 GHz in equatorial climates are subjected to many fade occurrences due to heavy rain. Rain rate analysis using 1-minute data for 10 years (1996-2006) measurements in Penang shows that the rain exceeded 126.8mm/h for 0.01% of a year (R0.01). Simultaneous measurements of Ku-band rain attenuation give A0.01 as 22 dB. The rain rate and attenuation are characterized by the presence of breakpoints in the respective exceedance curves. The attenuation exceeds the fade margin for about 8.8 hours in a year.
A non-coherent theoretical model of sea-ice thickness with air-borne microwave radiometer (ABMR) was deduced based on the analysis of air-ice-water three-layer media. In the model, the highorder item of the brightness temperature was expressed and obtained. From the analysis of the penetration depth of sea-ice and its high-order item in the model, we found that ABMR with a wavelength can only be used to detect a certain range of sea-ice thickness. The maximum detectable sea-ice thickness is dependent on wavelength and precision of ABMR, whereas the minimum detectable sea-ice thickness is only related to wavelength. On this basis, the detectable sea-ice thicknesses of ABMR were calculated. The results were given on the selection of suitable ABMRs in different sea-ice conditions when ABMR is used to detect the ice thickness in Bohai Sea.
High frequency field expressions for a two dimensional reflector are derived. The reflector is placed in a homogenous and reciprocal chiral medium. Since geometrical optics fails at caustics so Maslovs method has been used to find the field expressions which are also valid around caustics. Examples of parabolic and circular reflectors have been considered.
This work demonstrates an efficient and simple PML absorbing boundary conditions (ABCs) implementation for the highorder extended-stencil M24 FDTD algorithm. To accomplish this objective, the integral forms of the PML split-field formulations were derived and discretized using the same M24 weighted multiple-loop approach, resulting in ABC performances that match the standard FDTD-based PML formulations. This proposed approach eliminates the impedance mismatches caused by switching from M24 to regular FDTD update equations within the PML regions and the necessary cumbersome subgridding implementations needed to minimize the effects of these mismatches. It also eliminates the need to use large separations between the scatterers and the PML regions as a simpler though more costly alternative. This achievement coupled with the recent effective resolution of the PEC modeling issue finally eliminates the last hurdles hindering the wide adoption of the M24 algorithm and its three-dimensional counterpart, the FV24 algorithm, as a viable option for accurate and computationally efficient modeling of electrically large structures.
A novel technique for the amplification and the compression of an optical pulse is proposed.Based on cascaded a semiconductor optical amplifier (SOA) and a nonlinear optical loop mirror (NOLM), the chirping effect induced by the SOA and the cross phase modulation effect between the signal pulse and control pulse can be utilized to shape the pulse.The picosecond pulse amplification and compression are demonstrated in this paper.A good theoretical model is designed with optimal parameters.Results show that the output signal pulse with high peak power, narrow pulse width, and low pedestal can be obtained using the designed model, which is suited for furture 640 Gbps optical communications.
This paper is devoted to the forward radar propagation over clean and contaminated seas, using the Ament model and by taking the shadowing effect into account. The well-known Rayleigh parameter, which characterizes the degree of roughness of a corrugated surface for the case of reflection on a rough surface, is presented. Then, it is extended to the transmission through a rough surface, and to the reflection on a layer of two rough interfaces. This extended Rayleigh parameter allows then to calculate the forward radar propagation over oil slicks on sea surfaces, using the Ament model. Moreover, the model is improved by taking the shadowing effect into account. Numerical results of contaminated seas are presented, and compared to that of clean seas.
Various electromagnetic scattering approximations beyond the Born assumption have been published during the recent years. This paper introduces a simple framework of analyses and investigates in a systematic way the fundamentals of the proposed theories. Our main focus is to demonstrate the link and similarities between the different scattering approximations employing a common physical basis. Based on analogies established we try to bridge the apparent gap between existing theories as well as introducing possible extensions and refinements.
The rain attenuation in the 12-GHz band and one-minuterain rate were measured at four satellite beacons located in South East Asia countries over a three-year period (2002-2004). The cumulative distribution of rain rate obtained as well as cumulative distribution of rain attenuation obtained are presented and compared with the rain prediction models. Most of the rain prediction models showed noticeable deviation to the measured values above the existence of the breakpoint (the point at which the slope changes). The results can be employed to guide the design and application of slant-path communication systems, especially in South East Asia countries.
A new computationally efficient algorithm for reconstruction of lossy and inhomogeneous 1-D media by using inverse scattering method in time domain is proposed. In this algorithm, cosine Fourier series expansion is utilized in conjunction with finite difference time domain (FDTD) and particle swarm optimization (PSO) methods. The performance of the proposed algorithm is studied for several 1-D permittivity and conductivity profile reconstruction cases. Various types of regularization terms are examined and compared with each other in the presented method. It is shown that the number of unknowns in optimization routine is reduced to about 1/3 as compared with conventional methods which leads to a considerable reduction in the amount of computations, while the precision of the solutions would not be affected significantly. Another advantage of the proposed expansion method is that, since only a limited number of terms are taken in the expansion, the divergence of the algorithm is far less likely to occur. Sensitivity analysis of the suggested method to the number of expansion terms in the algorithm is studied, as well.
A new type of antenna named as compound box-horn antenna is designed and analyzed for its radiation pattern. The present analysis is based on plane wave spectra for three-dimensional fields. The compound box-horn antenna is obtained by combining modified box-horn and pyramidal horn antennas, in which modified box-horn is coupled to pyramidal horn to excite TE10- and TE30- modes at the input of pyramidal horn. Thus, the compound boxhorn antenna has properties and advantages of both the modified box-horn and pyramidal horn antennas. The radiation patterns and corresponding half-power beam widths (HPBWs) of compound boxhorn antenna in free-space are computed at 10 GHz and compared for different flare angles in E- and H-planes of larger size pyramidal horn section of the compound box-horn. The results for HPBWs in Eand H-planes demonstrate that the radiation patterns in E- and Hplanes for compound box-horn can be made narrower by decreasing the flare angles in both E- and H-planes of larger size pyramidal horn section of the compound box-horn. The radiation patterns of compound box-horn are also compared with those for TE10-mode pyramidal horn of same aperture size and it found that the former horn is narrower in E- as well as H-plane than the latter. The analysis has been validated against the experimental results available in the literature. The work presented here can provide useful design guidelines for development of prototypes of compound box-horn which may find potential application as a high-directivity transmitting horn for antenna measurements in the laboratory or as a range illuminator, or in microwave communication etc.
Maxwell's equations are solved to determine transient electromagnetic fields inside as well as outside a large conducting plate of an arbitrary thickness. The plate is carrying a uniformly distributed excitation winding on its surfaces. Transient fields are produced due to sudden interruption of the d.c. current in the excitation winding. On the basis of a linear treatment of this initial value problem it is concluded that the transient fields may decay at a faster rate for plates with smaller value of relaxation time. It is also shown that the energy dissipated in the eddy current loss may exceed the energy stored in the initial magnetic field.
A detailed study of surface TM modes at the interface between an isotropic medium and a uniaxial plasma is presented. Four cases for the isotropic medium, including normal, Left-handed, magnetic, and metallic media, are considered. The conditions for the existence of surface modes in each case are analyzed, showing that the existence is determined by the parameters of media, working frequency, and the direction of the principle axis. The Poynting vector along the propagating direction is also calculated. Depending on the media parameters and the frequency, the surface mode can have time-average Poynting vector in the opposite direction of the mode phase velocity.