In this paper, we describe a new full-wave integral equation model to tackle electromagnetic scattering problems arising from objects buried in layered media. Such a model is a rewriting of the usually adopted Contrast Source integral equation and is named Contrast Source-Extended Born (CS-EB) owing to this circumstance and to the relationship existing among its linearization and the Extended Born approximation. By means of this alternative formulation, it is possible to modify the relationship among the scatterer permittivity and the field it scatters, thus possibly reducing the degree of non-linearity of this latter relationship. Accordingly, in these cases, the adoption of the CS-EB model may be convenient with respect to traditional ones in both forward and inverse scattering problems.
This paper presents the 3-D dispersion analysis of finite-difference time-domain (FDTD) schemes for doubly lossy media, where both electric and magnetic conductivities are nonzero. Among the FDTD schemes presented are time-average (TA), time-forward (TF), time-backward (TB) and exponential time differencing (ETD). It is first shown that, unlike in electrically lossy media, the attenuation constant in doubly lossy media can be larger than its phase constant. This further calls for careful choice of cell size such that both wavelength and skin depth of the doubly lossy media are properly resolved. From the dispersion analysis, TF generally displays higher phase velocity and attenuation errors due to its first-order temporal accuracy nature compared to second-order ETD and TA. Although both have second-order temporal accuracy, ETD has generally lower phase velocity and attenuation errors than TA. This may be attributed to its closer resemblance to the solution of first-order differential equation. Numerical FDTD simulations in 1-D and 3-D further confirm these findings.
A model for the two-dimensional analysis of microstrip lines, named Rigorously Coupled Multi-conductor Strip (RCMS) is introduced. In this model, the width of the strip of a microstrip line is subdivided into a large number of rigorously coupled narrow strips. So, a microstrip line can be considered as a coupled multi-conductor transmission line. Determination of the capacitance and inductance matrices of the model is introduced, also. The voltages and currents induced by electromagnetic fields for the coupled multi-condutor strips problem can be obtained using Bernardi's method. The effect of an external EM wave on a microstrip line with non-uniformity in its width is computed by adding the circuit model of transverse discontinuity (narrow slit) to the RCMS model. Finally, the validity and efficiency of the introduced method is investigated using previous work and full wave EM-simulation software.
In this paper, the performances of thinned arrays based on Almost Difference Sets are analyzed in the presence of mutual coupling effects. The geometry under test is composed by thin dipole elements and the arising mutual interactions are modeled by means of the induced EMF method. To assess the robustness of the ADS-based thinning technique also in such a non-ideal case, an extensive numerical analysis is carried out by considering several test cases characterized by different aperture sizes, lattice spacings, and thinning factors. The obtained results show that the peak sidelobe estimators deduced in the ideal case still keep their validity although, as expected, a deterioration usually arises due to the mutual coupling.
A method to enhance gain of a circularly polarized (CP) microstrip patch antenna is proposed. We etch coupled square-shaped split ring resonators (CSSSRRs) on both sides of a superstrate which is separated from the patch by an air layer. Thickness of the air layer is around 0.1λ, which keeps the radome in low profile. Open gaps of each CSSSRR on opposite sides of the superstrate are orthogonally oriented to each other. This unique orientation allows the radome not only enhance gain but also maintain good CP performance.
The common approaches to sample a signal generally follow the well-known Nyquist-Shannon's theorem: the sampling rate must be at least twice the maximum frequency presented in the signal. A new emerging field, compressed sampling (CS), has made a paradigmatic step to sample a signal with much less measurements than those required by the Nyquist-Shannon's theorem when the unknown signal is sparse or compressible in some frame. We call a compressed-sampling filter (CSF) one for which the function relating the input signal to the output signal is pseudo-random. Motivated by the theory of random convolution proposed by Romberg (for convenience, called the Romberg's theory) and the fact that the signal in complex electromagnetic environment may be spread out due to the rich multi-scattering effect, two CSFs via microwave circuit to enable signal acquisition with sub-Nyquist sampling have been constructed, tested and analyzed. Afterwards, the CSF based on surface acoustic wave (SAW) structure has also been proposed and examined by the numerical simulation. The results has empirically shown that by the proposed architectures the S-sparse n-dimensional signal can be exactly reconstructed with O(Slogn) real-valued measurements or O(Slog(n/S)) complex-valued measurements with overwhelming probability.
The Finite Volume Time-Domain (FVTD) method finds limited application in the simulation of electromagnetic scattering from electrically large scatterers because of the fine discretization required in terms of points-per-wavelength. An efficient implementation of a higher-order FVTD method is proposed for electrically large, perfectly conducting scatterers. Higher-order and fine-grid accuracy are preserved, despite using only a first-order spatial accuracy and a coarse grid in substantial parts of the FVTD computational domain, by partially incorporating a time-domain Physical Optics (PO) approximation for the surface current. This can result in considerable savings in computational time while analyzing geometries containing electrically large, smooth sections using the FVTD method. The higher-order FVTD method in the present work is based on an Essentially Non-Oscillatory (ENO) reconstruction and results are presented for two-dimensional perfectly conducting scatterers subject to Transverse Magnetic (TM) or Transverse Electric (TE) illumination.
ℜThis paper presents a dimensional synthesis method for designing wide-band quarter-wavelength resonator bandpass filters. In this synthesis method, an alternative lowpass prototype filter and the edge frequency mapping method are proposed and applied. The improved K- and J-inverter model with the exponent- weighted turns ratio is also proposed in order to incorporate the frequency dependence of inverters. Based on the edge frequency mapping method and the improved inverter model, an iterative dimensional synthesis procedure is then presented. As design examples, a four-pole rectangular coaxial bandpass filter with 63% fractional bandwidth is designed and fabricated. The simulation and measurement results show good equal ripple performance in the passband.
We present a new approach to the modeling of angle and time of arrival statistics for radio propagation in typical office buildings, in which the majority of interior scattering objects are either parallel or perpendicular to the exterior walls. We first describe the reradiating elements in office buildings as randomly distributed arrays of thin strips. The amount of clutter and the amount of transmission/reflection loss are then accounted for through several key parameters of the site-specific features of indoor environment, such as the layout and materials of the building under consideration. Subsequently, the important channel parameters including power azimuthal spectrum (PAS) and power delay spectrum (PDS) are derived. An appealing observation is that when the path angles from multiple channel trials are measured and collectively analyzed, deterministic angle clustering becomes evident. This phenomenon agrees well with the existing ray-tracing (RT) results reported by Jo et al. in buildings of this type and cannot be explained by other geometric channel models (GCMs). Furthermore, the proposed model predicts an asymmetric cluster PAS for a single-channel-trial scenario, which yields an excellent fit to the experimental data presented by Poon and Ho. Finally, we have also investigated the behaviors of the superimposed PAS and PDS under various channel conditions.
In recent years, Computer Aided Design (CAD) based on Artificial Neural Networks (ANNs) have been introduced for microwave modeling, simulation and optimization. In this paper, the characteristic parameters of edge coupled and conductor-backed edge coupled Coplanar Waveguides have been determined with the use of ANN model. Eight learning algorithms, Levenberg-Marquart (LM), Bayesian Regularization (BR), Quasi-Newton (QN), Scaled Conjugate Gradient (SCG), Conjugate Gradient of Fletcher-Powell (CGF), Resilient Propagation (RP), Conjugate Gradient back- propagation with Polak-Ribiere (CGP) and Gradient Descent (GD) are used to train the Multi- Layer Perceptron Neural Networks (MLPNNs). The results of neural models presented in this paper are compared with the results of Conformal Mapping Technique (CMT). The neural results are in very good agreement with the CMT results. When the performances of neural models are compared with each other, the best results are obtained from the neural networks trained by LM and BR algorithms.
In this paper a linear series fed Yagi-like antenna array is introduced leading to an end-fire fan beam with low sidelobe level, SLL, high front to back ratio, F/B, and wide impedance bandwidth. The array can provide -29 dB SLL at centre frequency of 16.26 GHz, -20 dB SLL bandwidth of 7.5%, 23 dB F/B and 10.6% impedance bandwidth. Further improvement in SLL can be achieved by extending narrow strips from the finite ground plane of the antenna structure leading to some -32 dB SLL at centre frequency and a -20 dB SLL bandwidth of 8.7%. To verify the accuracy of the simulation results, both of the arrays are fabricated and tested. Finally, to show the applicability of the proposed design, the linear end-fire array of the above are stacked on top of each other and simulation results for a 2-D phased array are provided.
In this article, a linear phased antenna array for beam scanning is considered with a fixed narrow/broad interference out of the scanning region. This interference is aimed to be suppressed by optimizing the positions of array elements while avoiding the rise of maximum sidelobe level (MSLL) during the main beam is scanning within the prescribed region. These two objectives; suppressing the fixed interference and avoiding the rise of MSLL during scanning are in conflict with one another. In order to evaluate the effectiveness of such multi-objective approaches it is important to report Pareto optimal solutions which are the objective way of solving multi-objective optimization problems. Thus, in this work, the genetic algorithm (GA) is introduced for the purpose of obtaining the Pareto optimal fronts for the two conflicting objectives to show the effectiveness of the proposed method.
A comprehensive review of radio wave attenuation in forest environments is presented in this paper. The classic analytical methods of propagation loss modeling and prediction are described first. This provides information on the physical processes that the radio waves undergo while propagating through a forest. The focus of this paper is on the review and summary of the experimental work done in this area and the development of empirical propagation loss prediction models. The propagation loss variation due to external factors such as antenna height-gain, depolarization, humidity effect etc. are examined and discussed individually. In view of current research work done in this area, some possible future work is proposed to improve the performance of radio links in forest environment.
A propagation model is presented in this paper for predicting the field strength in microcellular environments. According to the Geometrical Theory of Diffraction, the total field at a given observation point is calculated by summing the Geometrical Optics contributions and the field diffracted by the edges of each structure. The diffraction contributions are here evaluated by means of a Uniform Asymptotic Physical Optics solution to the corresponding canonical problem. Such a solution, expressed in terms of the standard transition function of the Uniform Theory of Diffraction, has resulted to be able to compensate the Geometrical Optics discontinuities at the shadow boundaries. In this framework, the structures are treated as constituted by lossy dielectric materials assumed to be non penetrable. The effectiveness of the here proposed model has been tested in some typical scenarios by means of comparisons with the Finite Difference Time Domain method.
This paper presents a basic analysis about the results of experiments using planar coils inner to ring coils, when planar coil is applied to a square wave voltage. In this study an uncommon phenomenon occurs in the ring coil, which is analyzed.
A method based on plant growth simulation algorithm (PGSA) is presented for pattern nulling by controlling only the element amplitudes of linear antenna array. The PGSA is a new and highly efficient random search algorithm inspired by the growth process of plant phototropism. Simulation results for Chebyshev patterns with the imposed single, multiple and broad nulls are given to show the performance of the proposed method.
We provide here a theoretical description of electromagnetic scattering by multi-wall carbon nanotubes based on an effective-boundary condition derived previously using a phenomenological quantum model. We present the basic analytical solution, extending it then to include the electromangetic interaction between multiple concentric tubes in the general multi-wall carbon nanotube case.
Nowadays, through wall imaging (TWI) is a emerging topic of research in which one of the most important tasks is to minimize the clutter through which detection accuracy can be improved. Clutter in TWI is due to many reasons like wall coupling, antenna coupling, multiple reflections etc. To analyze the clutter reduction techniques, firstly we indigenously assembled a TWI system (i.e. step frequency continuous wave radar (SFCW)) in UWB range (freq. 3.95 GHz to 5.85 GHz), and different observations have been taken. We have considered metallic plate and one more material with low dielectric constant (Teflon) as a target and kept them behind the plywood wall. A-scan and B-scan observations have been carried out. The observed data are preprocessed for imaging and then different types of clutter reduction techniques like Principal Component Analysis (PCA), Independent Component Analysis (ICA), Factor Analysis (FA) and Singular Value Decomposition (SVD) have been applied, and results were analyzed. Signal to noise ratio (SNR) of the final images (i.e., after clutter removal with different techniques) has been computed to compare the results and know the effectiveness of individual clutter removal techniques. It is observed that ICA has better capability to remove the clutter in comparison to other applied techniques; especially it is found that ICA has a capability to distinguish the difference between clutter and low dielectric target whereas other clutter removal techniques are not showing significant result.
A compact, ultra-broadband coplanar-waveguide (CPW) bandpass filter (BPF) is demonstrated. The proposed CPW-BPF is essentially designed by exploiting CPW short-stub and open-stub structures. Technically, the proposed filter comprises shunt short-stub and series open-stub structures that are connected in a cascade topology. The higher and lower cutoff frequencies are mainly related to the electrical length of the shunt short stub and the series open stub, respectively. In addition, the stopband rejection is enhanced through an incorporation of CPW bandstop structures. The proposed filter design is verified through experimental demonstration. The corresponding lumped equivalent and transmission-line equivalent circuits are provided for circuit design purpose. Compared with the classical CPW-BPFs, the proposed filter is of a relatively simple and compact configuration. The demonstrated CPW-BPF has about 110% 3-dB fractional bandwidth, sharp selectivity, and great stopband rejection.
In this paper, Enhanced Practical Swarm Optimization (EPSO) algorithm is proposed to be applied to pattern synthesis of linear arrays. Updating formulas of global best particle position and velocity are modified to improve the convergence accuracy of classical Practical Swarm Optimization. The developed EPSO is tested and compared with a standard benchmark to be validated as an efficient optimization tool for beamforming applications. Different numerical examples are presented to illustrate the capability of EPSO for pattern synthesis with a prescribed wide nulls locations and depths. Collective multiple deep nulls approach and direct weights perturbations approach are considered to obtain adaptive wide null steering subject to peak side lobe level and minimum main beam width constraints. Starting from initial chebyshev pattern, single or multiple wide nulls are achieved by optimum perturbations of elements current amplitude or complex weights to have either symmetric or asymmetric nulls about the main beam. Proper formation of the cost function is presented for all case studies as a key factor to include the pattern constraints in the optimization process.