This paper presents the analysis and design of a two-probe excited circular ring antenna. The analysis is conducted by using induced emf method and transmission line model. The design process is to choose a suitable radius of the ring for a single probe antenna. Then, the suitable probe length and ring length are determined for the two-probe antenna. Finally, isolation between the two probes is enhanced by insertion of an inductor coil between the probes. The operational characteristics of the prototype antenna at the frequency of 5.2 GHz are measured and compared with calculation results. It is evident that these results are in good agreement. The antenna achieved isolation in excess of 20 dB and VSWR less than 2:1 over the desired bandwidth and a bidirectional radiation pattern with 4 dBi gain. This antenna is suitable for Multiple-Input Multiple-Output (MIMO) system covering a long and narrow environment.
We studied the practical limitations of a linearly transformed invisibility cloak due to the loss and discretization. We found that in order for the cloaking applications to be practically useful, for example, to reduce the scattering by two orders, the maximum loss tangent allowed in the cloak needs to be of or within the order of 0.01, which also limits the radius of a concealed object to be roughly within one wavelength. For a large cloak, if its size is increased by one order, the maximum allowed loss tangent needs to be reduced by one order accordingly. For discretization, we studied both lossless and lossy cases and found that a little loss will expedite the convergence of scattering with increase of the number of layers. Insufficient layers may increase the scattering and thus make the object more visible instead of invisible.
In this paper, a novel technique for electronic beam steering in time modulated linear array (TMLA) is proposed. The beam steering technique is realized at the first sideband by controlling the switch-on time sequences of each element in the TMLA without using phase shifters. The differential evolution (DE) algorithm is employed to improve the gain and suppress the sidelobe levels (SLLs) at both the center frequency and the first sideband, simultaneously. An S-band 8-element double-layered printed dipole linear array was used to verify the technique experimentally. Measured results are compared with numerical data, and good agreement is reported. Moreover, some simulation results on the binary phase shift keying (BPSK) modulated signals arriving from different directions received by the proposed approach are presented, which validates the application of the proposed beam steering technique.
Tracking a target is a fundamental and crucial problem in wireless sensor networks. It is well known that non-line-of-sight (NLOS) propagation will significantly degrade the tracking accuracy if its effects are ignored. In this paper, a line-of-sight (LOS) identification approach for range-based tracking systems is developed to discard the NLOS measurements. Based on Lp-norm LOS identification strategy, a novel target tracking method is devised with the use of cost-reference particle filter, which does not require the knowledge of the measurement noise distribution. Computer simulations are included to verify the effectiveness of the proposed approach under different noise distributions.
The capacitance of the circular parallel plate capacitor is calculated by expanding the solution to the Love integral equation into a Fourier cosine series. Previously, this kind of expansion has been carried out numerically, resulting in accuracy problems at small plate separations. We show that this bottleneck can be alleviated, by calculating all expansion integrals analytically in terms of the Sine and Cosine integrals. Hence, we can, in the approximation of the kernel, use considerably larger matrices, resulting in improved numerical accuracy for the capacitance. In order to improve the accuracy at the smallest separations, we develop a heuristic extrapolation scheme that takes into account the convergence properties of the algorithm. Our results are compared with other numerical results from the literature and with the Kirchhoff result. Error estimates are presented, from which we conclude that our results is a substantial improvement compared with earlier numerical results.
This paper presents a substrate independent empirical formulation for the bridge inductance of inductively tuned RF MEMS shunt switches, allowing a systematic design approach to tune their isolation bands. Inductive tuning of RF MEMS switches is achieved by inserting recesses in the ground plane and meanders to the bridges, allowing the tuning of the isolation band of the switch from the X-band to the mm-wave band. The bridge inductance is first extracted from parametric EM simulations of the RF MEMS shunt switches and then fitted to the proposed formulations using empirical coefficients. The accuracy of the formulations is verified with the measurements on the switches that are fabricated using an in-house surface micromachining RF MEMS process on a 500-µm thick glass substrate. Measurement results verify that the bridge inductances can be determined by the provided empirical formulation.
In this paper, we propose an iterative numerical approach based on the stochastic second degree (SSD) algorithm in combination with a new splitting of the impedance matrix to analyze electromagnetic scattering from 1-D dielectric rough surfaces. The embedded matrix-vector product is computed using the banded matrix iterative approach/canonical grid (BMIA/CAG) and the spectral acceleration (SA) technique. For Gaussian surface with Gaussian spectrum, through extensive numerical simulation, it is observed that for HH polarization, the proposed method is slightly less computationally efficient in terms of run time and number of iterations than its counterpart without the SSD algorithm. However, the proposed method obviously improves the convergence properties over its counterpart by changing cases from divergent to convergent when the rms height and rms slope are large. For VV polarization, the relative performance in terms of number of iterations of the proposed method shows appreciable improvement and becomes better starting from the rms slope of 0.55 uniformly across all rms heights. As far as the convergence properties are considered, the proposed method obviously improves over its counterpart for certain large rms slopes. In short, the proposed method demonstrates its superiority when dealing with truly rough surfaces.
The high frequency scattering of a scalar plane wave from an impenetrable sphere with a diameter of several thousand wavelengths is treated by the Sommerfeld-Watson transformation, the saddle-point technique (SPT), and the numerical steepest descent method (NSDM). Both the near and far fields for the sphere are computed within the observation angle range of 0 to 180 degree. First, with the aid of the Watson transformation, the fast-convergent residue series replacing the slow-convergent Mie series is derived. Second, a new algorithm for finding the zeros of the Hankel functions is developed. Third, a novel NSDM, which is adaptive to frequency and is hence frequency independent, is proposed to overcome the breakdown of the traditional SPT in the transition region. Numerical results show that when the observation angle is very small, the Mie series solution of the near-field will not be accurate due to error accumulation. Furthermore, using the proposed methods, the CPU times for both the near-field and far-field calculations are frequency independent with controllable error. This work can be used to benchmark future works for high-frequency scattering.
An easy and fast Probability-based Electrical Resistivity Tomography Inversion (PERTI) algorithm is proposed. The simplest theory follows from the principles of the probability tomography imaging, previously developed for the ERT method of geophysical prospecting. The new inversion procedure is based on a formula which provides the resistivity at any point of the surveyed volume as a weighted average of the apparent resistivity data. The weights are obtained as the Frechet derivatives of the apparent resistivity function of a homogeneous half-space, where a resistivity perturbation is produced in an arbitrary small cell of the discretised surveyed volume. Some 2D and 3D synthetic examples are presented, for which the results of the PERTI method are compared with the inverted models derived from the application of the commercial inversion softwares ERTLAB by Multi-Phase Technologies and Geostudi Astier, and RES2DINV and RES3DINV by Geotomo Software. The comparison shows that the new approach is generally as efficacious as the previous methods in detecting, distinguishing and shaping the sources of the apparent resistivity anomalies. Less certain appears, however, its ability to approach the true resistivity of the source bodies. Main peculiarities of the new method are: (i) unnecessity of a priori information and hence full and unconstrained data-adaptability; (ii) decrease of computing time, even two orders of magnitude shorter than that required by commercial softwares in complex 3D cases using the same PC; (iii) real-time inversion directly in the field in complex 3D cases using the same PC; (iii) real-timein complex 3D cases using the same PC; (iii) real-timein complex 3D cases using the same PC; (iii) real-time; (iv) total independence from data acquisition techniques and spatial regularity, (v) possibility to be used as an optimum starting model in standard iterative inversion processes in order to speed up convergence.
In this paper, a multilevel Green's function interpolation method (MLGFIM) is developed to analyze electromagnetic scattering from an arbitrarily shaped three-dimensional objects comprised of both conductor and bi-isotropic media. The field decomposition method is adopted to split the homogeneous bi-isotropic media into two uncoupled isotropic media instead of direct calculation of complicated Green's function in bi-isotropic material. The problem is formulated using the Paggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) approach for multiple homogeneous isotropic media and electric field approach for conducting bodies. The resultant integral equations are discretized by the method of moment (MoM) and iteratively solved by MLGFIM. Numerical examples illustrate accuracy of this algorithm and CPU time of O(Nlog N) and memory requirement of O(N).
A novel, low profile and broadband plate loaded planar monopole antenna is investigated. The proposed antenna consists of a rectangular planar monopole with small plates attached to its radiating edges. Two types of plates, rectangular and cylindrical shapes are fabricated and tested. The characteristics of the antennas are investigated in both frequency and time domains. The study shows that the proposed antennas are capable of achieving broadband and omnidirectional radiation characteristics within 2.9-17.9 GHz with the cylindrical loading plates and 2.9-16.7 GHz for the rectangular loading plates with a gain of up to 7 dBi.
In this paper, the most adequate architecture to implement dual frequency amplifiers is shown. Composite Right/Left Hand (CRLH) and Extended Composite Right/Left Hand (ECRLH) transmission lines are studied and evaluated to find the most suitable structure for dual band power amplifiers. As an example, the performance of a class CE amplifier, working in TETRA and GSM frequency bands, is compared with simulations and measurement, showing good agreement.
This paper presents a semi-physical simulation system for 61-channel DBF array transmitter antenna on LEO satellite. It consists of a hardware platform for digital beamfoming network (BFN) and a software simulation system for DBF array. The background and wideband input interface are described, and the signal process of digital beamforming network is discussed in detail. General DFT filter bank, distributed arithmetic (DA) algorithm and Hartley image rejection structure are adopted to design the digital BFN, which make the calculation of BFN reduced by 98.41% and get the multiplier consumption decreased to 7.11%, compared with conventional algorithms. A novel digital BFN hardware platform with distributed structure is designed, which can complete the high speed array signal processing with maximum throughput of 32.025 Gbps. Ultimately, the measurements of semi-physical simulation system show good agreement with the ideal simulation result. The derivation of radiation pattern from energy distribution of earth's surface demonstrates that the DBF array has good performance on beam coverage with equal flux density and satisfies the application in mobile satellite communication.
An 61-channel digital beamforming transmitter array antenna used in mobile satellite communication is presented in this paper. It can steer 16 beams simultaneously. The interface, architecture and subunits are described in detail. Standard hexagonal array (SHA) and 61-channel RF front ends are designed. Genetic Algorithm is adopted to realize the pattern synthesis with muti-objective optimization. The signal flow and hardware platform of the digital beamforming network are discussed, which can complete the high speed array signal processing with maximum throughput of 34.16 Gbps. A novel calibration scheme with high feasibility of project implementation is also proposed. The measurements of array antenna match well with simulation result, which validates the rationality and feasibility of the algorithms and project design.
This is a numerical investigation of a recently proposed formulation, called coupled transverse-mode integral equation (CTMIE), for analyzing EM field properties in general 2-D dielectric waveguide devices. The device is first approximated by stack of piece-wise 1-D horizontally layered structures. Transverse field components on the interface between waveguide slices are unknown functions, which are governed by a coupled integral equation. When unknowns are expanded as a linear combination of given functions, CTMIE is converted to a coupled block matrix equation. We study three waveguide devices, in detail, to understand the relation between modeling parameters and accuracy and convergent rate of the solutions. Examples include a step waveguide junction, a multi-mode interferometer power cross coupler and a linearly tapered waveguide. All results are verified with independent calculations using other proven methods.
The effects of the fibroglandular tissue distribution of the breast on data-independent microwave imaging algorithms are investigated in this paper. A data-independent beamformer is a beamformer whose weights do not depend on the array data and are chosen, based on a channel model, to compensate for path-dependent attenuation and phase effects. The effectiveness and robustness of data-independent UWB beamforming algorithms relies upon two specific characteristics of breast tissue at microwave frequencies: firstly, that there exists a significant dielectric contrast between cancerous tissue and normal healthy breast tissue; secondly, that the propagation, attenuation and phase characteristics of normal tissue allow for constructive addition of the UWB returns using the Confocal Microwave Imaging (CMI) technique. However, two recent studies by Lazebnik et al. have highlighted a significant dielectric contrast between normal adipose and fibroglandular tissue within the breast. These results suggest a much more difficult imaging scenario where clutter due to fibroglandular tissue is a significant concern and that constructive addition of backscattered signals is potentially much more problematic than previously assumed. In this paper, three existing data-independent beamformers are tested on several different breast models, examining the effect of different fibroglandular tissue distribution on the performance of the data-independent imaging algorithms.
A 3D full-wave approach, based on the Foldy-Lax multiple scattering equations, is successfully extended to model massively-coupled multiple vias using differential signaling and shared antipad in high speed vertical interconnects. For the first time, this method has been used and tested on via-pair with shared antipad in multilayered structure. The magnetic frill current source on the port is calculated by using the finite difference method. Banded matrix iterative method is applied to accelerate the finite difference calculation. Numerical example of 15 signal via-pairs and 20 ground shielding vias in 6-layer board demonstrates that this approach is able to model the via-pair with shared antipad and to include all the coupling effects among multiple vias. The electrical performances of different signal driving schemes are provided and discussed. The coupling crosstalk on various via-pairs is compared. The improvement of signal integrity is shown by using differential signaling and shared antipad for via-pair in multilayered structure. The results are compared with HFSS and SIwave in accuracy and CPU. The CPU using Foldy-Lax approach is three orders of magnitude faster than using HFSS, and two orders of magnitude faster than using SIwave. The accuracy of Foldy-Lax is within 2% difference from HFSS up to 20 GHz, and outperforms SIwave in accuracy.
This paper presents a new hybrid finite-difference frequency domain --- mode-matching method (FDFD-MM) for the analysis of electromagnetic wave scattering from configuration of metallic or dielectric cylindrical posts with arbitrary cross-section. In our approach each scatterer is treated as an effective circular cylinder represented by impedance matrix defined in its local coordinate system. In order to obtain the scattering parameters of arbitrary configuration of objects in global coordinate system an analytical iterative scattering procedure (ISP) is applied. This work is an extension of our previously published results, where our consideration were limited to two dimensional (2D) problems with TM excitation. In this paper we extended our analysis to two-and-a-half dimensional (2.5D) problems. The accuracy of the proposed method is presented and discussed. To verify our approach some numerical examples are presented. The obtained results are compared with the results published in literature and the ones obtained from own measurements and commercial software.
In this work, a probe fed microstrip antenna design for the implementation of two dimensional arrays with individually fed radiating elements is presented. The performance of the antenna element, both isolated and in a 4×4 fixed array topology, is analysed using ADS and HFSS simulation software. Prototypes of the antenna element and of the array are manufactured and measured for the experimental validation of the design.
Microwave tomography deserves attention in biomedical imaging, owing to its potential capability of providing a morphological and functional assessment of the inspected tissues. However, such a goal requires the not trivial task of solving a non linear inverse scattering problem. In this paper, the factors affecting the complexity of the inverse problem are exploited to trace guidelines aimed at setting the matching fluid, the frequency range and the number of probes in such a way that the dielectric parameters of female breast tissues can be reliably retrieved. Examples, concerning 2D realistic numerical phantoms obtained by NMR images, are given to asses a osteriori the effectiveness of the proposed guidelines.
A sensing device comprising of a parabolic reflective surface and a bi-conical metal structure is proposed to focus terahertz energy on sample material in the sensing zone to create a strong interaction between terahertz signals and the sample under test. The signal enhancement by the sensing device is confirmed by modeling and simulation results. The proposed sensor is applied to investigate the polarization dependency of a split ring resonator (SRR), and spectral signatures of the SRR under different incident wave polarizations are obtained.
This paper presents a microwave imaging method for malignant tumors using flanged parallel-plate waveguide probes, based on detecting the significant difference in complex permittivity that exists between the tumor and its surrounding tissues. The presence of a tumor is identified from a frequency scan of the resonant scattering parameters. The tumor location can be estimated using S21 obtained at various positions of the region of concern, e.g. human organ, biological tissues, etc., while another probe transmits at the position yielding maximum resonating response of S11, with triangulation technique. A tumor can also be distinguished from clutter items. With specific reference to the detection of breast cancer, simulation studies are presented to verify the performance of this probe and the proposed detection technique.
An open-ended waveguide probe has been adapted for complex permittivity determination and hence mechanical property inspection of cement-based materials. The probe uses amplitude-only reflection measurements at different frequencies for this goal, which is suitable for industrial based applications when cost and ease of use are important considerations. We have derived expressions by taking into account of the wavematerial interaction. The reference plane for measurements is set inside the waveguide to measure solely the reflected signal of the dominant mode. It is shown that the measurement results are in good agreement with the theory.
A simple, closed-form expression for the time-domain reflection coefficient for a pulsed TE10-mode wave incident on a dielectric material discontinuity in a rectangular waveguide is presented. This formula may be used to represent the transient field reflected or transmitted by a dielectric-filled waveguide section, which is useful in material characterization routines. An exponential function approximation to the reflection coefficient is presented, and the formula is validated both numerically and experimentally.
A one dimensional tunable periodic structure in microstip technology on gallium arsenide (GaAs) substrate is numerically investigated. The unit cell contains a number of patches positioned between the ground plane and the microstrip line. The patches, representing reactive loads, can be selectively short-circuited by externally-ontrolled FET switches integrated in the hosting substrate. The possibility of controlling the position of the band-gap, and implicitly the value of the effective dielectric constant along the line, for different combinations of the switches is demonstrated.