The design of a thin tunable and steerable Fabry-Perot antenna is presented. The subwavelength structure is analyzed both by an efficient transmission line model and by full-wave simulations. The tunable antenna consists of a low profile resonant cavity made up of a Partially Reflecting Surface (PRS) placed in close proximity of a tunable high-impedance surface. The active ground plane is synthesized by loading the high-impedance surface with varactor diodes. Such design allows both tuning the high-gain operational frequency and obtaining a beam steering/shaping for each resonant frequency. The transmission line model here presented includes averaged analytical expressions for modelling the tunable high-impedance surface and the frequency selective surfaces. All the theoretical speculations are verified by full-wave simulations on a finite size structure.
This paper presents a system with experimental complement to a simulation work for early breast tumor detection. The experiments are conducted using commercial Ultrawide-Band (UWB) transceivers, Neural Network (NN) based Pattern Recognition (PR) software for imaging and proposed breast phantoms for homogenous and heterogeneous tissues. The proposed breast phantoms (homogeneous and heterogeneous) and tumor are constructed using available low cost materials and their mixtures with minimal effort. A specific glass is used as skin. All the materials and their mixtures are considered according to the ratio of the dielectric properties of the breast tissues. Experiments to detect tumor are performed in regular noisy room environment. The UWB signals are transmitted from one side of the breast phantom (for both cases) and received from opposite side diagonally repeatedly. Using discrete cosine transform (DCT) of these received signals, a Neural Network (NN) module is developed, trained and tested. The tumor existence, size and location detection rates for both cases are highly satisfactory, which are approximately: (i) 100%, 95.8% and 94.3% for homogeneous and (ii) 100%, 93.4% and 93.1% for heterogeneous cases respectively. This gives assurance of early detection and the practical usefulness of the developed system in near future.
Microwave properties for a bilayer structure made of the high-temperature superconducting and the ferromagnetic materials are theoretically investigated. The properties are explored through the effective surface impedance calculated by using the enhanced two-fluid model for high-temperature superconductors together with the transmission line theory. The calculated effective surface impedance will be numerically analyzed as a function of the frequency, the temperature, and the thicknesses of the constituent layers. It is found that, for a thinner superconducting film, the effective surface resistance is a strong function of the frequency, and the effective surface reactance exhibits a peak and a dip in the frequency-domain. In the study of the effect of thickness in ferromagnetic substrate, there is a peak frequency in the surface reactance for a thinner substrate. There is also a threshold thickness for the ferromagnetic substrate such that it behaves like a bulk substrate when its thickness is larger than this threshold value. In the temperature dependence of surface reactance, the peak near critical temperature is shifted to lower temperature and broadened as the film thickness decreases.
A new type of evanescent-mode substrate integrated waveguide (SIW) bandpass filter is presented in this paper, with complementary split ring resonators (CSRRs) introduced on the top or bottom metal planes of the waveguide. Both positive and negative couplings are obtained between the CSRRs by changing their locations and orientations. In comparison with conventional SIW filters, the proposed filters are compact since their passbands are below the cutoff frequency of SIW. A third- and a fourth-order cross-coupled filter prototypes were designed using standard PCB technology. They operate at the same central frequency of 3.8 GHz, with their fractional bandwidths of 15% and 20%. The proposed filters have a wide upper stopband as the cutoff frequency of TE10-mode in the SIW is much higher than the central frequency. Their good performance is demonstrated by both the simulated and measured S-parameters.
The size of an antenna should be relatively large in order to get high radiation directivity. However, in some applications, the antenna is restricted in small region, while high directivity is still required. In this paper, we propose the method of realizing antennae with large effective apertures using arbitrary shaped small PEC reflectors and small volumes of left-handed materials based on coordinate transformation. Using this method, antennae with effective large parabolic apertures are designed using both a small parabolic reflector and a planar reflector. This design method is validated by the numerical simulations based on the Finite Element Method (FEM).
In this study, an inverse microwave scattering model for sea ice has been developed for the purpose of sea ice thickness retrieval using radar backscatter data. The model is loosely based on the Radiative-Transfer-Thermodynamic Inverse Model for Sea Ice Thickness Retrieval from Time-Series Scattering Data. The developed inverse model is a combination of the Radiative Transfer Theory with Dense Medium Phase and Amplitude Correction Theory (RT-DMPACT) forward model and the Levenberg-Marquardt Optimization algorithm. Using input data from ground truth measurements carried out in Ross Island, Antarctica, together with radar backscatter data extracted from purchased satellite images, the sea ice thickness of an area is estimated using the inverse model developed. The estimated sea ice thickness is then compared with the ground truth measurement data to verify its accuracy. The results have shown good promise, with successful estimation of the sea ice thickness within ±0.15 m of the actual measurement. A theoretical analysis has also revealed that the model faces difficulty once the sea ice thickness exceeds 1.7m. This can be considered in the future development and improvement of the model.
A novel self-calibration scheme for rotating array antennas is proposed. It is based on the acquisition of some near field samples using a static probe providing information about the actual behavior of the antenna. If any error, fault or obstacle modifies the desired behavior, the weights applied to the feedings of the array elements are modified so that specifications are fulfilled again. Additionally, coupling between the elements of the arrays is also accounted for. Different disciplines such as near field to far field transformation, antenna modeling, adaptive filtering or automatic learning are involved in this system. Some significant results are also presented.
An accurate and efficient finite-difference time-domain (FDTD) method for characterizing transient waves interactions on axially symmetric structures is presented. The method achieves its accuracy and efficiency by employing localized and/or fast Fourier transform (FFT) accelerated exact absorbing conditions (EACs). The paper details the derivation of the EACs, discusses their implementation and discretization in an FDTD method, and proposes utilization of a blocked-FFT based algorithm for accelerating the computation of temporal convolutions present in nonlocal EACs. The proposed method allows transient analyses to be carried for long time intervals without any loss of accuracy and provides reliable numerical data pertinent to physical processes under resonant conditions. This renders the method highly useful in characterization of high-Q microwave radiators and energy compressors. Numerical results that demonstrate the accuracy and efficiency of the method are presented.
This paper presents various applications where wide-band signals are the dominant factor. The approaches applied here are based on the present knowledge in the field of white light theory (the THz band), the particle theory of light, and the wave theory of light. White light theory is used to investigate wide-band applications of non-coherent electromagnetic waves in the GHz range represented by noise. In addition, the theoretical approaches to the field of white light are confirmed by various experiments with noise fields applied in the GHz range. These experiments show clear advantages of measurements performed by means of noise fields. The most important feature of these fields is the absence of interference effects.
In this paper, we report experimental results on detecting and analyzing the Brillouin precursor through vegetation at frequencies from 100MHz to 3GHz. An experimental method to collect data is reported. The outcomes in terms of energy and time-spreading are presented using modulated rectangular and Gaussian pulses, as well as a sequence of rectangular pulses. Using field-collected data, this study shows the estimated dynamical evolution of the Brillouin precursor fields for wideband wireless systems, such as those represented by IEEE 802.16. The advantages of Brillouin precursors in terms of power spectrum density and bit energy are discussed. Complex relative permittivity is extracted from the experimental data and is used in theoretical formulation to analyze dispersive propagation for any kind of input waveform. Finally, a near-optimal pulse is proposed to achieve maximum propagation distance and/or signal-to-noise ratio for the transmission of bit stream sequences through vegetation.
Novel formulas are presented that allow the rapid estimation of the number of terms L that needs to be taken into account in the translation operator of the vectorial Nondirective Stable Plane Wave Multilevel Fast Multipole Algorithm (NSPWMLFMA). This is especially important for low frequencies, since the L needed for error-controllability can be substantially higher than the L required in the scalar case. Although these formulas were originally derived for use in the NSPWMLFMA, they are equally useful in at least three other fast matrix multiplication methods.
A circular waveguide loaded with dielectric and metal discs was chosen to evaluate its dispersion characteristics and dispersion shaping with change of structure parameters for wideband coalescence of beam- and waveguide-mode dispersion characteristics for wideband gyro-TWT performance. The azimuthally symmetric TE-mode analysis of the structure was carried out in field matching technique by considering the propagating wave in cylindrical free-space region having radius equal to the hole-radius of metal disc, and the stationary waves in free-space and dielectric regions between two consecutive metal discs. The dispersion relation and, in accordance, a computer code were developed. Further, the roots of the dispersion relation for various sets of the structure parameters were obtained using the developed computer code; the dispersion characteristics were plotted; and the dispersion shaping was projected for typically chosen TE01-, TE02- and TE03-modes. The analytical results were validated against those obtained for the conventional and earlier published structures, and also those obtained using commercially available simulation tool. Finally, a study on azimuthal electric field available over the radial coordinate was carried out to show the control of structure parameter on the gyrating electron beam position for the chosen operating mode of a dielectric and metal discs loaded gyro-TWT.
In this contribution a model based on asymptotic methods is proposed to compute the scattered field from complex objects on a sea surface. The scattering model combines the geometrical optics, the physical optics and the method of equivalent currents. It includes the shadowing effects and multiple-bounce up to order 3. This model is used, in the following, for Radar Cross Section (RCS) estimation and to generate Synthetic Aperture Radar (SAR) raw data for imaging applications. The theoretical aspects are reviewed in this paper and the proposed model is detailed. Numerical results are provided to validate the approach through the computation of RCS for canonical objects and complex scenes. Both the bistatic and the monostatic configurations are studied in this work. Finally some first results dealing with SAR imaging of objects on a sea surface are provided. These images are constructed from the simulated raw data thanks to a chirp scaling-based algorithm.
We theoretically investigated optical properties of phase shift defects in onedimensional rugate photonic structures at oblique incidence. Transmission spectra and energy density distributions of such continuous gradient-index structures with phase shift defects were numerically calculated for TE and TM waves using the propagation matrix method. The study shows that when the angle of incidence increases, (1) the wavelength of the defect mode shifts to a shorter wavelength, (2) the full width at half maximum (FWHM) of the defect mode decreases for TE wave but it increases for TM wave, (3) the stop band of the rugate structure moves toward a shorter wavelength region, (4) the bandwidth is enlarged for TE wave, but it is shortened for TM wave, (5) the peak energy density increases and then drops for TE wave, while it always decreases for TM wave. The effect of number of periods of rugate structures on the energy density distribution was also examined.
In this paper we present the design, fabrication and measurements for a Wband metal Photonic Band Gap (PBG) Channel-Drop Filter (CDF) diplexer, which can also be employed as a combiner to combine signals of different frequencies into a single waveguide. A PBG CDF is a device that allows channeling of a selected frequency from a continuous spectrum into a separate waveguide through resonant defects in a PBG structure. A PBG CDF transmits straight through all the frequencies except for the resonant frequency, and thus it represents a diplexer. Reversing the wave flow directions causes it to combine signals of different frequencies from two different waveguides into a single channel, representing a combiner. The device is compact and configurable and can be employed for mm-wave spectrometry with applications in communications, radio astronomy, and radar receivers for remote sensing and nonproliferation. High ohmic losses in metals constitute the main challenge in realization of a metal CDF at W-band. To mitigate the problem of ohmic losses, the filter was designed to operate at coupled dipole resonant modes instead of coupled fundamental monopole modes. The experimental samples were fabricated in two different ways: by conventional machining and by electroforming. The comparative results of the samples' testing are presented in the paper. Frequency selectivity of 30 dB with a 0.3 GHz linewidth at 108.5 GHz was demonstrated. In addition, we suggest an experimental method to check the frequencies of separate resonant cavities of fabricated samples which do not properly operate and a possible way to adjust the geometry of the cavities for the frequencies to meet the required specifications.
In this paper, a wideband microstrip antenna for X-band (8.2 GHz--12.4 GHz) applications is introduced. First, simple patch antennas are studied. The resultant design demonstrates better performance than the previously published narrowband microstrip reflectarray antennas. The important features of these elements are simple structure, linear operation, and use of RF MEMS switches for programmable pattern control. Next employing our novel method, this narrowband structure is converted to broadband reflectarray antenna that can cover the whole X band. This novel idea is based on introducing several ground plane slots and controlling their electrical lengths by RF MEMS switches. By means of this method, 952 and 587 degree phase swing is achieved for continuous and discrete slot length variation, respectively. Application of this method along with smaller switches results in phase swing improvement of up to 1616 degree. In all structures a RT duroid (5880) substrate is selected to lower the back radiation. The achieved return loss in all cases is less than 0.32 dB. In comparison with the previous publications, our novel method has more generalization capability and results in single layered broadband reconfigurable microstrip reflectarray antennas with linear phase swing, lower cost, and ease of RF MEMS implementation.
This paper presents dual-band equal/unequal Wilkinson power dividers based on a coupled-line section with short-circuited stub (called as the ``coupled-line section" for short), which consists of a pair of parallel coupled lines and a short-circuited stub. With the analyses of the phase shift and equivalent characteristic impedance, the coupled-line section is used to replace the quarter-wavelength branch line in the conventional equal/unequal Wilkinson power divider to obtain excellent dual-band operation. The closed-form equations and design procedures of dual-band Wilkinson power divider are given, where one degree of design freedom is obtained and design flexibility is shown. As two examples, a dual-band equal Wilkinson power divider with the frequency ratio of 1.8:1 and an unequal one with the high power dividing ratio of 7:1 and frequency ratio of 1.8:1 are designed, fabricated and measured. The measurements are in good agreement with the simulations. It is shown that the proposed power dividers have simple topologies, and can be easily fabricated with small frequency ratios and high power dividing ratios.
Agricultural wastes are considered not useful and are commonly dumped or burned after crop harvesting. Rice husks from paddy (Oryza sativa) are example of agricultural wastes. Rice husks have been investigated as the material for the pyramidal microwave absorbers. The setup for the fabrication and measurement of the rice husks pyramidal microwave absorbers are discussed. An 8×8 array of pyramidal microwave absorber using the rice husks-polyester-MEKP mixture has been designed and fabricated. There are four main stages in this work: the collection of the raw rice husks materials, the mould fabrication, the pyramidal microwave absorber fabrication and the experiments performed to determine the reflection loss performance of the rice husks pyramidal microwave absorbers. Experimental results show close agreement with the simulation results (using CST Microwave Studio). Results so far have indicated that rice husks have great potential to be used as the material for the pyramidal microwave absorbers.
The forward problem of calculating the electromagnetic (EM) field of a circular current loop in presence of a layered earth structure, given the geometrical and EM parameters of the layers, is solved fast. Efficient computation is obtained through a quasi-analytical procedure that allows to transform the field integrals into expressions involving only a known Sommerfeld Integral. The final explicit forms of the fields are in terms of modified Bessel functions. To validate the method, the magnitudes of the EM field components versus induction number and versus frequency are calculated assuming two- and three-layer earth models. The achieved results are in good agreement with the ones provided by the commonly used digital filter algorithms. The computational time taken by the application of this technique is shown to be much less than that required by both digital filters and other recently developed integration techniques for similar problems. This paper is an extension of an earlier conference paper.
In this work we report the modeling of an one-dimensional photonic heterostructure which presents a giant omnidirectional photonic band gap. This omnidirectional reflector is made by the union of lattices with the same filling fraction and index contrast, but with different lattice periods. Using the scalability of the electromagnetic wave equation we present a simple manner to enlarge ---as large as desired--- the omnidirectional mirror. We apply our method to design an omnidirectional reflector for all the visible range.
This paper presents an experimental study of a flanged parallel-plate dielectric waveguide (PPDW) probe for detecting dielectric inclusions in a dielectric host medium, with different electrical properties from the inclusions. The S-parameter signals from an inclusion (modelled as a conducting sphere) are shown to have resonant characteristics, from which the size and location of the inclusion can be deduced. As an example of a possible application for this technique, we use parameters of host medium and inclusions relevant for detection of tumors in body tissues. An experimental study was performed on solid tissue-simulating phantoms with embedded conducting dielectric inclusions. The measurements show promising results.
In the first part of this work, we develop a model to compute linkage fields in Outer Rotor Permanents Magnets synchronous machines (OR-PMSM), a structure which is often used in the automotive traction motors. To carry out such a design, we usually employ Finite Element analysis (FEA) software even if it is time consuming. Other designers prefer the Permeances Network Method (PNM) which is less accurate and needs offline FEM results to evaluate the unknown air-gap permeances. Comparatively, between FEM and BEM, the first method is more precise whereas the second is faster in computing times. We propose here a new technique using the hybridization of both the methods in order to gain the advantages of the two techniques, i.e., a relatively accurate and fast methods, so the high ratio fast of running/computing errors has been checked out. The second part deals with the multi-objective design optimization of the studied motor. To do this, we choose the decrease of cogging torque and the increase of torque as objectives applied to multi-objective optimization (MO) process.
With the increasing threat of terrorism in recent years, the detection of concealed weapons, plastic bombs and other contraband at secure locations attracts more and more countries' attention all over the world. Three-dimensional (3D) microwave imaging surveillance systems, allowing for acquisition of full 3D microwave images of volumetric scatters of human body, have been developed for security applications. In this paper, we firstly propose a 3D imaging algorithm which not only accounts for the free space propagation losses and wavefront curvature but also avoids 3D interpolation in the 3D wavenumber domain without suffering from any approximations and truncation errors. Then, the sampling constraints and the resolution issues associated with proper and alias-free implementation of the 3D reconstruction are analyzed. Finally, the focusing capabilities of our proposed imaging algorithm are investigated and verified by means of numerical simulations as well as theoretical analysis, and an approach for better displaying projected images is examined.
In this paper, novel uniplanar tunable and switchable bandpass filters are designed by using the centrally-loaded slot-line resonator. From the voltage-wave distribution along the resonator, the appropriate location for the loading element is determined to be the center of the slot-line resonator, where the voltages of the fundamental signal and second harmonic are maximum and zero, respectively. As a result, the fundamental frequency can be tuned while the second harmonic remains almost unchanged. For the first time, the properties of the centrally-loaded slot-line resonator are analyzed by using the even- and odd-mode method, and their respective resonant frequencies are derived. The demonstrated tunable bandpass filter can give a 30.9% frequency tuning range with acceptable insertion loss when a varactor is used as the loading element. By replacing the loading varactors with PIN diodes, a switchable bandpass filter is realized in which the attenuation in the fundamental passband can be controlled. In experiments, the switchable bandpass filter exhibits a 2.13 dB insertion loss in the fundamental passband when the PIN diodes are off and more than 49 dB isolation across the passband when the PIN diodes are on.
Using a building block approach which combines a transverse resonance method with a mode-matching technique, a rigorous analysis of a lossless bi-isotropic H-guide is presented. First, the modal equation of a parallel-plate waveguide containing the inner medium of the H-guide is obtained. Then, a mode matching technique is used to develop a full-wave analysis of the H-guide. The influence of nonreciprocity on the guidance properties of the structure is discussed.