Applying an iterative scheme, the differential phase shift provided by the circular waveguide with a coaxial dielectric cylinder and an azimuthally magnetized ferrite toroid, is figured in normalized form for normal TE01 mode. The method is based on a repeated numerical solution of the structure's characteristic equation, derived by the complex Tricomi and the real Bessel function, followed by a calculation of the normalized in a suitable way guide radius and phase constant of the wave. The phase shift is found as a difference between the computed numerical equivalents of constants in question for negative and positive magnetization at selected values of the dielectric cylinder to guide radius ratio and the off-diagonal ferrite tensor element. The relative permittivity of the dielectric is assumed larger than that of the ferrite. The results are presented graphically and debated.
This study presents an implementation of direction-of-arrival estimation using signals received from a Rotman lens array antenna. The algorithm is based on the magnitude comparison method. The Rotman lens array provides multiple beams toward different directions simultaneously. The beam port outputs, which are converted to the video band using envelope detectors, form an output vector. It is used to find the most likely arriving angle based on a higher order interpolation process. In this work, a planar Rotman lens consists of 6 antenna ports and 13 beam ports was fabricated with an FR4 printed circuit board. The lens was connected to 6 broadband Vivaldi horns to form the receiving array. Array patterns are verified in a spherical near field chamber, while the direction finding algorithm was implemented offline using data taken from an open site. Improved direction finding accuracy demonstrates the effectiveness of the proposed Rotman lens array antenna and the developed algorithm.
In medical image diagnosis using optical waves of laser, image responses of optical transmitted projection include optical scattering characteristics that disturb transmission properties through biological structures depending on optical absorption effects. We have studied spatial filtering by lossy grid array for optical scattering superposed on transmitted and attenuated waves to improve image diagnosis. In this paper, reflection and transmission characteristics of waveguide-type spatial filter are studied by FDTD method, comparing with approximate analytical method for optimum design of spatial filter.
The use of ultra wideband radar for security systems is of interest because of the high range resolution. Much research has focused on developing effective methods for detecting, locating, tracking and imaging a human body with multiple radar systems. One important challenge in this field is how to handle data for multiple targets, because many conventional algorithms assume only a single target. In this paper, we propose a technique for separating two people walking using the texture of the time- range image. This method calculates the image flow angle that depends on the motion and velocity of the target. We demonstrate that the proposed method can separate two people walking in opposite directions in the measurement.
Fundamental limitations restrict the bandwidth of electrically small antennas. A method to obtain such limitations is based on stored electric and magnetic energies. Vandenbosch recently proposed a set of integral expression for the stored energies. These expressions provide a method to determine optimal currents and physical bounds on antennas for maximal bandwidth and desired radiated fields. In the present paper, we generalize the expressions for the stored energies to include magnetic sources for small structures. We give an expression for the antenna Q for electrically small shapes. Examples for small spheres are tested and the results agree with the published results.
We present analytical closed-form expressions for the radiation patterns of 2D line sources and 3D point dipoles embedded in a general multi-layered configuration. While the former are simplified model sources, used as a preliminary analytical step to reduce derivation complexity, the latter have been shown experimentally to reproduce the electromagnetic behaviour of elementary (molecular) optical sources. By decomposing the sources to current elements generating pure transverse electric (TE) or transverse magnetic (TM) polarized radiation, we arrive at a unified format for the radiation pattern expression for all sources. Analyzing the common 1D Green's function, we show that the normalized TE-polarized emission of the model 2D electric line sources reproduces exactly the TE-polarized radiation of molecular (3D) dipoles, and discuss the relations between the TM-polarized emission of the two species. These results specify the precise relations between the 2D and 3D models, thus providing intuition as well as guidelines for proper usage of simplified 2D results for analysis of realistic 3D optical systems.
This paper explores how wideband and multi-band performance can be achieved in Fabry-Perot resonant cavity antennas using two design methodologies, one based on a Reflection Model of a unit cell and the other based on a Transmission Model of a unit cell. In particular, two wideband antenna designs and two dual-band designs are considered. They include low-profile planar metallo-dielectric antennas based on one printed dielectric slab and very simple antennas based on two unprinted all-dielectric slabs. Desired wideband or multi-band performance is achieved either by engineering the reflection phase and magnitude of the superstrate using the Reflection Model or by extending the defect-mode bandwidth using the Transmission Model. Key theoretical and experimental results are presented to highlight the advantages of selected antenna designs.
Metamaterial absorbers synthesized by extremely-thin High-Impedance Surfaces (HIS) are analyzed by resorting to a simple transmission line model. The equivalent circuit representation, which takes into account also the high-order Floquet modes effects, allows to interpret the absorption properties of the analyzed structure and to derive closed form relations containing all the degree of freedom involved in the design. By exploiting the guidelines achieved from the circuital analysis, a λ0/108 thick absorber operating within the UHF RFID frequency band has been designed and tested.
In this paper near-field coupling in UHF-RFID systems is investigated. The wireless power transfer among reader and tag antennas is addressed through a numerical model involving different reader antennas and a short-range tag. System performance is investigated in terms of both mutual impedance and power transfer efficiency. Finally, a new nearfield reader antenna based on coplanar waveguide technology will be described.
A compact and low profile microstrip antenna is proposed as a framework to design a frequency-reconfigurable radiating device with four distinct and almost independent resonant frequencies with other single or multiple available resonances that can be usefully exploited by the cognitive radio system. The instant frequency reconfiguration is obtained by using pin diodes as RF switches whereas the biasing network comprises four high-impedance microstrip lines and a bias-tee.
Electromagnetic imaging of buried targets is an important task that arises in several applicative fields, such as civil engineering and archeology. In the present paper, an algorithm based on a regularizing approach in Lp Banach spaces is applied to the integral equations of the inverse scattering problem. The effectiveness of the approach is verified by means of preliminary numerical simulations in which buried target are illuminated by a set of incident waves in a noisy environment.
In this study, we consider the high-frequency asymptotic analysis methods for the scattered field when a cylindrical wave is incident on a conducting circular cylinder. We derive the asymptotic solution applicable in each of the transition regions divided by the shadow boundary into the shadow and the lit side. The asymptotic solutions include a novel extended Pekeris caret function to which the second order term in the argument of the exponential in the integrand is added as compared with the Pekeris caret function including the UTD (uniform GTD) solution. By applying the residue theorem and the saddle point technique to the novel extended Pekeris caret function, we derive respectively the surface diffracted ray solution and the reflected geometrical ray solution which are effective exterior to the transition regions. The validity of the various asymptotic solutions derived here is confirmed by comparing with the exact solution.
Stimulation of deeper brain structures by transcranial magnetic stimulation (TMS) may be beneficial in the treatment of several neurological and psychiatric disorders. This paper presents numerical simulation of deep transcranial magnetic stimulation (dTMS) by considering double cone, Hand Halo coils. Three-dimensional distributions of the induced electric fields in realistic head model by dTMS coils were calculated by impedance method and the results were compared with that of standard figure-of-eight coil. Simulation results show that double cone and H-coils have significantly deep field penetration at the expense of induced higher and wider spread electrical fields in superficial cortical regions. The combination of Halo coil with a conventional circular coil produce deeply penetrating electric field the same as double cone and H-coils, but the stimulation in superficial brain tissues are much lower.
In this paper, the function expansion based topology optimization is employed to the optimization of the waveguide dispersion property and the optimum design of low-dispersion slow-light photonic crystal waveguides (PCWGs) is demonstrated. In order to realize low-dispersion and large group index, the objective function to be optimized is expressed by the weighted sum of the objective functions for the desired group index and the low-dispersion property, and the weighting coefficients are updated through the optimization process.
We propose modeling method for the wall through radar by using near-field GTD as a near-region target model and delayed path-length for multi-layered dielectric sheets. Radar image can be constructed by AF (array-factor), which is a kind of synthetic aperture imaging. For near-region target, we apply focusing procedure of optical ray to the AF summation and the wall through pass. Refraction coefficient of N-layered dielectric sheets is exactly derived as boundary wave problem and applied to the wall through radar imaging. Theoretical near-field AF images are compared with far-field model, traditional SAR (synthetic aperture radar) image, and measured data.
In this paper, we have analyzed the guiding problem by dielectric waveguide with defects area composed of dielectric circular cylinder array loaded with deformed rhombic dielectric structure in the middle layer, and investigated the influence of the distribution of energy flow for defect area by using the propagation constants of the guided region. Numerical results are given for the complex propagation constants and distribution of enegy flow for case of comparison of both rhombic dielectric structure and deformed rhombic dielectric structures by using the combination of improved Fourier series expansion method and multilayer method. As numerical results, it is shown that we can be obtained the confinement efficiency by rhombic dielectric structure compared with defomed rhombic dielectric structures for TE and TM modes.
Calculating interaction integrals in a Method of Moments technique is highly challenging in a conductive medium. The specific form of its wave number leads to a strongly oscillating and exponentially damped Green's function, making standard numerical evaluation schemes inapt to accurately evaluate the interaction integrals. In this paper, we present an accurate 2D Method of Moments technique for arbitrary dielectric, magnetic and conducting media and apply the method to solve shielding problems.
In this paper we present a new UWB antenna and its linear phased array. The single UWB element has omnidirectional and stable radiation patterns over a wide-bandwidth that make it suitable for UWB wireless communication. In addition an E-plane phased array design of four proposed UWB antennas has been simulated to achieve beam steering capability which is used in high accuracy phased array radar. Phase of each element applied by the well-known progressive phase shift method. The proposed phased array antenna has a wide beam steering capability of ±30° and an average of -10 dB side lobe level (SLL) in over a wide bandwidth from 3 to 11 GHz. The simulated and measured results of return loss for the single antenna, both single and array Gain, and beam scanning feature will be discussed. The simulation results confirm that the proposed UWB phased array has a stable radiation pattern and perfect cross polar isolation in the entire band of operation for mentioned beam scanning angles.
We derive analytical shape integral formulas for the shape derivatives of the system matrix arising from the Rao-Wilton-Glisson (RWG) discretized electric field integral equation.Using these formulas and the adjoint variable method (AVM), we inspect sensitivity of input reflection coefficient of a certain UWB dipole antenna with respect to infinitesimal variations of the computational mesh.The sensitivity obtained with the analytical formula is compared against one calculated with the finite difference approximation.
