A tunnel diode integrated E-shaped patch antenna is proposed and analyzed using equivalent circuit concept. It is found that bias voltage of tunnel diode controls the performance of the antenna. Various tunable frequency bands are obtained by selecting suitable bias voltage while antenna topology remains unchanged. Bandwidth of the tunnel diode integrated patch improves to 40.26% over the 32.58% bandwidth of the patch. The radiation pattern also varies with bias voltage and a considerable improvement in beamwidth is observed however radiated power remains almost same.
This paper presents a square cylindrical monopole antenna easily fabricated using a cross-shaped metal plate for wideband omnidirectional operation. A prototype of the proposed antenna with a cross-sectional area of 8 × 8mm2 is implemented, and the antenna provides a wide operating bandwidth of about 7.5 GHz (1.8-9.4 GHz here), making it very promising for WMAN operation with the 802.16e standard in the 2 to 6 GHz. In addition, over the operating bandwidth, the antenna shows very good omnidirectional radiation patterns.
This paper proposes a novel beamforming technique to form an arbitrary-shaped cell for the high altitude platforms (HAPs) mobile communications. The new technique is based on pattern summation of individual low-sidelobe narrow-beams which constitute the desired cell pattern weighted by an amplitude correcting function. The new cell pattern can be adapted to cover the main highways forming worm-shaped cells which may cover the highway for long distances up 100km and it will has an important role in reducing frequent handoffs and signaling traffic of location updating from moving users over the long highways.
The electronic structure of finite parabolic GaAs/AlxGa1-xAs superlattices is studied. A detailed analysis of the miniband formation is given and the importance of all system parameters is discussed. The dependence of the equidistant miniband separation on the superlattice size is revealed. A comparison with different theoretical methods and experimental data is presented. The calculations are conducted in the framework of the semi-empirical sp3s* tight-binding model including spin applying the Green function formalism and the Surface Green Function Matching Method (SGFM) method.
Obtaining scattering field for an ellipsoid irradiated by electromagnetic wave with arbitrary polarizing and propagating direction is a hard topic that has caused large attention in the world. Literatures relative to it are seldom found. In this paper, the scattering field for an ellipsoid is presented by utilizing the scales transformation of electromagnetic field and coordinate system rotation, as the incident wave irradiating the target with arbitrary polarizing and propagating direction. The result obtained is in good agreement with that in the reference when all the scale factors changes into 1. We take a conductor ellipsoid as an example, simulations both for ellipsoid and plant leaf are presented respectively by way of choosing the different scale factor. Results show that the scattering field is sensitively affected by polarization of the incident wave and varies not too greatly with the incident wave and changes with the observing point. At some points the scattering energy arrives to its maximum.
The techniques of ground-cut slots and miniaturization are applied in the design of microstrip antenna which reduces the resonance frequency and size of antenna and achieves the Radar Cross Section (RCS) reduction. Compared with the rectangular patch antenna working at the same frequency, the designed antenna realizes the RCS reduction in the whole frequency band of 2-8 GHz. And the RCS can be reduced 2-4 dB at its working frequency. The RCSp eaks are efficiently controlled to get a smooth curve while the gain loss is only approximately 0.9 dB, which assures the radiation performance. The measured results of radiation performance accord with the simulation results and it implies that this method is feasible.
Generally all Magnetic Resonance Imaging (MRI) techniques are affected by magnetic and electric properties of measured materials, resulting in errors in MR image. Using numerical simulation we can solve the effect of changes in homogeneity of static and RF magnetic fields caused by specimen made from conductive and/or magnetic material in MR tomograph. This paper deals with numerical simulation of material susceptibility influence to magnetic field.
This paper overviews the latest trends of millimeterwave (MMW) imaging technologies, focusing mainly on applications of and technical parameter variations for security surveillance and nondestructive inspections (NDI).We introduce a smart NDI tool using active W-band imaging, which is capable of detecting hidden surface cracks in concrete structures.
The paper presents the detailed analysis of the interconnect capacitance, crosstalk time and peak crosstalk voltage. The dependency of the couple capacitance and fringe capacitance on the interconnect layer dimensions affects significantly to the interconnect capacitance. The peak crosstalk time obtained to be 13 femtoseconds for 9.6 femtoseconds of propagation delay, while the maximum crosstalk voltage obtained to be 178 mV.
Three-dimensional (3D) microfabrication of photostructurable glass by femtosecond (fs) laser direct writing is demonstrated for manufacture of biophotonic microchips. The fs laser direct writing followed by annealing and successive wet etching can fabricate the hollow microstructures, achieving a variety of microfluidic components and microoptical components in a glass chip. One of the interesting and important applications of the 3D microfluidic structures fabricated by the present technique is inspection of living microorganisms. The microchips used for this application are referred to as nanoaquarium. Furthermore, the optical waveguide is written inside the glass by the fs laser direct writing without the annealing and the successive etching. It is revealed that integration of the microfluidic and microoptical components with the optical waveguides in a single glass chip is of great use for biochemical analysis and medical inspection based on optical sensing.
The former Senate building, Saint-Petersburg, Russia is being refitted for using it by the Constitutional court of Russian Federation. The team of Remote Sensing Laboratory was invited to participate in this work. The case is that the underfloor water heating system had been installed in the Senate building. The arrangement of pipes hasn't been precisely documented. Besides, there are power and communications cables as well as metal mesh under the concrete floor of the building. Workers were afraid of damaging pipes and cables during laying the parquet floor. Main purpose was to investigate the building floor and to define exact position of pipes and cables with the help of subsurface holographic radars developed by Remote Sensing Laboratory.
The electronic structure and mobility trends in a n-type delta-doped quantum well in Si, matched between p-type delta-doped barriers of the same material, is presented. The distance between the n-type well and p-type barriers is varied from 50A to 500A; and also the impurity density from 5 × 1012 cm-2 to 5 × 1013 cm-2, for both, donors and acceptors. An increase in the mobility by a factor of 1.6 at interwell distance of 50A with donor and acceptor concentrations of 5 × 1012 cm-2 and 5 × 1013 cm-2 compared with a single delta-doped well without p-type barriers is found. This improvement in mobility could be attributed to a better confinement of carriers, which favors excited levels with nodes in the donor plane. This trade-off between carrier concentration and mobility could be exploited in high-speed, high-power and high-frequency applications.
We present the electronic spectrum of a n-type deltadoped quantum well in Si coupled to a p-type delta-doped barrier within the envelope function effective mass approximation. We applied the Thomas-Fermi approximation to derive an analytical expression for the confining potential, and thus, we obtain the electronic structure in a simple manner. We analyzed the electron subband structure varying the distance between the doping planes (l) as well as the impurity density in them (n2D, p2D). We also study the mobility trends through an empirical formula that is based on the electron levels, the electron wave functions and the Fermi level. We find a monotonic decrease in the mobility as the p-type barrier moves away from the n-type well, and optimum parameters, l = 70A and n2D = 5 × 1012 cm-2 and p2D = 5×1013 cm-2, for maximum mobility.
An analytical formula of the current distribution for the VLF horizontal wire antenna located above the ground is presented in this paper. This formula is suitable for the VLF horizontal antenna which is fed at arbitrary position and with arbitrary loaded impedance at the end. In order to validate the analytical formula, a numerical code based on MoM is also developed. The comparison between the results obtained by two methods proves the validity of the analytical formula proposed in this paper.
Long-term variations in strong geomagnetic storms are analyzed and linked to electric fields induced on Earth. In fact, geomagnetic disturbances generate electric fields that drive currents in the Earth which may have significant effects on electrical systems and pipelines. The present study will be carried out using aa, AE and Dst index data to estimate long-term variations in strong geomagnetic disturbances. The results are extended then to the space weather topic through a rough assessment of the expected Earth electric field from measured horizontal components of the surface magnetic field, and also through a qualitative estimation of the consequent currents and voltages induced in a pipeline using the distributed source transmission line (DSTL) theory.
Improving the performance of a microstrip antenna array has been considered based on the innovative use of an absorbing radar cover.Since the surface wave between antennas array elements plays a major role in mutual coupling and scattering behavior of array antenna. The main objective of this work is to reduce the effect of surface wave between array elements using radar absorbing cover.The absorbing cover has been designed with spatial configuration to get maximum performance at the resonant frequency of the fabricated microstrip antenna array.The measured results of the tested antenna array show a significant reduction of both mutual coupling between array patches and radar cross section of the tested antenna array with minimum side effects on the antenna parameters.
The paper presents the faster, simpler, and accurate algorithm to solve time independent Schrodinger equation based on transfer matrix method. We can thus calculate all bound and quasi bound energy and the corresponding probability density. A central part of this paper deals with the solving of Schrodinger equation for quantum well structure. Our results show that the transfer matrix method is accurate, it is easier to implement. The increase in well width increases the FWHM from 5.4 nanometer to 9.4 nanometer, while the increase in the Aluminum concentration the FWHM decreases from 8.98 to 5.4.
The enigma of the wave-particle duality of photon has remained unimpressively explained for a century since Einstein presents the concept of the photon in 1905. This article establishes a classical geometric structure model of a single photon based on field matter, educes a formula for the size of a photon; assumes that there only are two kinds of photon of right hand and left hand circular polarized, and suggests the frequency ω of photon polarization rotated to be its spin frequency. It ascribes the wavelike of photon to its spin motion and the particle-like to its translation motion. From the point of photon particle instead of wave view to re-analyze Young's double-slit interference and polarizer experiments, gives reasonable mechanism. It defines the phase velocity and the group velocity of a photon. It gives a unified and consistent understanding of quantum particle of light and classical electromagnetic waves field. Evidently, such a precisely defined conceptual model is reasonable, objective and easy to accept for classical physicists.
A novel ultra-wideband bow-tie slot antenna fed by CPW is proposed in this paper. This antenna has been demonstrated to provide an UWB with return loss less than -10 dB from 9.5 GHz to 22.4 GHz. The bandwidth is up to 80%, which is quite better than the traditional bow-tie slot antenna. Simulated and measured results are presented.
Reflection and transmission coefficients (R and T) of high frequency waves propagating in the ionosphere are studied taking collisions into account. This was done approximating the expression (1 + Z2)-1 in the refractive index using binomial expansion and neglecting terms of order higher than Z2, where Z is the ratio between the electron collision frequency and the wave frequency. R and T height profiles were assessed using the International Reference Ionosphere, IRI, to estimate the ionosphere plasma parameters. Although no significant differences are found between the estimation with and without collisions, the method employed to include collisions may be useful for other purposes where collisions should be taken into account.
It has long been known that the conical antenna has broadband characteristics and good radiation efficiency. The design considerations in reducing the size of top loaded conical antenna by using posts with lumped resistive loading are presented. The resulting antenna can achieve a VSWR of better than 2.0 over 100-800MHz frequency range. Results indicate that the addition of posts and lumped resistive loading has significant role in designing broadband antennas which are in small size.
This paper presents a design of wireless broadband (WiBro)-multi-input multi-output (MIMO) and personal communication service (PCS) antenna for practical mobile phone. To decrease the mutual coupling of WiBro-MIMO antenna, it is considered on the projected ground structure. In addition, two type PCS antennas for multi-function mobile phone are designed. The proposed antennas are well resonated in each operating frequency band. The measured bandwidths of 3-dimensional (3D) and 2-dimensional (2D) PCS antennas are 110MHz and 130MHz below -10 dB, respectively. The isolations between WiBro-MIMO and two PCS antenna are below -15dB by 2D antenna type and -20dB by 3D antenna type, respectively. The printed IFA has shown a better performance than modified planner IFA with spiral and shorting strip.
This paper introduces a 3 dB tunable symmetric left handed coupled line coupler implemented on ferrite substrate. The proposed coupler is realized in LH coplanar waveguide configuration constructed using interdigital capacitors and meandered line inductors. The analytical analysis and the numerical verification of the proposed couple line coupler are presented. The full wave numerical simulation results for different DC magnetic bias indicate that a tunable left handed coupled line coupler propagation with transmission coefficient up to 3 dB and isolation level more than 25 dB over a wide bandwidth can be achieved.
A new wideband and small size star shaped patch antenna fed capacitively by a small diamond shape patch is proposed. To enhance the impedance bandwidth, posts are incorporated under the patch antenna.HFSS high frequency simulator is employed to analyze the proposed antenna and simulated results on the return loss, the E and H-plane radiation patterns and Gain of the proposed antenna are presented at various frequencies.The antenna is able to achieve in the range of 4-8.8 GHz an impedance bandwidth of 81% for return loss of less than -10 dB.
The most difficult step in the analysis of the capacitance of arbitrarily shaped conductingplates is the determination of the electric center, or the expansion point of the charge density. This paper presents the generalized Huygens' principle, which indicates that the charge distribution on a conducting plate of convex shape has a tendency to be a circle before approachingthe fringe. Therefore, the center of the largest extended circle can be taken as the electric center. The agreement with numerical methods is demonstrated.
A new method for improving shielding effectiveness (SE) of a rectangular enclosure with multiple apertures has been proposed. In this method in order to compensate the effects of the apertures on reduction of (SE) parameter, instead of the one wall, two metallic walls containing apertures has been used. The numerical simulation uses a symmetric condensed node of TLM-TD (Transmission line Modeling Method-Time Domain) and subsequent Fourier Transform. The shielding effectiveness response to an electric field impulsive excitation is obtained. A study of the influence of the place of apertures in the walls and the distance between the two walls is presented.
The problem regarding top possible (hopefully, total) field suppression of a filamentary source placed above nonuniform impedance plane is discussed. New designs of the electromagnetic field absorbers and resonators are suggested which may be engineered with the use of metamaterials.
The electrostatic potential associated to the interface oscillation modes in nitride-based heterostructure is calculated with the use of a complete phenomenological electroelastic continuum approach for the long wave optical oscillations, and the Surface Green Function Matching technique. The crystalline symmetries of zincblende and - isotropically averaged - wurtzite are both considered in the sets of input bulk frequencies and dielectric constants.
A new circular ultra-wideband fractal monopole antenna based on descartes circle theorem (DCT) with elliptical iterations is presented. The proposed fractal design is optimized for return loss below -15 dB. The basic structure is slightly modified to ensure an overall smooth current distribution limited by the junction point nature of the fractal geometries. The measured return loss of the proposed design is below -15 dB within its impedance bandwidth along with omni-directional radiation pattern. Moreover due to the fractal shape, the proposed design has less weight and wind loading effect.
This paper presents a novel technique for efficiently combining genetic algorithms (GA's) with method of moments (MOM) for planar inverted-F antennas (PIFAs). MOM is applied to analyze rectangular patches fed by a coaxial probe and shorted with a shorted pin. The impedance matrix of such a mother structure is, then manipulated by a GA optimization procedure in order to detect the optimal patch shape matching the required frequency properties. GA adoption enables optimal shape detection among all possible shapes allowed by the mother structure dimensions. The design example of dual-band antenna is presented, and measurement result is compared to numerical results. Excellent agreement between numerical and measured results is observed.
The most common and simple structure to reduce the level of the reflected power from a metallic surface is the single layer structure known as Salisbury screen which is a sheet of porous material impregnated with graphite and spaced a quarter-wavelength off a metallic backing plate. The main disadvantage of this mechanism is the narrow frequency bandwidth. Many techniques have been reported to improve the working frequency bandwidth but with some degradation in the other technical properties of the overall structure. In this paper a novel technique has been introduced based on a spatial kind of material called circuit analog screen. Theoretical analysis shows that the bandwidth of the reflected power will be improved if the graphite sheet of Salisbury screen has been loaded by circuit analog screen with spatial geometry with spatial parameters.