An active-antenna array with 18 transmit elements and 18 receive elements is designed and fabricated. This T/R array can work at two different frequencies (19.5 GHz and 21.5 GHz) with multiple levels of isolation between the transmit and receive channels. A hybrid element-level vector finite element and adaptive multilevel fast multipole method (ELVFEM/AMLFMA) is applied to simulation the performance parameters of the array element and the full array fast. To obtained the maximum directivity of the array,the best distances of the T/R elements in the array are optimized by using the genetic algorithm (GE) combining with VFEM/AMLFMA. The design efficiency of the array is improved at a ratio of 30%. Finally the performance of the T/R array fabricated is measured in experiments and some good results are obtained.
Radar Cross Section is most of the time defined in far field. In that case, RCS is totally independent of the range between the radar and the target. However, in several kinds of military scenario, it can be more realistic to deal with the target nearfield scattering characteristics. Using a relation to define near-field RCS, this communication proposes simple and approximated analytical formulas to express monostatic near-field RCS of perfectly conducting flat targets observed in normal incidence.
In order to meet the approximate plane-wave irradiation condition, adequate large field or compact range system is needed for RCS measurement of large aircraft targets. However, an outside testing field site or a compact range system is very expensive, so some kinds of RCS extrapolation methods based on near-distance testing have been presented. In this overview, two categories of extrapolating technique are summed up, which are based on Huygens Equivalent Reradiating Source (HERS) and Inverse Synthetic Aperture Imaging (ISAI) respectively. Each method is fully elaborated. The comparison and analysis of these extrapolating techniques are discussed in detail.
This paper focuses on the radar cross section (RCS) reduction for the three-dimensional object with anisotropic impedance coating. In this work, a genetic algorithm is adopted to optimize the RCS of the anisotropic impedance object in desired angle range. The surface impedances are considered as the optimized parameters and the scattering of the object is computed by the PO method. The optimization process is demonstrated by considering the RCS reduction of two typical targets: the cone and the cone/cylinder composite structure. It is found that the optimization process can reduce the RCS of the targets remarkably and the anisotropic impedance coating has better RCS reduced effect than the isotropic impedance coating.
With the global search method of adaptive genetic algorithm (GA), an improved methodology is proposed to identify the equivalent radiating dipoles of real sources on substrates such as printed circuit boards (PCB) and then to regenerate the radiating far field. This methodology is based on a set of elemental electric- and magnetic dipoles which model the real sources. The numbers, positions and orientations as well as the elevations of each dipole are positioned by adaptive GA based on the comparison between the simulated and measured magnetic field. The methodology provides a possible way to identify the radiating source of planar circuits with ground plane.
A new non-air conduct speech detecting method is introduced in this paper by means of millimeter wave (MMW) radar. Due to its special attribute, this method may provide some exciting possibility of wide applications. However, the resulting speech is of less intelligible and poor audibility since the present of the combined and colored additive noise. This paper, therefore, investigates the problem of the MMW radar speech enhancement by taking into account the frequency-domain masking properties of the human auditory system and reduces the perceptual effect of the residual noise. Considering the particular characteristics of MMW speech, the perceptual weighting technique is developed and incorporated into the traditional spectral subtraction algorithm to shape the residual noise and make it inaudible. The results from both acoustic and listening evaluation suggest that the background noise can be reduced efficiently while the distortion of MMW radar speech remains acceptable, the enhanced speech also sounds more pleasant to human listeners, suggesting that the proposed algorithm achieved a better performances of noise reduction over other subtractive-type algorithms.
Circularly-polarized arrays of cavity backed slot (CBS) antennas are proposed for X-band satellite-earth communications. Two configurations of such circularly polarized arrays are investigated: cross-shaped and square-shaped arrays. Both configurations can produce right-hand circular polarization (RHCP) as well as lefthand circular polarization (LHCP) by proper setting of excitation phase for each element in the array. The finite-difference timedomain (FDTD) method is used to analyze the characteristics of the proposed arrays including the input impedance, S-parameters, radiation pattern, gain and axial ratio. The results show that the proposed array configurations seem very promising and useful for geostationary satellite applications.
The measurement of the field radiated from an antenna placed above a finite ground plane experiences the effects of the field scattered by the edges of the ground plane. A new numerical method to remove these effects from measured data is presented here. It resorts to the image theorem and can be used for both near-field and far-field measurements. A simple and effective algorithm has been developed to apply that method to fields described by means of spherical wave expansion. A numerical validation shows the effectiveness of the method.
This paper reports on an experimental investigation of modes propagating along a conductor-backed slotline: the dominant mode, and the surface leaky mode. The measurement and the numerical experiments performed in the CST Microwave Studio verify theoretical findings of modes obtained by the method of moments applied in the spectral domain. The dispersion characteristic of the dominant mode on the conductor-backed slotline is determined by substituting this line by a flat slotted waveguide.
A novel dualband frequency selective surface (FSS) with both a dielectric substrate and superstrate constructed by double-fourlegged loaded slots (DFLLSs) is investigated, in which each periodic cell consists of two neighboring DFLLSs with different dimensions, its resonant frequencies occur at 183 GHz and 220 GHz. Good selectivity performance can be easily achieved both in lower passband and higher passband by tuning the dimensions of the DFLLSs. Besides, the passbands are mainly determined by the neighboring perturb cells and can be designed independently. According to the explicit physical concept and some formulas, the design process become straightforward and simple. Its frequency performance is obtained by using numerical simulation software CST based on finite difference time domain method (FDTD). The simulated results show the good stability of the resonant frequencies and bandwidths at different polarization states and various incident angles.
This paper presents the design of a dual stacked microstrip antenna over the frequency range of 9.5-16 GHz. Investigations show that in the new structure the impedance bandwidth of the antenna is increased to 44% and the thickness of the antenna decreases to 0.14λ. Furthermore, the gain bandwidth of the antenna (above 8 dB) is increased to 5.1 GHz (40%).
This paper presents a novel elliptic shape defected ground structure (DGS) for low pass filter (LPF) applications. An equivalent RLC circuit model is presented and its corresponding parameters are also extracted from the measured S-parameters. The filter presents the advantages of compact size,high selectivity; low insertion loss and high out-band suppression from 5.15 GHz to 10 GHz below -31 dB. Good agreement with response of equivalent circuit, electromagnetic simulation, and measurement is demonstrated.
The permittivity tensor of an anisotropic material can be predicted with use of the presented technique. A slab of this substance possessing infinitesimal thickness is illuminated by a normally incident plane wave and rigorous expressions for the transmission coefficients are obtained. The derived formulas are linearly expanded with respect to the small thickness of the slice, while simple approximations of the material permittivities are produced by measuring the transmission coefficients for suitable polarizations. These simplified expressions provide a physical intuition about the use and the function of the anisotropy parameters which cannot be achieved via more precise but also more complex patterns. Some diagrams of the prediction error with respect to the dielectric constants, the size of the slab and the operating frequency are included and discussed.
In RFID system, tag collision is a main problem for fast tag identification. On the base of binary search algorithm of backtracking, an enhanced binary anti-collision search algorithm for radio frequency identification (RFID) system is presented in this paper. By dynamically transferring the ID of the tag, the length of the data transferred can be decreased dramatically. Mathematical simulation result shows that compared with the binary search algorithm of backtracking, the proposed algorithm can save channel by more than 43.75% when handling multiple RFID tags simultaneously. Finally the proposed algorithm is successfully applied to a RFID device, which validates itself.
In this paper, an integrated and manifold study of the combined electromagnetic and thermal effects, caused by human exposure to microwave radiation is carried out. In essence, we numerically calculate the amount of electromagnetic power absorbed by biological tissues for various exposure conditions and types of emitting sources, utilizing a detailed model of the human head. The severity of the obtained results is evaluated via comparisons with the guidelines of international safety standards, while further insight is gained by investigating the induced thermal effects. The latter are properly quantified through the solution of the bioheat equation, when combined with the outcome of the electromagnetic simulations. Spatial distributions of the corresponding temperature changes are thus calculated, their relation to the dissipated power is established, and the thermal response of human tissues in marginal cases of exposure is predicted.
Fractional curl operator has been used to derive solutions to the Maxwell equations for fractional rectangular cavity resonator. These solutions to the Maxwell equations may be regarded as fractional dual solutions. Behavior of field lines and surface current density in fractional cavity resonator have been investigated with respect to the fractional parameter. Fractional parameter describes the order of fractional curl operator.
Anechoic chambers are used for both emission and immunity testing but the ferrite tiles used to line the inside of the chamber are extremely expensive. This paper describes a method of reducing the number of tiles, whilst ensuring a reliable test environment. In this paper, the ray-tracing method for waves propagation is used for evaluation of the reflectivity level of an anechoic chamber, and genetic algorithms are used. And use genetic algorithms to optimize the layout of ferrite tile absorber in a partially lined enclosure to produce a best performance. The results show that it is possible to cover just 80% of the surface of the enclosure with ferrite absorber and obtain good agreement by fully lined enclosure with an error of less than 3 percent over the whole test points.
In this article the details of Erbium doped Fiber Amplifier (EDFA) in presence of Silicon nanocrystal (Si-Nc) is investigated. In this analysis Si-Nc and Er ions in matrix of fiber are assumed two and five levels respectively. For this structure rate equation for transient and steady state analysis is considered. The range of Er^{(+3)} concentration and pump intensity at 488nm are considered [10^{17} - 10^{21}]1/cm^{3} and [10^{17} - 10^{23}] photon/cm^{2} ^{.} sec respectively in this paper. Based on numerical simulation of this problem we observed that with increasing of concentration of the Si-Nc the fiber length for given optical gain is decreased. For example in the case of 40 dB optical gain, we calculated fiber length to be 1.1 × 10^{5} cm without Si-Nc and 5 × 10^{2} cm for σ_{CCa} = 1 × 10^{-17} cm^{2} (confined carrier absorption cross-section) and 5 cm for σ_{CCa} = 1 × 10^{-19} cm^{2} respectively. Our simulations show that for second level with increasing pump intensity the population rise and fall times are decreased. But, for third level the population rise time is decreased and fall time is depends to level of Er ion interactions. We observed that with increasing Er ions optical net gain is increased and finally has a maximum. After this special value of Er ions because of increasing in interaction between ions the net gain finally begin to decrease. In this analysis we let to Er ions have inhomogeneous distribution. Also, we observed that in this case with increasing of the distribution peak, the net gain is increased, interaction between ions is increased, the coupling coefficient to the Si-Ncs is increased and losses due to Si-Ncs are decreased. Finally effect of K_{exiton} (maximum number of exciton in single Si-Nc) on amplification process is considered and we observed that in the case of K_{exiton} = 2 the optical gain considerably and introduced losses due to Si-Nc are increased.
We develop in this paper a theoretical approach to describe the electrodynamics of carbon nanotubes (CNTs). A lattice dynamics formalism is employed to model the mechanical response of matter to the radiation field. We start first by deriving the normal modes of the free lattice. Then, a simple and general microscopic model for light-matter interaction is proposed and the resulting mechanical equation of motion is derived using a suitable Lagrangian formalism. The symmetry group of the CNT is employed to explicitly probe the nonlocal structure of the fields and to carefully insure that higher-order Floquet modes are included in the derivation. The normal modes are then employed to perform an eigenmode expansion for the solution of the mechanical equation of motion, leading to the susceptibility tensor of the CNT medium. The final expression of this tensor describes the electrodynamics in the CNT viewed as a low-dimensional surface and is shown to be reduced effectively to a one-dimensional response function.