This paper investigates the channel characterization of Rayleigh fading channel using K-band frequency-modulated continuous wave (FMCW) radar system. An IF (intermediate frequency) signal of K-band FMCW radar can be treated as time and frequency domain signals due to a unique property of linear frequency modulation (LFM). First, channel sounder FMCW radar stability has been confirmed by measuring power flatness of transmitted radio frequency signal and estimated range in anechoic chamber before conducting the experiment for channel characterization of Rayleigh fading channel. Next, the measurement setup has been conducted in reverberation chamber which emulates multipath fading phenomena. In reverberation chamber, four different cases have been examined by changing the boundary conditions inside it with and without flat microwave absorbers. This investigation leads to obtained scattered plots, normalized propagation delay profiles (PDPs), mean excess delay, root-mean-square (RMS) delay spread and envelope distribution of Rayleigh fading channel at about 24.591 GHz.
The airborne or vehicle-based SARs are very vulnerable to the influences of airflows or road conditions so as to deviate from the predicted trajectory, which undermines the uniformity of the azimuth sampling. As a result, the SAR image quality can get impaired in varying degrees. Since the SAR systems are sensible to the track deviation, the motion compensation (MOCO) algorithms are always applied as pre-processing of SAR raw data. In this paper, mainly with regard to the motion error caused by the forward velocity variation, a `resampling MOCO' algorithm is proposed as an auxiliary of the widely used bulk MOCO. The simulation result has verified that the performance of the fundamental bulk MOCO algorithm is greatly improved utilizing the proposed method.
Eddy current test has been widely used in many fields because of its simplicity and robustness. In this paper, numerical simulations based on the finite-difference time-domain method were carried out to validate if the eddy current coil can effectively be used in the logging while drilling system. The simulation results showed that the impedance of the eddy current coil is a function of conductivity of the surrounding media. The formation conductivity is strongly dependent on the concentration of hydrocarbons, so different formation layers can be distinguished by measuring coil impedance. Different source frequencies were applied, and it was found that this method works well in frequency range from 100 MHz to 1 GHz. The investigation depth was studied in this paper, and a 3-layer formation model was simulated in this paper. The results showed that this novel method could be effectively used in a well logging system.
In this paper, the problem of predicting the parameters (positions and magnetic moments) of an Equipment Under Test (EUT) composed of a magnetic dipole and quadrupole is studied. Firstly, a multiple magnetic dipole and quadrupole model (MDQM) is developed to simulate the magnetic behavior of the EUT. The parameters of the model are calculated using the values of the near field measurements applying the Particle Swarm Optimization (PSO) algorithm. For the evaluation of the method, extended simulations were conducted, producing theoretical values and distorting them with noise, and then the developed algorithm was used to create the proper MDQM. As an evaluation criterion, the relative difference between the theoretical and the MDQM's magnetic field is considered.
We propose a method to recognize targets by using the signature of jet engine modulation (JEM) generated by the rotating blades in jet engines. The method combines time-frequency transform, 2-dimensional (2D) principal component analysis, and a nearest-neighbor classifier. In simulationsusing five propellers composed of isotropic point scatterers,the proposed method was insensitive to signal-to-noise SNR variation; this insensitivity wasa result of the effective 2D time-frequency feature and the noise suppression by the matchedfilter. In simulations using a reduced training database, the result was most sensitive to variation in the rotation velocity of the blades.
Metamaterials provide the opportunity for designers to create customisable artificial materials by independently tailoring the electric and magnetic response of sub-wavelength geometric structures to electromagnetic energy. Due to the increased complexity of these geometric structures, exacerbated by the increased interest in generating inhomogeneous and anisotropic metamaterials, direct optimisation of these designs using conventional approaches often becomes impractical and limited. In order to alleviate this issue, we propose an alternative optimisation approach which exploits the Kriging methodology in conjunction with an adaptive sampling plan to simultaneously optimise multiple conflicting objectives. Results show the effectiveness of the outlined algorithm in calculating a uniform spread of optimal trade-off designs, balancing the real and imaginary components of the refractive index over a wide range of values.
In this paper, we present improved Lumped-Parameter Models for simulation of a Interior Permanent Magnet Synchronous (IPMS) machine to calculate PM flux linkage, and Q and D-axis inductances which can be used for torque calculation. These improved models include all details of flux barriers and air bridges of rotor and also the eect of saturation in central posts and stator core. To validate the accuracy of these models, results are compared with the Finite Element Method results for a candidate three-layer IPMS machine.
A compact dumbbell-shaped split-ring DGS is introduced between array elements of a sixteen-element microstrip array in order to reduce the mutual coupling between antenna elements and eliminate the scan blindness. The proposed DGS is inserted between the adjacent rectangle-shaped slotted microstrip antenna elements separated by 0.35λ, as a technique to suppress the radiation in the horizontal direction. Simulated results show that a reduction in mutual coupling of 36 dB is obtained between elements at the operation frequency of 2.45 GHz (WLAN band). The scan properties of microstrip array with and without DGS have been studied, and the result indicates that the scan blindness of the array has been well eliminated because of the effect of the DGS. We have developed experimental models that have proved the concept of scan blindness elimination. Finally, the influence of other antenna parameters at the presence of DGS in the array system has been studied. Prototype antennas of sixteen-element array with and without resonator have been fabricated, measured, and the idea has been verified. A good agreement is observed between measured and simulated results.
Rain attenuation is a major source of impairment to signal propagation at microwave and millimeter wave bands. The procedures for the estimation of rain attenuation value regard to microwave signals however rely mainly on 1-minute rain rate statistics, particularly those obtained locally from experimental measurement campaigns over a given location. In this paper, we present recent results on 1-minute rain rate statistics required for satellite and terrestrial link designs, as obtained from a 2-year measurement over Akure, Nigeria. The performance of the existing rain rate models: Rice-Holmberg (RH) model, the Kitami model, Moupfouma model and the global ITU rain rate model were tested based on four metrics namely: Prediction error, Root Mean Square Error (RMSE), Spread-Corrected Root Mean Square Error (SC-RMSE) and the Spearman's rank correlation. Result indicates that no single model completely outperforms all others. Interestingly, the RH model is particularly best behaved over the distribution, while the Moupfouma model performs suitably well. Others seem to vary largely from the measured rain rate distribution. Results for the rain rate exceeded for 0.01% of the time agrees with earlier estimates for the cumulative rain rate distribution derived from higher integration-time statistics over this tropical site.
In this work, new ``extended gauge transformations'' involving current and fields are presented. The transformation of Maxwell's equations under these gauges leads to a massive boson field (photon) that is equivalent to Proca field. The charge conservation equation and Proca equations are invariant under the new extended gauge transformations. Maxwell's equations formulated with Lorenz gauge condition violated give rise to massive vector boson. The inclusion of London supercurrent in Maxwell's equations yields a massive scalar boson satisfying Klein-Gordon equation. It is found that in superconductivity Lorenz gauge condition is violated, and consequently massive spin-0 bosons are created. However, the charge conservation is restored when the total current and charge densities are considered.
Novel 2-D Time Domain Electric Field Integral Equations (TD-EFIE) are established in order to predict transient response of a wire enclosed within a rectangular cavity. The wire and cavity are excited by an external incident transient electromagnetic wave through a slot in the cavity wall. The formulation of the TD-EFIE is based on equivalence principle and boundary conditions taking account the effect of reflection from cavity walls. The equations are efficiently solved by Method of Moments. The transient unknown coefficients of the electric current at the wire and magnetic current at the slot are approximated using a set of orthonormal temporal basis functions derived from Laguerre Polynomials. The analysis demonstration is presented to prove that the novel TD-EFIE combined to MoM is able to solve this critical problem. No late-time instability is encountered.
The static circuit parameters extracted from the field results of non-uniform microstrip line provides an efficient way to predict dynamic effect of non-uniform structure. The predictable frequency range of the static circuit parameters on prediction of the transmission characteristics of step microstrip line is researched in this paper. The circuit parameters are extracted from the full wave results of step line, respectively, at three frequencies (9 GHz, 15 GHz and 20 GHz). On one hand, the time domain transmission characteristics of step line can be solved from the equivalent circuit constructed by these extracted circuit parameters. On the other hand, the frequency domain S-parameter can be derived by the static distributed characteristic impedance. By comparing these time and frequency domain results obtained from the static circuit parameters with those obtained directly from the full wave method, the available condition of the static circuit parameters of the step microstrip line can be analyzed. This comparison shows that the static circuit parameters can be used in frequency bands from DC up to 20 GHz. To verify the accuracy of the static parameters used to predict the transmission characteristics of step line, the measured S11 is also given for comparison with static circuit parameters measurements.
By using some special passive structures and correction of boundary conditions, a novel method to improve the electromagnetic (EM) simulation accuracy is proposed. With this method, the substrate parameters, such as thickness, loss, dielectric constant, loss tangent, sheet resistance, square capacitance and conductivity of the metal, can be described more accurately, and a lot of high frequency effects caused by skin effects, parasitic effects, coupling between micro-strip lines and fluctuation from the sheet resistance, etc. can also be simulated more precisely. Then an accurately scalable small-signal model for millimeter-wave HEMTs is proposed and presented. Combined with distributed modeling, pulsed IV and S parameter measurements, this model can be made scalable freely. The measurements agree with simulated results very well, which also proves that this method applied to the scalable small-signal models has a good consistency and accuracy.
This paper presents the design, fabrication, and measurement of triple band metamaterial absorber at 8 GHz, 10 GHz and 12 GHz which are in the X-band frequency range. The unit cell of the metamaterial consists of three concentric copper rings at different radii, printed on 0.8 mm thick FR4 substrate in order to obtain triple resonant frequencies. The highly symmetrical ring structure in nature makes this absorber insensitive to any polarization state of incident electromagnetic (EM) waves for normal incident waves. The proposed structure is capable to operate at wide variations angle of incident wave. The simulated result shows that the triple-band metamaterial absorber achieves high absorbance for normal incident electromagnetic waves of 97.33%, 91.84% and 90.08% at 8 GHz, 10 GHz and 12 GHz respectively, when subjected to normal incident electromagnetic. With metamaterial absorber maintaining 50% of absorbance value, the corresponding full width half maximum (FWHM) are 5.61%, 2.90% and 2.33%. The operating angles in which the metamaterial structure can maintain 50% absorbance at TE mode and TM mode are 670 and 640 respectively. The experimental result verifies that the absorber is well performed at three different resonant frequencies with absorbance greater than 80%.
A pattern synthesis approach based on a modified alternating projection method in an affine coordinate system is proposed in this paper. The approach is suitable for large planar arrays with periodic parallelogram element layout. According to the affine transformation theory, the radiation pattern of the array with a periodic parallelogram element layout could be written down immediately from that of a conventional one with rectangle cells when a pattern invariant group is defined. Just as known, the conventional alternating projection method is sensitive to the starting point and easy to fall into local optimum; in this paper we introduce a modified alternating projection method with a variable projection operator. To verify the rationality of the proposed method, several examples have been performed on our personal computer. Results show that the method could quickly synthesize the array patterns to the required with high accuracy. In addition, if the array has a triangle or parallelogram element layout, the required antennas to fill up the aperture is reduced when compared with the conventional one with antennas arranged along a rectangle grid. In our examples, the maximum reduction is about 18.09%, which is quite beneficial to reduce the weight and cost of the array.
This paper presents an optimized design of Litz-wire coil pair with ferrite substrates based on a set of analytical expressions and a 2-D finite-element analysis (FEA) in a way that the coupling coefficient is maximized. An investigation is made on key structure parameters of coils (e.g., structure of Litz-wire, number of turns, and number of layers) to determine their influence on self-inductance and mutual inductance respectively. The influence of ferrite substrate (e.g., relative permeability and thickness) is also considered. Different types of fabricated coils are used to verify all analytical expressions and optimization methods, and it is found that the theoretical predictions and simulations are in agreement with the measured results.
Wireless communication along the stairwell in a high rise building is important to ensure immediate response to take place via consistent relaying of necessary information or data in emergency situations. Thus, a good understanding of signal wave attenuation along the stairwell is necessary to allow a better wireless network planning. This paper presents empirical path loss prediction model for multi-floor stairwell environment. The proposed model is based on measurement in 4 different stairwells, at 900 MHz and 1800 MHz which are near public safety communication bands. The model incorporates the effect of different floor heights and unique path loss-to-distance relation on several stair flights observed during measurement campaign. The proposed model demonstrates higher accuracy than 3 standard path loss models at 2 other stairwells.
Electromagnetic wave absorption inside a human body is investigated. The human body has been modeled using 3D voxel based dataset considering different electrical parameters. At GSM 900 band, Specific Absorption Rate (SAR) induced inside the human body model exposed to a radiating base station antenna (BSA) has been calculated for multiple number of carrier frequencies and input power of 20 W/carrier. Distance (R) of human body from BSA is varied in the range of 0.5 m to 5.0 m. Values of whole-body average SAR obtained by hybrid FDTD method closely match with that obtained by SFDTD method. For number of carrier frequency equal to five and R = 0.5 m, maximum value of whole-body average SAR obtained by both hybrid FDTD and SFDTD method is found to be 0.69 W/kg which decreases either with increase of R or decrease of number of carrier frequencies. Safety distance for general public is found to be 1.5 m for number of carrier frequencies equal to five. Summary of performance comparison shows that hybrid FDTD method is faster and requires less memory than SFDTD method.
This paper is devoted to the study of beam-wave interaction behavior of a 35 GHz photonic band gap cavity (PBGC) gyrotron operating in a higher order TE341 mode. For the present gyrotron, PBGC is used instead of conventional tapered cylindrical cavity due to its promising feature of the mode selectivity. In order to observe the beam-wave interaction behavior, multimode theory has been used for the PBG cavity operating at the fundamental harmonic mode. Multimode theory provides the performance of a gyrotron in the presence of all competing modes. Results obtained from the analysis have been validated using a commercially available 3D PIC code. The energy and phase variations of electrons demonstrate the bunching mechanism as well as energy transfer phenomena. RF power output obtained from the analysis as well as PIC simulation is compared and is found in close agreement within 12%. More than 45 kW of stable RF power output is achieved in TE341 mode with ~17% efficiency. The existence of competing modes has been considerably reduced, and the single mode operation of PBGC gyrotron has been achieved.
The near-field scattering characteristics of rough target are analyzed by using a revised bidirectional reflectance distribution function (BRDF) of a rough surface based on least squares support vector machine (LS-SVM). The revised BRDF is more reliable in a larger range of incident angles and scattering angles that beyond the scope of experimental measurements. The basic principle of LS-SVM and the modeling process are firstly introduced in detail. Then the comparison among LS-SVM, the back propagation neural network (BPNN) and the measured data is carried out．The results show that the LS-SVM model has better integrative performance, stronger generalization ability and higher precision. On this basis, the calculation of the near-field radar cross section (RCS) of a complex target is safely performed and analyzed. The method proposed is helpful to better investigate the near-field scattering characteristics of rough target.