In medical microwave imaging applications, electromagnetic (EM) waves propagate through human tissues, which are inherently attenuative and dispersive. In the resulting image, these effects translate to a lack of resolution that increases with time/distance. To produce microwave images with high resolution, there is a strong need for a technique that is able to compensate for the energy loss and correct for the wavelet distortion. Gabor nonstationary deconvolution was developed in the field of Seismology to compensate for attenuation loss, correct phase dispersion, and produce images with high resolution. In this study, the Gabor algorithm is proposed to deal with the nonstationarity in EM wave propagation and attenuation. Gabor deconvolution is essentially based on the assumption that the anelastic attenuation of seismic waves can be described by a constant Q theory. We investigate the Q characterization of EM wave propagation, the frequency-dependency of EM Q, and the effectiveness of Gabor deconvolution to deal with high loss and dispersion. To accommodate for the EM application conditions, several adjustments are made to the proposed algorithm. Our test results indicate that Gabor nonstationary deconvolution is able to sufficiently compensate for attenuation loss and correct phase dispersion for EM waves that propagate through lossy and dispersive media.
A LEO-ground infrared laser occultation (LGIO) technique is proposed to retrieve the greenhouse gas (GHG) profiles around a specific location, including the analysis of key factors and practical issues that may affects its efficacy. A harmony search with ensemble consideration (HS-EC) algorithm is applied to retrieve the volume mixing ratio (VMR) profiles of H2O and three major GHGs, CO2, CH4 and N2O. The vertical resolution of retrieved GHG profiles is 1 km from ground level up to 20 km at height. The errors in VMR of H2O, CH4, N2O and CO2 are below 10, 5, 5 and 3%, respectively, up to 45 km above ground.
Two approaches to reconstruct the S-matrix of N-port waveguide reciprocal devices from 2-port S-matrix measurements are proposed and discussed. The main advantage of the proposed approaches is that measurements are done always at the same two ports, without moving the device. The remaining N-2 ports are loaded with different loads, either matched or short. The first approach, based on a manipulation of the 2-port S-matrices, requires N-2 matched and two other loads, while the second approach, based on the evaluation of an equivalent circuit, requires N-2 short and two other loads. The measurement technique is based on the standard loads (short, shift and matched) in the waveguide calibration kit of the 2-port VNA.
Synthetic aperture radar (SAR) raw signal simulation is profoundly useful for validating SAR system design parameters, testing the effectiveness of different processing algorithms, studying the effects of motion errors, etc. Simulating signal data in frequency domain is more efficient than in time domain. However, the former is difficult account for the effects of both sensor trajectory deviations and antenna pointing error for the stripmap SAR mode. In this paper, we attempt to extend the possibility of extending the Fourier domain approach to account for trajectory deviations as well as antenna beam pointing errors, which is more concerned for airborne SAR systems. After demonstrating a full two-dimensional Fourier domain simulation, an efficient simulation approach is proposed under certain reasonable assumptions. The proposed approach has higher computational efficiency than simulation in time-domain and also allows for imaging an extended scene. The validity of the proposed approaches is analyzed and discussed. Finally, numerical examples are presented to verify the effectiveness and efficiency of the approach.
A novel selectable multiband isolation of Double Pole Double Throw (DPDT) switch with switchable transmission line stub resonators has been proposed for applications of WiMAX and LTE in 2.3 and 3.5 GHz bands. In this paper, two DPDT switch designs are proposed; the first design is a fixed DPDT switch, and the second is a selectable DPDT switch. The second design allows selecting only one band and unselecting the other or selecting both of them. However, the first design does not allow so. The transmission line stub resonator used in this design is an open stub resonator with quarter wave of the electrical length. By using a simple mathematical model, the theory of the transmission line stub resonator was discussed where it can be cascaded and resonated at center frequencies of 2.3 and 3.5 GHz. Moreover, the cascaded transmission line stub resonators can be reconfigured between allpass and bandstop responses using discrete PIN diodes. The key advantage of the proposed DPDT with switchable transmission line stub resonators is a multiband high isolation with minimum number of PIN diodes. Therefore, the simulated and measured results showed less than 3 dB of insertion loss, greater than 10 dB of return loss and higher than 30 dB of multiband isolation in 2.3 and 3.5 GHz bands.
Radar holography has been established as an effective image reconstruction process by which the measured diffraction pattern across an aperture provides information about a threedimensional target scene of interest. In general, the sampling and reconstruction of radar holographic images are computationally expensive. Imaging can be made more efficient with the use of sparse sampling techniques and appropriate interpolation algorithms. Through extensive simulation and experimentation, we show that simple interpolation of sparsely-sampled target scenes provides a quick and reliable approach to reconstruct sparse datasets for accurate image reconstruction leading to reliable concealed target detection and recognition. For scanning radar applications, data collection time can be drastically reduced through application of sparse sampling. This reduced scan time will typically benefit a real-time system by allowing improvements in processing speed and timeliness of decision-making algorithms. An added advantage is the reduction of required data storage. Experimental holographic data are sparsely sampled over a two-dimensional aperture and reconstructed using numerical interpolation techniques. Extensive experimental evaluation of this new technique of interpolation-based sparse sampling strategies suggests that reduced sampling rates do not degrade the objective quality of holograms of concealed objects.
In this paper, two-dimensional (2-D) analytical magnetic field calculations are used to compute crucial quantities of Brushless permanent-magnet (PM) machines with surface-inset PMs. The analytical magnetic field distribution is based on the subdomain technique in which the slotting and tooth-tip effects have been considered. It includes both different magnetization patterns (e.g., radial, parallel and Halbach) and different spatial distribution of winding (e.g., concentrated and distributed with one or more layers). The saturation effect of the magnetic circuit is neglected. In this investigation, the phase and line induced back electromotive force (EMF) waveforms, electromagnetic/cogging/reluctance torques, self-/mutual-inductances and unbalanced magnetic forces (UMFs) have been analytically calculated. The analytical expressions can be used for Brushless machines having surface-inset PMs with any radius-independent magnetization pattern. In this study, two slotted Brushless PM machines with surface-inset PMs have been selected to evaluate the efficacy of the analytical expressions by comparing the results with those obtained by the finite element method (FEM). One of the case studies is a 9-slots/8-poles Brushless DC (BLDC) machine with radially magnetized PMs, non overlapping all teeth wound winding and six-step rectangular armature current waveforms. The other is a 15-slots/4-poles Brushless AC (BLAC) machine with Halbach magnetization PMs, double-layer overlapping winding and sinusoidal armature current waveforms.
We develop an efficient semi-analytical technique to calculate the electromagnetic scattering from fabric structures modeled as crossed gratings of circular coated fibers of any material composition, arranged arbitrarily in yarns. The method relies on a matrix formulation based on multipole expansion for modeling conical scattering from uniaxial gratings of fibers, and employs a scattering matrix approach to obtain co- and cross-polarized transmission and reflection coefficients. The lattice sums are evaluated using an efficient adaptive algorithm based on Shank's transformation. The method can be employed for analyzing the scattering characteristics of fabric structures embedded in any arbitrary layered media. The validity of the method is verified through comparison with full-wave finite-difference time-domain simulations. A substantial performance gain is obtained, which makes the proposed method applicable to solve large-scale fabric structure.
Magnetically coupled resonant wireless power transfer (WPT) has been employed in many applications, including wireless charging of portable electronic devices, electric vehicles and powering of implanted biomedical devices. However, transmission efficiency decreases sharply due to divergence of magnetic field, especially in under coupled region. Electromagnetic (EM) metamaterial (MM) can manipulate the direction of EM fields due to its abnormal effective permittivity or permeability. In this paper, an ultra-thin and extremely sub-wavelength magnetic MM is designed for a 13.56 MHz WPT system to enhance magnetic field and its power transfer efficiency (PTE). The WPT systems are investigated theoretically, experimentally and by simulation. A relatively high maximum efficiency improvement of 41.7% is obtained, and the range of efficient power transfer can be greatly extended. The proposed MM structure is very compact and ultra-thin in size compared with early publications for some miniaturized applications. In addition, large area, homogeneous magnetic field is obtained and discussed using the proposed MM. Finally, the proposed MM is applied in a more practical WPT system (with a low power light bulb load) to reveal its effects. The bulb brightness intuitively verifies the efficiency improvement in the WPT system with the MM.
In this paper a multiple input multiple output (MIMO) radio channel measurement system is presented that utilizes several software defined radio (SDR) platforms at the transmitter and at the receiver. The system hardware buildup and its calibration technique are presented. The channel measurement results are afterwards exploited for a special antenna synthesis method that was already proofed by raytracing channel simulations. The antenna synthesis method is applied to a mobile single and to a mobile multiple channel receiver. The resulting synthesized antenna systems are evaluated in terms of antenna radiation patterns and the corresponding channel capacities. The results reveal the superiority of synthesized antenna systems compared to conventional omnidirectional antenna systems in the considered urban street scenario. Moreover, the findings from the antenna synthesis based on dynamically measured MIMO radio channels confirm the results from the raytracing channel simulation based antenna synthesis.
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