Simulations based on electromagnetic topology (EMT) have been carried out to analyze an external electromagnetic pulse interaction with a shielded coaxial cable linking two systems together. The proposed EMT approach, combined with the SPICE model of the shielded cable, can be applied in the transient simulation directly and used for the electromagnetic interference analysis of systems including nonlinear devices. The effects of the outer terminators, cable length, and connection of the voltage limiter on the induced voltages at the systems are studied by using the proposed EMT approach. It has been found that adding a resistance between the system's shielding enclosure and the ground can effectively reduce the coupling through the shielded cable. The cable length affects the pulse-widths rather than the magnitudes of the induced voltages. The results also show that the voltage limiter can reduce the induced voltages but at the same time result in mismatch at the source or load.

Passive millimeter (MMW) imaging can penetrate clothing to create interpretable imagery of concealed objects. However, the image quality is often restricted by low signal to noise ratio and temperature contrast as well as low spatial resolution. In this paper, we explore a four-channel passive MMW imaging system operating in the 8 and 3 mm wavelength regimes with linear vertical and horizontal polarization directions. Both registration between different channel images and segmentation of concealed objects are addressed. Multi-channel image registration is performed by geometric feature matching and affine transform, and then multi-level segmentation separates the human body region from the background, and concealed objects from the body region, sequentially. In the experiments, several metallic and non-metallic objects concealed under clothing are captured in indoors. It will be shown that our method can separate objects with higher accuracy than the conventional method.

A novel design of decoupling network for a compact three-element array is presented. The proposed decoupling network has simple and compact structure that can be implemented easily with microstrip lines. The conventional microstrip open stubs can be used to match the decoupled ports of the array. The proposed decoupling and matching network is applied to a compact three-monopole array operating at 2.4 GHz. Both the simulated and the measured results show that the ports of the array are well matched and decoupled at the operating frequency.

The utility of slotted waveguide antennas would be maximized if the bandwidth of the radiating elements matched that available in the waveguide. This was achieved using a spiral shaped slot cut through the broad-wall of a rectangular waveguide. The predicted total efficiency and peak realized gain were relatively uniform across the entire bandwidth. The current distribution around the slot was predicted to be similar to that around a conventional, center fed, slot spiral antenna, indicating similarity of radiation mechanisms. Finally, the antenna patterns for spiral shaped slots in waveguides manufactured from copper and carbon fibre reinforced polymer (CFRP) were shown to be similar to that predicted.

Tape-helix transmission lines and helical coils have important applications in communication technology, signal measurement, pulse delay, pulse forming and antenna technology. In this paper, a set of fully dispersive propagation theory based on matrix method is firstly introduced to explain the propagation characteristics of travelling electromagnetic waves in multiple stages of helical Blumlein transmission lines with finite lengths. The different stages of helical transmission lines are filled with different propagation dielectrics, and the effects of dispersion and dielectrics on the propagation matrix and S-parameter matrix of the travelling waves are analyzed in detail. Relations of the exciting current waves in the series-connected helical Blumlein transmission lines are studied, and the dispersive transmission coefficients and reflection coefficients of electromagnetic waves at different dielectric ports are also initially analyzed. As an innovation, the proposed fully dispersive propagation theory which was demonstrated by simulation and experiments can substitute the non-propagating tape-helix dispersion theory and the non-dispersive telegraphers' equation to analyze the helical transmission lines.

An analytical method based on combination of Fourier transform and Taylor's series expansion is presented for analyzing interaction of electromagnetic cylindrical waves with inhomogeneous planar media. In the proposed method, constitutive parameters and Fourier transformed electric and magnetic fields of the inhomogeneous layer are expressed using Taylor's series expansion. Then, the unknown coefficients of the fields are obtained based on Maxwell's equations and boundary conditions. The validity of the method is verified by considering some special types of inhomogeneous media and comparing the obtained results by this method with those of other reported methods. The results show that when Fourier transform is combined with Taylor's series expansion, a powerful and quick approach is provided for solving such problems.

In this paper, we propose a new antenna structure that can be adjusted for narrow band as well as UWB applications. The proposed antenna is of very simple geometry and easy to manufacture. It is monopole type antenna and made of copper. We present antennas with the same geometrical concept and different dimensions. Antenna designed for narrow band operation exhibits 3.7% bandwidth at 800 MHz frequency (S₁₁ < -10 dB). Two UWB antenna designs exhibit 77% bandwidth (from 2 to 4.5 GHz) and 54% bandwidth (from 2.6 to 4.5 GHz) and are of smaller size compared to the dielectric resonator antennas (DRA). Furthermore, it can be easily shown that using the proposed geometry broad family of antennas (for operation in various frequency bands) can be designed.

We present numerical time-domain modeling and validation framework for impulse-driven near-field thermoacoustics imaging. It has been recently demonstrated that this new imaging approach comprises a viable alternative for high performance and low-cost imaging using the thermoacoustic phenomenon. Placement of the imaged object in a close vicinity (near field) of an antenna elements along with generation of ultrashort (nanosecond) duration high-voltage excitation impulses further provide high imaging resolution and ensure that sufficient level of electromagnetic energy reaches the object under investigation. In order to analyze the measured results and also provide a design and optimization framework, this work presents a full-wave computational electromagnetic framework which couples the near-field electromagnetic field to the acoustic signal generation. The numerical method comprises a finite integral time domain method (FITD) based on the industry standard CST 2010 software package. The results can be further utilized for normalization and quantification of the generated images.

In this paper, a new technique is proposed to optimize the conflicting parameters like low value of maximum side lobe level (SLL), narrow beam-width of the main beam and low value of maximum sideband radiation level (SRL) of time-modulated linear antenna arrays (TMLAAs). The method is based on minimizing a multi-objective fitness function by using single-objective differential evolution algorithm (DEA) technique. The method is applied to both uniformly excited TMLAA (UE-TMLAA) and non-uniformly excited TMLAA (NUE-TMLAA) to synthesize low side lobe optimum pattern at operating frequency by suppressing the sideband radiation level to a sufficiently low value. For UE-TMLAA only the switch-on time durations of the array elements and for NUE-TMLAA the switch-on time durations and the static amplitudes with predetermined dynamic range ratio (DRR) of static amplitudes are taken as the optimization parameters for the DEA. To show effectiveness of the proposed approach, the single-objective DEA optimized results are compared with those obtained by other single objective and multi-objective techniques that has been reported previously. Also, first null beam width (FNBW) and half power beam width (HPBW) of the DEA optimized patterns at fundamental radiation are compared with those of the Dolph-Chebyshev (D-C) pattern of same SLL.

The practically important case of a dielectric-loaded tape helix enclosed in a coaxial perfectly conducting cylindrical shell is analysed in this paper. The dielectric-loaded tape helix for guided electromagnetic wave propagation considered here has infinitesimal tape thickness and infinite tape- material conductivity. The homogeneous boundary value problem is solved taking into account the exact boundary conditions similar to the case of anisotropically conducting open tape helix model [1,2]. The boundary value problem is solved to yield the dispersion equation which takes the form of the solvability condition for an infinite system of linear homogeneous algebraic equations viz., the determinant of the infinite-order coefficient matrix is zero. For the numerical computation of the approximate dispersion characteristic, all the entries of the symmetrically truncated version of the coefficient matrix are estimated by summing an adequate number of the rapidly converging series for them. The tape-current distribution is estimated from the null-space vector of the truncated coefficient matrix corresponding to a specified root of the dispersion equation.

With the renewed application of millimeter technology in remote sensing, radio astronomy, and meteorological satellite, millimeter wave antennas of electrically large aperture are frequently deployed. Shaping techniques are accordingly developed to meet different requirements. In this paper, a shaping technique for the scanning reflector antenna system of a remote sensing spacecraft is presented. The shaping technique is based on Fourier optical theory to control the maximal radiating direction of the antenna system. To implement such functionality, a new shaping technique of the sub-reflector has been developed. In addition, rotation of the shaped sub-reflector can achieve scanning purpose with identical footprints in all scanning angles. Case studies have been performed to verify the shaping technique.

This paper presents a novel quasi-elliptic function lowpass filter (LPF) by using quasi-lumped elements. The proposed LPF is firstly based on a seven-order Chebyshev response lowpass prototype. Then, a series branches of shunt resonant LC circuit is introduced in the filter design to provide a transmission zero close to the transition band, which can improve the roll-off rate of proposed LPF significantly. To implement the lumped elements of lowpass prototype, the high-impedance meander lines are employed to realized the inductors while inter-digital microstrip lines and the microstrip parallel-plate structures are used to realize the capacitors. To validate the proposed method, a LPF with 3 dB cutoff frequency fc at 1.9 GHz is designed and fabricated. The measured results show that the fabricated LPF has a sharp roll-off rate up to -142 dB/octave and -15 dB harmonic suppression from 1.1f_c to 9.7f_c. Moreover, the fabricated LPF also has a compact size of 0.1λ_gc × 0.11λ_gc. Good agreement can observed between the simulation and measurement.

This paper presents a comparative study on practical evaluation of measurement uncertainty for complex-valued RF and microwave quantities in polar coordinate. The measurement uncertainty is first evaluated in rectangular coordinate to avoid the biased effect, and then transformed into the desired polar coordinate. In this work, uncertainty coordinate transformation from rectangular coordinate to polar coordinate is focused and performed in two ways; the law of propagation of uncertainty and the coordinate rotation. Their performances are compared through practical evaluations and simulations, and found to be highly consistent when the uncertainty region is distant from the origin of a complex plane.

An integrated compact circular-polarized annular ring slot antenna is proposed in this paper. It consists of an annular ring slot radiator and a hybrid patch coupler. The hybrid patch coupler is integrated with the annular ring slot antenna to radiate the circular-polarized wave, while size of the antenna remains the same. Both the impedance bandwidth and axial ratio bandwidth of the proposed design almost cover the entire UHF band of RFID system and it has the features of easy fabrication and low cost. To verify the proposed design, a prototype is fabricated. Measured results agree well with the simulated results.

A compact multiple band-notch ultra-wide band (UWB) band-pass filter (BPF) with surface area of 18 x 12 mm² is introduced in this article. The proposed filter is a combination of novel symmetrically tapered elliptic rings (STER) and contiguous split ring resonators (SRR), with stepped impedance resonator (SIR) structure to realize the multi-band notch UWB pass band characteristics. In the proposed structure, band-notches are generated for interfering microwave bands such as, WiMAX, WLAN and X-band applications. These notches are achieved by optimizing structural parameters of SRR sections. The proposed filter is fabricated on RT/Duroid 5880 substrate with ε_r = 2.2 and thickness of 0.787 mm. The fabricated prototype is measured and a good agreement between simulated and measured results ensures suitability of the proposed filter for UWB applications.

Spacial coaxial resonator plays an important role in spacial system. However, its multipactor effect has not been reported so far. This paper presents a novel type of coaxial resonator structure with low multipactor risk. Compared with conventional coaxial resonator structures, the proposed structure improves the multipactor threshold of filters nearly 3 dB. Experimental results and 3D full-wave analysis show good accordance with the predicted characteristics.

Evaporation duct is a manifest phenomenon that can affect microwave propagation seriously with low elevation angles near the sea surface. As an important parameter to describe the characteristic of the evaporation duct, duct height can be estimated from radar sea echo using a technique called as "refractivity from clutter". In this study, we proposed a novel approach to estimating the evaporation duct height. The signal power received by a ground-based GPS receiver is used when the GPS satellites rise or set at the local horizon over the sea. A forward propagation model and genetic algorithm are adopted to implement this method. The performance is evaluated via numerical simulation for inferring evaporation duct with different height. The results showed that the proposed method is well effective, especially for the conditions with higher evaporation duct height.

This paper presents an analytical formula to evaluate even- and odd-mode characteristics of infinitely parallel coplanar waveguides (CPW) with the same dimensions in each CPW, given name as periodic coplanar waveguides (PCPW). The analysis yields a closed-form expression based on the quasi-TEM assumption and conformal mapping transformation. Calculated results show that both the even- and odd-mode characteristic impedances are in good agreements with the results generated by numerical solvers and available experimental data. The results are important especially for highly demand on miniaturization of circuit design to place multiple CPWs in parallel.

Based on the altitude-dependent model of the ITU-R slant atmospheric turbulence structure constant model, we present scintillation index calculations for a partially coherent Gaussian Schell-model (GSM) beam under all irradiance fluctuation conditions. The longitudinal and radial components of the scintillation index are treated separately. Our results correctly reduce to the result of the horizontal path with atmospheric structure constant fixed; and simplify to a fully coherent Gaussian beam with source coherence parameter ζ representing unit. The numerical conclusions indicate that within specific source and parameter ranges, a partially coherent GSM beam is capable of offering less scintillation in comparison with the full coherent Gaussian beam. Before the maximum value of the scintillation, the scintillation index of the partially coherent GSM beam will decrease with the increased altitude. However the off axis radial scintillation index will vanish when the Rytov variance is infinity.

According to literature, a significant and up to date research direction to increase the performance level of automatic target recognition (ATR) systems is focused on the use of information coming from an appropriate set of EM sensors and high-quality decision fusion techniques, respectively. Consequently, in this paper a genetic optimized version of Sugeno's fuzzy integral is discussed. In addition, using a real database belonging to the high-resolution radar (HRR) imagery, the superiority of the proposed decision fusion technique related to its standard version and other well-known decision fusion methods is also demonstrated.