This paper presents the effect of gimbal geometry parameters on the electromagnetic performance of streamlined radome for airborne applications. The work demonstrates that the gimbal position significantly affects the boresight error performance. The optimization of gimbal position is performed, and the resultant boresight error is limited to 1.5 mrad while keeping the insertion loss below 0.25 dB over the entire antenna scan angle range. The analysis of the antenna-radome system is carried out using the 3D ray tracing method. This work shows that the gimbal geometry parameters provide additional degree of freedom for improving radome performance parameters and can be applied to both the gimbal mounted and electronically scanning antennas enclosed by streamlined radomes.

A simulation tool to characterize the radar cross section of a pedestrian in near field is presented in the paper. The tool has been developed in order to predict and optimize the performance of the short-range radar systems employed in autonomous vehicle operations. It is based on an analytical model which joins the modeling of the human body with the theory of the physical optics. Our studies first focused on the implementation of the electromagnetic code where the human body, the radiation properties of the antenna and the scenario to be analyzed have been analytically expressed. Then, the proposed model has been validated in terms of accuracy comparing simulated and experimental data regarding the radar cross section of a metal sphere and of an adult, in the frequency range 23-28 GHz. In the end, an evaluation of the performance in terms of required computer memory and execution time has been carried out, comparing the proposed simulation tool with other numerical computational methods.

This paper introduces the design and analysis of a compact bandpass with sharp attenuation. The filter topology employs three different cells of a bisected-Π/Π configuration of a negative refractive index metamaterial transmission line. The filter centre frequency is 3.65 GHz, and its 3 dB cutoff frequencies are 2.55 GHz and 4.6 GHz (57% fractional bandwidth). The filter attenuation increases to 20 dB in only 100 MHz (at 4.7 GHz). Moreover, the filter has only 0.2 dB insertion loss within the passband. The filter stopband is characterized with typical flat with 0.2 dB return loss within the stopband (4.7 GHz-5.75 GHz) and very close to 20 dB insertion loss. Moreover, the filter has two frequency independent designed transmission zeros within this stopband. Along with previous specifications, the filter size is only 0.22λ_g × 0.20λ_g (12 × 11 mm²) at centre frequency. The filter performance has been validated through circuit model, electromagnetic simulation, and experimental measurements.

This paper presents a hybrid sliding mode control of a multicell power converter. It takes into account the hybrid aspect of the conversion structure which includes the converter continuous and discrete states The idea is based on using a hybrid control and an observer-type sliding mode to generate residuals from the observation errors of the system by including diferent types of faults in the transition between modes. The case when a DC motor is coupled to the multicell converter is also considered. In this case, it is shown that under certain admissible assumptions, the voltages across the capacitors and the speed of the motor can be acceptably estimated. The simulation results are presented at the end to illustrate the performance of the proposed approach using stateflaw in sumulink (matlab). The developed method is illustrated in an example of the DC motor supply via a three cell converter which is a real example of an SDH characterized by continuous and discrete variables.

This paper introduces a balanced (differential) multiband reconfigurable (tunable) bandstop filter (BSF) using all lumped elements. The main features of the design include its ultra-compact size as well as flexibility to control any frequency band independently in terms of both center frequency and absolute bandwidth (ABW). In the proposed structure, the corresponding non-resonating nodes (NRN) of the symmetrical bisections are connected to N number of LC π-circuits (N-band cell) through capacitors. Again, in each symmetrical bisection, K number of NRNs are series cascaded through LC π-circuits. This results in a Kth order N-band stopband (notch) response in differential mode (DM) operation whereas provides a passband response when excited by a common mode (CM) signal. Reconfiguration of any DM stopband is obtained by using tunable capacitors for the corresponding LC π-circuit in each N-band cell and also, for its coupling capacitors to the NRNs. To validate the proposed topology, a dualband differential tunable BSF is designed and fabricated where both DM stopbands are controlled independently in the range of 1.16 GHz-1.32 GHz. Also, the bandwidth of each band is varied independently by 20-50 MHz without affecting the other band. At any tuning state, DM stopband rejection for each band is found to be ≥19 dB, resulting in a minimum CMRR value of 19 dB. The fabricated prototype occupies an area of 0.13λ_g×0.04λ_g (21 mm×7 mm) where λ_g is the guided wavelength at the center frequency of the entire spectral range, and the experimental results show a good agreement with the simulation results.

A meandered line multi-resonator design is proposed for a chipless Radio Frequency Identification (RFID) tag. The tag is equipped with a set of identical resonant elements and two orthogonally polarized monopole ultrawide band (M-UWB) antennas. The proposed multi-resonator design is realized on an FR-4 substrate (ε_r = 4.4; tanδ = 0.01) in a surface area of 13 x 17 mm², occupying a coding density of 4.52 bits/cm² by encoding 10 bits of data. The bit is encoded using absence/presence coding and frequency shift coding technique. The data can be read and transmitted from the multi-resonator structure through the orthogonally polarized M-UWB antennas operating in the frequency range of 2 GHz to 4.5 GHz. The span of the meandered line multi-resonator design is 13 mm x 17 mm. The tag is designed using ADS software and tested using vector network analyzer (VNA).

This paper presents a numerical study on the application of radar and communication (RadCom) sensor nodes operating in the frequency band from 57-64 GHz. The sensor nodes are embedded in the laminate of wind turbine blades, enable a quality inspection directly after rotor blade manufacturing as well as a structural health monitoring (SHM) throughout the service life of the blade. Given by a lack of dielectric properties for typical rotor blade materials, we have performed experimental studies on material characterization including glass fibre composites, balsa wood, infusion glue, etc. This material database serves as input for wave propagation simulations in a full scale 3D rotor blade model. The analysis also includes a parametric study on path losses as well as an optimal sensor placement strategy.

Magnetic nanoparticle (MNP) based thermal therapies have shown importance in clinical applications. However, it lacks a compromise between its robustness and limitations. We developed theoretical strategies to enhance the heating efficiency, which could be utilized in thermal therapies and calculated parameter dependence for superparamagnetic MNPs (approximative ellipsoid-shaped) within a sphere-shaped ball. Then we calculated specific loss power (SLP) for magnetic particles in a magnetic ball. The dependency of features of the nanoparticles (such as mean particle size, a number of particles, frequency and the amplitude of the exposed field, relaxation time, and volume gap between particles and a sphere-shaped ball) on the SLP or the heating effect in superparamagnetic MNPs was analyzed. In this study, optimal parameter values were calculated using Kneedle Algorithm as the optimization technique to represent the accurate heating efficiency. The influence of a number of particles in a sphere-shaped ball shows that SLP of magnetic particles increases with the increasing number of particles (N); however, after N = 10 particles, the SLP increment is insignificant. The most remarkable result arising from this analysis is that when particles are more closer together (less volume gap of a sphere-shaped ball), high SLP is found for the same number of particles. This model also predicts that the frequency dependency on the SLP is negligible when the frequency is higher than 10 kHz depending on the size of a sphere-shaped ball and nanoparticle parameters. This analysis has shown that the SLP of MNPs in a sphere-shaped ball strongly depends on magnetic parameters and properties of the particles. In brief, we have demonstrated, for the first time, impact on SLP of the accumulation of ellipsoid-shaped superparamagnetic nanoparticles into a sphere-shaped ball. This finding has essential suggestions for developing links between heating properties with loose aggregate and dense aggregate scenarios in the superparamagnetic condition.

A fast direct solution of the electric current volume integral equation (JVIE) with the Sherman-Morrison-Woodbury (SMW) formula-based algorithm is presented to analyze electromagnetic scattering from inhomogeneous dielectric objects. The JVIE is discretized with the nonconformal face-based Schaubert-Wilton-Glisson (SWG) basis functions. Compared with conformal discretization that is advantageous to discrete homogeneous regions, the nonconformal discretization provides a more flexible and efficient scheme to separately handle the inhomogeneous subdomains depending on local parameters. Moreover, to take full use of both discretization methods, the mixture discretization is adopted. With the increase of object size, the impedance matrix equation arising from the JVIE becomes too large to solve and store for direct solution. In this paper, the SMW formula-based algorithm is adopted, leading to remarkable reduction on the computational complexity and memory requirement in contrast with conventional direct solution. This algorithm compresses the impedance matrix into a product of block diagonal submatrices, which can be inversed rapidly in direct way. Numerical results are given to demonstrate the efficiency and accuracy of the proposed method.

Passband flatness and band-edge selectivity in microwave filters with finite quality-factor resonators can be improved by the synthesis of lossy filters. This paper demonstrates the extension of this technique to a lossy diplexer by means of resistive coupling. A dual-mode stub-loaded resonator (SLR) junction and a fork-like feedline are used in the diplexer to address the challenge of independently controlling the external coupling from the common port to the two channel filters and therefore enable flexible realization of the channel bandwidth. The coupling matrices with resistive couplings for the lossy diplexer are generated. For verification, a microstrip lossy diplexer operating at 1.91 and 2.6 GHz was designed and tested. The flatness of the passband has been significantly improved, with a reduction of the passband insertion loss variation from 1.4/1.2 dB to 0.66/0.63 dB for the low/high band. The measured results are in good agreement with the simulations as well as the theoretical responses from the coupling matrix. This was also experimentally compared with a reference diplexer without resistive couplings.

Proximity Detection Systems (PDSs) are used in the mining industry for protecting mine workers from striking, pinning, and crushing injuries when they work in close proximity to heavy machines such as continuous mining machines (CMMs). Currently all PDSs approved by the Mine Safety and Health Administration (MSHA) are magnetic field based systems which can be influenced by the presence of steel wire mesh that is commonly used for supporting roof and ribs in underground coal mines. In this paper, researchers at the National Institute for Occupational Safety and Health (NIOSH) characterized the influence of the mesh on the performance of magnetic PDSs by measuring the magnetic field difference around a CMM caused by the presence of the mesh. The results show that the magnetic fields are generally enhanced by the mesh which causes PDS detection zones to be increased correspondingly. It was discovered that the fields around the joints of two mesh sections have the greatest enhancement and thus deserve more attention. In addition, it was found that the presence of mesh can also cause a variation in the generator current. The experimental results show that the generator current variation and thus the magnetic field change caused by the mesh can be significant (on the order of ten) when the mesh is extremely close to the generator (e.g, less than 1 cm) and is negligible when mesh is relatively far (greater than 0.15 m). The findings in this paper can be used to develop guidelines and best practices to mitigate the influence of mesh on PDSs.

This paper describes the measurement of a driver's instantaneous heart rate corresponding to R-R interval in electrocardiogram and heart-rate variability (HRV) using 24 GHz radar reflectometers. Elimination of the spurious component due to random movement of a driver has been the most difficult problem for microwave measurement. Auto-gain control of the receiver, template matching and cross-correlation technique among multiple reflectometers enable motion artifact elimination, signal peak detection, and data processing for various parameters. The measurement of vital signals is considered useful for predicting the change in a driver's state, such as a heart attack as well as detecting drowsy driving, drunk driving, and fatigue.

In this paper, a quadruple-band metamaterial polarization-insensitive absorber with low profile is proposed. The proposed unit cell is composed of three conformal modified rings with square patches at corners. 10*10 periodic unit cells constitute the proposed metamaterial absorber. The absorber offers low profile, and overall dimensions are 100 mm*100 mm. The surface current distribution and equivalent circuit model are presented to explain the mechanism. The proposed structure is fabricated, and experiments are carried out to validate the design principle. The simulated and measured results show that the proposed structure exhibites four absorption peaks of 98.87%, 95.11%, 93.97%, and 99.99% under normal incidence at 8.16-8.29 GHz, 10.275-10.38 GHz, 14.255-14.38 GHz, and 15.465-15.7 GHz which cover X- and Ku-bands, respectively. The designed structure is exactly symmetrical which makes it insensitive to polarization angle variations. Furthermore, the four operating bands of the absorber can be adjusted independently which makes the design suitable for absorbing electromagnetic energy and reducing the radar cross-section (RCS) of target.

Frequency diverse array (FDA) has gained remarkable attention in both radar and communication applications over the years due to its unique range-dependent beamforming. On the other hand, extremely less attention is paid to the exploitation of FDA in electronic countermeasures (ECM). Hence, this paper proposes a symmetric frequency diverse array via Chebyshev window function in ECM applications. Specifically, we utilize Chebyshev window function to design the coefficient of both transmit weights and frequency diverse increments to uncouple range-angle response of the true target to counteract deceptive ECM signals. In addition, we consider real constraint scenario, i.e., the propagation of the electromagnetic signal arriving at the true target position, which has been usually neglected in the FDA literature. The attribute of the proposed scheme is that it is able to discriminate between true target location and false target(s) location. This implies that the generated false target(s) by the jammer can be significantly suppressed in either angular or range profiles mismatch. Further, we adopt Swerling 1 model to devise generalized Neyman-Pearson design rule to evaluate the probability of detection of the proposed scheme. Numerical results illustrate the achievements of the proposed scheme.

Propagation mechanisms for short range, low altitude conditions are reviewed for their use in communications of unmanned aerial vehicles (UAVs). This study is based on measurements conducted in an obstacle-free area. The testbed is made up of a testing UAV (in particular a drone) and a set of four ground station terminals (GSTs) located in a football field; the antenna heights of radios (onboard the drone and GSTs) are equal to 1.4 m and the maximum distance between them is 50 m. Under these conditions, a plane earth geometry is well suited, and therefore the two-ray propagation model is considered. Measurement results for a radial configuration of the drone with respect to a ground station follow the trend of this model, but with a shift, which is attributed to the scattering from the grass. Then, an adjusted two-ray model is proposed for which experiments report good results. For another configuration where the drone has different positions in a square area of 30 × 30 m and there are four ground stations in the corners of the square, the general trend of the power decay of measurement results follows this model, but in some positions a difference around it is found even for locations at the same distance drone-GTSs. This behavior is attributed to the interaction of the print circuit board to the radiation characteristics of the antenna used in the radios. Thus, this effect is also analyzed by simulations, whose results show a deformation of the antenna radiation pattern, concentrating the energy in a certain direction and reducing it in another.

This paper specifies optimization of a low active reflection coefficient (ARC) array element with a cavity-backed microstrip patch (CBMP) using a genetic algorithm (GA) at wide-band and 2-dimensional (2D) wide angle. Both the GA implemented with a user-defined MATLAB code and a 3-dimensional (3D) full-wave electromagnetic simulator CST MWS are simulated with a real-time direct link. An optimization method using not a traditional unit cell ora small array but a 15 × 15 finite array structure is proposed to apply to a large-scale array antenna. The CBMP array antenna to meet a design goal of a max ARC is optimally designed at equally divided 9 frequencies and 11374 beam angles for S-band 400 MHz operating frequency bandwidth and beam scan coverage (Az = -60° ~ +60°, El = -3° ~ +90°). Measurement results show that a prototype and a full-scale array antenna have low ARC below -8.1 dB and -6.9 dB respectively for required wide frequency bandwidth and beam scan coverage. It is confirmed that the proposed method is a good solution for optimizing a large-scale array antenna.

A new family of substrate integrated waveguide metamaterial bandpass filters is proposed which support the backward and forward wave propagations with two adjacent passbands under the cutoff frequency of the structure. Through varying the fractal slots sizes etched overthe SIW structures, different frequency transmission responses were realized. Extraction of the metamaterial parameters was achieved via scattering parameters. The equivalent circuit model was analyzed to provide comprehensionon the SIW-metamaterial unit cells. The equivalent electrical length of a fractal slot is larger than the conventional slot, making it suitable to design highly miniaturized filters. Three filters using the 3rd iteration H-shaped SIW-metamaterial unit cells were designed and testedusing subwavelength resonators. Filter designwas used to extract the coupling coefficient and external quality factor to obtain the filters' optimized physical dimensions. The out-of-band rejection can be enhanced by configuring the fractal slots or the SIW. A wide upper out-of-band rejection with attenuation >50 dB with the range 5.5 GHz to 9 GHz was realized. The proposed filters offer advantages through low insertion loss, easy fabrication, high selectivity, small size, and low cost. The measured scattering parameters S₂₁ and S₁₁ were in agreement with the simulated.

The paper presents a method of extracting noise source impedance of electrical equipment under working condition. Firstly, based on the theory of two-port network, the measurement method of noise impedance is analyzed theoretically, and the injection probe and receiving probe are calibrated by two known resistors. No special calibration fixture is needed to calibrate the injection probe and receiving probe. Secondly, the port structure of the noise impedance measurement method is analyzed, and the noise source impedance is calculated by using the theory of microwave transmission. Compared with the traditional method, this method does not require calibration fixture and simplifies the experimental process. Finally, passive devices and active systems are tested respectively, and the experimental results show that the method is effective and feasible.

Metasheets are ultra-thin sheets built from sub-wavelength resonators designed to achieve certain frequency-dependent transmission behavior. A semianalytical approach based on an equivalent circuit representation is proposed to calculate the microwave transmission through metasheets consisting of two-dimensional periodic arrays of planar circular metal rings on a dielectric substrate. In the semianalytical approach, the impedances of the equivalent circuit are parameterized and fitted to match the values of transmission coefficients obtained by full-wave simulations at selected frequency points. As dimensional parameters, the outer radius and the width of the ring are considered. A metalens with four concentric zones is designed by using this semianalytical approach to correct the phase distortions due to a polypropylene hemispheric radome at frequencies around 28 GHz in the Ka band. It is shown that the designed metalens works well for 27 GHz, 28 GHz, 29 GHz and 29.5 GHz, implying the bandwidth of approximately 2.5 GHz. The field transmitted through the metalens and the radome is calculated by Physical Optics (PO). The electrically large integration area is divided into small square facets to calculate the PO integral. The calculated and measured results are shown to agree well.

The combination of low peak sidelobe level (PSLL) with wide sector nulling digital beamforming (DBF) is achieved for large planar array antennas. This combination is carried out using the iterative Fourier transform (IFT) method. The method is based on the iterative Fourier technique to derive element excitations from the prescribed array factor using successive forward and backward Fourier transforms. A 1024-element rectangular uniformly spaced array is used as an example to demonstrate the performance of the proposed method. Numerical examples show that the proposed method achieves very low PSLL with very wide nulling sectors up to the half plane of the far-field pattern. Moreover, numerical results show that the proposed method is effectively functional even when the mainbeam is steered to directions other than the broadside.