This paper details the work of the LAPLACE Electromagnetism Research Group to develop an original measuring setup dedicated to the detection of an EMDrive like force. Recent peer-reviewed experimental results [1, 2] were obtained using similar setups based on a torsion pendulum combined with an optical sensor. These very accurate measurement setups are appropriate for measuring such an extremely weak force. They also appear costly, which may discourage other research teams from working on this topic. Our main goal is then to provide an alternative configuration, based on a commercial precision balance, in order to build a measuring setup more affordable, handy, and accurate enough to measure an EMDrive like force. Our experimental system is capable of feeding a truncated cone shaped 2.45 GHz resonant cavity with power up to 140 W. To calibrate the EMDrive force and avoid false positive thrusts, an original setup has been proposed and evaluated. It allows us to really consider that the parasitic effects do not alter the hypothetical force measurement by the use of force direction switching during the measurement.

High resolution wide swath (HRWS) imaging and ground moving target indication (GMTI) are similar in terms of system architecture and are based on a multi-channel system in the azimuth direction. However, in order to achieve their respective performance requirements, the HRWS SAR requires a lower pulse repetition frequency (PRF), and the GMTI system requires a relatively higher PRF. In consideration of this contradiction, the parameters of the moving target are introduced into the reconstructed filtering vector constructed by each signal reconstruction algorithm, so that the HRWS imaging of the moving target can be realized. In this paper, considering the characteristics of the Relax algorithm, a motion-adapted signal reconstruction algorithm is proposed, and the iterative process of the new method is described in detail. This method can perform GMTI on moving targets with a lower PRF without changing the PRF of the HRWS SAR system. By the simulation of point target echo, and comparing with the traditional signal reconstruction algorithms, the reliability and effectiveness of the new method are verified.

A single-layer substrate integrated waveguide (SIW) is developed to design a dual-band band-pass filter (BPF) operating below the cut-off frequency of the SIW, known as evanescent-mode excitation. Gap-coupled excitation is used to demonstrate multiple transmission poles (TPs) and transmission zeros (TZs) below the cut-off frequency of the SIW. The structure is reported to realize two independent evanescent-mode poles on a single-layer SIW which reduces the size and complexity of the structure compared to those of the recent multi-layer evanescent-mode structures. Lumped-element equivalent circuit is employed to describe the EM behavior of the structure for TZs and TPs realization. A compact single-layer dual-band SIW filter is fabricated based on the proposed structure. A good agreement is reported between the measured and simulated performances.

Matrix completion (MC) theory has attracted much attention for its capability of recovering a low-rank matrix through its partial entries. In this paper, we investigate the novel suppression methods of wind turbine clutter (WTC) and introduce the application of MC in WTC suppression for weather radar. First, the vectors of weather signals contaminated by WTC are sequentially constructed into a low-rank snapshot matrix satisfying random undersampling, and then, the weather data can be accurately recovered by minimizing the nuclear norm in the inexact augmented Lagrangian multiplier (IALM) method. The proposed algorithm can effectively suppress not only the wind turbine clutter but also the noise, greatly improving the signal-to-noise ratio of the echo. An experimental test validates the effectiveness of the proposed MC algorithm, and its performance is superior to the widely-used multiquadric interpolation algorithm with potential engineering applications.

In this paper, the double-walled carbon nanotube composite material (DWCNTs-composite) and bundle of DWCNT-composite material (CB-DWCNTs) for antenna applications at terahertz frequency range are presented and investigated. The mathematical modeling and analysis of DWCNTs-composite material is presented for the purpose of modelling and simulation approach. The bundle of DWCNTs-composite material is constructed and designed, based on this modeling approach. The DWCNT-composite material consists of double-walled carbon nanotube coated by a thin jacket of another different material. The dependency of the electrical conductivity of B-DWCNTs-composite on the different parameters is presented and investigated. The performance evaluation of B-DWCNTs-composite and CB-DWCNTs materials are presented based on their electromagnetic properties. For this purpose, the dipole antennas of these composite materials are designed and implemented using CST (MWS), where the cross sections of B-DWCNTs-composite and CB-DWCNT materials are circular geometry. Furthermore, comparative studies are performed to show the dependency of size and frequency of the DWCNT-composite material. The results obtained from the DWCNTs-composite and CB-DWCNTs dipole antennas are presented based on S₁₁ parameters, resonant frequency, gain, bandwidth, and efficiency.

In order to reduce the underwater electric field generated by corrosion of ship, a boundary element method (BEM) combined with nonlinear polarization curve was employed to investigate the influence of output current of compensate anode in an electric field protection system on underwater electric field. Moreover, the BEM model was verified by physical scale modeling (PSM). The distribution characteristic of electric field and the variation trend of electric field with compensate current obtained by simulation are consistent with the experimental results. Moreover, the errors of peak-to-peak value of electric field obtained by experiment and simulation are within 20%. Compared with 0 mA compensation current, the peak-to-peak values of X component, Y component, Z component, and modulus are reduced by 52%, 70%, 72%, and 62% respectively when compensation current is 40 mA. The phenomenon of over-compensation will occur if compensation current is greater than 40 mA.

A frequency continuous reconfigurable microstrip patch antenna with operation band covering S-band and C-band is introduced. The antenna consists of a central rectangular patch and four parasitic patches with a symmetrical structure, connected by four varactor diodes in the middle position of the edge of each patch. With help of HFSS microwave studio simulation, results have shown that, by altering the bias voltage on varactor diodes, the operated frequencies vary continuously within a wide range from 3.29 to 4.01 GHz and 5.35 to 7.00 GHz, which cover S-band and C-band. Further measurement, which verifies the simulation by reasonable agreement, has been carried out. Besides, this frequency reconfigurable antenna maintains broadside radiation and stable radiation pattern. Specifically, the gain is basically maintained at around 4.5 dBi with the working frequency increasing from 3.60 to 7.00 GHz. Compared with other frequency-reconfigurable antennas available in previous literature, the proposed antenna has advantages of a wide frequency tuning range, high frequency selectivity, simple and stable structure, low cost, and miniaturization, which make it a promising candidate as cognitive radio and future wireless communication systems.

Refractive index (RI) measurements find extensive use in biochemical sensing field. However, currently available RI sensors exhibit excessive temperature crosstalk and have low sensitivity in the low RI range. To solve this, a high-sensitivity and temperature-insensitive refractometer based on a tapered no-core-hollow-core fiber (TNHF) structure is proposed for low-range RI measurement. The TNHF comprises two Mach-Zehnder interferometers that are introduced within the tapered no-core fiber and hollow-core fiber, thereby establishing a composite interference. The results of an experimental evaluation demonstrate that maximum sensitivities of 482.74 nm/RIU within an RI range of 1.335~1.3462 can be achieved, which is greater than that achieved using a traditional modal interferometer structure. Significantly, the refractometer exhibits ultra-low temperature sensitivities of 0.062 dB/°C and 6.5 pm/°C, which can alleviate the temperature crosstalk. The refractometer can be realistically applied in many fields requiring high precision RI measurement due to its advantages of low cost, ease of manufacture, high sensitivity, and temperature insensitivity.

In this paper we are concerned with a microwave imaging problem for a non-magnetic two-layered background medium, where objects are buried in the lower half-space, and the scattered field is collected in the upper one according to a multi-monostatic configuration. In particular, we are interested in estimating the achievable transverse resolution. As well known, range resolution mainly depends on the working frequency band whereas transverse resolution depends on the geometrical parameters of the configuration and is usually computed in correspondence to the highest (or even the average) adopted frequency. Determining transverse resolution is much more difficult, and closed form estimations have been actually found only for the case of unbounded observation domain. However, in real scattering scenarios measurements have to be necessarily collected under an aspect limited setup. Therefore, in order to fill such a theoretical gap, here the focus is on the estimation of transverse resolution for bounded observation domains. To this end, we consider a single-frequency 2D scalar prototype configuration where the buried scattering object domain is represented by a strip parallel to the half-space interface. More in detail, we succeed in finding an analytical estimation of the transverse resolution which highlights the role of the configuration parameters as well as the dielectric permittivity of the lower half-space.

Partitioning large arrays into subarrays can reduce system cost. In this paper, we use identical subarrays to partition a large rectangular aperture. The periodical structure in a large array is broken down by changing the orientations of the subarrays. In each subarray, the element positions are optimized by particle swarm optimization (PSO) to obtain low sidelobe levels. In order to reduce the coupling among the elements, the minimum element distance measured in Euclidean space is restricted in the procedure of optimization. And a modified PSO is proposed to solve the optimization problem with this constraint. Better results can be obtained than the element distance constraint measured in Chebyshev space. This simple but efficient subarray design method is demonstrated through several numerical simulations.

The presence of the ground affects the propagation on overhead lines through a magnetically induced earth return current. Numerous researches have been conducted to study this influence by considering a homogeneous earth. In the current paper, the transient response of Multi-conductor transmission Lines (MTL) considering a lossy stratified earth is presented. Based on the finite difference time-domain (FDTD) and an improvement of the convolution integral arising from time-domain modeling of frequency-dependent conductors' parameters through the Vector Fitting (VF) algorithm, a novel numerical procedure for solution of a system of telegraph equations is presented. Many simulations are introduced to highlight the effect of soil stratification on the response of the line for a given excitation. The efficiency of an equivalent model, using an equivalent single-conductor, of a multiple conductor system is also established in this work.

This paper considers the class of Iterative Shrinkage Threshold Algorithm (ISTA) to solve the linear inverse problem that occurs in magnetic resonance (MR) image recovery. The ISTA algorithm adheres to the principle of minimizing the L1 norm. This method can be considered as an extension of the classical gradient algorithm. However, it is known that the ISTA algorithm converges slowly, and the accuracy of the algorithm is not sufficient. In many MR image recovery problems, using non-convex log-sum norm minimization can often obtain better results than the l1-norm minimization. In this paper, we firstly transform the MR image recovery into a non-convex optimization problem with log-sum norm regularization and combine it with a faster global convergence method. Then a Log-sum generalized iterated shrinkage threshold algorithm (LISTA) for solving the MR image recovery problem is proposed. Finally, numerical experiments are conducted to show the superiority of our algorithm.

An eccentric harmonic magnetic gear (EHMG) with Halbach array is proposed in this paper. According to the theory of magnetic field modulation and one-side effect, the permanent magnets (PMs) on the inner rotor and outer stator are arranged in a Halbach array. The PMs of inner rotor are divided into three segments per pole, and the PMs on the outer stator are divided into two segments per pole. The proposed EHMG with 15 pole pairs on inner rotor PMs and 16 pole pairs on outer stator PMs is established. The finite element analysis (FEA) is used for simulating the proposed model. The corresponding magnetic field and static torque of the EHMG are calculated. Compared with the conventional EHMG, the results show that the torque density of the proposed EHMG is substantially improved.

Today, worldwide more than five billion of wireless devices are directly communicating for voice and data transmission. The amount of data utilization has increased remarkably and here comes 5G technology with more prominent features, offering high data rate, low latency rate, efficient EM spectrum utilization, an immense machine-2-machine communication, etc. The efficient implementation of 5G technologies requires efficient and compact antennas. This work presents a novel multiband rectangular dielectric resonator antenna for future 5G wireless communication system, having stacked radiator with semi-circular slots etched on the left and right sides of an upper radiator. Additionally, a semi-elliptical slots rectangular microstrip patch antenna of the same dimensions for the purpose of comparison is designed. 28 and 38 GHz, which are the proposed 5G bands by most researchers, are the core target of this work. Alumina with a high relative permittivity of 9.8 is used as a radiator in the design of DRA, while common in the design of both proposed antennas, Rogers RT/DUROID 5880 with a relative permittivity of 2.2 having standard thickness is used as substrate material. Both the proposed antennas have an overall same size of 13 x 11.25 mm². The proposed dielectric antenna resonates at 25.4, 34.6, and 38 GHz with a 7.34, 4.04 and 3.30 GHz of wide impedance bandwidth covering the targeted 5G, 28 and 38 GHz bands, having a good return loss of -34.7, -31.8 and -33.5 dB, respectively. Further, the proposed dielectric antenna has a maximum radiation efficiency of 97.63%, with overall radiation efficiency greater than 90%, and maximum gain of 7.6 dBi is also noted. On the other hand, the proposed microstrip antenna resonates at 28 and 38 GHz with a 1.49 and 1.01 GHz of moderate impedance bandwidth, having -23.6 and -27.1 dB of satisfactory return loss. Further, the proposed patch antenna has a maximum radiation efficiency of 90.33% at 28 GHz, with overall radiation efficiency of greater than 84%, and moderate gain of 5.45 dBi is also noted. Both the proposed antennas have a nearly omnidirectional radiation pattern at resonance frequencies, with VSWR less than 2. Comparative study of the two proposed antennas regarding radiation efficiency, return loss, gain, data rate and impedance bandwidth evidently shows that performance of DRA over MPA at millimeter wave is very good. The proposed antennasare simulated in CST Microwave studio v18.

Degree of the electric field (EF) amplification at the tips of thin and long conductive rods array has been calculated. It is shown that such amplification depends on the rods height (H) and radius (R), as well as on distance between separate rods in the array. For simulation, an approach to numerical calculation of the EF near conductive rods with a large ratio of height to radius: H/R>10²-10⁴ has been proposed. Rods with such parameters may represent carbon nanotubes, channels of breakdowns in insulation, lightning leader channels, lightning rods, etc. The proposed approach is based on the finite integration technique. It uses also the analytical law of decrease of the EF strength and potential of a conductive ellipsoid under potential in the directions perpendicular to the ellipsoid axis and above its tip. As a result, numerical calculations of the EF distribution in systems with such rods were carried out applying calculation grids with steps proportional to the rods length, not their diameters. It permits substantial decrease of the required computational resources such as memory and time.

We introduce a six-switch integrated ultra wideband (UWB) - frequency reconfigurable system for cognitive radio applications. With respect to the requirements of the cognitive radio, this proposed design incorporates a UWB section for sensing the frequency spectrum, and the same design is frequency reconfigured using switches to get narrow bands for communicating within the spectrum. The proposed design has a compact size of 40 mm x 40 mm x 1.6 mm and is printed on an FR4 substrate with relative permittivity 4.4. The first configuration of switches allows the antenna to have UWB characteristics from 3.10 to 12 GHz and beyond as per simulations and 3.13 to 12 GHz and beyond as per measurements. Configurations II to V cover the ultrawide band from 3.54 to 12 GHz through five narrow bands. Measured results match well with the simulated one. The comparative analysis of the antenna in terms of frequency reconfigurability is also included in this work which proves that the proposed design is an effective candidate for Cognitive Radio applications.

Symmetrically excited meandered microstrip line RF coil elements are widely utilized in multichannel approaches which have been proposed to be integrated in ultra-high field MRI system (i.e., 7T and higher). These elements have demonstrated strong magnetic field in the deep areas in the object under imaging. Designing a radio frequency (RF) coil array that employs these elements without decoupling networks might cause non-optimized driving performance of coil array which in turn result in non-clear image. In this paper, two different methods of decoupling have been studied: port decoupling and array elements decoupling. For port decoupling, the coil elements have been designed at Larmor frequency (297.3 MHz) whereas for array elements decoupling, the coil elements have been designed at higher frequencies but matched at Larmor frequency. Port decoupling does not always mean element decoupling. Conventional decoupling methods, such as single capacitor or inductor, face challenges to realize the coil element decoupling for meandered microstrip arrays. An optimized reactive (T-shaped) network is needed in order to achieve element decoupling which in turn prevents distortion of the EM field. All simulation results have been obtained using the CST time domain solver (CST AG, Darmstadt, Germany).

In this paper, a novel meta-surface with polarization conversion characteristic in an ultra-wide band is proposed. Based on the principle of the reflected wave cancelation, the proposed meta-surface is distributed as a checkerboard to obtain an ultra-wideband radar cross section (RCS) reduction, resulting from the out-of-phase difference in normal incidence. The relationship between the polarization conversion ratio (PCR) and RCS reduction is investigated and verified by the simulation. Finally, a sample is fabricated and measured in an anechoic chamber. Compared to the metal board with same size, a 5 dB RCS reduction is achieved ranging from 3.7 GHz to 15.9 GHz, which indicates a fractional bandwidth of 124.5%. Moreover, the size of the unit cell is only 0.125λ₀×0.125λ₀×0.059λ₀, where λ₀ is corresponding to the lowest frequency, namely 3.7 GHz, indicating the merits of miniaturization and low profile. Experiment results are in good agreement with the simulated ones, which demonstrates the validity of the proposed strategy.

A novel compact 4-way power divider is presented here, which consists of 1/64^th mode elliptically curved substrate integrated waveguide (SIW) resonators and radial transmission lines. A direct coaxial fed circular patch acting as the radial transmission line is connected with four elliptically curved 1/64^th mode SIW resonators, and these resonators are then connected to output terminals. An equivalent circuit model is developed to understand its behavior. It is designed to operate at 3.6 GHz covering the frequencies assigned for 5G in sub-6 GHz band. Conventional PCB techniques are used to fabricate the prototype. The measured bandwidth is 2.2 GHz, ranging from 2.5 GHz to 4.7 GHz, for which the return loss is less than -10 dB. Also, the transmission coefficient between input and each output for the above-mentioned frequency band is -6.4±0.5 dB. It has a very compact footprint of 0.32λ_g², which is at least 40% smaller than various SIW based state of the art power dividers.

A compact four-element multiple-input-and-multiple-output (MIMO) antenna system is proposed based on substrate-integrated-waveguide (SIW) cavities. By bisecting a square SIW cavity, two rectangle half-mode cavities with opened edges are formed. They are arranged side by side sharing a row of metallic vias. Then two narrow T-shaped slots are etched along symmetry planes to divide these two cavities into four quarter-mode sub-cavities. Excited by feeding ports, four antenna elements with compact size are constructed, which radiate incident wave through opened cavity edges and etched slots. Moreover, antenna isolation can be easily improved by adjusting slot length though these elements interconnect. A prototype with the cavity size of 0.22λ₀ × 0.86λ₀ has been fabricated. The fabricated MIMO antenna system exhibits the center frequency of 3.51 GHz, port isolation of 14 dB, envelope correlation coefficient of 0.03, peak gain of 4.9 dBi, and high efficiency of 77.4%. The compact size and effective isolation improvement make the proposed design attractive for practical applications.