This letter proposes a compact single-layer balanced bandpass filter (BPF), which is realized by a new arrangement of eighth-mode substrate integrated waveguide (EMSIW) cavities. Under differential-mode (DM) operation, the half bisection topology of the proposed EMSIW filter can be equivalent to a quadruplet scheme based on four coupled EMSIW cavities. The negative cross coupling can be easily realized by the nature of the fringe electric fields of opened ends of EMSIW cavities. For the demonstration, a balanced EMSIW filter with the operating frequency at 2.4 GHz is designed, fabricated, and measured.

In this paper, a sensor based on a meta-surface absorber loaded with microfluidics is proposed foridentification of edible oil species and provides a non-destructive, rapid and convenient technology for the measured samples. First, a narrow-band absorber with absorption frequency of 9.887 GHz and Q value of 147, which is implemented with four W-shaped meander line resonators, is designed by Finite Element Method. Its corresponding electromagnetic resonance mechanism is explored to reveal absorption characteristics, build its corresponding equivalent circuit model and guide the design of the palindromic microfluidic channel. The sensor shows a high sensitivity of 500 MHz/ε'_r, and the corresponding sensing performance is experimentally validated by the fact that the distinguishableresonance absorption frequency shift is 461 MHz, 458 MHz, 449 MHz, 444 MHz and 436 MHz when rapeseed oil, corn oil, peanut oil, sesame oil, and olive oil are loaded into the microfluidic channel, respectively. The identificationis successfully achievedaccording to the resonance absorption frequency shift. Moreover, a good agreement between the simulated and measured results demonstrates that the proposed meta-surface-inspired sensor is a promising candidate to monitor and determine the quality of edible oil to some extent, and is relatively valuable to the modern agriculture and food industry.

The problem of ambiguity in defining effective dielectric permittivity is studied theoretically in application to a plane layered heterogeneous medium, compounded by two and more alternating homogeneous layers with different dielectric permittivities (water and glass), for the range of wavelengths from 1 to 10 cm. The effective permittivity for such a heterogeneous medium is usually determined by the phenomenological semi-empirical Braggeman's power rule, and the aim of the given investigation is validation of this rule by means of rigorous model of plane wave transmission and reflection. It is shown that the complex values of effective dielectric permittivity for a layered dielectric, determined by measuring its transmission and reflection coefficients, differ noticeably from one to another. It is also shown that in a wide frequency range, the Braggeman's formula gets as a close approximation only for such an effective dielectric permittivity, which is determined by a transmission coefficient.

Loss and temperature rise are important parameters for performance evaluation of bearingless switched reluctance machine. In this paper, a 12/8 outer-rotor single-winding bearingless switched reluctance motor (SWBSRM) is studied for its loss and temperature rise under high speed operation. Firstly, a 2D finite element model is established by using Ansoft Maxwell, and the magnetic flux density waveform and the variation law of different parts of the core are obtained. Furthermore, various losses including core loss and copper loss are coupled to the temperature field analysis module as a heat source. Thirdly, the thermal model is established by Motor-CAD, and the transient and stable temperature field is simulated and analyzed. Finally, the temperature field distributions of the core and windings are obtained.

In this paper, the Compressive Sampling Matching Pursuit Algorithm (CoSaMP) is applied to microwave reconstruction of a 2-dimensional non-sparse object. First, an adaptive discretization method, DistMesh method, is applied to discretize the image domain based on the region of interest. The dual-mesh method is able to provide denser and smaller discretized cells in more important areas of the object and larger cells in other areas, thereby providing more details in the interest domain and keeping the computational burden at a reasonable level. Another benefit of using the dual-mesh method is that it automatically generates size functions and adapts to the curvature and the feature size of the geometry. In addition, the size of each cell changes gradually. Next, the inverse scattering problem is solved in frame of Distorted Born Iterative Method (DBIM). During each iteration of DBIM, the near field scattering problem is modeled as a set of linear equations. Furthermore, a compressive sensing (CS) method called the Compressive Sampling Matching Pursuit Algorithm is applied to solve the nonlinear inverse problem. During this process, two innovative steps are applied. First, for the reconstruction of the non-sparse object, the signal input to our algorithm is processed via a wavelet transformation to obtain sparsity. Second, as the dual-mesh method discretizes more important cells in smaller sizes, these cells have high potential to be filtered by the threshold of CoSaMP. As a result, a regularization matrix is introduced to reduce the effect of size. Finally, we present numerical experiment results based on our dual-mesh method combined with the regularized CoSaMP algorithm.

In this paper, a simple approach for enhancing the gain of a planar dipole antenna using the concept of grounded metamaterial (MTM) has been proposed. In this regard, a magnetic metamaterial with Mu-very large (MVL) property has been utilised to increase the gain of the electric dipole source. A fully planar structure has been configured due to the placement of the metamaterial just over the ground plane. A significant amount of gain improvement (about 3.7 dB) of the dipole antenna can be attained using the metamaterial. In addition, a fair increase of fractional bandwidth by 2.2% has been obtained due to the loading of the metamaterial. A comparative study with respect to recently reported literature for the gain enhancement of planar dipole has also been discussed. The proposed antenna is a worthy candidate for wireless communication owing to the high gain, low profile, and wide bandwidth characteristics.

Underwater electric field is an important source of exposure for warship targets, so we try to track the ship's movement by measuring its underwater electric field in this paper. Considering the nonlinear distribution characteristics of underwater electric field, the unscented particle filter method is applied for tracking. First, the equivalent electric field model based on point-electrodes methods is studied. Second, the equivalent electric field model of a scaled ship is used as the electric field source, and the source's movement is tracked by measuring the three components of the underwater electric field induced by the source. To meet the requirements of mine applications,only one measuring node is used in the tracking process. Thenumerical simulation result shows that the target can be tracked stably within 200 meters of the measuring node. Finally, a sea trail experiment is carried out to examine the effectiveness of this method. In this experiment, the electric field source is composed by two graphite electrodes, and only the horizontal components of underwater electric field are measured. The results show that the tracking performance is good within 150 m of the measuring node.

As one of the important means in discriminating every mode in a high power microwave (HPM) multimode system, utilizing a mode-selective directional coupler to quantitatively analyze multi-modes and power measurement has been proposed. The first step of this method is to calibrate the coupling coefficients of each coupled mode in the HPM system. Moreover, the conventional calibrating method must make the corresponding single mode exciter or mode generator. In this manuscript, a different calibrating method is presented by measuring the output power from each output port of two back-to-back identical mode-selective couplers, including the backward wave power, then the coupling coefficients of each coupled mode can be calculated by combining and solving equations. In this way, it is not necessary to manufacture the single mode exciter or mode generator for each mode in the HPM system, and also to repeat iteration solution; therefore, this method is more precise, convenient, efficient, and has lower cost than the current other methods.

A CPW-fed compact multiband planar printed monopole antenna for WLAN/WiMAX/X-Band applications is presented in this paper. The structure size of antenna is 0.144λ₀×0.176λ₀×0.008λ₀. The proposed antenna is composed of three monopole radiators, a microstrip feed line and the ground with chamfer. With these structures employed, the antenna can generate four different resonances to cover the desired bands while maintaining low profile. The antenna simulation results show four distinct bands from 2.24 to 2.85 GHz, from 3.29 to 4.12 GHz, from 5.13 to 6.24 GHz, and from 6.58 to 8.57 GHz, which cover the entire WLAN bands (2.4-2.484, 5.15-5.35, and 5.725-5.825 GHz), WiMAX bands (2.5-2.69, 3.4-3.69, and 5.25-5.85 GHz), and X-band satellite communication systems (7.25-7.75 and 7.9-8.4 GHz). For verification of simulation results, a prototype of quad-band antenna is designed, fabricated, and tested. The simulated and measured return losses, radiation patterns, and gains are presented. The proposed antenna possesses compact size, simple structure, high gain, and omnidirectional radiation pattern, which make it a suitable candidate used in small/portable WLAN/WiMAX/X-Band devices.

A direction-of-arrival (DOA) estimation algorithm for non-circular signals with nested array is proposed. A closed formula is given to construct a partitioned fourth-order-cumulant (FOC) matrix by using the FOCs of received data. Then, an improved multiple signal classification (MUSIC) algorithm for non-circular signals (NC-MUSIC) based on FOC is introduced. The proposed algorithm shows higher estimation accuracy and angular resolution than some traditional NC-MUSIC algorithms, especially in the low SNR case. Some simulation experiments are proposed to prove the validity of the proposed algorithm.

This paper introduces an innovative circuit theory of analog voltage compressor (AVC) and decompressor (AVD). This electronic function can also be assumed as an analog voltage converter. Analytically, it acts as power function synthesizer topology designed with an analog nonlinear circuit. The AVC/AVD topologies are based on an operational amplifier associated with resistor and non-linear diode components. Given the positive parameter a>0, the main x-y characteristic of the AVC/AVD is formulated by y=x^a for the input and output x and y, respectively. The synthesis formulas allowing to determine the AVC/AVD parameters in function of a are established. To validate the original AVC/AVD concept, static and dynamic simulations and experimentations with a proof-of-concept circuit using operational amplifier UA741 are carried out. As expected, well correlated x^1/2-AVC and x²-AVD characteristics are realized with the static testing for the voltage range varied from 0 to 9-V and 0 to 3-V for AVC and AVD circuits, respectively. The simulation and experimentation of dynamic test results are in good agreement for the sine wave voltages with frequency varied from DC to 1-kHz. The simulated and experimental results confirm the relevance of the developed compressor/decompressor analog circuit. The AVC/AVD functions for instrumentation system applications can be potentially applied to the amplitude matching especially for digital systems.

Recently we derived generalized sheet transition conditions (GSTCs) for electromagnetic fields at the surface of a metascreen (a metasurface with a ``fishnet'' structure, i.e., a periodic array of arbitrary spaced apertures in a relatively impenetrable surface). The parameters in these GSTCs are interpreted as effective surface susceptibilities and surface porosities, which themselves are related to the geometry of the apertures that constitute the metascreen. In this paper, we use these GSTCs to derive the plane-wave reflection (R) and transmission (T) coefficients of a symmetric metascreen, expressed in terms of these surface parameters. From these equations, we develop a retrieval approach for determining the uniquely defined effective surface susceptibilities and surface porosities that characterize the metascreen from measured or simulated data for the R and T coefficients. We present the retrieved surface parameters for metascreens composed of five different types of apertures (circular holes, square holes, crosses, slots, and a square aperture filled with a high-contrast dielectric). The last example exhibits interesting resonances at frequencies where no resonances exist when the aperture is not filled, which opens up the possibility of designing metasurfaces with unique filtering properties. The retrieved surface parameters are validated by comparing them to other approaches.

The authors propose a new method based on spatial cumulants for estimating the parameters of multiple near-field and far-field sources. The Toeplitz property used in some studies is not applicable to fourth-order statisticsto separate sources components. Therefore, in this paper, a method is proposed to computeoutput cumulants of specified sensors in special arrangements, by which the components of the near-field and the far-field sources are effectively separated using differencing. The angle and range estimations, as well as the classification of the sources, are obtained based on the data from two spatial cumulant matrices. One of them contains the angle information of all sources, and the other only contains the information of the near-field sources. The parameters extraction algorithm is based on the ESPRIT technique; therefore, the proposed method does not require any spectral search. This leads to a significant reduction in computational complexity. Unlike some approaches, the proposed method does not suffer from array aperture loss. Also, the parameters pairing procedure is done automatically. Analysis and simulation results confirm the good performance of the proposed method in terms of computational complexity, estimation accuracy, correct classification of signals, and aperture loss.

Multipacting is electron discharge that occur in components operating in RF high-power electromagnetic fields. In this paper, we will study on a new coaxial structure with ceramic window. A similar structure is utilized in many high power devices for power transfer. Due to the multipactor effect, it will generate huge heat and cause damage to the window, ultimately affect the performance of microwave devices. In order to suppress of the surface multipactor effect and improve the transmitting power, the application of an external DC bias is analyzed and simulated. A Monte Carlo algorithm is used to track the secondary electron trajectories and study the multipactor scenario on the surface of a ceramic window in a coaxial line by using 2-D particles distribution code. Since secondary electron multiplication needs to meet specific resonance conditions, an appropriate DC bias will generate a compensating trajectory and collision, which can suppress the secondary electron avalanche. The optimal value of this external bias voltage that will avoid the multipactor phenomenon in the coaxial line will be calculated by simulation in MATLAB.

In this paper, the reconstruction problem of inaccessible objects buried into a three-part space with locally rough interfaces is solved by Distorted Born Iterative Method (DBIM). DBIM requires the calculation of the background electric field and Green's function in every iteration step via the solution of the direct scattering problem. Here, they are calculated numerically by using the buried object approach (BOA) which is very useful in the solutions of the problems including stratified media with locally rough interfaces. Various numerical applications have been performed to demonstrate the applicability and efficiency of the method. The method was found to be very successful in reconstructing moderate contrast objects when they were buried in the middle space. In this case, the method works effectively even if the buried objects and interface roughnesses have complex geometric structures. Moreover, the multiplicity of buried objects has no negative effect on the reconstruction results. Nevertheless, the results of reconstruction deteriorate when objects are buried in the bottom space. However, the accuracies of them are still on an acceptable level in this situation.

The ideal ultra-wideband (UWB) antenna feed for lens and reflector systems radiates a uniform and customizable beamwidth vs. frequency. Here, a new antenna concept for radiating frequency-independent Gaussian beams with arbitrary bandwidths and beamwidths is reported. It is analytically shown how to resistively load a transmission line network to maintain a Gaussian amplitude taper across an antenna array aperture. In contrast to many other feed antennas, the radiation properties here can be tailored without time-consuming full wave optimizations. The radiated beamwidth, bandwidth, antenna size, radiation efficiency, and gain can all be quickly estimated using the derived closed-form expressions. An example, 16x16 Vivaldi element array is fed with a network of resistively loaded microstrip lines. The simulated array radiates a Gaussian beam with 10 dB full beamwidth of 35°±5° and directivity of 20 dB±1.5 dB over 6.5 GHz-19 GHz (3:1 bandwidth ratio). However, the radiation efficiency is inherently low due to the large loss associated with generating the Gaussian amplitude taper at all frequencies. The example array has a simulated radiation efficiency of 1% at the higher operating frequencies. The array was fabricated and measured. The measured beamwidths agree well with simulation to validate the reported theory. This architecture is a particularly attractive option for feed antennas that require customizable directivities, and can tolerate low radiation efficiencies such as test and measurement.

A band-pass frequency selective surface (FSS) structure using capacitance layers is proposed to improve the performance of angular stability. It consists of band-pass FSSs, supporting dielectrics, and capacitance layers out of band-pass FSS. The supporting dielectrics and capacitance layers work as a transmission line and capacitance impedance matcher. Through the impedance matcher, the bandwidth is stabilized, and insertion loss at passband is reduced from -0.76 dB to -0.39 dB for incident angles up to 60°. The equivalent circuit of the proposed structure is presented, and the Smith chart is given to explain the mechanism of the capacitance layers. Finally, a prototype is manufactured and measured. A relatively good agreement is obtained between simulations and measurements. Therefore, the proposed structure can be an effective solution to improve the angular stability performance of band-pass FSS design.

In this work, a compact planar dual-square ring (DSR) microstrip patch antenna is investigated to acquire dual-band resonance with dual-mode excitation for Wi-Fi/WLAN and 5G-NR based wireless applications. This dual-square ring geometry is employed on single layer dielectric, excited through EM coupling by using a quadrilateral feed patch, which offers massive flexibility in impedance matching for dual-band resonance with minimum coupling effects in common excitation and ground plane. This planar DSR structure shows the resonance at 2.4 GHz and 3.7 GHz frequency bands with bandwidths greater than 100 MHz and 200 MHz, respectively and a maximum gain response of 4.3 dBi with VSWR of <<2. Here the simulation results are verified through experimental results of the fabricated antenna. This proposed antenna design can be configured for Wi-Fi/WLAN application at 2.4 GHz in lower-order resonance mode (TM₀₁) and for 5G-NR application by utilizing the fringing benefits of higher-order mode (TM₁₀) at 3.7 GHz.

The literature lacks detailed information about the electrical properties of the plastic filaments used in 3D printing. This opens the way for research on characterizing the types of materials used in these filaments. In this work, a method for the extraction of the dielectric constant and loss tangent of materials is described. This method, which is suitable for characterizing any dielectric material, is then used to characterize 3D-printed samples based on different filament materials and infill densities over a very wide frequency range [0.02-10 GHz]. The selected materials are Polylactic Acid (PLA), Acrylonitrile Butadiene Styrene (ABS) and a semi-flex filament that combines the two important features of flexibility and endurance. These three types are the most commonly used in 3D printing. The two$-$line technique is applied to extract the complex permittivity of the material under test (MUT) from the propagation constant. This method employs the uncalibrated scattering parameters with different types of transmission line for any characteristic impedance. A rectangular coaxial transmission-line fixture has been used to validate the theoretical work through simulations and measurements involving the 3D filament samples.

This paper presents a novel engineered artificial dielectric superstrate for improving the radiation characteristics of a CPW-fed planar antenna. Even though the permittivity of the material used for the superstrate is only 4.4, it attains an effective permittivity of more than 18 because of the periodic pattern printed on it. Due to the high value of effective permittivity an improvement in radiation pattern, impedance matching and gain of the antenna are obtained. From the measured results an impedance bandwidth of 374 MHz from 2.453 GHz to 2.827 GHz is observed for the antenna loaded with superstrate. The periodic pattern is fabricated on a substrate of thickness 1.6 mm, and it occupies an area of 56.45×42.48 mm².