The key challenges in the design of multi-band filters are realizing highly independent, controlled asymmetric-wide and narrow dual-band response. To address these challenges, this paper proposes the design and development of a dual-band band-pass filter (BPF) with highly independent, controlled wide and narrow band responses. The proposed filter is constructed using only two resonator structures, asymmetric step impedance resonator (A-SIR) and metacell. The wide and narrow band responses are independent and are controlled independently by impedance ratio (R) and the number of cells (N) in metacell structure, respectively. Additionally quasistatic circuit model of the metacell is used to analyze independently controlled narrow passband response. The prototype of the filter is fabricated, and the simulation results are validated through experimental measurements.

A novel circuit structure is proposed to design a small size band-stop filter. The structure consists of five pairs of short coupled-lines. The bandwidth, roll off and center frequency of the filter can be flexibly controlled by changing the data of different pairs of coupled-lines. By disconnecting the left-most pair of coupled-lines, the band-stop filter can be transformed into a full resistance filter. The center frequency of the band-stop filter is 2.40 GHz. The measured 20-dB stopband insertion loss bandwidth is 29.2% (2.05-2.75 GHz, the highest measured rejection is 44.21 dB). The simulation results agree well with the measured ones, which verifies the effectiveness of the proposed structure. The use of coupled-lines makes the structure more compact. The circuit size is 0.35λ_g × 0.27λ_g (25.63 mm × 19.70 mm).

This manuscript introduces an advanced architecture for a reconfigurable band-pass filter, utilizing substrate-integrated waveguide (SIW) technology. To induce a transmission zero in the passband response of the filter, the design involves coupling two identical open-loop ring resonators in a back-to-back configuration on top of the SIW cavity. The work includes a comprehensive investigation of the variation in notch frequency with respect to the ring diameter. Further incorporating PIN diodes into the structure enabled the realization of a reconfigurable filter that can be switched between a broad passband and two narrow passbands with a notch. Also, a planar DC biasing network has been specifically designed to bias the diodes. Additionally, a prototype has been developed to validate the concept and the performance in terms of reflection and transmission coefficients. The miniaturized reconfigurable filter design presented is well suited for the use in both Ku- and K-band applications due to its specific performance characteristics.

The active component nonlinear (NL) effect causes undesirable RF and microwave system electromagnetic interference (EMI) problems which penalizes the communication system performance by signal distortion. Therefore, a relevant NL component measurement method is needed to predict the transceiver system EMI effect. However, the NL measurement characterization of RF and microwave active devices remains a fastidious and time cost task. An innovative NL test bench automatized by LabVIEW® control interface is featured in this research work. The design technique of the NL test methodology is described. The developed automatic test bench is tested with a microwave power amplifier (PA) operating at 2.4 GHz based on double-frequency (DF) method. The experimental test setup including the LabVIEW® test control parametrization and data acquisition is described. The test bench effectiveness was assessed by the third-order intermodulation (IMD3) PA measurement with DF method. The theoretically calculated and measured IMD3 amplitudes based on DF input signal are in very good correlation. Thanks to its advantages in terms of simplicity, flexibility, and time cost, the innovative NL automatic test bench is very useful for transceiver system EMI analyses.

A novel artificial magnetic conductor (AMC) structure as a reflector is presented to enhance the gain of a fractal ultra-wideband (UWB) multi-input multi-output (MIMO) antenna. Unit cell of proposed AMC structure is achieved through 4 iterations to obtain better characteristics as reflector. An in-phase reflection from 2-16 GHz is achieved by the unit cell. The proposed AMC structure 6 × 6 array and 6 × 12 array are examined with single element and 2 element fractal MIMO antennas respectively. The fractal MIMO antenna backed with an AMC structure achieved an operating band from 2.2 to 15.8 GHz, and the isolation between the elements is greater than 23 dB. The proposed AMC is structure is fabricated, and experimental results are analysed in comparison with simulation ones. An average gain improvement of 6.1 dB is observed by the proposed AMC structure in the operating band. Surface current distributions, EM fields, and radiation patterns are investigated at various frequencies. MIMO performance parameters such as diversity gain, total active reflection coefficient, envelope correlation coefficient, and channel capacity loss characteristics are analyzed in this paper. The fractal MIMO antenna backed with an AMC structure exhibits good diversity performance characteristics with improved radiation properties for UWB applications.

As an important part of the primary circuit system of a nuclear power plant, the safe and stable operation of the canned motor of a nuclear main pump is crucial. The existence of stator can and rotor can in the air gap of a canned motor will generate additional eddy current loss during the operation of the motor, which will be detrimental to the long-term stable operation of the motor. Therefore, in this paper, in order to analyze and weaken the eddy current loss generated on the shielding can, using the empirical formula method, the eddy current loss generated by the shielding can before optimization is calculated, and the relationship among the eddy current loss, can thickness, and motor speed is derived. Subsequently, two shielding can structure optimization schemes were proposed, and the reduction of eddy current loss after optimization was calculated using finite element simulation software. The effects of different optimization schemes were compared. Finally, peak torque and current experiments are conducted on the original motor to verify the accuracy of the finite element calculation results. The results show that both optimization schemes proposed in this paper can reduce the eddy current loss, and the axial segmentation scheme has a better reduction effect on the shielding can.

Frequency diverse arrays (FDAs) have drawn great attention because they can provide a time-range-angle-dependent beam pattern that has many promising potential applications in navigation and radar systems. However, due to the limitations of measurement systems, this attractive beam pattern has not been experimentally observed. Here, a far-field measurement system for the time-range-angle beam pattern of FDA is proposed by improving the existing near-field mapping system. Without loss of generality, two types of time-range-angle-dependent beam patterns for FDA systems with different frequency sets are observed using the proposed far-field measurement system. The high efficiency and accuracy of the proposed system is verified by good agreement between the measured and simulated results. This work marks significant progress toward the practical implementation and application of FDAs.

Deep learning network has the advantages of strong learning ability, strong adaptability, and good portability. Therefore, synthetic aperture radar (SAR) automatic target recognition (ATR) based on deep network is widely used in both military and civilian fields. However, due to the imaging conditions, radar angle, imaging distance, and other reasons, it is difficult to obtain efficient and usable SAR image datasets. SAR images' recognition under small sample conditions is still a challenging problem. In this paper, a SAR target recognition method based on multi-view differential feature fusion network is proposed to address this problem. Considering the correspondence between RCS and target features, the network extracts dissimilarities between features from SAR images of different angles of the same target and fuses them with the original features of one angle to form new features, which enriches the available training data. Experimental results on the Moving and Stationary Target Acquisition and Recognition (MSTAR) public dataset show that the proposed method has a higher target recognition rate than other deep network methods, as well as single angle input recognition methods.

This study investigates the preparation and characterization of barium titanate-epoxy resin composites, focusing on main factors influencing the dielectric properties of that composite materials. Using a 2^k fractional factorial design, the effects of heating temperature, stirring speed, stirring time, and hardening process on the permittivity were thoroughly investigated. Sixteen samples were prepared and analyzed using Design-Expert software, with permittivity measurements conducted via the waveguide method and a Vector Network Analyzer (VNA) in the 4-6 GHz range. Results show significant impacts from stirring time and speed, with optimal conditions identified as 50°C heating, 500 rpm stirring speed, three minutes stirring time, and room temperature hardening from two-level factorial analysis (TLFA). These findings provide valuable insights into the best fabrication conditions for barium titanite-epoxy resin composites, contributing to the development of antenna substrate with a permittivity value of 7.0208 and a loss tangent of 0.0238 that is suitable for high-frequency communication applications.

In this paper, the feasibility of using additive manufacturing (AM) technologies for the fabrication of corrugated horn antennas for the E-band (60 to 90 GHz) is investigated. Stereolithography apparatus (SLA) and selective laser melting (SLM) are identified as the most suitable technologies for manufacturing horn antennas in this frequency range. To ensure good manufacturing, slanted corrugations are utilized. The antennas have a gain of 13 dBi at 72 GHz and are designed in CST Microwave Studio. For the fabrication of the plastic parts, SLA and the finer-scaled projection micro stereolithography (PμSL) technology are applied. The metal antennas are printed with direct metal laser sintering (DMLS) from the aluminum alloy AlSi₁₀Mg and the finer scaled micro metal laser sintering (μMLS) from 316L stainless steel. Overall, four antennas are fabricated. The plastic antennas are plated with copper. Dimensional tolerances and surface roughness of the antennas are evaluated. The antennas are investigated considering H- and E-plane beam shapes, input reflection, and realized gain. The measurement is conducted in an anechoic chamber using the Single-Antenna method. The μMLS antenna supplies the best results.

Streamlining the on-demand design of metamaterials, both forward and inverse, is highly demanded for unearthing complex light-matter interaction. Deep learning, as a popular data-driven method, has recently found to largely alleviate the time-consuming and experience-orientated features in widely-used numerical simulations. In this work, we propose a convolution-based deep neural network to implement the inverse design and spectral prediction of a broadband absorber, and deep neural network (DNN) not only achieves highly-accurate results based on small data samples, but also converts the one-dimensional (1D) spectral sequence into a 2D picture by employing the Markov transition field method so as to enhance the variability between spectra. From the perspective of a single spectral sample, spectral samples carry not enough information for neural network due to the constraints of the number of sampling points; from the perspective of multiple spectral samples, the gap between different spectral samples is very small, which can hinder the performance of the reverse design framework. Markov transition field method can enhance the performance of the model from those two aspects. The experimental results show that the final value of the soft required accuracy of the one-dimensional fully connected neural network model and the two-dimensional residual neural network model differ by nearly 1%, the final value of the soft accuracy of the one-dimensional residual neural network model is 97.6%. The final value of the two-dimensional residual neural network model model is 98.5%. The model utilises a data enhancement approach to improve model accuracy and also provides a key reference for designing two-dimensional layered materials (2DLMs) based metamaterials with on-demand properties before they are put into manufacturing.

For the complex marine environment, the water flow disturbance causes the receiver offset, which leads to the decrease of mutual inductance and the decrease of system efficiency. This paper proposes an estimation method of dynamic coupling coefficient without communication, and further realizes the maximum efficiency point tracking (MEPT) on the receiving side. By collecting the effective value of the fundamental current on the receiving side, the equivalent impedance mode equation of mutual inductance is established, and the mutual inductance is identified in real time by numerical solution method. On the basis of the identification results, the impedance matching is realized by the closed-loop controller designed on the receiving side, and the maximum efficiency point tracking of the system is realized. In this paper, the experimental platform is built, and the effectiveness of the method is verified by experiments. The experimental results show that the accuracy of mutual inductance estimation is more than 95%, and the efficiency of the system is improved by 18% after using the maximum efficiency point tracking.

One of the major challenges of today's rotating machine manufacturing industries is finding effective techniques to prevent early mechanical or electrical failure. Efficient troubleshooting methods must be developed for rotating electrical machines, such as three-phase and multiphase electrical induction or synchronous machines. A novel method for fault detection in a Wound Rotor Induction Machine (WRIM) is presented in this paper. Its originality lies in the determination of current rise and fall times in healthy and InterTurn short-Circuit Fault (ITSCF) cases. The method is based on using the two-current (i_sd, i_sq) sigmoid transform (ST) of Park's vector approach. A WRIM with a nominal power of 0.3 kW is used for the analytical and experimental studies. The type of fault detection being studied is short circuit InterTurns on one phase of the stator winding. The results are promising because the methodology used is simple, fast, and accurate for diagnosing this type of fault, and can detect a low number of short-circuit InterTurns in the stator winding.

In this paper, to address the low transmission efficiency problem caused by large magnetic leakage and insufficient anti-deviation performance, an integrated symmetrical coil (ISC) structure is proposed. The ISC structure eliminates the need for an external active shielding coil to counteract the leaked magnetic field, and enhances anti-offset performance by utilizing an integrated coil. Additionally, a deep learning-based method for optimizing the coil structure is employed to determine the optimal parameters. The theoretical simulation is validated using Maxwell software, and based on this, the design and parameters of the ferrite structure are adjusted to improve the magnetic shielding effect and transmission efficiency of the coil. Subsequently, a 2 kW prototype experiment is conducted to validate the findings. Results indicate that when the ISC structure is offset by 200 mm in the X-direction, the research demonstrates that the coupling coefficient fluctuation remains below 5%, achieving a transmission efficiency of up to 96.37%. Furthermore, the magnetic leakage is significantly reduced to below 27 μT at 800 mm on both sides of the door in the X-direction.

Josephson Traveling Wave Parametric Amplifier (JTWPA) has the potential to offer quantum limited noise and a large bandwidth. This amplifier is based on parametric amplification of microwaves traveling through a transmission line with embedded non-linear elements. In this paper, starting from the fabrication of the JTWPA, based on Quantum Electrodynamics (QEDs), operating as a nonclassical quantum source for generating a signal-idler entangled state, its characterization in terms of scattering parameters is presented. The cryogenic and room temperature experimental results are discussed. The good performance of the JTWPA in terms of wide bandwidth and increased transmitted power makes it an ideal candidate for Microwave Quantum Radar (MQR) applications. Finally, the performance of an MQR based on the JTWPA developed at INRiM is reported, showing a radar maximum range equal to 82.2 m, which represents a greater value than previously published works.

Weight-size optimization is the main challenge of high-power antenna design. This paper presents a low-profile, metasurface-based wideband antenna. The proposed antenna comprises an N-type-to-waveguide transition to excite the metasurfaces and handle high-power excitations. A metasurface array of 4×4-unit cells is integrated into the waveguide. The proposed waveguide is 3D printed, and its internal faces are covered by copper tape to maintain a low weight (less than 200 g). The prototype is experimentally tested, and the results confirm the prototype's functionality from 2.1 GHz to 3.6 GHz with a bandwidth of 52.6% and a peak gain of 8.5 dBi. Furthermore, the high-power handling capability of the proposed design has been experimentally confirmed by exciting it with a 7 kV pulsed source. These results demonstrate the applicability of the proposed antenna in satellite communication, radar applications, and wireless communication between Unmanned Aerial Vehicles (UAVs).

In this paper, the deviation generated by actual multiport vector network analyzer (MVNA) hardware specification is derived. Based on the error flowchart of the n-port VNA, the generalized matrix expression of the raw scattering parameters for each error term is solved by introducing the generalized node method. Combined with incremental method, the generalized matrix expression of the final relative scattering parameter measurement deviation is calculated after ignoring the infinitesimals above the second order. Thus, the method of variable controlling is applied to make difference so that the deviation associated with every error term can be obtained. The validness and effectiveness of this method are verified by utilizing Agilent N5230C to measure a 20 dB direction coupler. The data is processed with an algorithm in MATLAB.

A novel bandpass-to-all-stop switchable absorptive filter with an ultra-wideband reflectionless range is proposed in this paper. The bandpass section of the filter consists of a dual-mode resonator and two L-shaped feeding lines. The dual-port reflectionless characteristic is achieved by loading absorption networks at the end of the open stubs of the feeding lines, which are composed of two parallel coupled lines and absorption resistors. The switching of the reflectionless bandpass filter (RBPF) to the all-stop filter (ASF) is realized by controlling the on/off behavior of the PIN diode through the bias voltage. Measurements show that the filter prototype at the center frequency of 2.43 GHz with the 3-dB fractional bandwidth (FBW) is 8.23%. For the RBPF state, the filter has an ultra-wideband reflectionless FBW of 214% and upper stopband rejection better than 33 dB up to 6 GHz. Besides, the rejection is better than 30 dB from 0 to 5.32 GHz in the ASF state.

It is expensive that each consuming power equipment needs to equip a separate wireless power charger. In addition, obtaining constant output power and high transfer efficiency in large coupling variation ranges is challenging. In this study, the two-load transmission characteristics of a WPT system with double transmitting coils are studied. The circuit model of the two-load WPT system is first developed, and the transmission characteristics are studied. The two-load WPT system achieving constant output power and transmission efficiency is then studied. Finally, the two-load WPT experimental system is designed. This system can achieve self-adjusting impedance compensation. Moreover, the constant output power and transmission efficiency are achieved in each receiver, where their fluctuations are less than 5%. Furthermore, the utilization of the charger is improved by more than 8% due to the two receivers. This topology can provide a solution for practical application problems, such as the two-load wireless charger of the vehicle mobile phone.

In this paper, a transmissive linear-to-circular polarization conversion (LCPC) multibeam metasurface is presented, which shows promise for point-to-multipoint transmission in satellite communications under interference conditions. The unit cell consists of four identical metal layers and three dielectric substrates, where each metal layer includes a square ring and a cross-shaped structure. By altering the arm length of the cross-shaped structure, independent control of the phase of x- and y-polarized waves can be achieved. Thus, by keeping the amplitude of the x- and y-polarized waves equal and the phase difference at 90˚, LCPC is realized. Based on the multibeam superposition theorem, the metasurface array is arranged using four discrete elements with a phase gradient of 90˚. It can convert linearly polarized (LP) waves into right-handed circularly polarized (RHCP) waves and generate transmitted multibeam at predetermined angles and gain ratios. Three-beam LCPC metasurfaces with equal and unequal gain in the Ka-band (26 to 40 GHz) were demonstrated to validate the proposed unit cell and methods. The equal gain metasurface has an approximate 11% bandwidth for the 3 dB axial ratio (AR) and a 12% bandwidth for the 3 dB gain. Furthermore, at the center frequency of 30 GHz, the unequal gain metasurface achieves gains of 22.9 dBi, 19.7 dBi, and 17.3 dBi, respectively, with an AR of less than 2 dB for all three beams.