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.

This paper introduces a novel compact microstrip-fed ultra-wideband (UWB) antenna, characterized by its unique square patch design and integrated parasitic circular patch for frequency band rejection. The antenna, fabricated on an FR4 substrate, exhibits dimensions of 0.17λ_g × 0.17λ_g, optimizing space without compromising performance. A significant innovation of this design is the incorporation of a parasitic circular patch with a meticulously optimized radius of 0.02 × λ_g mm, achieving a remarkable return loss of -43 dB at 3.55 GHz, while frequencies ranging from 5.43 to 7.1 GHz exhibit significant notching. This feature effectively eliminates unwanted frequency bands, enhancing the antenna's application in UWB systems. Comprehensive analysis demonstrates that the antenna maintains an omnidirectional radiation pattern and achieves a desirable gain, making it highly compatible with a variety of UWB-enabled devices. The integration of the parasitic circular patch within the compact design not only improves the antenna's spectral purity but also contributes to its practical applicability in modern wireless communication systems. The findings underscore the potential of this antenna design in advancing UWB technology applications, offering a balance among compactness, efficiency, and performance.

This paper presents a novel reconfigurable multi-band antenna with a partially dredged cloverleaf shape that is tailored for size reduction and suitable for compact devices and urban environments. The antenna is capable of covering three distinct frequency bands: 3.22-4.06 GHz, 4.44-6.12 GHz, and 3.8-4.77 GHz, with respective bandwidths of 22%, 31.8%, and 22.6%, demonstrating its wideband capabilities. Utilizing various feeding configurations, the antenna enables the realization of multiple radiation patterns and frequency tuning. Validated through simulations and measurements, this design shows promise for 5G and advanced communication systems.

As a popular nondestructive technique, ground penetrating radar (GPR) is extensively utilized for detecting underground pipelines. In this paper, an efficient and automatic scheme is presented for the detection and classification of underground pipelines by combining electromagnetic modeling and machine learning techniques. By virtue of open-source gprMax software, the B-Scan signatures of underground pipelines are simulated and analyzed in detail, with four types of underground pipelines taken into account, i.e., iron pipelines, concrete pipelines, copper pipelines, and PVC pipelines. On the basis of electromagnetic modeling, B-scan profiles of underground pipelines are preprocessed by using the average method and time gain compensation method to obtain a dataset for training neural network of YOLOv8 model. The simulations indicate that our scheme combining simulated B-Scan profiles and YOLOv8 model is able to detect and classify underground pipelines with high accuracy, and the category and material of underground pipelines can be determined with a high confidence level. Specifically, the detection time of a single B-scan image for underground pipelines is about 0.02s, and the average detection accuracy can reach 0.995, which is potentially valuable for the automatic detection and classification of underground pipelines in GPR applications.

In this paper, a meandered slot line (MSL) is proposed to miniaturize a substrate-integrated waveguide (SIW) band-pass filter (BPF) and independently realize a dual-band response. The suggested MSL is symmetrically etched on the upper layer of the SIW resonator; hence, maximum space utilization is realized to increase the miniaturization factor. The TE₁₀₁ and TE₁₀₂ modes were excited and controlled independently through the size and shape of the MLS to highly perturbate the electric field distribution inside the SIW cavity. A systematic procedure was employed to design the proposed dual-band SIW-BPF at the desired specifications. Ansys EDT (2022 R1) full wave simulator was used to analyze and optimize the proposed second-order dual-band BPF. The suggested filter was fabricated using printed circuit board technology on Rogers RO4003 with a dielectric constant (ε_r = 3.55). The proposed MSL-SIW structure achieved an overall miniaturization of 68.3% at the lower band compared to the conventional SIW filter, where the resonance frequency of the TE₁₀₁ shifted from 16.43 GHz to 4.61 GHz. The overall area of the proposed filter is 0.08λ_g² at 4.61 GHz with a physical length of 14 mm and width of 7 mm. The operating dual bands are centered at 4.61 GHz for the first band and 6.91 GHz for the second band, with fractional bandwidths of 7.6% and 3.6%, respectively. Measurement results, which highly match the simulation findings, achieved a return loss (RL) of 25 dB and 18 dB and an insertion loss (IL) of 0.95 dB and 1.5 dB for the first and second bands, respectively. Accordingly, a simple, low IL, and compact SIW-based BPF was realized, making it an excellent candidate for 5G and beyond applications.

A Negative Group Delay (NGD) prototype filter design, based on the ratio of two Chebyshev filter transfer functions, is presented. The two transfer functions are of the same order, but with different in-band ripple amplitudes and different 3 dB-bandwidths. The overall transfer function exhibits both an in-band ripple and an out-of-band steep-slope magnitude transition characteristic of a Chebyshev filter, while also exhibiting an in-band NGD. For high-order designs and in the upper asymptotic limit, the NGD-bandwidth product of the filter is shown to be a linear function of out-of-band gain in decibels. A resonator-based methodology is used to show how frequency upshifted filter designs can be implemented in a Sallen-Key topology or in an all-passive ladder topology. An in-band combined magnitude/phase distortion metric is evaluated for examples of the NGD filter. It is shown that the distortion metric is proportional to the design order, the in-band ripple amplitude, and the out-of-band gain. For a prescribed distortion metric value, it is demonstrated that the proposed design can achieve a higher NGD-bandwidth product than an equivalent Butterworth design, which has a flat in-band magnitude characteristic. Additionally, input waveforms with bandwidths extending to the entire frequency range where the group delay is negative (typically larger than the 3dB-bandwidth) should not be applied to this filter design as it results in strong levels of distortion.

A highly miniaturized bandpass filter with quad-band response is demonstrated in this article. The proposed quad-band bandpass filter has a novel topology comprising series quarter wavelength transmission lines loaded with tri stepped impedance open-ended resonators and a dual stepped impedance short-ended resonator. The proposed quad-band bandpass filter configuration is validated by theoretically verifying the transmission zeros and poles frequencies using even-odd mode analysis. A prototype operating at 0.47 GHz, 1.68 GHz, 3.47 GHz, and 4.51 GHz is designed, implemented, and experimented. The tested insertion losses at these center frequencies are 0.38 dB, 0.71 dB, 1.03 dB, and 1.22 dB, and the return loss is better than 10 dB in each passband. Each passband is isolated by a transmission zero with a rejection better than 40 dB. The proposed quad-band filter occupies a compact size of 0.146 × 0.087λ_g2 and is distinguished by its high compactness, wide bandwidth, multiple transmission zeros and poles, and high performance compared to benchmark designs making it more suitable for multi-band wireless applications.