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.

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.

Nowadays, deep learning schemes (DLSs) have gradually become one of the most important tools for solving inverse scattering problems (ISPs). Among DLSs, the dominant current scheme (DCS), which extracts physical features from the dominant components of the induced currents, has shown its successes by simplifying the learning process in solving ISPs. It has shown excellent performance in terms of efficiency and accuracy, but the increasing number of channels in DCS often requires higher computational costs and memory usage. In this paper, a lightweight deep learning model for DCS is proposed to reduce the burden of memories in the training and testing processes of network structure. And extensive tests of the model are conducted, where comparisons with results from the U-Net structure are provided. The comparison results validate its potential application in utilizing DCS under limited resource conditions.

This paper presents the design and development of 3D printed multi-band frequency selective surface (FSS) for RF shielding applications. The developed FSS significantly rejects the frequency at Wi-Fi, Wi-Max and ISM/WiMax bands. The FSS has been fabricated using a 3D printed ABS substrate and metalized with a copper paint as per design. Its unit cell consists of three independent sub-geometries in which two are mostly like a concentric square loop that encircles the third one, i.e., modified Jerusalem structure. All of these sub-geometries are individually designed for the different rejection bands where their combination is optimized as a unit cell of FSS. The designed unit cell rejects the Wi-Fi, Wi-Max and ISM/WiMax centered at 2.45 GHz, 3.5 GHz and 5.8 GHz with attenuation level more than 35dB. The developed FSS is a prototype of RF shielding structure to be utilized for the fabrication of an interference-free test chamber which isolates the Wi-Fi, Wi-Max and ISM/WiMax interference. The design of FSS is very simple and can be printed in large scale for the development of shielding applications.

A highly-isolated dual-polarized magnetoelectric (ME) dipole antenna is proposed in this letter, where a modified cross-shaped differentially-feeding structure is designed to realize dual-linear polarizations (LPs). To broaden the bandwidth of the differentially-driven ME dipole antenna, a pair of L-shaped branches are loaded on the positions where a triangle is cut out of each patch to introduce a new resonant frequency at the upper frequency region. Meanwhile, a two-stepped structure is added to each of the four ports of the cross-shaped differentially-feeding structure to improve the impedance matching characteristic of the antenna. In this way, the 10 dB bandwidth is improved from 64.9% (1.54-3.02 GHz) to 83.5% (1.52-3.70 GHz), i.e., 28.7% bandwidth enhancement is achieved. A prototype is fabricated and measured. The results show that the proposed antenna can achieve a high differential port-to-port isolation of better than 38 dB, cross-polarization level (CRPL) lower than -25 dB, and peak gain up to 10.5 dBi.

The design of a compact low-loss diplexer based on complementary microstrip spiral resonators is described. The resonant elements are two: one is low-pass (channel A) and the other is passband (channel B). The low-pass element is composed of spirals departing from a circle, whereas the passband element is composed of spirals etched on a circle. The former element is novel and has been extensively analyzed here. These elements are connected using a star nonresonant Y-junction to form a single-layer vialess diplexer. As an example, a diplexer working at 0.87 and 2.0 GHz for satellite communications is manufactured and tested. The measured data show an insertion loss equal to 0.58 dB (0.66 dB) for channel A (B). The return loss exceeds 15 dB for both channels, and the dimensions are 0.129λ × 0.265λ ≈ 0.0343λ².

This paper addresses the issue of sidelobe imbalance due to spurious coupling in quasi-elliptic filters designed in groove gap waveguide (GGW) technology using TE₁₀₂ overmoded cavity based resonator to realize the cross coupling in the cascaded quadruplet topology. The filter is designed at 38 GHz with 750 MHz bandwidth (1.97% fractional bandwidth) to demonstrate its potential as a narrow-band, high-power output filter at mm-wave frequencies in next-generation high throughput satellites. The filter is designed for production yield avoiding any complex structures to realize the negative cross coupling and using an all-capacitive iris structure. Systematic studies have been performed to identify and mitigate the sidelobe imbalance issue, and a final design has been proposed with a very low (<1 dB) sidelobe imbalance. The measured results of the realized hardware closely match simulated ones. The proposed design configuration is an ideal filter option for next generation SATCOM applications as it provides benefits of narrowband symmetrical frequency response with low insertion loss, sharp near band rejection, and high-power handling capability along with the benefits of gap waveguide technology in terms of ease of fabrication, low passive intermodulation (PIM) level, and low sensitivity towards surface imperfections and misalignment issues.

Wireless power transfer (WPT) for electric vehicles (EV) is a promising technology that can help with e-mobility because of its convenience and ability to reduce range anxiety issues. The safety concerns of such systems have received a lot of attention recently. Magnetic coupler is the most important component of WPT systems in terms of thermal safety as its temperature rises because of power outages during the charging process, which could cause damage to the surroundings and other components associated with the system. This article proposes a new thermal and magnetic coupler design by utilizing a Silicon-Cobalt wafer using the Spin Seebeck effect (SSE) phenomenon fabricated through the sputtering technique which can enhance the efficiency of the transmission coil as well as act as a heat exchanger to remove the heat from the coil as well as reduce temperature with the design model.

The current paper describes a compact, long-reading-range tag antenna for radio frequency identification (RFID) applications in the UHF (ultra-high frequency) band, operating at 915 MHz. The antenna's miniaturized design is achieved through the utilization of the meandering line technique. A T-matching structure matches the chip impedance to that of the antenna. Polytetrafluoroethylene, or PTFE, is used as the substrate for fabrication. The UHF tag's physical dimensions are 44.4 × 14.4 × 0.8 mm³. This antenna was first designed, simulated and then optimized by software CST-MWS (Computer Simulation Technology-Microwave Studio) before being fabri-cated. The Measured reflection coefficient at 915.5 MHz is approximately -24 dB, exhibiting a bandwidth of 7,9 MHz (911.5 MHz-919.4 MHz). The proposed tag is shown to have gain of 1.56 dB and radiation efficiency of 90% at the resonant frequency of 915 MHz. Its long-reading-range at 915 MHz is roughly 18.41 m, for an EIRP of 4 W. The measured results closely align with the simulated ones.

This paper details the design and realization of a high-isolation multiple-input-multiple-output (MIMO) antenna tailored for fifth-generation (5G) wireless applications. The antenna consists of a 2-element array, with each unit being a patch antenna loaded with six uniformly sized complementary split-ring resonators (CSRRs). These CSRRs are strategically etched to minimize the antenna's overall size. In addition, the fragment-type split ring resonators (SRRs) are horizontally positioned between the antenna units to further improve isolation. The placement and structure of these fragment-type SRRs are optimized through a combined use of High-Frequency Structure Simulator (HFSS) and genetic algorithm (GA) techniques, which enables significant isolation levels exceeding -40 dB between antenna units. The proposed MIMO antenna operates within the 5G C-band with a -10 dB bandwidth ranging from 4.84 to 5.00 GHz, while the isolation at 4.9 GHz improves from 14.73 dB to 42.88 dB. Moreover, the maximum Envelope Correlation Coefficient is 0.002, and the antenna dimensions are 50 mm × 44 mm × 1.6 mm. Antenna samples are fabricated using wet etching on an FR4 substrate. The measured and simulated values are found to be in good agreement. Compared to the traditional antenna design method, which relies on parameters sweeping, the algorithmic approach used in this paper significantly enhances both the design's effectiveness and efficiency.

Radio frequency energy harvesting (RF-EH), which uses an ultra-wideband (UWB) antenna, is the best substitute for traditional batteries for continuously powering sensor networks. The UWB antenna helps to receive the ambient radio frequency energy that radiates from communication applications for harvesting purposes to power devices or recharge batteries. A novel aspect of this design is the use of dual antenna ports with four ``A" shaped in radiating patches and ground plane, which permits the harvester to completely utilize all accessible frequency bands. The design analysis of a compact dual-port (2 × 1) ultra-wideband multiple-input multiple-output (UWB-MIMO) antenna based on four ``A" shaped and shared ground plane for RF energy harvesting in the band of 2.3-21.7 GHz is presented. The proposed antenna has been implemented on a Rogers RT 5880 substrate with a size of 39 mm × 30 mm, a thickness of 0.8 mm, and a dielectric constant of 2.2. It achieves S₁₁ ≤ -10 dB at (2.3-21.7) GHz and a maximum peak gain of 10.29 dB at 20.53 GHz. The proposed antenna is designed and simulated with ANSYS HFSS and fabricated. The results of simulation and measurement of the proposed antenna are in good agreement, and the antenna achieves bandwidth of 2.3–20 GHz that supports radio frequency energy harvesting in addition to UWB applications across satellite, Wi-Fi, Wi-Max, and mobile applications.

This article presents a miniaturized dual layer angularly stable quadband frequency selective surface (FSS) for shielding applications. The shield consists of four metallic square rings on a thin FR4 substrate of relative permittivity 4.4 and thickness 0.5 mm with two rings on top layer and other two rings in the bottom layer. The dimension of the shielding unit cell is 0.2λ × 0.2λ, for the lowest frequency. These shields have been analyzed in both planar and conformal configurations. The equivalent circuit models as well as analytical model are determined. The shield exhibits quad band band stop characteristics with transmission zeros at 5 GHz (4.3-5.8 GHz), 6.6 GHz (6.3-6.8 GHz), 8.3 GHz (7-8.8 GHz) and 15 GHz (11-17 GHz). These bands find their application in shielding upper WLAN band, sub 6 GHz 5G band C/Ku band for satellite communication. The proposed FSS prototype is fabricated and tested for shield effectiveness in an anechoic chamber. The proposed FSS design offers stable angular response up to 60˚ for planar and geometry. Simulated and measured transmission coefficients are in good agreement and hence well suited for shielding applications. As the structure is fourfold symmetric, it exhibits polarization insensitive and angular stability in all four bands.

In this paper, we present our measurements about 3D printable microwave absorber materials. First, we determined the electromagnetic parameters of the material using different measurement techniques, whose some examples we present. Knowing the material parameters, a geometry for a 3D printable absorber was selected, and simulations were performed to optimise the geometry from X-band (8.2 GHz to 12.4 GHz) to Ka-band (26.5 GHz to 40 GHz). Pieces of absorbers were 3D printed using the optimised dimensions and were mounted to a metallic corner reflector as test subject. The corner reflector camouflaged in this way was then measured in an anechoic chamber, and measurements with and without the 3D printed absorbers are compared. We found good agreement between the measurements and simulations and found the structure and the material we used as usable candidates for the reduction of the radar cross section of an object.

A phase-only and amplitude-phase genetic algorithm (GA) has been investigated to restore the array pattern of a 4 × 2 planar array in the presence of centre-elements phase malfunctioning. A single and double adjacent antenna elements are considered for phase malfunctioning. The new array weights for functioning antenna elements are computed with GA to restore the value of array peak gain and sidelobe level (SLL). The simulation results, which are verified with measurements, indicated that complete recovery of array pattern without SLL constraint in the presence of malfunctioning elements was possible with the phase-only GA weights. It is shown that the uncorrected pattern can also be compensated for main beam scanning with phase-only GA weights. However, pattern compensation with SLL constraint is not possible using the phase-only GA weights. Therefore, amplitude-phase GA weights are estimated to restore the peak gain and the desired SLL simultaneously at the cost of widening the main beam. A prototype of X-band 4 × 2 microstrip patch array controlled through X-band phaser evaluation boards was used in the in-house anechoic chamber measurements facility to validate the full-wave HFSS simulation results.

In this paper, a low profile UHF-RFID reader antenna with high front-to-back ratio is presented. The antenna consists of a probe-fed U-slot rectangular patch antenna loaded with a slotted AMC reflector, formed of 2 × 2 unit cells. By incorporating the AMC reflector, a compact profile height of 0.049λ (λ is the wavelength at 910 MHz) is achieved with high gain and front-to-back ratio. The proposed reader antenna is fabricated and measured. The experimental results are similar to those predicted by electromagnetic simulation and validate the proper operation of the antenna across the entire UHF-RFID band (860-960 MHz). Moreover, the realized prototype exhibits a measured realized gain and a front-to-back ratio (F/B) greater than 5 dBi and 24 dB, respectively. The proposed design offers the advantages of low profile, high gain and F/B ratio, rendering it suitable for compact RFID readers.

In this paper, three kinds of filters are designed, all of which are based on the basic multi-layer structure of microstrip-slot wire-microstrip wide edge coupling. The ultra-wideband filter is realized by three-class connection. The intermediate coupling layer of coplanar waveguide and multimode resonator is designed to realize the double broadband filter. The ultra-wideband filter is realized by using a curved T SIR structure and changing the middle coupling slot structure. The purpose of this paper is to construct a stable and easy to generalize multilayer filter design method, which can achieve broadband and high selectivity, and can realize dual passbands.

In the landscape of wireless communication, smart antennas, or adaptive array antennas, have emerged as vital components, offering heightened gains and spectral efficiency in advanced communication systems such as 5G and beyond. However, augmenting network coverage, capacity, and quality of service remains a pressing concern amid advancing communication technologies and escalating user demands. Array antennas with reduced sidelobe levels, high directivity, and increased beam steering capabilities are sought after to address these challenges. This paper explores convex optimization as a potent tool for array synthesis problems, offering robust performance and solution efficiency. By formulating optimization problems as convex programming, sidelobe reduction challenges can be efficiently addressed. The paper presents a comprehensive investigation into convex optimization-based approaches for array pattern nulling, assessing their performance and computational efficiency in various scenarios. Numerical examples demonstrate the efficacy of the proposed methods in maintaining the main lobe, controlling sidelobe levels, and placing nulls at interfering directions, thereby advancing the state-of-the-art in smart antenna technology.

A new dual-polarized compact crossed-notched dielectric resonator antenna (DRA) array with high-gain and wideband performance is proposed for low-band massive multiple-input multiple-output (MIMO) applications at the 700 MHz band of 5G new radio (5G NR) technology. The DRA element consists of three dielectric layers with relatively high relative permittivity constants (ε_r1 = 15 for the bottom and top layers and ε_r2 = 23 for the middle one) for a compact antenna. Characteristic mode analysis (CMA) of a rectangular DRA reveals that two pairs of degenerate modes, namely M2/M3 and M4/M5, resonating at 0.4 and 0.6 GHz respectively can be used to achieve dual polarizations with a proper feeding strategy. By jointly reshaping the conventional DRA along with adding a notch into the middle dielectric layer the two pairs of degenerate modes are merged to produce a broad bandwidth with a compact size of 0.2λ_max × 0.2λ_max (λ_max being the wavelength at low-frequency point). The measured results show an impedance bandwidth of 13.15% (710 MHz-810 MHz) and an isolation of less than -17 dB. Furthermore, the antenna exhibits a good radiation pattern over the working band with a high gain of 7 dB. Finally, the proposed element is tested in a massive MIMO system of 3×4. The results exhibit a wideband of 17.7% and high isolation of more than 12 dB along with a stable gain of 5 dBi within the operating band.

In this paper, a mode control technology of a slotline resonator is proposed and utilized to guide the design of the slotline resonator. With this method, characteristic modes generated by the slotline resonator are more controllable. With characteristic mode analysis, which is the core of this technology, the desired and unwanted modes of the slotline resonator are easy to be analyzed, controlled, and further used to expand the stopband bandwidth. By applying this technology, a multi-mode slotline resonator with a T-shaped coupling structure (MMSR-T) is proposed by modifying a multi-mode slotline resonator (MMSR), and its unwanted modes out of the passband are more controllable without influencing the expected modes in the passband. Based on the proposed MMSR-T, a balanced bandpass filter (BPF) is proposed, which consists of a U-shaped microstrip/slotline transition as the input/output structure, a T-shaped slotline feeding structure as a feeding terminal, and MMSR-T as the filtering unit. Through the mode analysis and design of MMSR-T, ultra-wide differential-mode (DM) stopband, high common-mode (CM) suppression, and high DM selectivity are obtained in this design. The measured results agree well with the theoretical predictions and simulated results. The effects of mode control technology on stopband extension are proven.