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.

In this paper, a wideband wide-beam circularly polarized (CP) antenna excited by sequential rotation feeding technology is proposed. The antenna is primarily constituted of a loop radiating element and a reactive impedance structure (RIS) cavity. The loop radiator is stimulated by a curved feeding line through six slots etched on the ground, thereby enabling the antenna to achieve broadband performance. In order to achieve a wide 3-dB axial-ratio beamwidth (ARBW), as well as exhibit less effect on the half-power beamwidth (HPBW), a RIS cavity is introduced beneath the loop radiator. To validate the proposed structure, a prototype was constructed and subjected to a series of tests. The results indicate that the bandwidth of the antenna is 187.5% (0.11~3.41 GHz) under a 10-dB return loss. In the frequency band spanning from 1.07 GHz to 2.1 GHz, the AR is less than 3 dB, yielding a bandwidth of 64.98%. Furthermore, at the frequencies of 1.2 GHz, 1.5 GHz, and 1.8 GHz, the proposed antenna demonstrates wide beam characteristics, with the HPBW exceeding 90°, and the 3-dB ARBW within 162°- 224°. In addition, since no extra feeding network is utilized, the antenna is compact in size.

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.

Ocean wave energy is an inexhaustible clean new energy resource, and wave direct-drive linear generator is an energy converter receiving wide attention, but it suffers from the deficiencies of difficult energy harvesting, slow movement speed, large size, and small power generation, etc., so there is an urgent requirement to develop high-efficiency small-scale energy conversion devices. In this paper, a pneumatic drive linear generator (PDLG) is provided as a high efficient compact wave energy converter (WEC). The structure design and automatic reciprocating control system for the PDLG are implemented. The field distribution characteristics and parameters effects are analyzed using the finite-element method based on scalar magnetic potential. Finally, a prototype was fabricated to verify the performance of the PDLG. The experimental results are in good agreement with that of the theoretical prediction. The results of the study show that the provided pneumatic drive linear generator can meet the requirements of high efficient wave energy harvesting, compact structure, and larger power generation.

In the paper, a wideband four-way filtering power divider with arbitrary power division ratio and input absorptive feature is proposed. Two sets of coupled lines (CLs) are used to achieve the wideband performance. To obtain absorptive properties, a set of T-type absorption structure consisting of two isolation resistors and a λ/4 short-circuit stub is connected between the two CLs. Meanwhile, high frequency selectivity and good out-of-band rejection are realized by introducing two stepped-impedance resonators. Besides, output impedance matching, isolation and unequal power distribution are achieved by the power division section in the second stage. In the analysis, the equations are derived by using the method of even-odd mode decomposition and voltage-current method. For demonstration, a prototype is designed, fabricated, and measured with the power distribution ratio of 2:1:1:2. Measurements show that an all-frequency band absorption of 200% is obtained with the 3-dB passband bandwidth of 78.1% and the out-of-band rejection of 14 dB. Besides, it also shows 15-dB isolations within more than 60% FBW, and has the feature of small size.

An effective empirical method of EMI analysis for transceiver (Tx-Rx) system implemented with nonlinear (NL) microwave power amplifier (MPA) dedicated to wireless communication is developed. The nonlinearity is experimentally quantified by the MPA gain, P1dB and third order intermodulation component via spectral response around 2.4 GHz 802.11b IEEE frequency band. The proof-of-concept represents the Tx-Rx system environment for wireless communication. The considered test signal emulates synchronization and physical broadcast different channels of downlink communication signals under QPSK modulation. The error vector magnitude (EVM) and signal-to-noise-ratio (SNR) due to the microwave Tx-Rx transmission undesirable EMI effect are assessed. Without MPA, the EVM and SNR of various channels fluctuate within a small range. Because of MPA nonlinearity, EMI becomes awfully significant due to the intermodulation generating SNR 20-dB decrease.

This paper presents a compact, highly isolated tri-band MIMO antenna for 5G and X-band communication applications. The overall dimensions of the antenna are 43 mm × 30 mm × 1.6 mm. It consists of two monopole radiating units and a metal base with branches and slit slots. The antenna achieves tri-band characteristics by improving the shape of the radiating patch. The isolation of the antenna is enhanced by slotting the floor and loading I- and T-shaped branches to absorb coupling currents. S₁₂ > 15 dB is achieved in the frequency ranges of 3.3 GHz-4.06 GHz, 4.62 GHz-5.28 GHz, and 8.14 GHz-9.28 GHz. Measurement results show that the measured S-parameters do not change significantly compared with the simulation. It also has a low envelope correlation coefficient and good radiation performance.

This paper proposes an antenna based on a rectangular waveguide to generate dual higher-order orbital angular momentum (OAM) beams. The OAM beams with modes l = -6 and l = -7 are produced by radiating the higher order TE_mn transmitted in the rectangular waveguide through a slot. The measurement results indicate that the impedance bandwidth of less than -10 dB is approximately 37.8% in the range of 15-22 GHz, and the mode purity of the antenna is above 55%. The proposed antenna feed structure is simple and does not require a complex phase-shifting network to generate multi-mode and higher-order OAM beams. Such an OAM-based antenna with dual higher-order OAM beams can be utilized in MIMO-OAM communication systems, radar imaging systems, and rotational speed measurement systems.

This paper presents the first microwave subsystem (MS) capable of changing its function, in this case between resonator and antenna, using liquid metal (LM). This is achieved by filling/emptying fluidic channels with Gallium-based LM and forming LM into different 2D shapes. The manufactured prototype of the proposed MS performs as a slot antenna, when the fluidic channels are empty of LM. On the other hand, it operates in resonator mode, when the fluidic channels are filled with LM. We also connected two MSs along with a microstrip resonator to realize functional change between complex functions i.e., antenna and filter. The proposed connection of MSs can act as a filter when the fluidic channels are filled with LM or as an antenna when LM is withdrawn from the fluidic channels. When operating in the antenna mode the proposed connection of MSs provides a measured peak realized gain of 7.23 dBi and a simulated total efficiency of 84%. When operating in the filter mode the connection of MSs provides a band pass response and exhibits a minimum insertion loss of 1.9 dB, within the passband. The filters 10 dB return loss bandwidth, of 340 MHz, ranges from 2.28 GHz to 2.62 GHz.

A novel design of a sharp-attenuation ultra-wideband bandstop filter is presented in this paper, which is composed of two transmission lines (TLs) and four pairs of coupled-lines. The five transmission zeros in the stopband can improve the bandwidth and roll-off factor of the filter. To verify the design, the filter is manufactured on printed circuit board (PCB), and its performance is measured. The 10-dB stopband insertion loss bandwidth of the filter is 0.45-3.76 GHz (relative bandwidth 157%), with good frequency selectivity. The 20-dB attenuation rate on the lower side of the stopband is about 154.5 dB/GHz.