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.

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.

Aiming at two problems of the low radiation efficiency of the transmitted antennas and facing strong interference in extremely-low-frequency (ELF) communication, a new structure of a receiving array is proposed, and the signal preprocessing scheme in the receiver front-end is designed, which can suppress 50Hz interference and its harmonic components effectively, thereby enhancing the detective ability on the weak desired signal. In order to suppress the interference within signal bandwidth, a novel improved generalized sidelobe cancellation algorithm (IGSCA) is proposed. By combining with the proposed receiving array structure, the problem on the desired signal radiated into the reference antennas has been addressed effectively. In order to test the proposed algorithm's performance, an experimental platform is set up under the laboratory environment, mainly adopting a data acquisition unit named NI 9184. The results show that the proposed algorithm can improve the better signal-to-noise-plus-interference ratio (SINR) to a great extent, and the more the number of reference antennas is, the higher the improved performance is.

A Dual-band Half Mode Substrate Integrated Waveguide (HMSIW) filter at 4.88 and 6.42 GHz are shown. Defective Microstrip Structure converts the HMSIW's high-pass response to bandpass. Circular Complementary Split Ring Resonator splits the wide passband to give the filter dual characteristics. The out-of-band properties are improved by using a DS-OCSRR-shaped Defected Ground Structure (DGS). PCB technology is used to build and test the filter using an RT Duroid 5880 substrate with 1.6 mm thickness. The measured and simulated values match. Good skirt selectivity, insertion loss of 1.5/1.42 dB, fractional bandwidths of 9.42% and 6.7%, and return loss profile of 21 dB in both passbands characterise the thin dual-band filter. The filter is small, measuring 0.86λ_g × 0.37λ_g at 4.88 GHz.

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.

A new type of compact line-fed MIMO antenna for 5G wireless communication is presented in this paper. A rectangular microstrip patch antenna with an inset feed is designed for the 28 GHz and 38 GHz bands. The T-shaped patch contains inverted I-shaped slots, providing a dual-band response at 28 GHz and 38 GHz. By integrating two T-shaped patches, the MIMO (Multiple Input Multiple Output) antenna significantly improves signal diversity and data throughput, making it highly suitable for modern wireless applications such as 5G networks. Slot-formed defected ground structures (DGSs) are inserted into a partial rectangular ground plane. To fit into handset devices for the upcoming 5G mobile revolution, the antennas are modestly configured on a substrate measuring 14×28 mm², occupying minimal area and reducing mutual coupling. The ECC, MEG, TARC, and radiation efficiency values obtained from the antenna systems are suitable for 5G mobile applications, with excellent reflection coefficient characteristics.