A prototype filter design exhibiting Negative Group Delay (NGD) is presented, based on the ratio of two low-pass classical Bessel filter transfer functions of the same order, but with different 3dB-bandwidths. The resulting design is a reciprocal-Bessel filter transfer function, capped at a finite out-of-band gain. The proposed capped reciprocal-Bessel design is based on a similar concept applied to previously reported capped reciprocal-Butterworth and reciprocal-Chebyshev NGD designs, which use ratios of corresponding classical low-pass filter transfer functions. It is shown that within the in-band frequency range, the synthesized NGD transfer function exhibits a maximally flat group delay characteristic (Bessel-like property). Due to its near-flat in-band group delay characteristic, the design is suitable for constant phase shifter applications. For high design orders, it is shown that the achieved NGD-bandwidth product has an upper asymptotic limit, given by the square root of the out-of-band gain in decibels. When the prototype baseband transfer function is translated to a non-zero center frequency, it is demonstrated that resonator-based implementations are feasible via Sallen-Key, as well as all-passive ladder topologies. A combined in-band magnitude/phase distortion metric is evaluated for selected design examples and applied Gaussian and sinc input waveforms, and it is shown to be proportional to the design order and out-of-band gain. The proposed design's distortion metric is also shown to be generally lower than the previously reported capped reciprocal-Butterworth and reciprocal-Chebyshev designs.

To deal with the problems of low gain and low data transmission rate of millimeter wave antenna during long-distance transmission, a high-gain millimeter wave array multiple-input-multiple-output (MIMO) antenna with series-parallel hybrid feed is proposed. The radiating structure consists of a combination of multiple rectangular patches, to make the proposed design resonate within the desired frequency band of 39 GHz. The antenna line array consists of eight radiating patches connected in series via transmission lines, providing an operating bandwidth of 1.02 GHz and a peak gain of 15.9 dB, and utilizing the Chebyshev synthesis method to control the side lobe level below -20 dB. In order to obtain higher gain, two antenna line arrays are connected through a Y-shaped feeding network, which utilizes the mutual coupling between the antennas to increase the bandwidth of the antenna to 1.25 GHz and provide a simulated gain of 17.6 dBi. Furthermore, the proposed array antennas are placed side-by-side to form a four-port MIMO antenna, which does not require any decoupling structure and has the isolation of more than 25 dB. The radiation efficiency is as high as 99%, the Envelope Correlation Coefficient (ECC) less than 0.003, and the Diversity Gain (DG) greater than 9.98. The measured results show that the operating frequency band of the antenna is 38.0∼39.6 GHz, and the operating bandwidth is 1.6 GHz. In the operating frequency band, the peak gain of the antenna is 17.45 dBi, Finally, the frequency characteristics and radiation characteristics of the antenna when bending are analyzed. The results show that the bending of the antenna leads to a slight shift in the resonant frequency, but the relative bandwidth remains unchanged. The gain has decreased, indicating that the antenna is able to work normally after bending and has a wider range of application scenarios.

This article presents an approach to expanding the impedance bandwidth of a bilateral slotted antenna backed by a substrate-integrated waveguide (SIW) cavity using high-order radiation modes. By trimming a section of the conductive ground plane and connecting one side of the bottom long slot with a via, the three hybrid modes of the cavity are perturbed and merged to achieve a broad bandwidth. The optimized antenna is fed by a microstrip transmission line for Ku-band applications, demonstrating an impressive impedance bandwidth of 6.68 GHz (a fractional bandwidth of 41%) ranging from 12.82 GHz to 19.5 GHz, with a peak gain of 6.6 dBi. Compared to previous studies, the proposed antenna offers not only a wide bandwidth but also a compact size, with dimensions of 29.7 × 22 mm², and its electrical dimensions are 1.6λ₀ × 1.19λ₀, where λ₀ is the free space wavelength at the center frequency f_center = 16.16 GHz. Additionally, it has low production costs due to fabrication on an inexpensive FR4 substrate. The antenna was initially simulated using HFSS software, and to validate the accuracy of the results, it was also analyzed with CST Microwave Studio. Moreover, a prototype was constructed for experimental testing, with measured results showing strong agreement with the simulations.

This study presents the design of a MIMO (multiple inputs, multiple outputs) antenna for the 5G application. This is an inexpensive, low-profile antenna with a dimension of 9 x 18 x 1 mm³. The highest gain of the antenna in the operating frequency range is 7.79 dBi. This antenna structure provides a minimum isolation of less than -20 dB for the working bandwidth. The antenna's operational bandwidth covers the 26 GHz band mm-wave (millimeter-wave) spectrum, from 26.86 to 31.11 GHz. Its salient features make it appropriate for 5G applications.

To explore higher-performance satellite communication antennas, a dual-frequency dual-circularly polarized antenna based on a Fabry-Perot (F-P) resonant cavity is proposed in this letter. An artificial magnetic conductor (AMC) is loaded onto the resonant cavity as a partial reflection surface (PRS) to reduce the profile. The electromagnetic (EM) waves from the feeder are reflected multiple times within the cavity and subsequently superimposed in phase, thereby enabling dual-frequency operation and high gain. Right-handed circularly polarized (RHCP) and left-handed circularly polarized (LHCP) waves are respectively generated in the lower and higher frequency bands by incorporating a dual-frequency polarization conversion surface (PCS). Two rectangular microstrip patch antennas with a simple feeding network are employed as the feeder for RHCP and LHCP, respectively. The measurement results show that the operating bandwidth is 4.77% (12.47-13.08 GHz) for the low-frequency band and 5.36% (16.51-17.42 GHz) for the high-frequency band. The maximum gains of 14.91 dBi and 14.33 dBi are achieved for the lower and higher frequency bands, respectively. The proposed antenna fulfills the requirements of the frequency division duplex satellite communication system, providing a promising candidate for ground equipment in high-speed satellite Internet applications.

Lasers emitting visible light based on high harmonic generation (HHG) have significantly enhanced measurement capabilities, enabling new applications across precision metrology, attosecond science, and ultrafast time-resolved spectroscopy. This paper discusses the theoretical framework of HHG with a focus on nonlinear effects, examining in depth second-harmonic generation (SHG) and third-harmonic generation (THG) mechanisms, as well as a thermal nonlinear model for pump stability analysis. The current state of HHG within integrated optical circuits is reviewed, with a particular emphasis on its implementation in high-index doped silica glass micro-ring resonators (HDSG MRRs). We conclude by addressing future directions for optimizing these systems to expand their applicability in advanced photonic technologies, highlighting their potential for innovation in both applied and fundamental sciences.

To solve the problem of low accuracy and real-time performance of direction of arrival (DOA) estimation in an impulsive noise environment, this paper proposes a single-snapshot DOA estimation method based on the median deviation correntropy of hyperbolic tangent kerne and designs an intelligent optimization algorithm for the segmentation and hunting mechanism of gold long-nosed raccoon to obtain accurate DOA estimation angle. The DOA estimation method proposed in this paper uses spatial smoothing technology to process the median deviation correntropy of single snapshot data, and then uses the hyperbolic tangent kernel to remove impulse noise from the pseudo-covariance matrix. The weighted signal subspace fitting method is used to obtain the accurate DOA estimation angle. The Monte Carlo analysis experiments of different schemes are verified, especially in the case of a single snapshot, low generalized signal-to-noise ratio (GSNR), and strong impulse noise.

A method for significantly improving the bandwidth of microstrip patch antennas is proposed, utilizing dual-layer metasurface (MS). The antenna employs coaxial probe feeding and consists of a truncated patch, an upper layer of 4 x 4 periodic N-shaped MS and a lower layer of 3×4 rectangular MS. By introducing multiple resonances via the dual-layer MSs, impedance matching of the patch antenna is greatly enhanced. Its overall geometric dimensions are 1.09λ₀ x 1.09λ₀ x 0.14λ₀ (f₀ = 5.5 GHz), and compared with patch antennas and single-layer metasurface antennas of the same size, it can substantially enhance the bandwidth and gain without significant cost and size increase. The proposed MS antenna operates from 4.7 to 6.66 GHz (39.8% fractional bandwidth), covering two-thirds of the C-band, with a peak realized gain of 9.3 dBi. Within 4.47-5.56 GHz, the realized gain of the antenna remains above 7.5 dBi, and the average gain across the entire operating band is 7 dBi.

The circularly polarized design of a 350° sectoral microstrip antenna is proposed. Orthogonal surface current components at TM₁₀ mode on the sectoral patch provide circularly polarized characteristics. With the substrate thickness of 0.087λ_cAR, it yields the simulated axial ratio bandwidth of 18 MHz (1.9%) that lies inside the reflection coefficient bandwidth of 487 MHz (44.66%). A reduction in the substrate thickness by 0.012λ_cAR in the 350° Sectoral design is achieved by employing an H-shape ground plane profile. This design yields the axial ratio bandwidth of 13 MHz (1.45%), which is present inside the reflection coefficient bandwidth of 386 MHz (36.9%). The antenna using modified ground plane offers peak broadside gain of larger than 6 dBi. On conventional and H-shape ground plane design, reconfigurable design of 350° Sectoral patch is presented that offers switching between the wideband and circularly polarized characteristics. For operation at TM₃₀ mode in the Sectoral patch, circularly polarized reconfigurable configuration for sectoral angle decreasing from 340° to 280° is presented. Over this angle variation, antenna offers tuning in the center frequency of axial ratio bandwidth by 367 MHz (20.6%) with a broadside gain of larger than 5 dBi. A design methodology for circularly polarized antennas functioning at TM₁₀ and TM₃₀ modes is proposed. It helps in realizing similar configuration as per specific wireless application. Experimental verifications for all the obtained results are carried out which show close agreement with the simulated results.

In response to the growing demands of modern communication systems for miniaturized devices, high selectivity, and multi-band characteristics, this paper proposes a design methodology for a dual-band filter based on a planar interdigital structure. Two dual-band filters are developed utilizing transmission zeros and cascading techniques. The filters exhibit high selectivity and wide stopband performance. They are also tunable through parameter adjustments while maintaining a compact form factor. By incorporating composite right/left-handed (CRLH) theory, the proposed filters demonstrate left-handed characteristics. Simulation and experimental results indicate that the designed filters achieve low insertion loss, a wide stopband, and excellent out-of-band rejection within the target frequency bands. Additionally, compared to existing designs in the literature, this approach offers notable advantages in terms of both size and performance. The findings of this study show significant potential for applications in RF and communication systems.

In this paper, a ray-tracing based mathematical model is proposed for the analysis and design of Fabry-Perot antennas with a nonuniform Partially Reflecting Surface (PRS). The use of nonuniform PRS in FPA's has recently gained attention due to its immense applications such as directivity enhancement and beam-steering. A spatially varying phase profile of the PRS is achieved by the arrangement of various distinct unit cells throughout the surface. The PRS phase and magnitude variation enables the alteration of wavefronts to achieve beam steering along a desired polar and azimuth angle (θ, Φ). Thus, a simple, robust and computationally efficient model to find the optimal FPA parameters and phase profiles for beam-steering has been developed in this paper. FPAs were designed using a square PRS for 1-D and 2-D beam steering with gains of up to 17 dBi. The model has been verified with the simulated results at 8 GHz and 8.5 GHz, demonstrating consistent field patterns with the full-wave simulations.

This work presents a new compact split-ring resonator (SRR)-loaded rasorber to achieve narrow in-band transmission while maintaining broad absorption over a wide frequency range. The unit cell on the top layer is made up of four 150-ohm lumped resistors and four modified split ring resonators that are capable of absorbing a wide range of frequencies. The bottom FSS layer comprises a multilayer cascaded structure where top and bottom most metal layers are inductive grids, and the middle-sandwiched layer is a folded square ring structure. This design serves as a band-pass filter, allowing in-band transmission frequencies to pass through and also serving as a ground plane for out-of-band frequencies. The proposed rasorber exhibits an absorption bandwidth of 124% for frequency band starting from 2.5 GHz to 9.5 GHz, which covers mostly ISM and Satellite communication bands. The rasorber also acts as a transparent structure with insertion loss of 1.3 dB at the IOT band of 4.8 GHz. The novelty of the rasorber lies in achieving a very narrow transmission bandwidth with sharp roll off and is well suitable for radome applications having high selectivity. The innovation in this design comes from its combination of wide out-of-band absorption, narrow in-band transmission, high angular stability up to 50° for oblique incidence, and a dual-polarized response. The study looked at polarization behavior, surface current distribution, and other important parameters to figure out how well the rasorber worked. The equivalent circuit response of the proposed rasorber is compared with simulated one to get more circuit level understanding. Our results indicate that the electrical equivalent circuit design closely aligns with the simulated data. The proposed rasorber is suitable for secure communication in defense, as a super-stratum on an antenna, with reduced RCS and stealth characteristics.

This paper presents the design and implementation of a novel S-band antenna utilizing low-temperature co-fired ceramic (LTCC) technology. LTCC enables low losses, efficient radiation performance, and robust packaging. The antenna operates at 2.4 GHz with a size of 40 mm x 26 mm and offers a gain of 5 dB. It features a −10 dB impedance bandwidth of 20 MHz within the frequency range of 2.39 GHz to 2.41 GHz with efficiency of 94%. This design highlights the adaptability of LTCC technology in producing antennas that excel in several application while maintaining a desirable balance of size and efficiency.

Uncertainty analysis has been widely used in electromagnetic compatibility (EMC) simulation. However, a comprehensive credibility assessment system for it has yet to be established. In this article, the concepts of failure domain and failure rate are introduced from the perspective of the practical application of uncertainty analysis methods. The study aims to assess the reliability of uncertainty analysis method from the perspective of system failure, providing a theoretical basis for guiding practical electromagnetic compatibility design through uncertainty analysis.

This paper proposes a broadband multi-input multi-output (MIMO) antenna array operating in the 3.3-6 GHz frequency range. The antenna array consists of eight identical Z-shaped radiation elements, and the coupling between the antenna elements is minimized through the use of an optimized defected ground structure. Each antenna element is composed of a modified Z-shaped radiation strip, an opposing L-shaped strip, and a rectangular strip. Based on simulation and measurement results, it can be concluded that the antenna array meets the -10 dB bandwidth requirement within the desired frequency band, with the transmission coefficient of less than -15 dB, and an envelope correlation coefficient (ECC) below 0.006. Additionally, the proposed antenna achieves a maximum gain ranging from 2.6-8 dBi, with an efficiency exceeding 76%. The overall size of the phone antenna is 150 × 75 × 7 mm³, while each antenna element measured only 7.8 mm × 7 mm × 0.8 mm (0.091λ × 0.082λ × 0.009λ, where λ represents the wavelength at 3.5 GHz). The high-isolation broadband MIMO antenna proposed in this study emerges as a promising candidate for fifth-generation (5G) New Radio (NR) and WLAN applications.

Super fast charging is a key solution to addressing the issue of electric vehicles. In response to the demand for increased current-carrying capacity and lightweight cables in super-fast charging system, optimization design and verification were conducted in this study employing a multi-physics field analysis method. A single-core cable was selected as the research subject, and both the Ohmic loss and temperature distribution were analyzed under the excitation of electric vehicle cold charging current. The influence of different cable core shapes, coolant flow rates, cooling channel structural parameters, and other factors on the maximum temperature rise of the charging cable were compared and analyzed. The calculation results indicated that, under the identical cable core cross-sectional and operating conditions, rectangular cross-section cables exhibited superior heat dissipation performance compared to circular cross-section cables. It was found that the flatter the cable core is, the better the heat dissipation performance is. Under specific operating conditions, the cross-sectional area of the flat linear shape could be reduced appropriately, as increasing the size of the liquid cooling channel would help reduce the overall mass of the cable. These findings provide valuable insights for enhancing the heat dissipation performance and lightweight design of liquid-cooled charging cables in supercharging applications.

A simple, low-profile, and broadband antenna is presented in this paper for bandwidth enhancement. The compact antenna is achieved through a 50% miniaturization of a full-mode substrate integrated waveguide (FMSIW) antenna, known as the half-mode substrate integrated waveguide (HMSIW). The low-profile design is the result of the thin substrate thickness. However, the miniaturized and low-profile antenna suffers from narrow impedance bandwidth, which limits its application in antenna implementations. To address this issue, this paper proposes a broadband antenna in a single HMSIW cavity, offering a simple solution. The broadband performance is achieved by the merging of triple resonances. These triple resonances are generated by the combination of TE₁₀₁, TE₁₀₂, and TE₂₀₂ modes, which are induced by a semi-rectangular ring slot on the top layer of the cavity. Good agreement is observed between the simulation and measurement results. The simulated fractional bandwidth (FBW) is 29.53% (9.67-13.02 GHz), while the measured FBW is 32.05% (9.51-13.14 GHz). Two identical antennas with different polarization directions are obtained by mirroring one of them with respect to the other.

In this study, a quad-port ultra-wideband (UWB) multiple input multiple output (MIMO) antenna with triple band-rejection characteristics is demonstrated. The suggested diversity MIMO antenna comprises four similar rectangular radiators positioned in orthogonal manner by utilizing polarization diversity. For superior interelement isolation, a fan-shaped decoupler is lithographed on the back of the substrate. The MIMO antenna exhibits an operational bandwidth of 9 GHz (3-12 GHz) for each port, with |S₁₁| ≤ -10 dB. This version is more concise and properly formatted. The MIMO aerial exhibits an impedance bandwidth 3-12 GHz) for each port (|S₁₁| ≤ -10 dB) along with an interelement isolation exceeding 20 dB. Additionally, to exclude the 3.5-4.1 GHz (downlink C-band), 4.43-4.79 GHz (INSAT), and 5.25-5.71 GHz (Wireless LAN) bands that coexist in UWB spectrum, the antenna elements are equipped with three U-shaped slots. The MIMO diversity metrics, including isolation, envelope correlation coefficient, diversity gain, TARC, CCL, multiplexing efficiency and group delay, were computed and reported. The reported aerial prototype has been constructed, and the measured results have been validated against the simulated findings.

A low-profile monolayer filtering antenna with compact size is presented in this paper. The antenna features a simple structure, comprising a substrate, a stepped defective ground structure, an asymmetric Y-shaped branch, and a microstrip feedline with an L-shaped branch. The asymmetric Y-shaped branch and L-shaped branch feedline collaborate to introduce two additional resonant frequency points, thereby broadening the impedance bandwidth. Furthermore, two radiation nulls are introduced on either side of the passband, which enhances the frequency selectivity of the band edges and optimizes the antenna's radiating and filtering performances. To verify the proposed design, a prototype of the compact filtering antenna was fabricated and measured. The measured and simulated results show good agreement. The design achieves a wide impedance bandwidth of 44.6% (4.88~7.68 GHz) at a center frequency of 6.22 GHz, a peak realized gain of 5.7 dBi, and a compact size of 35 mm × 29 mm × 0.8 mm. Two radiation nulls on either side of the passband result in an excellent bandpass response, with out-of-band rejection reaching 18.2 dB. Finally, the antenna's excellent radiation performance and filtering characteristics make it suitable for wireless communication applications in the 5G Sub-6 GHz and WiFi-6E bands.

This work is focused on predicting the return loss and gain characteristics, where a new MIMO-OFDM radar waveform design is proposed and then simulated for a line impedance antenna system. A suggested radar waveform is implemented on an FR4 substrate normally used in microwave applications. It is obtained that, after extensive modeling, the return loss for the MIMO-OFDM radar waveform is -31.7265 dB at a frequency of 6.86 GHz, thereby showing minimum reflection and good impedance matching. At this frequency, the gain for the system comes out to be 7.1276 dB, which refers to the fact that this waveform would help in enhancing the performance of radar systems. These results demonstrate how the MIMO-OFDM radar waveform can be used for advanced radar applications because it gives better return loss and gain, some of the critical specifications required for high-performance radar systems.