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To address the constraints associated with conventional fitting techniques for temperature demodulation in the context of subway tunnel fires, a new method of demodulation grating sensing spectrum using long short‐term memory convolutional neural network (LSTM‐CNN) is proposed in this paper. Build the monitoring platform based on LSTM‐CNN ultra‐weak fiber grating temperature measurement system, predict its sensing signals by LSTM‐CNN algorithm, select 18000 spectra as sample data for training, use AdamW stochastic optimization algorithm for training, and carry out the temperature calibration and demodulation error analysis of the Fiber Bragg Grating within the temperature range of 25–75°C. Compared with GRU algorithm, LSTM algorithm and traditional maximum peak method, the algorithm of this paper is good and can effectively improve the measurement accuracy, the experimental results show that: the demodulation accuracy of temperature wavelength prediction in this paper can be up to 99.27%, and the root mean square deviation is 0.08528°C, through the experiments, it is verified that the method proposed in this paper has a certain reference and support in terms of theories and technology significance. It is suitable for the identification and monitoring of fire hazards in underground tunnels, and also has application value in the signal processing of grating array sensing demodulation system. [ABSTRACT FROM AUTHOR]

This paper proposes a wide bandpass filter (BPF) with high out‐of‐band suppression and wide stop‐band characteristics. An interdigital coupled line structure loaded by a rectangular resonator ring is employed to generate three transmission poles in the pass‐band and an additional transmission zero (TZ) in the stop‐band, thereby achieving a wider pass‐band while enhancing stop‐band suppression. Compared to traditional coupled‐line structures, the structure mentioned in this paper offers significant advantages in designing filters with wide stop‐bands and high out‐of‐band suppression. Furthermore, open‐circuit T‐stub, and a pair of open‐circuit stub are used to generate multiple parasitic TZs at high frequencies, which is adopted to further expand the stop‐band range. Measurement results shows that the insertion loss of the BPF is of −2.86 dB within the range of 7.05–12.20 GHz. The stop‐band ranges from 13 to 48 GHz with an out‐of‐band suppression of −27 dB, especially when the out‐of‐band suppression is −40 dB, the stop‐band frequency range is 16.40–31.35 GHz. [ABSTRACT FROM AUTHOR]

This paper points out that the commonly used normalized frequency for noncircular dielectric waveguides, which is based on the semiminor axis, causes the cross‐sectional area to vary with the cross‐sectional shape. Consequently, the shape effects described with the conventional normalized frequency are not due to the shape alone but the combined effects of the shape and area. Our numerical results show that the area effect is greater than the shape effect. An improved definition of normalized frequency based on an equivalent radius is proposed in this paper. Conversion formulas to convert from the conventional normalized frequency to the proposed normalized frequency are provided for elliptical and rectangular waveguides. Our numerical results show that the shape effects described by the proposed normalized frequency are free from the area effect. Consequently, the proposed normalized frequency is more accurate than the conventional normalized frequency in describing the shape effect of noncircular dielectric waveguides. [ABSTRACT FROM AUTHOR]

Waterborne bacteria cause many dangerous diseases as well as several health‐related issues hence detection of them is a global challenge today. A plus‐shaped graphene sensor to detect waterborne bacteria is presented in this paper. The detection mechanism is based upon the refractive index difference between waterborne bacteria sample and pure water which causes a change in resonance peak in the transmittance graph. The use of graphene material increases the sensitivity and also gives the tuning behavior by changing its potential. The effect of various parameters such as sensitivity (S), Q factor, figure of merit (FOM), and detection limit are discussed in the paper. The maximum values Q factor and FOM are 13.46 and 4.03 RIU−1 respectively. The minimum detection limit is 0.277 RIU. The proposed sensor exhibits the highest sensitivity of 255 GHz/RIU at the optimum condition which is comparably higher than previously published papers on biosensors. The proposed design with its highest sensitivity and good detection parameters can be helpful in detecting waterborne bacteria. [ABSTRACT FROM AUTHOR]

In this study, a novel freeform surface lens coupler is designed to realize the coupling functions in the hollow‐core photonic crystal fiber (HCPCF) resonator optical gyroscope. One surface of the lens is an ellipsoid. Coupling of the two HCPCF loop's ports can be directly accomplished via reflection on the ellipsoid surface. The other surface of the lens is the Biconic Zernike surface. Transmitting through the above two surfaces, the coupling between the intracavity and extracavity is completed. In this paper, simulations were performed based on two types of HCPCFs, a hollow‐core photonic bandgap fiber of HC19‐1550 and a state‐of‐the‐art nested antiresonant nodeless fiber. The volume of the lens coupler is calculated to be approximately 4 × 2 × 4 mm3. The simulation results show that the intracavity coupling loss can be as low as 0.011 dB, and the coupling loss between the intracavity and extracavity can be as low as 0.4 dB. Compared with the traditional fusion scheme between hollow‐core fiber and polarization‐maintaining fiber, the freeform surface lens coupler in this paper can achieve lower coupling loss and higher resonance fineness. Compared with other spatial coupling schemes, it has lower coupling loss and fewer coupling components. [ABSTRACT FROM AUTHOR]

In this paper, a behavioral model for the variable gain amplifiers working in the liner region is proposed. An iterative least‐square algorithm for complex curve fitting is proposed to model the variable gain amplifiers as an infinite impulse response filter. The polynomial fittings are used to obtain the coefficient matrix for the gain response and phase response to the frequency at different control voltages. The relationship between gain and control voltage is fitted by a hyperbolic tangent function. The modeling flow is given in this paper. Comparing the frequency response of the behavioral model and circuit model, the simulation results are similar at the operating frequency. Finally, an application is given, which is used to compare the effect of the nonlinear phase system with two different band signals modulated by 4QAM. This application proves that the model can be used in the simulation of large‐scale systems. [ABSTRACT FROM AUTHOR]

This paper introduces a beam‐scanning holographic antenna composed of a substrate‐integrated waveguide (SIW) feeding structure and a rectangular microstrip array. The antenna innovatively combines holographic theory with liquid crystal electrical tunability to realize single‐frequency large‐angle beam scanning function which can effectively solve the problem of beamforming reconfiguration in traditional array antenna systems. In this paper, the variation of dielectric constant of liquid crystal under different bias voltages is quantitatively analyzed. Additionally, the beam forming technology is analyzed under hologram amplitude weighting theory. The relevant theories are verified by manufacturing and testing. The prototype antenna achieves the ultra‐wide beam scanning angle of −63° to 63° at 36 GHz. [ABSTRACT FROM AUTHOR]

The traditional infrared inspection of substations is usually done by employees with handheld infrared equipment, but the traditional inspection efficiency is not high, and some of the inspection locations have harsh environments, high voltage levels, and high‐risk factors. Given the above problems, this paper proposes an improved defect detection algorithm for substations based on YOLO v7 to solve the difficult problem of infrared inspection of substations. First, the lighter SE‐GhostNetV2 feature extraction network is designed to reduce the computation volume; second, the de‐weighted BIFPN structure is designed for the substation infrared image features to improve the ability of information interaction; finally, the new C‐NWD Loss is proposed to realize the detection of smaller substation equipment and reducing missed detections. The experimental results show that the hybrid accuracy of the algorithm designed in this paper is improved from 92.1% to 96.6%, the model parameters are reduced by 40.1%, the computation amount is reduced by 65%, the detection speed is improved by 87 FPS, and the false detection and missed detections is less, which can achieve real‐time infrared inspection of substations and solve the difficulties existing in traditional substation infrared detection. [ABSTRACT FROM AUTHOR]

In this paper, we propose an array antenna that can work in reflection and transmission modes simultaneously or separately. Reflection and transmission at two frequencies are determined by designing and implanting frequency selective surfaces for the antenna. An antenna array prototype including 14 × 14 units and a horn‐fed antenna is designed and measured. The peak gain is 24.6 dBi when the array operates in reflection mode at 12 GHz and 21.3 dBi in transmission mode at 7 GHz. The peak gains are at least 10 dBi higher than the feed source. Moreover, a shift in the beam direction was observed when the feed horn moved along the axis during the measurement. A ±16.4° beam scan can be achieved with a ±60 mm shift in the feeder, as presented in the paper. The proposed transmission/reflection array antenna has potential applications in wireless communication systems. [ABSTRACT FROM AUTHOR]

In this paper, we report the first Q‐switching operation utilizing black phosphorus (BP)/SnSe2 heterojunction as the saturable absorber (SA) in an Er‐doped fiber laser. The BP/SnSe2 heterojunction was prepared by the liquid phase combination method and its properties were observed. Stable Q‐switching operations were achieved based on the BP/SnSe2 SA. The maximum peak power of 71.27 mW and the minimum pulse width of 910 ns were produced, respectively. This paper demonstrates the pulse modulation characteristics of BP/SnSe2 heterojunction SA in the midinfrared region for the first time, laying an important foundation for the application of heterojunction based on BP and two‐dimensional transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

In this paper, a MIMO antenna with broadband circular polarization is designed in a single‐layer substrate for the next‐generation Wi‐Fi 7 applications. The top of the substrate is designed with a periodic array of 5 × 5 circle patches and orthogonally placed four L‐shaped aperture CPW feeds on the bottom face of the substrate are used to feed the patches. The stubs are arranged across the apertures to achieve a broad bandwidth. The array of patches is used to achieve high gain over resonant frequency range and L‐shaped apertures are used to achieve circular polarization. The designed antenna with the above specifications has gained an impedance bandwidth of 20.4% (5.37–6.59 GHz), a 3 dB axial ratio bandwidth over the entire resonant frequency range of 25.61% (5.14–6.65 GHz) and a peak gain of 8.5dBi. [ABSTRACT FROM AUTHOR]

This paper presents a novel design method for a tri‐band multiple in multiple out (MIMO) antenna. The antenna consists of four sets of identical antenna pairs arranged on the two side frames. Three resonant modes can be obtained using a microstrip coupling feed structure by employing different branches in antenna unit design. The working frequencies of the modes can be adjusted independently. Moreover, in each pair of antennas, two antenna units were closely arranged and a decoupling grounding branch was employed between the adjacent antennas to ensure good isolation. The tri‐band eight‐element MIMO antenna operates at 3.5, 4.9, and 5.6 GHz and the isolations were better than 14 dB. The proposed antenna had a low profile of 0.06λ0 ${\lambda }_{0}$ and good isolation so it has potential applications in 5G mobile terminals. [ABSTRACT FROM AUTHOR]

This paper proposes an innovative design approach for a voltage‐controlled (variable) attenuator that allows continuous control of attenuation through analog voltage. Different from fixed attenuators, this work employs PIN diodes and compensated gold wire inductors to configure the attenuation network. It is based in imperfect matching theory, ensuring to obtain the acceptable S‐parameters over the operating band. Measurement results demonstrate effective performance of the attenuator within the voltage range of 0.7–1.03 V. Return losses of the attenuator are all better than 15 dB in the operating range of 10.5–19 GHz. The insertion losses exhibit continuous variation from 2 to 15 dB, requiring only a single controlled voltage to adjust the attenuation value. [ABSTRACT FROM AUTHOR]

An ultra‐wideband low‐noise amplifier (LNA) design was developed based on distributed network synthesis to achieve impedance matching of an active device by parasitic absorption. The equivalent device models of a low‐noise device were generated using negative‐image device modeling and traveling‐wave matching, and matching circuits were produced using the Chebyshev approximation. The minimum insertion loss and ripple of the matching networks were adjusted correctly to allow the parasitic absorption to match the device models. This paper describes the design methodology for distributed matching circuits and its application to the design of an ultra‐wideband LNA. [ABSTRACT FROM AUTHOR]

This paper presents a novel 2.5D miniaturized frequency‐selective surface (FSS) measuring 6.1 mm × 6.1 mm, designed to effectively shield smartphones and tablets from unwanted electromagnetic radiation. The FSS is notable for its stable attenuation peaks in the high‐frequency stopband under transverse magnetic (TM) polarization, offering dual‐frequency response and exceptional angular stability in both transverse electric and TM modes. An equivalent circuit analysis, prototype fabrication, and empirical evaluation confirmed its effectiveness. The prototype exhibits superior polarization stability and minimal peak attenuation reduction of just 1.9 dB (10%) across a 0°–60° incidence angle, outperforming similar studies. [ABSTRACT FROM AUTHOR]

Ultra‐wideband (UWB) multiple input multiple output (MIMO) radar has been widely used in detection systems due to its advantages, such as low cost and high data acquisition capability. The detection system is applied in various ground‐penetrating applications, including mine detection and earthquake rescue. In this paper, a novel UWB MIMO radar system based on step‐frequency continuous wave is designed for underground target detection. To improve the penetration depth and high‐range resolution, a new miniature Vivaldi antenna with a bandwidth of 1–3 GHz is designed and integrated into the ground‐penetrating imaging system. Furthermore, a multiscale weighted time‐domain back projection (BP) algorithm is proposed to suppress artifacts and reduce the computational complexity of the BP algorithm. The designed system is tested by detecting stationary targets. The experimental results agree well with the simulation. The reconstructed images show that the designed MIMO radar system can successfully image underground targets. [ABSTRACT FROM AUTHOR]

In this paper, a new 180° broadband phase shifter with coupled microstrip line with enhanced coupling by etched slots is proposed, which uses the energy coupling between the parallel‐coupled microstrip lines on the upper layer of the dielectric substrate and the etched rectangular slots (RS) structure on the bottom floor to circumvent the problem for achieving wide operating broadband and low insertion loss with compact size and simple structure. First, the main line and the reference line of the proposed phase shifter are composed of two parallel coupled lines and a uniform transmission line, respectively. Then, its working mechanism is described. Afterward, the phase shifter introduced an RS structure to increase the coupling strength, achieving a broadband of 69.7% and very low insertion loss (0.09 dB) with a phase shift of 180 ± 5°. Finally, a prototype 180° phase shifter with a center frequency of 3.0 GHz was designed, fabricated, and measured, and the measured results are good in agreement with the simulated ones. [ABSTRACT FROM AUTHOR]

In this paper, a novel iterative method is proposed to find the matching impedances for all‐port simultaneously conjugate matching of N‐port networks. This method takes advantages of the reciprocal and lossless features of the matching network, which leads to the unitary and symmetric properties of its S matrix. As a result, the computing complexity of this proposed method is analyzed and proved to be very efficiently reduced compared to previously reported methods. A two‐port network, two three‐port networks, a ten‐port network, and a four‐port 2 × 2 antenna array are presented to demonstrate the efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

This article proposes a Ka‐band substrate integrated waveguide (SIW) quasi‐Yagi array antenna with the advantages of thinness, compactness, wide bandwidth, and higher gain. Analyzing the microstrip‐to‐SIW transition structure to confirm that the designed structure provides the best performance, the optimum reflectance coefficient bandwidth can be obtained. With the optimized rectangular etched slot structure at the antenna end, the impedance matching can be tuned to improve the bandwidth. The designed array antenna is fabricated and measured for verification. The substrate is based on Al2O3 ceramic and the antenna size is 23.3 mm × $\times $ 13 mm × $\times $ 0.5 mm. The measurement results indicate that the antenna achieves an impedance bandwidth of 13.59% below −10dB, with an average gain of approximately 7 dBi and a peak gain of 7.4 dBi in 28.1–32.2 GHz. Therefore, the 1*2 antenna proposed in this paper has the advantages of compact and planar structure, easy fabrication, and easy integration into RF circuits, which is very suitable for Ka‐Band applications. [ABSTRACT FROM AUTHOR]

In this paper, the design of a low sidelobe level (SLL) 10 × 10‐element series‐fed patch antenna array is presented. A ridge waveguide‐based nonuniform feeding layer is employed to excite the array. Each column of the antenna array includes a tapered 10‐element series fed patch antenna array. By using a simple and compact center‐fed ridge waveguide, a low loss feeding layer is achieved. The coupling between the ridge waveguide and the standard WR‐75 flange is performed by employing a proposed stepped transition. The measured results indicate that the maximum gain is 24.1 dBi and the SLL is lower than −20 dB in both H‐ and E‐planes at 12.7 GHz. The proposed low SLL planar series‐fed patch antenna array can be utilized as an acceptable candidate for radar applications. [ABSTRACT FROM AUTHOR]

An embedded series resonator for compact co‐polarized circular patch antenna pairs is presented in this paper. With a compact center spacing (CS) of 0.32λ0 and edge spacing (ES) of 0.03λ0 (λ0 is the free‐space wavelength at the center frequency), strong mutual coupling inevitably arises. However, by introducing a cross‐shaped fence and two quarter‐wavelength open‐ended slots onto a circular patch, port isolation of the first proposed antenna pair is significantly enhanced by 25.2 dB within a bandwidth of 6.2%. Moreover, the effectiveness of the embedded series resonator is demonstrated by achieving a wider 20‐dB decoupling bandwidth of 10.4% for the second proposed compact bandwidth‐enhanced antenna pair. For validation, both proposed prototypes are fabricated and measured, showing good agreement between measurements and simulations. To demonstrate the universality, a 1 × 8 patch array with an embedded series resonator can achieve a beam scanning angle of ±70◦ with a gain attenuation of 2.6 dB. Benefiting from compact size, high isolation, and enhanced decoupling bandwidth, the proposed designs hold promising potential for application in multiple‐input multiple‐output system and antenna array. [ABSTRACT FROM AUTHOR]

A novel approach for generation of the multiple three‐directional and controllable beams from a cubical electromagnetic (EM) wave radiator is proposed in this paper. This cubical radiator is a multiple‐mode EM resonator, which is formed by a cubical metal cavity. Three resonant modes are excited in this cavity resonator by a feeding slot. Besides the feeding slot, a few additional slots are opened on the side wall(s) of the cavity to act as the EM wave radiation elements. Various combinations of radiation slots contribute to different beam directions, for example, side‐direction (single radiation slot), edge‐direction (two radiation slots), and vertex‐direction of the cavity (three radiation slots). More combinations of these slots are further studied in the cases of side + edge and edge + vertex to illustrate the diversity in the directions of the produced EM beams. To validate the predicted results, two prototypes are fabricated and measured to display their far‐field radiation patterns. The measured results agree well with the full‐wave simulated ones, thereby demonstrating the possibility of a large number of the flexible EM beams, as well as the capability of the controllable beam directions. [ABSTRACT FROM AUTHOR]

This paper presents the deep neural network‐based infinitesimal dipole model using either near‐ or far‐field radiation patterns. Based on the radiating characteristic of an infinitesimal dipole, we generated a data set including near and far field radiation patterns corresponding to the phases of infinitesimal dipoles. We used the data set to train and validate the deep neural network (DNN) model. After checking the statistic of the fit function and the average error in expecting the phases of the infinite dipoles, we conclude that the proposed infinitesimal dipole modeling using DNN is sufficient to predict the characteristics of electromagnetic radiation. [ABSTRACT FROM AUTHOR]

In this paper, a low profile polarization insensitive ultrathin Circuit Analogue Absorber is presented for wideband absorption, encompassing the entire X‐band and Ku‐band applications achieving stable angular performance up to 45° angle of incidence in TE and TM polarized configurations. The absorber design being proposed consists of a multislotted square loop resonator loaded with lumped resistors, accompanied inside by a quadruple‐split annular copper ring. These components are arranged in a stacked configuration, with a grounded dielectric substrate serving as the base and an air spacer between the substrate and ground displaying absorptivity above 90% from 8.19 to 22.20 GHz with a 14.01 GHz and 92.2% of actual and fractional bandwidth respectively under the normal incidence. The thickness of designed wideband absorber is 0.0819λL ${{\boldsymbol{\lambda }}}_{{\bf{L}}}\,$(λL ${{\boldsymbol{\lambda }}}_{{\bf{L}}}\,$is the wavelength corresponding to the lowest operating frequency) making absorber Low profile and Ultrathin. [ABSTRACT FROM AUTHOR]

In this paper, a novel radial spatial power combiner based on the WRD650 standard double‐ridge waveguide has been proposed. The combiner exhibits a significant increase in operating bandwidth due to the utilization of the upper ridge taper and the lower ridge extension. The principle prototype is designed, processed, and tested. The test results show that the overall return loss of the dual‐ridge waveguide power combiner is better than −10 dB at the input port, and the insertion loss at each output port is better than −2 dB in the 6–18 GHz band, and the maximum phase difference at each port does not exceed 11°. Due to the limitations of the processing accuracy, the final overall synthesis efficiency is higher than 70%. [ABSTRACT FROM AUTHOR]

This paper presents accurate, prompt, and cost‐effective relative permittivity and loss tangent measurements of low‐loss dielectrics such as DuPontTM VESPEL® SP‐1 and VictrexTM polyetherketone (PEEK) 450G, which are commonly used materials in space communication antennas. It is essential for an antenna engineer to have the information regarding the electrical properties, that is, dielectric permittivity, dielectric loss tangent, magnetic permeability, and magnetic loss tangent at the frequency of interest. The test method relies on the accurate measurements of the S‐parameters of the sample under test by means of Through‐Reflect‐Line (TRL) calibration using a Vector Network Analyzer (VNA). Nicholson‐Ross‐Weir (NRW) method is employed to get the conversion from S‐parameters to both complex permittivity and permeability values of the samples. The experimental results are verified with the literature data of Teflon and relative permittivity and loss tangent measurements of VESPEL® SP‐1 (εr=3.119±0.043 ${\varepsilon }_{r}=3.119\pm 0.043$, tanδ=(20.893±4.042)*10−3 $\tan \delta =(20.893\pm 4.042)* {10}^{-3}$) and PEEK 450G (εr=3.119±0.015 ${\varepsilon }_{r}=3.119\pm 0.015$, tanδ=(5.654±1.877)*10−3 $\tan \delta =(5.654\pm 1.877)* {10}^{-3}$) are presented for X‐band (8‐10 GHz) frequencies. [ABSTRACT FROM AUTHOR]

This paper proposes a return‐to‐zero pulse position modulation (RZ‐PPM) impulse tone‐based channel state information (CSI) estimation for adaptive threshold decision (ATD) in free‐space optical (FSO) communications. RZ‐PPM is characterized by impulse tones in the spectrum. Therefore, CSI can be extracted by applying a local oscillator (LO) with the frequencies of impulse tones and low pass filter, which is then used to realize ATD. The proposed method was studied in simulation under RZ‐PPM signals with various number of pulse positions and frequencies of LO. The simulation results show that in FSO communication systems, the use of optimized weighting factor for impulse tone CSI estimation method significantly improves the performance in the absence of accurate CSI, approaching the performance of the traditional ATD with precise CSI knowledge. It proves that the proposed technique was feasible for adaptation in FSO communication systems. [ABSTRACT FROM AUTHOR]

Measuring silicon carbide (SIC) fibers is a widely used technique in searching for SIC materials with high absorbing properties. Nevertheless, obtaining reasonable electromagnetic properties in most of the existing experimental setups with SIC fiber materials remains difficult. Additionally, being a critical load‐carrying component of composite materials, the properties changing during oxidation conditions would directly impact the practical application of SIC fibers. Aiming at solving such problems, this paper investigates and analyzes the variation of electromagnetic performance under different oxygenation times for SIC fabric cloths (provided by Aerospace 703) and uses separated cylindrical resonant cavities to investigate SIC fiber cloths' electromagnetic properties. Eventually, testing results indicated that the dielectric constant decreases with the increase in oxidation time for SIC fiber cloths. The findings presented here are of guiding significance toward applications of SIC fibers in high temperature conditions. [ABSTRACT FROM AUTHOR]

A stacked dual‐band antenna system based on frequency selective surface (FSS) is proposed in this paper. The system consists of lower band (LB) and higher band (HB) antenna elements with a frequency ratio of 2.5. FSS is introduced between LB and HB elements, which can fully reflect LB wave and transmit HB wave without reflection. LB and HB antenna arrays can be designed independently and combined with only a few screws, allowing for flexible combination of different arrays according to different needs. The stacked scheme can avoid the generation of grating lobes caused by excessive spacing of HB elements. Two different arrays were analyzed, simulated, and measured to validate the excellent features of the proposed scheme, such as easy to combine, stable radiation patterns, and lower mutual interference for LB and HB elements, respectively. The proposed system can be a promising candidate for dual‐band wireless communication with large frequency ratio. [ABSTRACT FROM AUTHOR]

This paper presents a new design method of digital baseband signal for generating fully digital programmable optical frequency comb (OFC), which solves the problem of how to optimally select the digital baseband signal when OFC is generated by binary digital signal modulation. The inverse Fourier transform is used to study the waveform of binary digital signal which is used to generate OFC. It is found that the number of "0" bits of digital signal determines the flatness of comb lines. Based on this, a tunable ultra‐fine and ultra‐flat OFC was obtained by using a digital signal containing a large number of "0" bits in the experiment. This saves substantial computing time and resources compared to the current method of the k‐means clustering algorithm. [ABSTRACT FROM AUTHOR]

When the COMS camera of optical camera communication (OCC) system acquired the information image, the grayscale value of pixels fluctuated due to the influence of blooming effect and light noise, so that the data logic could not be correctly judged by the decision threshold, which affected the bit error rate (BER) performance transmission distance and data rate, and degraded the system performance. In this paper, the adaptive exponential weighted moving average algorithm is proposed, and the optimal grayscale value matrix of signal demodulation is verified by experiment, so as to reduce the fluctuation of grayscale value and improve the performance of OCC system. The experimental results show that for data processing and analysis based on ZYNQ7020 experimental platform, a 7% forward error correction（BER = 3.8 × 10−3）requirements can be satisfied at 150 cm when the data rate is 3 Kbps, and a 7% forward error correction（BER = 3.8 × 10−3）requirements can be satisfied at 100 cm when the data rate is 5 Kbps. [ABSTRACT FROM AUTHOR]

This paper demonstrates a 3.4 GHz micro‐acoustic filter with excellent in‐band insertion loss, rectangle coefficient, and out‐of‐band rejection. The proposed filter was based on a novel topology by integrating the bulk acoustic wave (BAW) resonators with an on‐chip clamping inductor, the introduction of the lumped components is beneficial for improving the filters' stopband rejection while having minimal influence on the rectangle coefficient and in‐band insertion loss. Al0.8Sc0.2N material was selected as the piezoelectric film of the BAW device and the inductor was fabricated on the same wafer with BAW devices. The manufactured filter has a minimum in‐band insertion loss of ~ 1.5 dB, a 3 dB bandwidth of about 170 MHz, and a stopband rejection of nearly ‐30 dB. The experimental results verify the design and show great applications for 5G communication and beyond. [ABSTRACT FROM AUTHOR]

A miniaturized microstrip grid array antenna (MGAA) in X‐band is proposed in the paper. The antenna consists of a radiation grid array, a feed network and a metal back cavity. The 2 × 2 planar grid array is constructed by using four MGAAs as subarrays. MGAA does not require complex feeders in contrast to microstrip patch arrays. Furthermore, a curved slow‐wave transmission line (SWTL) is adopted as the long side of grid. The SWTL not only reduces the physical size of the grid while keeping its electrical size unchanged, but also improves the impedance matching and greatly broaden the bandwidth of the antenna. A fabricated prototype was measured in the microwave chamber. The results indicate that the impedance matching band of |S11| < −10 dB is from 9 to 10.5 GHz (15.4%), and the maximum gain is 19.2 dBi. Meanwhile, the projected area of the antenna is reduced by about 40% by loading the SWTL. [ABSTRACT FROM AUTHOR]

In this paper, the flower‐shaped microstrip antenna (FSMA) is investigated theoretically and experimentally for the first time. A theoretical model is proposed to investigate the radiation characteristic of an FSMA using conformal mapping technique. The flower shape is mapped to a circular shape with the help of an appropriate mapping relation. The wave equation is solved in the transformed domain using Galerkin technique to obtain the approximate solution of eigenfunction and eigenvalue. Resonant frequency, internal field patterns, input impedance, and far‐field radiation patterns of the FSMA are investigated. Three antenna prototypes are fabricated for experimental verification. The acceptable agreement is found among the calculated, simulated, and measured data. Our theory shows an error of less than 1.45% in predicting the resonance frequency. Quality factor and bandwidth are also described. This theoretical approach not only quickly evaluates the performance of an FSMA but also provides the instruction to design an FSMA. [ABSTRACT FROM AUTHOR]

This paper simulates and measures a compact broadband rectifier for voltage doubler Schottky diode. Among them, a two‐stage microstrip line impedance matching network for voltage doubling circuits is used. The imaginary part of the diode impedance is limited by the short‐circuit branch. The impedance conversion transmission line matches the impedance to 50 Ω. The impedance matching in the circuit is only realized by two‐stage microstrip lines, which reduces the physical size of the rectifier and makes the rectifier more compact. Judging the measurement results from 0.8 to 2.5 GHz, the conversion efficiency is greater than 30% at 0 dBm, the bandwidth is 103%, and the maximum conversion efficiency reaches 66.3% at 8 dBm. In addition, the compact size of the rectifier is 23 × 20 mm2. [ABSTRACT FROM AUTHOR]

This paper presents a compact self‐quadruplexing antenna (SQA) designed through the utilization of substrate‐integrated rectangular cavity (SIRC) technology for quad‐band applications. It operates at four distinct frequencies, which are 3.29, 4.27, 5.20, and 5.72 GHz. The antenna's maximum gains were estimated to be 5.09, 6.46, 5.79, and 6.21 dBi at their respective operating frequencies. The proposed antenna has minimum 24.42 dB isolation among the any two resonance frequencies. Moreover, variation in the patch length enables individual control over all resonant frequencies. The proposed antenna exhibits high isolation, compactness, and independent impedance control, making it well‐suited for compact and planar radio frequency systems. [ABSTRACT FROM AUTHOR]

In this paper, an omnidirectional circularly polarized (OCP) antenna is designed for base stations, providing high gain and wide axial ratio (AR) bandwidth. The six‐stage OCP antenna is built from cascaded spiral rings and vertical dipoles. To improve the roundness and enlarge the AR bandwidth, spirals in shunt are utilized in proximity to the feeding. Then, network characteristic mode theory is employed to provide frequency reconfiguration, to further expand AR bandwidth. Four internal ports are introduced at the current maximums of the OCP antenna. With proper reactive loads at the internal ports, the CP performances with omnidirectional patterns are reconstructed at a higher frequency band. As a result, the OCP antenna operates at the band of 3.3–3.78 GHz, with a maximum gain of 7.38 dBic. The out‐of‐roundness of pattern is less than 2.5 dB, indicating robust omnidirectional radiation performances. [ABSTRACT FROM AUTHOR]

A novel Quasi‐Yagi‐Uda antenna on a flexible material is designed and demonstrated in this paper. The antenna is developed on an ultra‐thin polyimide substrate to support dual‐frequency bands centered at 3.8 and 5.2 GHz for 5G and WiFi‐enabled wireless communications. The proposed Quasi‐Yagi‐Uda has a twin‐F‐shaped driven element which is excited using a microstrip line feed. The arms of the driven element are suitably designed to meet the frequency specifications of the proposed antenna. The design of the antenna is carried out using Computer Simulation Technology Microwave Studio while the antenna optimization is performed using the Fire‐Fly algorithm. The optimum geometrical details of the proposed antenna are obtained with a higher rate of convergence. The proposed dual‐band antenna provides 205 and 195 MHz bandwidth in both frequency bands guaranteeing high‐speed wireless communications in the 5G domain. The Quasi‐Yagi‐Uda provides a gain greater than 4.5 dBi in both operating bands with an efficiency greater than 80%. The prototype antenna optimized using the Fire‐Fly algorithm is fabricated and the simulation results are validated. [ABSTRACT FROM AUTHOR]

In this paper, a single‐layer filtering antenna based on half‐mode patches is proposed. It consists of a main driven patch and a parasitic patch. A U‐shaped slot is first etched on the main driven patch to generate a new resonant mode and a radiation null simultaneously. Four pairs of shorting pins are introduced on the main driven patch to raise its operating frequency to near that of the U‐shaped slot, thus broadening the impedance bandwidth (IBW). Additionally, a parasitic patch is introduced near the driven patch to introduce an extra half‐TM10 mode and an extra radiation null, significantly enhancing the IBW and the upper‐edge selectivity of the antenna. A prototype was fabricated and tested for validation. It achieves a peak realized gain of 6.55 dBi and −10‐dB IBW of 8.8%, and exhibits good out‐of‐band rejection performance while maintaining a low profile of 0.017 λ0 and a compact transverse size of 0.29 λ02. [ABSTRACT FROM AUTHOR]

In this paper, an ultrabroadband linear array in which horn‐reflector antennas are used as radiating elements by adding a central ridge to the rectangular waveguide, leading to an increased bandwidth of 3:1. With a reflector embedded in the H‐plane sectoral ridged horn, a desired narrow beam can be easily achieved. Moreover, due to the compact enclosed structure, the proposed reflector array can not only eliminate the illumination loss but also significantly reduce size compared with those of conventional array‐fed parabolic cylinder antennas. Good agreement between the calculated and measured results is obtained, showing that the proposed antenna array has a high aperture efficiency of about 80%, a ±45° scanning range in the E‐plane and 5° beam coverage with low side lobes in the H‐plane within the frequency range of 6–18 GHz. [ABSTRACT FROM AUTHOR]

The finite‐difference time‐domain (FDTD) method often demands numerous grids for fine structure analysis, leading to high computational costs. To address this challenge, a subgridding scheme emerges as an attractive solution. However, the explicit nature of the FDTD subgrid method, constrained by Courant–Friedrichs–Lewy (CFL) conditions, can lead to inefficiencies with complex structures. In response, the leapfrog alternating‐direction implicit (ADI)‐FDTD method, exhibiting unconditional stability, has been developed to overcome CFL limitations. This paper presents a hybrid approach merging the one‐step leapfrog ADI‐FDTD method with a subgridding scheme using heterogeneous computing. By optimizing hardware usage and leveraging different device performances, this approach maximizes throughput in heterogeneous systems. Central processing units and graphics processing units handle workloads to minimize system latency. Simulation results on heterogeneous platforms demonstrate superior efficiency over single processor setups while maintaining simulation accuracy, especially in analyzing electromagnetic scattering from multiscale structures. [ABSTRACT FROM AUTHOR]

This letter was to present an attempt of large‐wavelength Gaussian deconvolution phase‐contrast computed tomography (LW‐GD‐PCCT) for promotion of image quality reconstructed in low‐frequency band of terahertz (THz) spectrum at 0.11 THz. The interaction between the imaging samples and the THz Gaussian beam were formulated firstly in this paper, where the unwrapped phase was extracted specifically to portray the spatial structure distribution of the samples. Additionally, a Gaussian deconvolution was employed for the further reduction of spatial distortions. Moreover, an image reconstruction was carried out with the obtained phase sinograms based on phase‐used inverse Radon transform from the different positions on the sample. For an experimental assessment of the concept of LW‐GD‐PCCT, a single ellipsoid reflector‐based THz Gaussian beam generating system was established and samples such as polystyrene (PS) foam cuboid (Sample 1), and cylinder (Sample 2) with hollow defects (air holes and triangles) were prepared carefully in this work. To experimentally evaluate the performance of the contributing to the structural imaging over soft samples. Two‐dimensional topographies of each sample were reconstructed successfully, and the obtained cross root‐mean‐square error (cross‐RMSE), cross peak signal‐to‐noise ratio (cross‐PSNR), and cross structural similarity (cross‐SSIM) were 151.6451, 26.3225, and 0.9616 for Sample 1 with a high dose of 180 projections respectively, as well as 30.3242, 33.3129, and 0.9711 for Sample 2 with a low dose of 36 projections, respectively. The obtained imaging indicators of this work showed a superiority of imaging quality over those of recent works. Furthermore, the investigation of the bearing capacity has shown promise in enhancing image quality even in low‐dose conditions. The presented results suggest that the unwrapped phase combining with Gaussian deconvolution in low‐frequency band of THz imaging would be useful to improve the reconstructed image quality, potential to highly feasible non‐destructive testing of polymer foam via large wavelength. [ABSTRACT FROM AUTHOR]

In this paper, we explored the different performances of the evolution of polarization control parameters under algorithm optimization in one‐dimensional, two‐dimensional, and three‐dimensional parameter space. We found that the genetic algorithm (GA) operation has a typical converging trend as the epoch increasing of groups in ultra‐fast pulse generation. The corresponding deviations were calculated to be 10.8%, 11.2%, and 5.0%, respectively, which is different from the traversal algorithm operation. The typical noise‐like pulse state was effectively automatically searched at different length cavities, with center wavelengths of 1973, 1988.7, and 2002.7 nm, repetition rate of 9.4, 10.4, and 5.4 MHz, and typical spike duration of ~224 fs. Our research shows the effectiveness of the GA in searching and controlling the ultrashort pulse output of a 2‐µm thulium‐doped fiber laser. [ABSTRACT FROM AUTHOR]

In this paper, a compact differential bandpass filter with wide‐stopband is presented. The proposed differential filter is designed using two circular substrate‐integrated waveguide (SIW) cavities coupled through a pair of symmetric coupling slots. The filter operates in TM110 mode of the circular SIW cavity. The degenerate TM110 mode is shifted to higher frequency by the introduction of two pairs of perturbation vias. The center frequency of the differential passband can be tuned by changing different design parameters such as location of perturbation vias and length of the slotlines. As a proof of the proposed concept, a second‐order differential bandpass filter is designed, fabricated, and measured. The measured results are in good agreement with the electromagnetic‐simulated ones. [ABSTRACT FROM AUTHOR]

Mid‐infrared (MIR) fiber lasers are highly demand after for a variety of technological applications, including uses such as laser surgery, frequency metrology, and spectroscopy. This paper demonstrates a stable continuous‐wave laser operation in the 2.8 µm using an Er3+‐doped ZBLAN fiber operating in a free space experimental setting. A laser output power of 12.4 mW was attained in a linear cavity when this fiber was pumped at 2.9 W of 980 nm laser diode. [ABSTRACT FROM AUTHOR]

In this paper, a broadband reconfigurable active frequency selective rasorber is proposed, which can be used as a radome for antenna radar cross section (RCS) reduction. By tuning the active components, the radome can achieve in‐band RCS reduction and reconfigurable absorptive/transmissive states. In the absorptive state, the max bandwidth with an absorption rate greater than 90% spanning from 1.62 to 5.37 GHz; in the absorptive/transmissive state, 2.2 GHz is the transmissive frequency with the insertion loss of 93% while absorbing in 0.94–2.06 GHz and 2.63–6.5 GHz, which demonstrate impressive characteristics of broadband and a high absorption rate. Additionally, the radome can maintain performance at ±35° angular incidence and is insensitive to incident wave polarization. Furthermore, it features a lightweight and low‐profile design, with a cell electrical size of just 0.078λ × 0.078λ × 0.066λ. The prototype test shows a noteworthy correlation with simulation. This study has wider applications in the electromagnetic stealth of communication antennas and aircraft, as well as in the control of electromagnetic pollution signals in space. [ABSTRACT FROM AUTHOR]

Terahertz (THz) bands are considered to have various anticipated applications. Output power is an important factor determining the operating distance of THz systems, but it is very challenging to achieve high output power under current solid‐state terahertz circuit technology. The paper first presents a four‐way G‐band radial combiner, which features high passive efficiency of 88% and compact size. Moreover, based on this radial combiner and in‐house fabricated gallium nitride chips, a solid‐state power amplifier prototype is further demonstrated. Measured results show that, the average saturated output power is 21.7 dBm across the 180–240 GHz band with a typical output power of 23.2 dBm at 189 GHz. [ABSTRACT FROM AUTHOR]

A novel reflect‐transmit‐array antenna is proposed in this paper, in which a single‐layer heteropolarized element with a thickness of 0.1 λ0 ${\lambda }_{0}$ at 11 GHz, consisting of only two layers of metal patches printed on a dielectric substrate and six metal vias, can integrate reflection and transmission modes in the same frequency band by reasonably distributing the positions of the reflection and transmission parts in the element. We designed, fabricated, and measured the reflect‐transmit‐array antenna with an aperture of 501.2 mm2. At 11 GHz, the maximum gain of reflection is 17.7 dB, and the peak gain of transmission is 20.4 dB, indicating that this scheme has good application prospects in bidirectional wireless communication. [ABSTRACT FROM AUTHOR]

This paper presents the design of 2.5D frequency selective surface (FSS) for X and Ku band applications. Proposed FSS's unit cell is constructed with two independent slitted rings on both side of the FR4 substrate and is connected with metallic vias. The FSS offers a wide stop band performance from 6.26 to 18 GHz, with a fractional bandwidth of 96.7% measured at S21 < −10 dB and has a low insertion loss (IL) of 0.018 dB. The footprint of the FSS is only about 0.11λL ${\lambda }_{L}$ with the shielding effectiveness of 83.365 dB, and the transverse electric and transverse magnetic mode performances are stable up to 70 degrees. Prototype FSS is fabricated and measured for its performance validation. The performance validation is carried out using applied wave research and the equivalent circuit model tools. [ABSTRACT FROM AUTHOR]

A high gain D‐band hybrid integrated on‐chip antenna (OCA) based on a low‐cost printed circuit board (PCB) packaging technology is analyzed and designed in a standard 40‐nm CMOS process in this paper. The proposed OCA is a hybrid structure of a slotted patch OCA with off‐chip PCB ground and off‐chip dielectric resonator (DR). The proposed OCA exhibits a simulated gain of 3.5 dBi and 53% radiation efficiency at 150 GHz. The simulated impedance bandwidth is 20 GHz. The radiation performance and impedance bandwidth of the OCA are observably improved with the proposed techniques. The proposed OCA occupies 0.52 × 0.56 mm2, and addresses the highly desirable yet challenging overall design of future low‐cost integrated millimeter‐wave (mm‐Wave) and terahertz (THz) systems, which hit the mark on cost and compatibility. [ABSTRACT FROM AUTHOR]