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In this study, a three‐dimensional bandpass frequency selective surface (FSS) with a new fabrication technology is proposed and designed based on slotlines. The proposed FSS consists of silver paste circuits printed on aramid paper, and is vertically and horizontally arranged to form a periodic array in honeycomb structure. To better understand the design principle of the proposed FSS, the equivalent circuit model (ECM), single‐polarized structure, and dual‐polarized structure are presented and analyzed, respectively. The proposed FSS exhibits a passband at 4.1 GHz with a fractional bandwidth of 71.5% at x‐polarization and 66.2% at y‐polarization with reflectivity less than −10 dB. Moreover, the reflection and transmission coefficients have relative stable properties up to 30° for the oblique incidence. Then, the proposed structure is fabricated and measured to verify the design strategies. The measured and simulated results have reasonable agreement under a large variation of incident angles. [ABSTRACT FROM AUTHOR]

How to monitor the freshness of packaged food, the safety of sealed medicine, or the other substances in sealed space wirelessly and environment‐friendly has become an urgent problem in recent years. After summarizing the theory of the LC sensor, a design of a paper‐based resonator (30 mm × 30 mm × 0.15 mm) consisting of a finger capacitor is proposed in this paper. The sensor is embedded inside the package by adhering it to the package's inner wall. Its response is remotely detected through a readout coil. This paper establishes a circuit simulation model and an electromagnetic simulation model to verify the feasibility of the design. Compared with the real object and the theoretical simulation model, the difference between the results only within 1 MHz, which verifies the correctness of the theory. Additionally, the measured results indicate that the resonant frequency of the resonator shifted from 102.441 MHz to 88.195 MHz, after dropping water on the sensor. Besides, the simple fabrication technology and inexpensive sensor material ensure a low cost, thus making this technology economically viable. [ABSTRACT FROM AUTHOR]

In this article, the authors conduct a study of bending effects of a paper‐based printed antenna in order to predict the behavior of an antenna placed inside a package with restricted dimensions. The study begins with a model of an electrical dipole consisting of two misaligned parts to evaluate qualitatively the effect of the angle between two parts and the proportion of their lengths on the radiation properties of the dipole. In order to validate the theoretical prediction, a wide‐band "mushroom‐shaped with two arms" monopole antenna structure printed on 0.104 mm thick paper is proposed. This antenna covers a very wide frequency range from 1.8 GHz to over 10 GHz, including two WLAN bands. Its radiation patterns are nearly omni‐directional at 2.45 and 5.5 GHz. The study of substrate bending effects shows that the matching properties of the antenna are maintained, but the antenna radiation patterns are rotated by an angle with respect to the case without bending. The results of our study can be used to predict the performance of an antenna when it is deformed in a telecommunication set‐top box with restricted dimensions. [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]

A compact 2-element antenna for MIMO applications with performance across the WLAN frequency bands is designed and fabricated on paper with a FUJI Film Dimatix 2800 material printer and conductive ink. This antenna is ∼1.1 cm × 3.5 cm and utilizes co-planar feeding techniques and ground design to allow for resonance in the 2.4 and 5 GHz frequency bands with a minimum 800-MHz bandwidth. The design is established using commercially available products for minimal processing. Factors such as ink handling, printing conditions, and paper selection are discussed qualitatively as they relate to antenna fabrication and performance. Successful simulation and fabrication is reported with low correlation, high isolation, and low reflection. [ABSTRACT FROM AUTHOR]

Abstract: A wide band flexible substrate based metamaterial is presented. The metamaterial is fabricated on photo paper using conductive nanoparticle ink targeting flexibility applications. The metamaterial structure shows a wide double negative region of 1.848 GHz (8.298–10.146 GHz). The transmission coefficient of the proposed metamaterial has been measured and verified with simulated one. The perceptible novelties of the proposed work are its simplicity, cost effectiveness, and flexibility with covering wide X‐band microwave spectra. [ABSTRACT FROM AUTHOR]

This letter presents a new technique to fabricate aperture type cylindrical frequency selective surface (FSS) with circular, tripole, and plus shaped element. The cylindrical FSSs exhibit band pass property from 5 to 9 GHz, 11.75 to 14.75 GHz, and 7 to 14 GHz, respectively. A novel method with aluminium foil paper is suggested for fabrication. Cylindrical FSS is fabricated with this technique in laboratory with commercially available aluminium foil paper and is measured practically. In this technique, with the help of laser cutting machine 0.01 mm precision label can be achieved. Both simulated and measured results are in good agreement. The aluminium foil paper made FSS proved to be very light weight, flexible and low cost. [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]

ABSTRACT A significant cost in the widespread deployment of UHF radio frequency identification (RFID) systems has been the passive RFID tags. To address some of this expense, this paper presents an antenna design for UHF RFID tags that can be printed on inexpensive paper substrates and operate in the near field of the UHF reader. This antenna design is based on meander line miniaturization techniques and open complementary split ring resonator (OCSRR) elements to reduce the amount of conducting material required to manufacture the antenna by 30%. For demonstration purposes, a prototype near-field UHF RFID tag was manufactured on a paper substrate and the read-range was measured at 920 MHz. It was shown that useful read-ranges could be achieved while reducing the overall cost and size of the antenna on the RFID tag. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1052-1056, 2017 [ABSTRACT FROM AUTHOR]

ABSTRACT Two key components, among several, in the design of a conformal antenna are the planar conductors and the flexible substrates. In this paper, a new approach of using graphene-based conductors instead of copper conductors in the design of a conformal antenna is presented. To determine the conductivity properties of the graphene-based conductor, the copper conductors in a well-known micro-strip transmission line (TL) and micro-strip antenna were replaced with the graphene-based conductors and were analytically evaluated, simulated in a full-wave simulation software and experimentally tested. Overall, it was shown that these graphene-based conductors have a conductivity that is high enough to design a useful micro-strip TL and micro-strip antenna. In particular, a conductivity of σ = 1.94 × [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents the design, manufacturing, and measurements of antennas on paper, realized using ink-jet printing of conductive inks based on nano-silver particles (nSPs). The extraction of the substrate characteristics such as the dielectric constant and dielectric loss is performed using a printed ring resonator technique. The characterization of the nSPs conductive inks assesses different parameters as sintering time and temperature. Two antennas are realized corresponding to the most common needs for wireless sensor networks in Trains Environment. The first one is a patch antenna characterized by a broadside radiation pattern and suited for operation on metallic structures. The second one is a quasi-yagi antenna, with an end fire radiation pattern and higher directivity, without requiring a metallic ground plane. Both antennas present a good matching ( S11 < −20 dB and S11 < −30 dB, respectively) and acceptable efficiency (55% and 45%, respectively) for the paper substrate used at the center frequency of 2.4 GHz, corresponding to the first channel of the IEEE 802.15.4 band. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:754-759, 2016 [ABSTRACT FROM AUTHOR]

ABSTRACT A pattern-switchable origami antenna is designed with paper using inkjet-printing technology. The proposed antenna can be switched between loop and dipole antenna modes by folding and unfolding the paper, respectively. Eutectic gallium-indium liquid metal is introduced in order to avoid cracks in the conductive ink when the paper is folded. The performance of the proposed antenna is demonstrated through simulation and measurement results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:668-672, 2016 [ABSTRACT FROM AUTHOR]

In this paper, work on a Ganesha‐shaped semi‐transparent patch antenna is presented for its use in vehicular application. The design of the antenna is opted from a commercially available Ganesha sticker that is mostly placed on the vehicle's window panes as a symbol of an auspicious deity. The geometry of the sticker without any variation in its dimension is made to work as an antenna. The antenna is fabricated using adhesive copper tape on a glass slab backed by an AgHT‐8 transparent conducting sheet which acts as the ground plane. Microstrip inset feeding technique is used to excite the patch and its return loss performance and free space radiation pattern measurements are carried out. Measured results show promising performances that can be used in future vehicular applications and are in good comparison with that of the simulated results. [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]

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]

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]

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]

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, 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]

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, 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]

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]

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]

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]

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]

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]

Nowadays, demand for active frequency‐selective surfaces (FSSs) is increasing due to their reconfigurable characteristics. Numerical simulations of reactive elements require a model that can replicate their physical realization. Traditionally, reactive elements are modeled as approximated lumped circuits during electromagnetic simulations. However, such lumped circuits might fail to replicate device characteristics at high frequencies, leading to approximate results. This paper presents an alternative method to model reactive elements using their simulation program with integrated circuit emphasis models (SPICE) in circuit co‐simulations. The proposed modeling method is investigated by realizing a varactor‐loaded active FSS‐based tunable absorber. Simulated results indicate that the proposed absorber provides tunability in a wide frequency range from 0.54 to 2.09 GHz under normal incidence when electrostatic bias varies from 0 to 28 V. Moreover, polarization‐independent and exhibits stable frequency response for oblique incidences up to 80° for dual‐polarizations. These characteristics make it a potential candidate for stealth applications. [ABSTRACT FROM AUTHOR]

In this paper, an orbital angular momentum (OAM) mode reconfigurable antenna based on a uniform circular array (UCA) is presented. The phase superposition method is presented to overcome the limitation of the number of array units on the mode order in the conventional four‐element UCA antenna, which is limited to generating first‐order OAM beams. The unit phase is introduced by a bifilar helical antenna in this method, and the unit phase is superimposed with the feed phase of the UCA to enable the generation of 3rd‐order OAM beams from the four‐element UCA. At the same time, the DC signal‐controlled feed network assigns three distinct feed phases to the UCA, which realizes the reconfigurability of the three OAM beams. To achieve mode reconfigurability, 20 p‐i‐n diodes were integrated as switches in the feed network for controlling the ON/OFF status of p‐i‐n diodes in the feed network using DC signals. Finally, simulated and measured results show that three OAM beams (lz = −1, −2, and −3) have been generated in the frequency band from 10.6 to 11.8 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a genetic‐based synthesis approach for an impedance matching section based on a composite right‐/left‐handed (CRLH) transmission line model called CRLH transmission line impedance matching section (CRLHTLIMS) in viewpoint of transmission phase shift and noise figure is newly presented. To find the unknown values of right‐/left‐handed inductances and capacitances of a CRLHTLIMS, a type of global optimization algorithm called continuous parameter genetic algorithm is used. The length, transmission phase shift, and noise figure of the CRLHTLIMS are computed by using simple equations. Different examples for a uniform CRLHTLIMS are given. According to the results, this approach is an easy and effective way for the synthesis of transmission line impedance matching sections in viewpoint of transmission phase shift and noise figure. [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]

In this paper, a novel three‐pole bandpass filter with a pair of controllable transmission zeros (TZs) is proposed first. The proposed structure is based on asymmetric dual‐postresonators and two external resonators. The fundamental mode and the first higher mode of the asymmetric dual‐postresonators are used as the nonresonant mode and the resonant mode separately. The nonresonant mode generates direct source to load negative coupling, thus providing one TZ located below the passband. The asymmetric dual‐postresonators and one of the external resonators R3 form a magnetically coupled cascaded triplet unit to produce the other TZ above the passband. Therefore, these two TZs are independently controlled. Moreover, the filter has a good quality factor (Qu ${Q}_{u}$), of around 2700, compact size and an excellent out‐of‐band performance. For further suppressing the harmonic response and improving the processing accuracy, a six‐pole bandpass filter with harmonic suppression is designed and fabricated by using metal 3D printing technology. The measured result matches well with the simulated one, which verifies the accuracy of the method. [ABSTRACT FROM AUTHOR]

The advancement of smart cities and intelligent industries has accentuated the necessity for reliable indoor communication and precise indoor positioning. In response, this paper presents an innovative integrated system for indoor visible light communication and positioning, designed to facilitate robust communication and pinpoint accuracy in positioning for indoor applications. We incorporate multiband carrierless amplitude and phase (m $m$CAP) modulation to mitigate interference between communication and positioning subcarriers. Unlike the conventional orthogonal frequency division multiplexing‐based subcarrier modulation (OFDM‐SCM), m $m$CAP demonstrates reduced out‐of‐band interference and a diminished peak‐to‐average power ratio (PAPR). Moreover, we introduce the frequency domain optical zero correlation zone (FD‐OZCZ) code, integrated within the m $m$CAP signal to optimize the distribution of positioning subcarriers. Simulation outcomes substantiate that our proposed m $m$CAP, augmented with FD‐OZCZ, outperforms OFDM‐SCM systems in delivering reliable communication and exceptional positioning accuracy. [ABSTRACT FROM AUTHOR]

This paper presents a design to realize extremely low cross‐polarization level in multibeam antenna. The antenna consists of two reflectors placed on top of each other. The front reflector is a panel made of metal grid, which is used to separate two orthogonal polarizations. The rear reflector serves as the actual multibeam antenna surface. The multibeam antenna and feed array operated at Ku band are designed and fabricated. The test results show that the gains of the 28 beams can be better than 40.42 dBi, and the cross‐polarization level can be lower than −40 dB. The proposed method provides a novel idea for the design of ultralow cross‐polarization multibeam antenna. [ABSTRACT FROM AUTHOR]

This paper presents an innovative carbon dioxide sensor leveraging a dense‐pattern multipass absorption cell. This novel design dramatically compacts an extensive optical path of approximately 11.4 m into a 70 mm inter‐mirror distance, effectively enhancing the system's sensitivity and reducing its size. Utilizing a 2004 nm diode laser, the sensor accurately targets a potent CO2 absorption line at 4989.9 cm−1. Experimental validation reveals remarkable linearity (R² =.999) and a detection limit of 59 ppb with 1 s integration time. The incorporation of Kalman filtering techniques further refines the sensor's performance, reducing the detection limit to 30 ppb—a substantial improvement of 49%. This advancement in sensor technology marks a significant step forward in efficient and precise CO2 monitoring. [ABSTRACT FROM AUTHOR]

The emission of carbon dioxide (CO2) by thermal power plants is the main factor leading to the greenhouse effect. The measurement of CO2 is of great significance to carbon emission data statistics. In this paper, a measurement system based on tunable diode laser absorption spectroscopy (TDLAS) was built to measure the spectrum of CO2 near 1579 nm. To simplify the experimental system, a direct absorption signal fitting method is proposed to replace etalons for time‐frequency conversion. The method was applied to the measurement of four different concentrations of CO2 in the range of 7%–16%, and the measurement results were compared with the multipeak method, another etalon‐free method. The results show that the mean relative error of the measurement results is 4.23%, which is 1.76% lower than the measurement results of the multipeak method. The experimental research provides a feasible idea to simplify the CO2 measurement system based on TDLAS. [ABSTRACT FROM AUTHOR]

We proposed a theoretical study of silicon nitride ring resonator configuration for the application of refractive index sensing. In this paper, a slot waveguide has been used to couple the light into the slab ring structure. We have designed the slab ring and slot waveguides with silicon nitride (Si3N4) on a substrate made of silica (SiO2). Transverse electric (TE) mode has been used for the entire analysis at an operating wavelength of 1550 nm. The presented structure has been geometrically optimized to get the better transmission results. The design shows a resonance wavelength of 1538.74 nm when the cladding refractive index(ntop) $({n}_{{top}})$ is equal to 1, which is placed at the top of the slab ring structure. We have also calculated the effect on the transmission curve for different waveguide parameters. For, ntop=1.35 ${n}_{{top}}=1.35$ the structure achieves a resonance wavelength around 1563.65 nm. The geometrically optimized structure achieved a Q‐factor of 750 and a sensitivity of 70 nm/RIU. In the proposed paper, the shift in the resonance of the transmission spectrum has been utilized to detect the Refractive Index (RI) changes on the surface of the ring. Therefore, the proposed structure can be used effectively in the applications of refractive index sensing. [ABSTRACT FROM AUTHOR]

The pulse laser using a saturable absorber as a passive device has the advantages of narrow pulse width, high repetition rate, and high pulse energy. Low‐dimensional materials have attracted research interest in recent years due to their excellent saturable absorption properties, ultra‐fast carrier response speed, high damage threshold, and so on. This paper gives a brief review of the state‐of‐the‐at 2 µm solid‐state lasers using saturable absorbers. The output performance of lasers in repetition rate, pulse energy, pulse width, and wavelength are summarized. The paper is expected to provide a development direction of novel materials as saturable absorbers in 2 µm solid‐state lasers. [ABSTRACT FROM AUTHOR]

In this paper, a dual‐polarized multibeam antenna in X‐band is designed and physically fabricated using a parabolic reflector. The antenna consists of a feed array and a metal reflector. A dual‐polarized microstrip antenna array combining two design approaches, T‐coupled feed and defective ground structure, is adopted as the feed array to improve polarization isolation. In addition, the electromagnetic bandgap structure is loaded between the antenna units to reduce the mutual coupling and improve the isolation between the units. A nine element of the highly‐isolated dual‐polarized microstrip antenna array is designed to be placed on the focal plane of the parabolic reflector as the feed, and the beam deflection is realized by using the lateral defocus effect of the parabolic plane, which can finally realize nine single beams covering a 30° scanning range in both horizontal and vertical polarization modes. Based on the scanning state of multiple point beams, this paper uses the Fourier series for beam assignment to form a flat‐top beam with a wide scanning angle. The application of the antenna with two operating modes of wide beam and multibeam to navigational satellite systems can greatly improve the accuracy and efficiency of navigation. [ABSTRACT FROM AUTHOR]

This paper presents a novel wideband circularly polarized antenna that is fed by substrate‐integrated waveguide. Based on the design of placing a pair of chamfered semicircular patches above a slot, a π ${\rm{\pi }}$‐shaped radiator is introduced between the semicircular patches. Multiple resonance points are generated by the combination of the entire radiating structure and a dumbbell‐shaped slot, resulting in improved impedance bandwidth and axial ratio (AR) bandwidth. The proposed element exhibits a wide impedance bandwidth of 50.5% (24.5–41.1 GHz) and an AR bandwidth of 44.2% (25.1–39.3 GHz) with a 44.2% overlapped bandwidth. Then, a 4 × 4 antenna array adopting the sequential rotation technique is constructed. The measured results demonstrate that a 40.6% overlapped bandwidth and a peak gain of 19.1 dBic are achieved. The proposed antenna array shows excellent performance, making it a good candidate for applications in millimeter‐wave wireless communication systems. [ABSTRACT FROM AUTHOR]

An arrayable dual‐polarized antenna is proposed in this paper, which exhibits a low profile and broad bandwidth. A metasurface and a square ring are introduced to realize the broadband operation of the low‐profile dual‐polarized antenna. The total size of the broadband antenna is 0.39λL×0.39λL×0.105λL $0.39{\lambda }_{{\rm{L}}}\times 0.39{\lambda }_{{\rm{L}}}\times 0.105{\lambda }_{{\rm{L}}}$ (where λL ${\lambda }_{{\rm{L}}}$ is the wavelength at the lowest frequency of the operation band [1.31 GHz] in free space), suitable for use as an element of an antenna array. Four elements of the proposed antenna are arrayed to develop an array to demonstrate its application for the base station. The measured impedance bandwidth (return loss >10 dB) of the array is about 70% (1.31–2.74 GHz). Stable radiation patterns are obtained with an average gain of 14 dBi. [ABSTRACT FROM AUTHOR]

Recently, vector beams with special intensity and phase distribution have received much attention due to their unique properties. In this paper, we construct the double‐petal linear edge dislocation (DPLED) beams based on Gaussian vortex beams. The distribution of intensity, polarization, and spin angular momentum (SAM) of the DPLED beams is analyzed in tightly focused based on the Richards‐Wolf vector diffraction theory. The significant difference is occurred in light field, polarization SAM, and polarization distributions before and after focusing of DPLED beams. It's of certain importance for expanding the application of vector beams in optical control, optical imaging, and other fields. [ABSTRACT FROM AUTHOR]

This paper presents the design and prototype development of a compact frequency‐selective surface (FSS) for shielding WLAN signals. The FSS unit‐cell geometry is evolved by modifying the arms of the conventional crossed dipole element. The footprint of the unit cell is only 6 mm × 6 mm × 1.6 mm. The proposed FSS offers stop band characteristics at 5 GHz for both transverse electric (TE) and transverse magnetic (TM) modes. In addition, the FSS offers angular stability up to 60°. A prototype of the proposed FSS is fabricated and measured to validate its simulations. Measured bandwidth of the stop band is 410 MHz, referenced at −20 dB for both TE and TM modes. Equivalent circuit model of the FSS is derived and the results are compared with the simulations. [ABSTRACT FROM AUTHOR]

This paper proposes a programmable solar‐powered radio frequency (RF) transmitter. It employs a novel five‐layer structure that effectively integrates solar cells, active circuits, and broadband antenna. This design can directly emit RF signals without the need for additional power supply, enabling efficient energy conversion and transmission. In addition, a U‐shaped coupling line model is introduced to evaluate the performance of the active circuit. We fabricated a sample and measured it. The results of the measurements indicate that the proposed RF transmitter can achieve self‐powering and programmable output at any frequency within the range of 2.08–4.1 GHz, with an output power of no less than 14 dBm. Moreover, the solar cells are placed on both sides of the circuits and antenna for energy harvesting, achieving 100% sunlight insolation with a 75.5% coverage ratio. This design can be used for self‐powered green wireless system applications. [ABSTRACT FROM AUTHOR]