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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]

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]

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 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]

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 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]

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 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]

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]

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]

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 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]

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]

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]

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]

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]

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]

This paper presents a small‐sized, planar antenna fabrication for ultra‐wideband (UWB) and vehicle‐to‐everything (V2X) applications. The design is inspired by a hexagonal ring, providing an UWB bandwidth of 16.61 GHz (from 3.33 to 19.94 GHz) and a fractional bandwidth of 142.75%. A suitably placed inverted‐U slot in the feed line helps in achieving the WLAN notch band (from 5.04 to 6.01 GHz). The overall design footprint is 0.17 × 0.23 λ02 in size, provides stable radiation characteristics, and a gain of 4 dBi in the pass‐band with stable time‐domain performance. The proposed antenna also covers both 3.5 GHz (LTE‐42 Band) and 5.9 GHz (DSRC Band), therefore being suitable for modern UWB frontends and V2X communication. [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]

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]

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]

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 proposes a broadband optical transparent antenna using a transparent conductor film on a transparent polyethylene terephthalate (PET) substrate. The planar wide‐slot antenna coupling fed by microstrip has a wide impedance bandwidth, so it is selected to design the transparent antenna. The upper surface of the PET substrate is a microstrip line with a fork‐shaped tuning branch, and the lower surface is a wide slot. They were made of transparent conductor film. Finally, a new capacitive coupling method is used to feed the transparent antenna. The transparent conductor film used in the antenna is metal mesh, which was developed by 3M company. The metal mesh with an open area greater than 80% to achieve high transmittance. The measured results show that the impedance bandwidth is 177% (0.30–5.0 GHz), and the gain of the antenna varies from 5.06 to 7.8 dBi over the entire frequency band. Therefore, it can be well applied to the current indoor mobile communication system. [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]

The paper proposes a circularly polarized dual band single feed microstrip monopole antenna. The proposed antenna consists of a radiating patch, a shrink ground plane, and a 50 Ω microstrip transmission line feed. The radiating patch is a combination of three modified metallic strips, a modified rectangular strip and a semicircular strip. The ground plane consists of two modified open ended slots. The substrate area of the antenna is only 40 mm × 42 mm × 1.6 mm. The antenna has been designed by HFSS simulation software and after getting simulated results the antenna has been fabricated to verify its results. The antenna provides measured bandwidths (−10 dB impedance bandwidth) of 600 MHz (2.2–2.8 GHz) in the lower band and 2.1 GHz (7.5–9.6 GHz) in the higher band. The measured results show its 3 dB axial ratio bandwidth of 120 MHz (2.2–2.32 GHz) for lower band and 1.4 GHz (7.2–8.6) GHz for the upper band. The high measured peak gain of 8 dBi has been obtained from the proposed antenna. The lower band is useful for WiMAX application and upper band is useful for C band application. The desired radiation patterns (RHCP and LHCP) have been obtained from the proposed antenna. [ABSTRACT FROM AUTHOR]

The present study focuses on the manifestation of the Doppler effect in low‐Earth orbit (LEO) satellite constellations with laser inter‐satellite links (LISLs). In this letter, the LEO satellite constellation parameters that influence the variation of the Doppler effect in LISLs are presented. The LEO satellite constellation configurations that perform LISLs with less possible Doppler effect could be designed based on the tendency of the Doppler wavelength shift (DWS) as a function of the LEO satellite constellation's parameters. The paper presents the main LEO satellite constellation parameters that involve the variation of the Doppler effect, such as the altitude of the satellites, the orbital plane number within the constellation, and the inclination angle of the orbital plane. In addition to the operating laser wavelength that is employed as a data carrier. These parameters could be helpful to control the Doppler effect in LISL before building an LEO constellation. [ABSTRACT FROM AUTHOR]

A waveguide‐fed reflector antenna with high gain and multi‐beam capability is introduced and demonstrated at 220 GHz. Terahertz waves have a very small wavelength, which poses great challenges to the fabrication of terahertz antenna arrays and the connection with the T/R components. In this paper, a horn array with an element spacing less than one wavelength for terahertz frequency is presented and demonstrated, and its excitations are fan‐out using curved waveguides. The horn array is used as a feeding source of an offset parabolic reflector to achieve high‐gain and multi‐beam performance. The reflector antenna achieves four beam positions with θ = −0.7°, −0.2°, 0.2°, and 0.7°, and each beam obtains the gain of about 45 dBi. The experimental reflector antenna is fabricated and tested. Good experimental results further confirm the feasibility of the antenna and the potential application in Terahertz systems. [ABSTRACT FROM AUTHOR]

In this paper, a single‐fed broadband circularly polarized (CP) filtering patch antenna based on metasurface is proposed. It consists of a corner‐truncated square patch, a nonuniform metasurface, and a U‐shaped strip. By placing the metasurface above the driven patch antenna, a radiation null is realized at the upper band, and an additional axial ratio (AR) minimum is simultaneously generated to enhance the CP bandwidth. Besides, two more radiation nulls are achieved at each side of the band edges by introducing a U‐shaped strip underneath the patch and embedding a shorting pin into the patch, which further improves the frequency selectivity and suppresses the radiation level. Measured results show that the designed antenna has a wide impedance bandwidth of 19.7% (4.8–5.85 GHz), a CP bandwidth of 19.9% (4.75–5.8 GHz), and an in‐band average gain of 7 dBic with suppression level of more than 18 dB at out of band. [ABSTRACT FROM AUTHOR]

In this paper, we come up with a unique technique to generate the ideal pattern diversity with the help of 24 Vivaldi antennas. With the help of a mathematical concept called golden angle, the 24 antenna elements are arranged in such a way that the radiation patterns will never overlap and the mutual coupling will be very low. It is also verified from the simulations and the measured results that the envelope correlation coefficient is less than 0.01 in the 3–4.2 GHz which is a sub‐6 GHz band for 5G. This same concept can be extended to a greater number of antennas also. [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]

This paper proposes a high aperture efficiency (AE) small size tensor holographic impedance metasurface (THIMS), which has the ability to create circular polarized (CP) high purity orbital angular momentum (OAM) multi‐beams with flexibly independent control of the individual beam direction, polarization and OAM mode. The tensor unit cell is a cross‐slotted circular patch. We design a THIMS at 14.6 GHz for dual CP OAM beams: Beam‐I (LHCP, l = 1, θ1 = 30°, φ1 = 0°), Beam‐II (RHCP, l = −1, θ2 = 30°, φ2 = 180°). The developed tensor dual CP THIMS has the following advantages: high purity in xoy plane at z = 9.73 λ (λ wavelength, measured purity 88.4% for Beam‐I, and 93.5% for Beam‐II), high AE 25.1%, and small size 5.986 λ × 5.986 λ × 0.0618 λ. The calculated, simulated and measured results agree well. The generated dual CP OAM beams have potential applications for high‐capacity wireless communication, radar high resolution imaging, and rotation velocity measurement. [ABSTRACT FROM AUTHOR]

This paper presents a miniaturized broadband microstrip patch antenna with a simple geometry. The radiation patch of this antenna comprises two rectangular patches with slightly different sizes, one side of each patch is grounded by metal via‐holes. Two rectangular patches are connected by a microstrip line and fed by a single port. Two rectangular patches produce two closely resonant frequencies achieving broadband performance. This antenna operates on the resonant method of short‐circuiting on one side. Metal via‐holes act as a short‐circuit wall allowing each patch to operate in TM0.5,0 mode. The size of a 1/4 wavelength resonant patch is only half of a conventional microstrip antenna, the overall size of this antenna is almost as same as a conventional rectangular microstrip antenna, making it compact in size. The wideband is achieved by combining two radiating patches, resulting in stable radiation and flat gain. Measurement results show that the antenna has an impedance bandwidth of 4.35− $-$5.10 GHz (15.8%) using a common dielectric substrate without air layer thickness additionally. The maximum measured realized gain is 4.61 dB. This antenna has advantages of wide bandwidth, low profile, flat gain and ease of manufacturing. [ABSTRACT FROM AUTHOR]

In this paper, the researchers offer a miniatured design of microstrip lines based on magnetic resonance imaging (MRI) coils that can be utilized to detect tumor tissues and to restore those tissues after radiotherapy. A 61.67% reduction in size was achieved in the MRI array dimensions when compared to the previously reported MRI coils. The reliability of the design specifications was verified. The proposed MRI coils could contribute two resonant modes. Primarily, these MRI coils were suitable for homogenous magnetic field and they enable radio frequency (RF) heating by generating a concentrated electric field |E|. The collective temperature and specific absorption ratio (SAR) have been estimated at Larmor frequency. In this study, it was possible to create a uniform magnetic flux density |B1| field operating at 500 MHz. These proposed coils were excited at 8.06 GHz. When simulating cancer in a biological system, healthy tissues were introduced into a Class A scenario and malignant tissues were introduced into a Class B scenario. According to these two scenarios, tumor tissues were magnetically (|B1|) homogeneous with a 44.1% standard deviation with rapidly raised temperature at 4.77°C. These MRI coils delivered an impact on diagnostic imaging and parallelly restored the cancerous tissues by hyperthermia. [ABSTRACT FROM AUTHOR]

This paper proposes a dispersion‐reconfigurable reflection‐type phaser based on the stepped‐impedance microstrip line structure. By configuring "ON" and "OFF" states of switches, the proposed phaser exhibits positive‐slope, negative‐slope, and zero‐slope linearly dispersive group delay responses. For proof‐of‐concept demonstration, we use line connection/disconnection to mimic the ON/OFF states of real switches. Three prototypes are hence fabricated to represent the three different states. The experimental results agree well with the expected responses, which finally validate the proposed concept. [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 presents a Ku‐band divide‐by‐2 direct injection‐locked frequency divider (ILFD) with a wide locking range (LR) and high input sensitivity. The proposed ILFD incorporates an auto‐adjusted injection bias that uses a power detector (PD) to convert the power of the injected signal to a DC voltage. The bias voltage of the injection transistor is then auto‐adjusted in response to the output of the PD. The proposed ILFD employs a 2‐bit switched capacitor array to further enhance the entire LR. Implemented in a 65‐nm CMOS process, the experimental results show that the proposed ILFD achieves an LR of 62.3% (10.5–20 GHz) and 51.2% (11.2–18.9 GHz) at 0 and −10 dBm injection power, respectively. The proposed ILFD consumes 3.6 mW from a 0.6 V supply, and the core area is 0.067 mm2. [ABSTRACT FROM AUTHOR]

A variable universe fuzzy proportional‐integral‐differential (PID) algorithm was designed and first application for a laser power stabilization system. To validate the algorithm's effectiveness, it is applied to the simulation model of Simulink and the experimental system based on an acousto‐optic modulator. The results demonstrate that the variable universe fuzzy PID presents higher control precision, better robustness, and can suppress long‐term drift phenomena compared with the traditional feedback control algorithm. The algorithm design method in this paper has significant reference and guidance value for laser power stabilization system. [ABSTRACT FROM AUTHOR]

This paper presents the design of multiband frequency reconfigurable patch antenna with switchable radiation pattern and polarization states. The antenna design is based on a circular patch radiator with a pair of metallic strips placed on diametrically opposite sides of it. Circular polarization (CP) from the antenna is excited by etching a pair of slots with a coaxial feed. When the diodes are OFF, the antenna resonates at 4.2, 6.6 GHz, (C band) and 8.07 GHz (X band) and the main beam is located at 0⁰ with CP at X band. The resonance at 4.2 and 8.5 GHz are observed when one of the diode is ON. The main beam at X band is being shifted from −30⁰ to 0⁰ and +30⁰ in the elevation plane during the change in operating modes. Peak gain of the antenna is 6 dBi in all the operating modes. [ABSTRACT FROM AUTHOR]

In this paper, a novel source second harmonic manipulation architecture achieving second harmonic control at device input is proposed to solve the issue of reduced operating efficiency of power amplifiers (PAs) caused by the input nonlinearity in continuous Class‐GF mode. The key to the proposed architecture lies in the use of a compact multibranch network to match the source second harmonics of the three design frequency points to the short‐circuit state, which can expand bandwidth while avoiding unexpected efficiency degradation. Considering the necessity of theoretical verification, a broadband continuous Class‐GF PA is designed, implemented, and assembled employing a commercially available 10‐W gallium nitride device. The measured results show that a fractional bandwidth of 100% across 1.1–3.3 GHz with a drain efficiency of 62.4%–72.5%, an output power of 40.1–42.2 dBm, and a gain of 10.1–12.2 dBm are achieved under saturated output power. [ABSTRACT FROM AUTHOR]

This paper equates chaff clouds to dipole clusters and studies the electromagnetic scattering problem of dipole clusters based on the linear method of moment (LMM) that solve the electric field Integral equation with the pulse basis function. Firstly, the radar cross section (RCS) of three dipole elements is calculated. The dipole element is divided into 11 segment line units using pulse basis functions. The actual chaff clouds are modeled as two nearest dipole cluster models, which are cubic dipole cluster with uniform distribution formed and spherical dipole cluster with Gaussian distribution formed. The total RCS and total E‐Field magnitude of two dipole cluster models were calculated. Finally, two physical models are constructed based on the simulation models and an experiment is designed. The electromagnetic scattering characteristics of the two models are measured, which verifies the accuracy of the simulation results and the operability of the experiment. [ABSTRACT FROM AUTHOR]

This paper presents a novel scheme to online measure the birefringence of the sensing fiber in all‐fiber optic current transformer (AFOCT) system, which monitors the current on direct current (DC) transmission lines using the Faraday magneto‐optic effect in sensing fibers. In this scheme, by purposefully varying the difference of square‐wave modulated phases via the phase modulator in the AFOCT system, different system transmittances can be obtained. On the basis of the relationship between the system transmittance and linear and circular birefringences, an online measurement scheme of both the linear and circular birefringences of the sensing fibers can be established. In this scheme, the AFOCT system is described by the transmission model based on the Jones matrices, with which the current on DC transmission lines can be measured from the phase shift caused by the Faraday effect. Then, under different square‐wave modulated phases, the system transmittance models are constructed with respect to the linear and circular birefringences of the sensing fiber. For a given sensing fiber with certain linear and circular birefringences, the specific system transmittances are determined and are the curves in space in the respective system transmittance models. Subsequently, these curves in space can be projected onto the coordinate plane composed of the linear and circular birefringence coordinate axes, where the intersection point of the projected plane curves gives the to‐be‐measured values of the linear and circular birefringences of the sensing fiber. The proposed scheme is validated by the preset linear and circular birefringences of the sensing fiber, with different linear birefringences of the polarization‐maintaining fiber. The measurement results show the values consistent with the preset ones. [ABSTRACT FROM AUTHOR]

Logic gates are an indispensable part of digital circuits, and therefore such devices with fast operating speeds and simple designs are vital for all kinds of electronic applications. This paper proposes simple Y‐shaped designs of all‐optical AND, OR, and NOT logic gates in two dimensions that are operational in both TE and TM modes. These gates are designed using silicon slab waveguides, which makes them relatively easy to fabricate. The logic gates are designed, analyzed, and optimized at 1.55 µm using the finite difference time domain method. The truth tables of the proposed all‐optical logic gates are realized for every input case. The propagation delay time is determined to be of the order of femtoseconds (10−15 s), which is very fast compared to the response time of the currently reported all‐optical logic gates (10−9 ‐ 10−12 s). [ABSTRACT FROM AUTHOR]

This paper presents an additive manufacturing technique to design and prototype a reflective metasurface antenna for Ka‐band applications. The dielectric cuboidal element with an air‐filled void is designed to act as a unit cell for designing a three‐dimensional (3D)‐printed phase‐graded metasurface reflector. The designed phase‐graded metasurface reflector is a 3‐bit quantized highly reflective surface, designed by rigorous unit cell optimizations. The quantized unit cells are distributed to provide a 45° phase gradient and wideband reflections operating from 24 to 38 GHz. The designed reflector is excited by a wideband 3D‐printed horn antenna placed at the optimized focal point. The simulated and measured results indicate the designed antenna achieves a maximum gain of 23.66 dBi with a gain enhancement of 60%. The designed antenna is found to have a 1 dB stable gain bandwidth of 4 GHz, from 28 to 32 GHz with a maximum gain of 23.66 dBi at 30 GHz. [ABSTRACT FROM AUTHOR]

In this paper, the volumetric shooting and bouncing rays method is proposed to investigate the electromagnetic (EM) scattering of the large‐scale target coated with plasma, which takes into account the EM rays propagating inside the interior of the plasma and fully captures the dominant scattering characteristics. Furthermore, an efficient graphics processing unit‐based implementation procedure with a ray management strategy is proposed to deal with the problem of the exponential increase of EM rays in plasma medium. The numerical results of a multilayer cuboid model and the RAM C‐II vehicle demonstrate the proposed method has a good computational efficiency and achieves a significant accuracy improvement compared to the traditional shooting and bouncing ray, with a root mean square error reduced from 13.29 dB to less than 4.96 dB. It indicates the proposed method has the potential to solve the EM scattering of the large‐scale target coated with plasma. Finally, some simulations of the RAM C‐II are performed at higher radar frequencies to illuminate that the plasma sheath causes complex scattering of the target of interest in terms of the flight speed, flight altitude, and radar frequency. [ABSTRACT FROM AUTHOR]

This paper presents a novel two‐element partially dielectric loaded planar Vivaldi antenna array for ultra‐wideband applications. This array is capable of operating between 380 MHz and 3 GHz and is designed on a 1.6‐mm thick low‐cost FR4 substrate with total size of 25 × 330 × 430 mm3. Innovative approaches to various gain enhancement techniques such as partial dielectric loading, corrugations, and U‐shaped back reflector used for planar Vivaldi antennas, are collectively employed in this design. Various elements of the array are interconnected. The two‐element Vivaldi array is fed by using a power divider. The array is designed by using a full‐wave three‐dimensional EM simulation tool. The designed antenna is manufactured and then measured. The simulation and measurement results are found to be consistent with each other. [ABSTRACT FROM AUTHOR]

Optically transparent dual‐band frequency‐selective surfaces (FSSs) are promising candidates to address the specific design challenges of the Internet of Things. This paper demonstrates their potential by discussing different configurations of the two single‐layer FSS designs on an innovative optically transparent polyvinyl chloride surface material. First, FSS cells consist of two cross dipoles placed forming angles of ±45∘ $\pm 4{5}^{\circ }$, where each rotated dipole structure parallel to the other. Then, in the second design, each one of the two cells is mirrored to enable polarization control for each band. As a proof‐of‐concept, five prototypes of each design having a unit cell size of 0.43λ0×0.43λ0 $0.43{\lambda }_{0}\times 0.43{\lambda }_{0}$ are fabricated through a combination of cost‐effective printing and shearing. The manufactured prototypes yield more than 93% transparency and robust dual‐band performance. Moreover, more than 20 and 40 dB isolation for lower‐ and upper‐frequency bands are achieved from the fabricated prototypes. High‐transparency, cost‐effectiveness, and robust high performance in terms of suppression make both structures suitable for sub‐6‐GHz fifth generation applications. [ABSTRACT FROM AUTHOR]

In this paper, mechanic–electric–circuit coupling algorithm based on the finite‐difference time‐domain (FDTD) method is proposed to analyze a one‐order microwave bulk acoustic wave (BAW) filter. FDTD method is used to solve the coupled mechanic–electric–circuit system equations to obtain the voltage and current at port position of the BAW filter in the time domain. Then S parameters of the BAW filter in the frequency domain are calculated using the Fourier transform. In our work, a one‐order BAW filter consists of two film bulk acoustic resonators (FBARs) by means of series and parallel. These two FBARs in the BAW filter are coupled together through an equivalent electrical connection. Similarly, multiphysical mechanic–electric–circuit analysis of the BAW filter is implemented in the commercial software COMSOL, which is realized by the time‐domain finite element method. The accuracy of the proposed method is verified by comparison with simulation results in COMSOL. In addition, the computational time and memory of the proposed method have obvious advantages over those of COMSOL. [ABSTRACT FROM AUTHOR]

This paper presents the design of a novel dual‐band quasi‐Yagi antenna for on‐body communications. The proposed antenna is designed on 0.05 mm thin microwave laminate and is designed to cover the 2.45 and 3.5 GHz spectrum to meet the needs of on‐body Internet of Things networks. Microstrip to slot‐line transition is used for the excitation of the feeder element. The conventional feeder of the quai‐Yagi is replaced with F‐shaped radiators to obtain a dual‐band response. In addition, a pair of directors are used to enhance the antenna gain. The proposed quasi‐Yagi antenna is optimized using the spider monkey algorithm. The chosen algorithm is used to synthesize the dimensions of the dual‐band radiator and is preferred to obtain quick convergence, unlike the traditional optimization algorithms. The optimized planar quasi antenna offers 5% bandwidth in both operating bands with a measured gain of 5.7 and 5.8 dBi, respectively. The optimization time is also considerably reduced in comparison with traditional optimization algorithms. The simulated and optimized antenna is fabricated and tested. [ABSTRACT FROM AUTHOR]

The utilization of unmanned aerial vehicles (UAV) has become prevalent nowadays. UAVs are autonomous devices, except for self‐charging. Wireless power transfer (WPT) technologies eliminate human intervention in UAV charging and enable independent charging. The factors making WPT systems popular are autonomizing charging, eliminating cable complexity, and avoiding difficulties caused by environmental conditions. WPT of the UAV in the near field is provided by inductive coupling. In this paper, two vertical rectangular coils and horizontal DDD (triple rectangle) coils were placed in the receiver and the transmitter for UAV wireless charging, respectively. The design of the coils was made in ANSYS Maxwell 3D. A wireless charger of the UAV was designed for 100 W output power at 140 kHz frequency. The misalignment tolerance of the proposed design concerning the x‐ and y‐axis was examined. In addition, the magnetic flux density and magnetic field distributions of the WPT system were investigated. The study found that the proposed design can transfer energy wirelessly with 94% efficiency up to 10.3 cm horizontal and 1.7 cm vertical misalignment. [ABSTRACT FROM AUTHOR]