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The design and optimization of laser-Compton x-ray systems based on compact distributed charge accelerator structures can enable micron-scale imaging of disease and the concomitant production of beams of Very High Energy Electrons (VHEEs) capable of producing FLASH-relevant dose rates. The physics of laser-Compton x-ray scattering ensures that the scattered x-rays follow exactly the trajectory of the incident electrons, thus providing a route to image-guided, VHEE FLASH radiotherapy. The keys to a compact architecture capable of producing both laser-Compton x-rays and VHEEs are the use of X-band RF accelerator structures which have been demonstrated to operate with over 100 MeV/m acceleration gradients. The operation of these structures in a distributed charge mode in which each radiofrequency (RF) cycle of the drive RF pulse is filled with a low-charge, high-brightness electron bunch is enabled by the illumination of a high-brightness photogun with a train of UV laser pulses synchronized to the frequency of the underlying accelerator system. The UV pulse trains are created by a patented pulse synthesis approach which utilizes the RF clock of the accelerator to phase and amplitude modulate a narrow band continuous wave (CW) seed laser. In this way it is possible to produce up to 10 μA of average beam current from the accelerator. Such high current from a compact accelerator enables production of sufficient x-rays via laser-Compton scattering for clinical imaging and does so from a machine of "clinical" footprint. At the same time, the production of 1000 or greater individual micro-bunches per RF pulse enables > 10 nC of charge to be produced in a macrobunch of < 100 ns. The design, construction, and test of the 100-MeV class prototype system in Irvine, CA is also presented.

This article presents a flexible four-element antenna for X-band applications. The proposed antenna covers the spectrum ranging from 10.6 to 11.9 GHz, including a significant portion of the X-band. The single antenna element comprises a modified E-shaped radiating patch, which is fed by a unique feeding structure consisting of a 50-Ω feeding strip connected with two rectangular stubs on both sides. All antenna elements are printed on a flexible felt 60 mm × 60 mm × 1 mm (2.12 λ × 2.12 λ × 0.035 λ at 10.6 GHz) substrate. The proposed antenna exhibits circular polarization over the desired bans of operation with an axial ratio (< 3 dB) bandwidth of 1.2 GHz, which is significant for X-band applications. The designed antenna is manufactured and practically tested. Both simulated and measured results agree well with each other, ensuring the optimal performance of the antenna. Moreover, the antenna achieves a maximum gain of up to 8 dBi in the desired band of operation. Further MIMO parameters, including envelope correlation coefficient (ECC), diversity gain (DG), channel capacity loss (CCL), and mean effective gain (MEG), are calculated to validate the MIMO performance. Finally, a conformal analysis was carried out to study the robustness of the antenna in various bending scenarios. Results show that the antenna reported in this article is the correct choice for conformal X-band MIMO applications. [ABSTRACT FROM AUTHOR]

In order to achieve high‐performance gallium nitride (GaN) high‐electron‐mobility‐transistors (HEMTs) capable of operating in the X‐band, a bilayer passivation technique is employed. The technique involves creating a stacked passivation layer consisting of a 20‐nm Si‐rich silicon nitride (SixN) passivation layer and a 100‐nm N‐rich silicon nitride (Si3N4) passivation layer. This effectively reduces radio frequency scattering in GaN HEMTs without compromising the breakdown voltage (BV). On the one hand, the SixN passivation layer effectively suppresses the surface states of devices, resulting in low current collapse. On the other hand, the Si3N4 passivation layer can effectively reduce gate leakage caused by the SixN passivation layer, allowing the device to reliably operate at higher voltages. Consequently, a GaN HEMTs with SixN/Si3N4 bilayer passivation achieve a low current collapse of 5% and a high BV of 157 V. The device features a current gain cutoff frequency (fT) and maximum oscillation frequency (fmax) of 57.9 and 96.8 GHz, respectively. Additionally, it exhibits excellent radio frequency performance in the X‐band, with an output power density (Pout) of 13.7 W mm−1 and power added efficiency of 60.8% at a drain voltage (VD) bias of 50 V. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surface (RIS) is one of the possible solutions to overcome challenges that bring up the 6G communication networks. Unit cell design for RIS is similar in many aspects to the design of artificial magnetic conductors (AMC) because both have a common nature of changing the phase of the reflected wave. However, RIS is aimed at controlling the angle of reflection to maintain requirements for the radiation pattern similar to phased antenna arrays such as low side lobes and beamwidth. The paper reviews the criteria for optimizing RIS: unit cell dimensions, phase span, frequency bandwidth, and loss. An optimization algorithm is proposed for the proper accounting of RIS optimization criteria. A new X-band unit cell is designed using the proposed optimization algorithm. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a meander-feed antenna system featuring circular polarization (CP) diversity and high isolation. The antenna design comprises a monopole antenna and an isosceles triangular partial ground on a single layer. This innovative structure departs from traditional antennas in three significant ways: it achieves structural asymmetry by modifying the antenna's shape and position, which enhances CP characteristics; and it transitions the feeding structure from a linear to a meander type. Experimental results show that the proposed antenna covers frequency ranges of 6.9–8.5 GHz and 9.2–10.1 GHz, with measured isolation below − 12 dB within the operating bandwidth. As a result, the single monopole antenna attains a CP bandwidth of 20.78% and 9.33%. The single-element CP antenna is then incorporated into a 4-port MIMO antenna, which is fabricated and measured, demonstrating excellent agreement between simulated and measured results. The proposed antenna system achieves an overall gain of 5 to 8 dBi across the operating spectrum, making it an ideal choice for X-band applications. [ABSTRACT FROM AUTHOR]

A ground station antenna system features a conical horn attached to a microstrip antenna as an alternate receiving feed antenna. The proposed microstrip antenna has circular polarization and operates in the X-band. The far-field parameters of the antenna are measured after developing and simulating the combination of a conical horn and a microstrip antenna. The modeling results for a microstrip antenna with a conical horn offer a working bandwidth of 930 MHz, spanning frequencies 7.44 GHz to 8.37 GHz. The axial ratio measurements for a microstrip antenna joined with a conical horn produce a working bandwidth of 150 MHz, covering frequencies ranging from 7.72 GHz to 7.87 GHz. The conical horn is attached to a microstrip antenna and has a gain of 15.1 dB. The proposed antenna is designed to meet ground station antenna requirements by pairing it with a parabolic reflector with a diameter of 3.7 meters. The primary focus antenna of the proposed design was chosen. The feed antenna and parabolic reflector should be positioned at a focus point distance of 1110 mm for a total gain of 38.9 dB at 7.8 GHz frequency. The proposed antenna can be applied on X-band remote sensing ground stations as a receiving antenna. [ABSTRACT FROM AUTHOR]

The EPFL Spacecraft Team (EST) is working on the Constellation of High-Performance Exospheric Science Satellites (CHESS) mission, which aims to launch a constellation of two CubeSats in 2027. These CubeSats will study the chemical composition of Earth's exosphere using time-of-flight mass spectrometry. To downlink the collected scientific data, the satellites will utilise a custom X-band transceiver, presented in this paper, operating in the amateur frequency range of 10.45 GHz to 10.50 GHz. The proposed transceiver architecture employs Software-Defined Radio (SDR) technology and can be easily adapted for different use cases. This modular approach has the potential to be suitable for future spacecraft missions, such as active debris removal or lifetime extension services, where flexible communication systems are required. • Hybrid SDR architectures enable versatile telecom systems for space missions. • IOD/IOV missions let students follow the entire life cycle of a space project. • Short development/prototyping cycles maximise the lessons learned in student teams. [ABSTRACT FROM AUTHOR]

Abstract This article presents a flexible four-element antenna for X-band applications. The proposed antenna covers the spectrum ranging from 10.6 to 11.9 GHz, including a significant portion of the X-band. The single antenna element comprises a modified E-shaped radiating patch, which is fed by a unique feeding structure consisting of a 50-Ω feeding strip connected with two rectangular stubs on both sides. All antenna elements are printed on a flexible felt 60 mm × 60 mm × 1 mm (2.12 λ × 2.12 λ × 0.035 λ at 10.6 GHz) substrate. The proposed antenna exhibits circular polarization over the desired bans of operation with an axial ratio (

In this research, a quad‐band sickle‐shaped MIMO antenna of compact size 32 × 32 mm2 (0.28λ0 × 0.28λ0 at lower resonant frequency 2.6 GHz) has been proposed using partial ground and tilted isolation stub at an angle of 45°. It covers 2.40 to 2.80 GHz frequency range with bandwidth (BW) of 15.38% (0.40 GHz) which is applicable for Wi‐Fi application in first band and in second band it covers from 4.48 to 5.75 GHz frequency range with BW of 24.83% (1.27 GHz) for WLAN application. In addition, the third band starts from 9.75 to 10.43 GHz frequency range with BW of 6.74% (0.68 GHz) for the X‐band whereas in fourth band it covers from 13.07 to 15.87 GHz frequency range with BW of 19.38% (2.8 GHz) frequency, which is applicable on Ku‐band application. Moreover, the isolation is < −15 dB in the entire resonating frequency band which is an acceptable limit for reduction of mutual coupling. ECC value is <0.5 in the entire operating band of frequency. The diversity gain of the proposed MIMO antenna is approximately 9.96 dB that shows the antenna exhibits good diversity property. The channel capacity loss value is <0.4 bps/s/Hz in the entire resonating band. In view of all the diversity parameters, the proposed MIMO structure fulfills all the requirements of the MIMO antenna. [ABSTRACT FROM AUTHOR]

The technique of electromagnetic characterization of materials in free space allows for the measurement of constitutive properties without making contact with the material being measured. Characterization methods in Free Space are naturally suited for Electromagnetic Radiation Absorbing Materials (RAM) but are also important in applications where the material sample to be measured does not undergo major interventions. They consist of evaluating a received signal resulting from a free-space transmission through two horn antennas with beam collimating lenses and a Vector Network Analyzer (VNA). The characteristics of the transmitted signal are modified by a material positioned between the transmitting and receiving antennas. This work presents methods for electromagnetic characterization in Free Space, in the frequency range of 8.2 to 12.4 GHz (X-Band), in a semi-anechoic chamber, seeking the development of measurement processes that present results with repeatability and reliability. The measurements were made with standard and electromagnetic radiation absorbing materials. The measurement technique presented 95% of efficiency. [ABSTRACT FROM AUTHOR]

This article is an attempt to design and develop a metamaterial-based microwave absorber with a low profile, broad incidence angle and compactness in the microwave frequency range. Further, equivalent circuit model of the proposed structure is discussed based on circuit theory. The unit cell focuses on achieving maximum absorption at C-, X-, and K-band. The dimensions of the proposed design are ultrathin and compact, having an overall size of 8 mm × 8 mm × 0.8 mm. The dimensions are optimized in such a fashion to achieve three different peaks at three various bands (C, X and K), thereby making the triple-band behaviour of the metamaterial absorber possible. The structure provides absorption of 98.26 % absorption at 7.76 GHz (C-band) while absorption of 96.74 % is achieved at 10.26 GHz (X-band) and 99.92 % absorption at 19.32 GHz (K-band) of microwave regime. The experimental verification of design conform that the measured results are found to be in close agreement to simulated ones. [ABSTRACT FROM AUTHOR]

The design and optimization of laser-Compton x-ray systems based on compact distributed charge accelerator structures can enable micron-scale imaging of disease and the concomitant production of beams of Very High Energy Electrons (VHEEs) capable of producing FLASH-relevant dose rates (∼ 10 Gy in less than 100 ns). The physics of laser-Compton x-ray scattering ensures that the x-rays produced by this process follow exactly the trajectory of the electrons from which the x-rays were produced, thus providing a route to not only compact VHEE radiotherapy but also image-guided, VHEE FLASH radiotherapy. This manuscript will review the compact accelerator architecture considerations that simultaneously optimize the production of laser-Compton x-rays from the collision of energetic laser pulses with high energy electrons and the production of high-bunch-charge VHEEs. The primary keys to this optimization are use of X-band RF accelerator structures which have been demonstrated to operate with over 100 MeV/m acceleration gradients. The operation of these structures in a distributed charge mode in which each radiofrequency (RF) cycle of the drive RF pulse is filled with a low-charge, high-brightness electron bunch is enabled by the illumination of a high-brightness photogun with a train of UV laser pulses synchronized to the frequency of the underlying accelerator system. The UV pulse trains are created by a patented pulse synthesis approach which utilizes the RF clock of the accelerator to phase and amplitude modulate a narrow band continuous wave (CW) seed laser. In this way it is possible to produce up to 10 µA of average beam current from the accelerator. Such high current from a compact accelerator enables production of sufficient x rays via laser-Compton scattering for clinical imaging and does so from a machine of “clinical” footprint. At the same time, the production of 1,000 or greater individual micro-bunches per RF pulse enables > 10 nC of charge to be produced in a macrobunch of < 100 ns. The design, construction, and test of the 100-MeV class prototype system in Irvine, CA is also presented.

AbstractCarbon fabric-reinforced polymer (CFRP) composites have replaced most aluminum and ferrous alloys in aerospace construction owing to their attractive high strength-to-weight ratio. CFRPs used in aircraft should have electromagnetic shielding ability in addition to structural properties. Hence, the study of Electromagnetic (EM) wave shielding by hybrid CFRPs is an important topic of research. In this article, we summarize research advancements for enhancing the EM wave shielding of CFRP composites in the X-band frequency range. This study focuses on the manufacturing and performance of carbon-fabric-based composites with metals, metal oxides, and carbon-based fillers. The factors influencing the EM wave shielding ability of the CFRP composites are also discussed. The EM wave shielding of Carbon fibers (CF) was remarkably improved by coating, electroless plating, and synthesizing nanoparticles on the carbon fiber surface. It was found that the carbonious fillers and metal nanofillers such as Nickel (Ni), Iron (Fe), and Silver (Ag)-loaded multilayer CFRP composites showed better absorption modes of EM wave shielding with good structural properties. Owing to the Ag nanowire coating on the CFs, the shielding effectiveness was drastically improved. However, in addition to the type of filler, the structural properties are also influenced by the manufacturing method and type of composite. In the case of laminated composites, the absorption-laminated EM shielding is influenced by the architecture of the plys and the type and number of interplay in the composite construction. In addition, the techniques adopted for the synthesis of nanoparticles and dispersion in composites for effective EM shielding are challenging tasks.

Zinc aluminate (ZnAl2O4) is widely recognized as a ceramic in high demand across various microwave applications. Furthermore, blending dielectric materials with ZnAl2O4 has demonstrated improvements in its dielectric properties, offering promising potential for advancing microstrip patch antenna technology. This paper presents the fabrication and characterization of a sol-gel composite nanoparticle consisting of titanium dioxide (TiO2) and zinc aluminate (ZnAl2O4) for use in a microstrip patch antenna designed for X-band applications. The composite nanoparticle, with a molecular composition of xTiO2(1-x)ZnAl2O4 where x = 8 %, was investigated using X-ray diffraction (XRD), revealing dominant peaks corresponding to ZnAl2O4 and TiO2 with a calculated crystallite size of 16.9 nm. Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM), and energy dispersive spectroscopy (EDS) were employed to assess functional groups, morphology, and elemental composition of the nanoparticles. The dielectric properties of the nanoparticles, characterized by a dielectric permittivity of 20.2 and a dielectric loss of 0.19, were measured using an LCR meter. These nanoparticles were utilized to fabricate a prototype patch antenna, exhibiting promising performance in both simulated and measured results. The fabricated patch antenna operated at 8.51/8.49 GHz with a return loss (RL) of − 25.94/−19.97 dB, featuring an enhanced bandwidth of 2.62/2.87 GHz and a voltage standing wave ratio (VSWR) below 2. Additionally, the antenna demonstrated a gain of 2.14, directivity of 3.58, and radiation efficiency of 59.7 %, making it suitable for X-band applications.

Due to the increase in electromagnetic waves emitted by the electrical and electronic equipment surrounding us, protection from electromagnetic waves has become a very important subject. It is thereby proposed that conductive textiles and fabrics are used for protection of sensitive equipment and personnel from electromagnetic interference. Conductive textiles are considered to be a particular sub-genre of technical textiles and exhibit favourable electromagnetic shielding properties together with a list of other attributes that make them suitable for such applications. In more detail, conductive textiles exhibit light weight and low volume while being comfortable to wear, conforming to different shapes of surfaces and everyday objects (thus being easily integrated within the surrounding environment), being aesthetically appealing, etc. In this context, most of the literature-available shielding textiles or fabrics used are either conventional or conductive fabrics that are further coated with metal layers for extra conductivity and shielding. However, metal shielding exhibits certain disadvantages: it is prone to corrosion while corrosion-resistant materials (such as silver or gold) are extremely expensive; it is difficult to process; and it compromises the comfortability and aesthetic appeal of the final product. Herein, we propose the usage of electrically conductive leather for efficient shielding from electromagnetic interference. The motivation for this work is twofold: first, leather materials are seldom if not at all used for electromagnetic shielding and we wanted to close that gap for an industry sector (leather clothes and garments) that is thriving. Second, we are using one or more layers of polypyrrole treatment (PPy) to inherit conductivity to leather surfaces. We show that PPy is sufficient treatment for inheriting very satisfactory electromagnetic shielding properties all the while maintaining the comparative advantages of a non-metal-processed fabric surface (e.g. comfortability, aesthetic appeal etc.). We demonstrate a variety of different PPy treated leather samples and illustrate that electromagnetic shielding is proportional to the number of PPy layers used for leather processing. The measurements results are obtained using RF and microwave high-frequency equipment in a controlled laboratory environment within the X-microwave band (8-12 GHz). [ABSTRACT FROM AUTHOR]

The latest developments in communication systems require an economical, light‐weight, compact size, and excellent performance in microstrip patch antennas in order to meet the requirements of the upcoming implementation. The optical, electrical, and physical properties of different materials have an impact on the design of antennas. An innovative composite photonic crystal microstrip patch antenna with outstanding gain has been developed. For composites of fumed silica embedded in RT‐Duroid dielectric material, the effective permittivity is calculated using the Maxwell‐Garnett model. The performance of composite antennas for different volume fractions and various dielectric substrate thicknesses is studied. The resonance frequencies of composites also shift from the X‐band to the C‐band with an increase in volume concentration, which is suitable for wireless communication systems. This investigation provides a perspective on how composite substrates can represent a communication revolution by providing an alternative to substrates that are readily accessible commercially in situations when the material qualities are insufficient. The photonic crystal composite antenna records the highest gain of 13.89 dB with the coverage of C‐band, X‐band, and Ku‐band, whereas the composite antenna reaches the best gain of 10 dB with the coverage of C‐band and X‐band. [ABSTRACT FROM AUTHOR]

• Reconfigurable graphene antenna. • Cognitive radio network. • Innovative solution for X-band satellite communications. • Improvement in satellite communication performance. This study introduces a graphene-based antenna tailored for X-band satellite communication within a cognitive radio network. Leveraging graphene's distinctive traits high conductivity and mechanical flexibility, the antenna design achieves reconfigurability in frequency, polarization, and radiation pattern. This adaptability enables dynamic adjustments to environmental shifts, bolstering the efficiency and dependability of satellite communication. Operating on software-defined radio technology, the cognitive radio system monitors and allocates the available frequency spectrum, allowing real-time adjustments to antenna parameters. Given the widespread usage of the X-band in satellite communications, this antenna proposal stands as an appealing solution for such systems. Its potential applications encompass providing broadband access in remote regions, supporting emergency communication networks, facilitating maritime and aeronautical communications, and enabling self-sustaining wireless networks. The approach involves a novel graphene antenna with slots to facilitate frequency reconfigurability. At 9 GHz, the graphene antenna achieves a gain of 6 dBi, surpassing the 4.3 dBi gain of a copper antenna. By varying the chemical potential of graphene from 0 to 4 eV , we achieved a high gain of 6.4 dBi at 9 GHz and an excellent reflection coefficient of −42 dB at 11.63 GHz. The graphene antenna's improved gain and tuning capabilities surpass traditional materials, showcasing adaptability across diverse frequencies, promising versatility for varied communication needs, and enhancing overall system reliability and effectiveness. [ABSTRACT FROM AUTHOR]

The quality of weather radar affects the reliability and effectiveness of monitoring severe convective weather. Therefore, rigorous calibration and validation are the foundation for the quantitative application of weather radar. Among the available methods, radial velocity validation is of great significance for reducing the false alarm rate in the identification of tornadoes and thunderstorms. Based on the traditional method that utilizes internal and external instrument radar velocity measurements, we propose a weather radar radial velocity validation method that uses RTK UAV to simulate external targets. In addition, according to the characteristics of the UAV application scenarios, we introduce the evaluation parameter of optimal absolute accuracy to supplement the original parametric system. The experimental results show that the evaluation parameter of optimal absolute accuracy can effectively reduce the interference caused by the systematic deviation of the UAV due to the internal and external environment, which can affect the validation results. When the UAV velocity is not greater than 10 m/s, the optimal absolute accuracy of the radial velocity validation is less than 0.05 m/s, which is essentially consistent with the external instruments' measurement results. This method can be effectively applied to the procedural handling of weather radar radial velocity validation. It is significant for ensuring the accuracy and quality of weather radar radial velocity measurements and improving the effectiveness of radar velocity data applications. [ABSTRACT FROM AUTHOR]

This letter demonstrates an X‐band transceiver front‐end in 130‐nm CMOS technology for phased‐array systems. To solve the problem that passive attenuator performance deteriorates significantly in wideband systems, a 6‐bit attenuator with source follower and common‐gate amplifier is proposed. Besides, an 8‐bit vector‐summing phase shifter is implemented in common path to realize the phase coverage of 360° with the least significant bit of 5.625°. In the frequency range of 8–12 GHz, the measured root‐mean‐square (rms) amplitude and phase errors of the attenuator in the transceiver are less than 0.36 dB and 2.2°, respectively. The rms phase and amplitude errors of the phase shifter in the transceiver are less than 4.8° and 0.56 dB, respectively. The whole chip area including pads is 3 × 2.3 mm2. [ABSTRACT FROM AUTHOR]

Recently, the difference in the most effective competencies is considered the main competitive factor in organizations. To this end, organizations seek to improve a number of their functional capabilities, expertise, and capacities to enhance their operational area. Therefore, when an organization focuses on the quality of its services or products, it is trying to improve maintainability to gain a competitive advantage. In this study, a closed-loop, multi-objective, multi-level, multi-commodity, and multi-period mathematical model for a supply chain with producer, and distributor components is presented to locate and allocate items. The presented model can control environmental, economic, and social factors along the chain. One of the most important and unique aspects of the current study is considering different scenarios in the closed-loop supply chain (CLSC) so that the quality of the produced and transported products is paid attention to according to perishability. In addition, to control environmental effects, the model can minimize total CO2 emissions. The problem is solved on small, medium, and large scales using Epsilon Constraint and NSGA-II methods. According to the obtained results, the flow according to the boom scenario is more than the stagnation scenario. Finally, according to the sensitivity analysis, the number of centers established increases with an increase in demand. The results show that the nondominated sorting genetic algorithm (NSGA-II) model can predict the behavior of the model well in the long term. For this purpose, Mean ideal distance (MID) index, has been used for evaluation of calculation. the value of standard MID is equal to 6.56 that shows the model accuracy is adequate. [ABSTRACT FROM AUTHOR]

Maintaining engine oil quality is critical for industrial machinery and transformers to ensure efficient operation and reduce the risk of failure. This paper presents a novel application of an X-band microwave sensor, using a third-order electroformed iris waveguide filter, for real-time, non-invasive engine oil quality monitoring. By detecting shifts in the dielectric properties of engine oil, the sensor accurately tracks oil degradation as it ages. Unlike traditional methods that require oil extraction and laboratory analysis, this sensor enables continuous, in-situ monitoring, providing immediate feedback without disrupting system operations. Any change in oil quality causes a frequency shift, as variations in its dielectric properties affect the waveguide’s resonance. This shift can be measured in real time, enabling accurate monitoring of oil degradation. Additional measurements were conducted using the coaxial probe technique to analyze the changes in the oil’s electrical behavior during various heating periods. Experimental results demonstrate the sensor’s sensitivity, with measurable frequency shifts of up to 10 MHz observed in the most aged oil samples. These shifts clearly correlate with the oil’s aging process, confirming the sensor’s potential for practical use in predictive maintenance. This system, utilizing an electroformed waveguide, offers a cost-effective and efficient solution for enhancing machinery longevity and optimizing maintenance schedules in industrial applications.

Accurate estimation of forest aboveground biomass (AGB) is crucial for research on terrestrial carbon cycling and global climate change. In this study, we introduce an improved approach for estimating forest AGB combining P-band and X-band interferometric synthetic aperture radar (InSAR) data. Forest AGB was estimated by combining unbiased forest height and volume backscatter intensity. For forest height, a multilayer model and subaperture decomposition technology were used to remove the penetration bias of the X-band and reduce the effects of forest scatterers on the extraction of a pure understory terrain phase based on P-band, respectively. For volume backscatter intensity, a ground cancellation algorithm based on P-band InSAR was used to eliminate ground scattering contributions unrelated to forest AGB. The proposed method was validated using airborne P-band InSAR data and spaceborne X-band InSAR data gathered over the study area on the Saihanba Forest Farm in Hebei, China. The unbiased forest height and volume backscatter intensity had stronger correlations with forest AGB than estimates derived from unimproved features. The proposed method returned high-precision estimates of forest AGB with an accuracy of 83.73%, an improvement of 8.80% over an estimate derived from unoptimized features. Additionally, AGB estimates combined with forest height and backscatter intensity were greater than those based on a single feature, with the contribution of the former is greater than that of the latter.

In this paper, we propose a dual-band shared-aperture antenna composed of array elements with high electromagnetic (EM) transparency. To increase EM transparency, the antenna consists of an optimized substrate with low effective permittivity by combining thin dielectric sheets and air-gap layers. To further improve the EM transparency, thin dual-loop radiators with optimized widths and lengths are adopted for the S-band element, and an E-shaped patch antenna is employed for an X-band element. This configuration minimize the pattern distortion in the X-band elements while enhancing antenna bandwidths. In addition, a calibration layer comprising four monopole probes and microstrip transmission lines is included for monitoring the phase and amplitude errors of each element. To verify the feasibility, the proposed antenna is fabricated to measure antenna characteristics, such as reflection coefficients, beam steering performance, and mutual coupling in a full anechoic chamber. The fractional bandwidths of the antenna in the S- and X-bands are 16.4% and 26.8%, respectively. The array gains at the bore-sight are 16.0 dBi in the S-band and 24.0 dBi in the X-band.

In this paper, two composites ZrB₂/Al₂O₃ and FeSiAl/Al₂O₃ were characterized using the Transmission/Reflection characterization technique. The volume contents of ZrB₂ and FeSiAl inclusions in these composites vary between 0 and 15%. The results obtained indicate that the percentage of the inclusions in the composites effectively improves the dielectric property. The comparison of the effect of ZrB₂ and FeSiAl inclusions on the dielectric properties of these composites confirms that reinforcing these composites with FeSiAl particles results in better dielectric properties. Furthermore, these results indicate that the dielectric property of the two composites studied decreases progressively with increasing frequency in the X band. This frequency dependence of the dielectric property of the composites studied is very important and shows that the composites studied are good candidates for microwave absorption applications in the X-band and for antenna design. Additionally, a comparison between the numerical results obtained in this work and the experimental results published in the literature reveals a close agreement, validating the reliability of the study's findings.

In this study, we fabricated a coplanar waveguide using a novel graphene-silver nanowire composite structure (GNCS) on a polyethylene terephthalate (PET) substrate and then investigated its radio frequency (RF) characteristics. According to the measured results, the coplanar waveguide employing GNCS exhibited a substantially lower loss of transmission line than conventional waveguides. Furthermore, compared to the conventional graphene-based coplanar waveguide, the proposed structure allowed for lower skin depth and higher conductivity, resulting from the high electric conductivity of the silver nanowire. In addition, repetitive bending tests, which were performed to investigate the electric stability of the graphene-silver nanowire, showed that the coplanar waveguide employing GNCS offered substantially better electrical stability than the conventional graphene-based coplanar waveguide. These results indicate that the graphene-silver nanowire structure is a promising candidate for application in flexible wireless communication systems. Notably, this is also the first study to investigate the RF performance and electrical stability of a graphene-silver nanowire/PET structure.

This study presents a comprehensive analysis of the design of a high-performance meta-material loaded square patch antenna arrays specifically tailored for X-band applications. To enhance the gain and front to back ratio (FTBR), a novel 1x3 series-fed linear array configuration that integrates solitary series-fed elements with metamaterial-based square patches at X-band frequencies is introduced. Later, parallelfed 1x2 and 1x4 antenna arrays are designed by considering the series-fed antenna array as a single element for further enhancement of gain and FTBR. The single element 1x3 series fed array is fabricated with dimensions of λx3.5λx0.028λ, whereas the respective 1x2 and 1x4 parallel fed antenna arrays has the dimensions of 2.86λx3.8λx0.028λ and 2.86λx4.3λx0.028λ, respectively. The Taconic substrate is chosen as the dielectric material, exhibiting a dielectric constant of 2.2 and a loss tangent of 0.0025. The empirical data presented substantiates the superior performance of the 1x4 parallel fed configuration. This is evident through the remarkable reflection coefficient of -25dB, the wide bandwidth spanning 47MHz, the substantial gain of 17.8dBi, and the FTBR of 30.7. The metrics serve to highlight the array's capacity in guaranteeing a superior level of signal fidelity, encompassing a wide frequency spectrum, amplifying incoming signals, and directing transmissions towards specific orientations. These metrics unequivocally validate its potential for advanced X-band applications. [ABSTRACT FROM AUTHOR]

The manufacturing of active RF devices like klystrons is dominated by expensive and time-consuming cycles of machining and brazing. In this article, we characterize the RF properties of X-band klystron cavities and an integrated circuit manufactured with a novel additive manufacturing process. Parts are 3D printed in 316 L stainless steel with direct metal laser sintering, electroplated in copper, and brazed in one simple braze cycle. Stand-alone test cavities and integrated circuit cavities were measured throughout the manufacturing process. The un-tuned cavity frequency varies by less than 5% of the intended frequency, and Q factors reach above 1200. A tuning study was performed, and unoptimized tuning pins achieved a tuning range of 138 MHz without compromising Q. Klystron system performance was simulated with as-built cavity parameters and realistic tuning. Together, these results show promise that this process can be used to cheaply and quickly manufacture a new generation of highly integrated high power vacuum devices. [ABSTRACT FROM AUTHOR]

This study presents an 8∼15 GHz low noise amplifier (LNA) using a 0.25 μm GaN on SiC process. The LNA is designed in three stages with source degeneration in the first stage to optimize the noise figure and operation bandwidth. Lossy matching using a resistor is applied to the drain nodes in each stage to enhance stability. An RC parallel equalizer is applied to the output port to flatten the frequency response. The chip size of the fabricated LNA MMIC is 3.0 mm×0.9 mm. At operating frequencies of 8∼15 GHz, the small signal gain is 23 to 27 dB, return loss is lower than 10 dB, and noise figure is 1.6 to 2.8 dB. [ABSTRACT FROM AUTHOR]

This paper will propose an innovative compact, lowcost, low-profile inverted U-shaped patch antenna with a single and dual band-notched ultra-wideband (UWB) with split ring resonators (SRRs). To achieve our main goal based on the reduction of electromagnetic interference in narrowband communications (WLAN, WiMAX, and satellite), four-element rectangular split-ring resonators (SRRs) array are placed nearby the feedline to create notch band at approximately 5.15-5.35 and 5.725-5.85 GHz. The SRRs antenna's measured data indicate a directivity of 8.52 dBi, a gain of 7.18 dBi, a reflection coefficient of -27 dB, and an efficiency of 84.3%. The realized prototype, including the SRRs and CSRRs structures, were carried out using a PCB prototyping machine. Reflection coefficient measurement is obtained using a vector network analyzer (VNA) PNA-X from Agilent Technologies. The measured values of the proposed antenna, with 50 x 38 x 1.6 mm3 in total and constructed on a FR4 substrate with permittivity of er = 4.3, loss tand = 0.0024 and substrate thickness of h = 1.6 mm, correlate well with the simulated values. The proposed antenna, compared with other published work, is a good candidate to operate in WLAN, X-band. [ABSTRACT FROM AUTHOR]

The role of antennas in wireless communication is critical for enabling efficient signal transmission and reception across various frequency bands, including those associated with IoT (Internet of Things), X-band, S-band, and RFID (radio-frequency identification) systems. This paper presents a small quadruple-band antenna with 25 × 40 × 1.5 mm3 dimensions designed for diverse wireless applications. It is adept at operating in the S-band (2.2 GHz), wireless local area network (WLAN) (5.7 GHz), microwave RFID frequency band (5.8 GHz), and X-band (7.7 GHz and 8.3 GHz). While the majority of existing research focuses on antennas covering two or three bands, our work stands out by achieving quad-band operation in the proposed antenna design. This antenna is constructed on a semiflexible Rogers RT5880 substrate, making it well-suited for wearable applications. Computer Simulation Technology (CST) Microwave studio (2019) simulation package software is chosen for design and analysis. The antenna design features a comb-shaped radiating structure, where each "tooth" is responsible for resonating at a distinct frequency with an appropriate bandwidth. The antenna retains stability in both free space and on-body wearability scenarios. It achieves a low specific absorption rate (SAR), meeting wearable criteria with SAR values below 1.6 W/Kg for all resonating frequencies. The proposed antenna demonstrates suitable radiation efficiency, reaching a maximum of 82.6% and a peak gain of 6.3 dBi. It exhibits a bidirectional pattern in the elevation plane and omnidirectional behavior in the azimuth plane. The antenna finds applications across multiple frequencies and shows close agreement between simulated and measured results, validating its effectiveness. [ABSTRACT FROM AUTHOR]

An investigation of a single‐layer band‐stop frequency selective surface (FSS) is designed and analyzed for X‐band application. The proposed FSS design primarily involves a cross‐shaped conductive patch with four square slots on each corner, and it is fabricated on the 3D‐printed polylactic acid (PLA) substrate. The design is resonating at 12 GHz with an insertion loss greater than 60 dB. The 10 dB bandwidth of the designed structure is 8.3% with respect to the resonant frequency. The results show that the design has polarization‐independent and angle‐insensitive transmission characteristics for incidence angles up to 60°. The simulation is carried out using CST Microwave Studio Suite, and the results are obtained. The physical mechanism of the designed structure is evaluated using the surface current distribution. The designed FSS is fabricated using two techniques, namely inkjet printing and conventional etching. Finally, the measurements of the fabricated structure are done using a vector network analyzer setup. [ABSTRACT FROM AUTHOR]

As one of the important means of tornado monitoring and early warning, weather radar uses Xband dual polarization phased array weather radar system with ultra-high space-time resolution to better capture tornadoes and facilitate tornado early warning. This work chooses a tornado that occurred in Nanhai, Foshan at 07:00 on June 19, 2022 to analyze the genesis and lysis of the tornado and the process of radar monitoring and early warning. With radar intelligent early warning software, the sensitive dual polarization and ultra-high space-time resolution data from X-band dual polarization phased array weather radar, real-time inversion of the three-dimensional wind field and analysis of tornado debris (TVS) characteristics can significantly enhance tornado monitoring and early warning. The tornado was successfully warned 18 minutes in advance in this case, which suggests that X-band dual polarization phased array weather radar is highly capable of strong convective weather detection. [ABSTRACT FROM AUTHOR]

In this paper, an X‐band dual‐band dual‐polarized medium‐gain antenna (MGA) is designed for deep‐space satellite applications. The MGA has isoflux radiation patterns in the 7.145–7.19 and 8.40–8.45 GHz frequency bands. The concentric ring horn qualification model named MGA is developed for TIAN WEN‐2 (TW‐2) mission. MGA is fabricated and the measurements are conducted on it and its installation on the deck of the TW‐2 Radiation Mockup (RM). The performance evaluation of MGA and its corresponding RM measurements indicate an axial ratio lower than 4.0 dB and a gain higher than 5.8 dBic on the operational bandwidth at the coverage limit of 40° for all azimuth angles (φ). The calculated and measured data align exceedingly well, confirming that MGA satisfactorily meets the requirements for the forthcoming TW‐2 deep‐space spacecraft. [ABSTRACT FROM AUTHOR]

The paper aims to utilize a metamaterial (MTM) structure, specifically the slotted plus‐shapes within a square split‐ring resonator, to analyze the characteristics of the reused oil and also used to classify different oil samples. The proposed MTM structure is designed to operate within the X‐band frequency range of 8–12.4 GHz. The MTM structure is simulated using the high‐frequency EM simulation tool, and the MTM properties are extracted using standard equations. The negative permittivity and permeability characteristics of the proposed MTM structure in the X‐band are studied to verify its suitability for X‐band applications. A sample container is designed to hold the oil samples, and the experiments were carried out using an X‐band waveguide setup with Vector Network Analyzer. The results were analyzed and presented in brief to examine reused oil and classify different oils. [ABSTRACT FROM AUTHOR]

An efficient broadband metasurface-based polarization converter is investigated in this communication. The proposed embodiment works in the reflection mode. It can efficiently convert the x-polarized fields to their y-polarized counterpart and vice versa, with a good oblique incidence of up to 50° over the entire X-band. The design portrays a good polarization conversion ratio of up to 98% for normal incidence and is more than 70% considering the cases of oblique incidences. A prototype is fabricated to confirm the operation of the proposed design. Good agreement between the simulation and experimental results is observed. Ryy (co-component: y-polarized transmission and y-polarized reception) is below -10 dB, and the Rxy (cross-component: y-polarized transmission and x-polarized reception) is above – 3 dB over the entire X-band. [ABSTRACT FROM AUTHOR]

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Remote sensing of the Earth is now widely used in various fields. One of the challenges of remote sensing is the creation of inexpensive satellite systems operating in polar circular orbits. These systems require the development of a receptiontransmission system that allows tens of gigabits of video information to be transmitted to an earth receiving station within ten minutes. That is, there is a need to create a communication system that provides high speed data transmission from small satellites weighing up to 50 kg. Objective. The aim of the work is to study the features of digital signal formation in modern satellite communication lines and to develop a communication system with a high data transfer rate (usually 300 Mbit/s), which can be applied to small Earth Observation satellites. Method. Proposed concept for building a high-speed data transmitter from a remote sensing earth satellite using commercially available off-the-shelf technology. Calculations of the power flow density created at the input of the receiving earth station were performed to find out the possible power of the on-board transmitter. Results. A diagram of a communication system based on the DVB-S standard using the technology of commercially available off-the-shelf products has been developed. The high-speed data transmitter is implemented on a Xilinx® Zynq Ultrascale+ ™ MPSoC FPGA microchip, which is located on an Enclustra Mercury XU8 module with a high-performance dual 16-bit AD9174 DAC. The on-board transmitter with a power of up to 2 W meets the requirements of the ITU Radio Regulations for the power flux density on the surface of the Earth, which is created by the radiation of the space station EESS in the range 8025–8400 MHz. It is shown that the energy reserve of the communication line of 3 dB is achieved for various commands for coding and modulation changes with an increase in the elevation angle, which allows to increase the speed of information transmission. Conclusions. An original receiving-transmitting system was developed for use in small satellites for remote sensing of the Earth. It is shown that the function of adaptive modeling of ACM of the DVB-S standard allows you to automatically change the transmission parameters in real time depending on the changing conditions of the channel, providing opportunities for more flexible and effective data transmission in various conditions, which will allow to increase the volumes of information transmitted by communication session. The proposed system operates in the X-band and is built using commercially available off-the-shelf products. An antenna with double circular polarization is used as the emitter. Two physical channels represent two polarization modes: right circular polarization and left circular polarization, each of which has three frequency channels. [ABSTRACT FROM AUTHOR]

This study presents an original parallel connected hybrid microstrip-substrate integrated waveguide (PCHM-SIW) bandstop filter. A low-pass filter implemented on a microstrip structure and a SIW-based high-pass filter are connected in parallel to each other. In this way, the aim is to obtain a bandstop filter in the novel hybrid design. The parallel connected hybrid microstrip-substrate integrated waveguide (PCHM-SIW) bandstop filter is synthesised, simulated, and produced. The effects of connecting filters in parallel are discussed. It is seen from the results of CST Studio Suite simulation that PCHM-SIW bandstop filter has a bandwidth of 2.85 GHz and a center frequency of 4.26 GHz. The frequency change rate of the center frequency between simulation and measurement is 7.02 % where it is just 3.76 % for the deviation in bandwidth. The results of the simulation and those of the measurement are close to each other. These results converge to ideal analytical results.