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Radio frequency interference (RFI) analysis is crucial for ensuring the proper functioning of a radio telescope and the quality of astronomical observations, as human-generated interference can compromise scientific data collection. The aim of this study is to present the results of an RFI measurement campaign in the frequency range of 4–5.8 GHz, a portion of the well-known C-band, for the Sardinia Radio Telescope (SRT), conducted in October–November 2023. In fact, this Italian telescope, managed by the Astronomical Observatory of Cagliari (OAC), a branch of the Italian National Institute for Astrophysics (INAF), was recently equipped with a new C-band receiver that operates from 4.2 GHz to 5.6 GHz. The measurements were carried out at three strategically chosen locations around the telescope using the INAF mobile laboratory, providing comprehensive coverage of all possible antenna pointing directions. The results revealed several sources of RFI, including emissions from radar, terrestrial and satellite communications, and wireless transmissions. Characterizing these sources and assessing their frequency band occupation are essential for understanding the impact of RFI on scientific observations. This work provides a significant contribution to astronomers who will use the SRT for scientific observations, offering a suggestion for the development of mitigation strategies and safeguarding the radio astronomical environment for future observational campaigns. [ABSTRACT FROM AUTHOR]

In order to meet the power source requirements of C-band linear accelerators for industrial applications, a C-band high power klystron operating at a frequency of 5 712 MHz was developed. For this klystron, the development objective of the output power is no less than 3.5 MW and the efficiency is no less than 35%. During the entire design process, the output power was optimized to over 4 MW and the power efficiency over 40% to compensate for the disadvantage effects caused by manufacturing and testing errors in the development processes. Firstly, the electron optics system with a Pierce gun and a combination of five forward and one reverse focusing coils was designed. The Pierce gun with a perveance of 2 μP was adopted and the beam voltage and current were chosen as 120 kV and 83.3 A. By iteratively calculating the structure of the electron gun with EGUN code and optimizing the magnetic field between the electron gun and the beam-wave interaction section, the final electron beam pass rate reaches 100% and the fluctuation of the beam envelop is only 4.8%. Secondly, the efficiency optimization and PIC simulation of the beam-wave interaction section were carried out using the one dimensional AJDISK code, 1.5 dimensional KlyC code and three dimensional CST code. The scheme of six resonant cavities was ultimately determined and the basic cavity parameters were optimized based on the principles of stagger tuning. The simulation results of different codes all indicate that the efficiency can reach above 46.5%, and the output power can all reach above 4.650 MW. And the influence of frequency errors and output external quality factor on efficiency was also analyzed to guide the manufacturing process. After that, the mechanical structure of cavities was designed and all cavities were manufactured with oxygen free copper. The cold test and tuning of all cavities were carried out and the frequency error is mostly within the range of ±5 MHz, which basically does not affect the output power. Finally, the electron gun, the beam-wave interaction section and the collector were welded together. And the high power test was conducted immediately after the first high power C-band klystron protype was completed. When the electron gun operates at the voltage of 115 kV and current of 79.6 A, the klystron peak output power reaches 3.52 MW, the gain reaches 45.5 dB and the efficiency reaches about 38.5%. The high power test results show that this C-band high power klystron achieves the expected development goals.

This paper presents a comprehensive overview of Gallium nitride (GaN)-based power amplifier (PA) design for various frequency bands. GaN-based technology has emerged as a promising alternative to traditional silicon-based amplifiers due to its superior performance characteristics, which are discussed in this paper. This paper also discusses the key design parameters and challenges associated with PA design. Various design techniques and topologies for GaN power amplifiers are explored besides addressing theoretical considerations of PA design along with a complete systematic design procedure for L-Band amplifier using the wolfspeed large signal GaN HEMT model. To further demonstrate the useful methodology, the designs of S-band and C-band PAs are also presented. GaN-based devices are very promising candidates for high-power applications. It is widely used in various high-power applications including communication and radar. [ABSTRACT FROM AUTHOR]

The rapid advancements in radar and electromagnetic communication technologies have sparked a pressing need for thin, lightweight, and highly efficient low-frequency electromagnetic absorbing materials (EAMs) tailored for the C-band. However, the close linear correlation between the real and imaginary permittivity components of EAMs at low frequencies hinders the decoupling of wave impedance and electromagnetic dissipation, posing a formidable challenge in achieving a satisfactory absorption performance. In this study, a strategy for targeting C-band absorption encompassing advancements in material design and structural engineering has been formulated. Leveraging the high-efficiency microwave plasma-assisted reduction chemical vapor deposition (MPARCVD) technique, FeCo/C magnetic nanocomposites were successfully synthesized, offering a cost-effective and energy-saving solution. The growth of carbon microspheres on the FeCo alloy particle surfaces significantly regulated the real and imaginary permittivities within a broad range, attributed to the drastic improvement in interfacial polarization and electrical conductivity. This versatile platform facilitated structural engineering, enabling the design and optimization of the impedance matching layer and wave absorption layer. Notably, our strategy achieved a minimal reflection loss of −36.8 dB, along with an effective absorption bandwidth spanning from 3.84 to 12 GHz, covering both the C-band and the X-band. This work provides a strategy for attaining superior microwave absorption performance in the C-band, opening up promising avenues for applications in electromagnetic interference shielding and stealth technology tailored for the C-band frequency range. [ABSTRACT FROM AUTHOR]

Spatial information about plant health and productivity are essential when assessing the progress towards Sustainable Development Goals such as life on land and zero hunger. Plant health and productivity are strongly linked to a plant's phenological progress. Remote sensing, and since the launch of Sentinel-1 (S1), specifically, radar-based frameworks have been studied for the purpose of monitoring phenological development. This study produces insights into how crop phenology shapes S1 signatures of PolSAR features and InSAR coherence of wheat, canola, sugar beet. and potato across multiple years and orbits. Hereby, differently smoothed time series and a base line of growing degree days are stacked to estimate the patterns of occurrence of extreme values and break points. These patterns are then linked to in situ observations of phenological developments. The comparison of patterns across multiple orbits and years reveals that a single optimized fit hampers the tracking capacities of an entire season monitoring framework, as does the sole reliance on extreme values. VV and VH backscatter intensities outperform all other features, but certain combinations of phenological stage and crop type are better covered by a complementary set of PolSAR features and coherence. With regard to PolSAR features, alpha and entropy can be replaced by the cross-polarization ratio for tracking certain stages. Moreover, a range of moderate incidence angles is better suited for monitoring crop phenology. Also, wheat and canola are favored by a late afternoon overpass. In sum, this study provides insights into phenological developments at the landscape level that can be of further use when investigating spatial and temporal variations within the landscape. [ABSTRACT FROM AUTHOR]

Soil freeze-thaw (FT) cycles over agricultural lands are of great importance due to their vital role in controlling soil moisture distribution, nutrient availability, health of microbial communities, and water partitioning during flood events. Active microwave sensors such as C-band Sentinel-1 synthetic aperture radar (SAR) can serve as powerful tools to detect field-scale soil FT state. Using Sentinel-1 SAR observations, this study compares the performance of two FT detection approaches, a commonly used seasonal threshold approach (STA) and a computationally inexpensive general threshold approach (GTA) at an agricultural field in New Hampshire, US. It also explores the applicability of an interferometric coherence approach (ICA) for FT detection. STA and GTA achieved 85% and 78% accuracy, respectively, using VH polarization. We find a marginal degradation in the performance of STA (82%) and GTA (76%) when employing VV-polarized data. While there was approximately a 6 percentage point difference between STA's and GTA's overall accuracy, we recommend GTA for FT detection using SAR images at sub-field-scale over extended regions because of its higher computational efficiency. Our analysis shows that interferometric coherence is not suitable for detecting FT transitions under mild and highly dynamic winter conditions. We hypothesize that the relatively mild winter conditions and therefore the subtle FT transitions are not able to significantly reduce the correlation between the phase values. Also, the ephemeral nature of snowpack in our study area, further compounded by frequent rainfall, could cause decorrelation of SAR images even in the absence of a FT transition. We conclude that despite Sentinel-1's ~80% mapping accuracy at a mid-latitude site, understanding the cause of misclassification remains challenging, even when detailed ground data are readily available and employed in error attribution efforts. [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]

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C-band high-power microwave devices have important application prospects in communication, radar and other fields, and the demand for compact and lightweight devices is becoming more and more urgent in the industrial sector. A C-band high-efficiency coaxial transit-time oscillator (CTTO) with three-cavity buncher and dual-cavity extractor is proposed and investigated in theory and 2.5-dimensional particle-in-cell simulations, which is good for high power microwave generation devices at low frequency towards miniaturization and compactness. In order to avoid the transverse electromagnetic mode (TEM) leaking to the diode region, the reflector is designed and adopted in front of the buncher, which also can pre-modulate the beams and lead to the higher conversion efficiency. In this simulation, the typical performance of the CTTO reveals that microwaves with a power of 1.83 GW are generated at a frequency of 6.37 GHz when the beam voltage and current are 458 kV and 9.6 kA respectively, under a guiding magnetic field of 1.05 T. The corresponding power conversion efficiency is as high as 41.6%. [ABSTRACT FROM AUTHOR]

There is a heightened risk of an oil spill occurring in the Arctic, as climate change driven sea ice loss permits an increase in Arctic marine transportation. The ability to detect an oil spill and monitor its progression is key to enacting an effective response. Microwave scatterometer systems may be used detect changes in sea ice thermodynamic and physical properties, so we examined the potential of C-band polarimetric radar for detecting diesel fuel beneath a thin sea ice layer. Sea ice physical properties, including thickness, temperature, and salinity, were measured before and after diesel addition beneath the ice. Time-series polarimetric C-band scatterometer measurements monitored the sea ice evolution and diesel migration to the sea ice surface. We characterized the temporal evolution of the diesel-contaminated seawater and sea ice by monitoring the normalized radar cross section (NRCS) and polarimetric parameters (conformity coefficient (μ), copolarization correlation coefficient (ρco)) at 20° and 25° incidence angles. We delineated three stages, with distinct NRCS and polarimetric results, which could be connected to the thermophysical state and the presence of diesel on the surface. Stage 1 described the initial formation of sea ice, while in Stage 2, we injected 20L of diesel beneath the sea ice. No immediate response was noted in the radar measurements. With the emergence of diesel on the sea ice surface, denoted by Stage 3, the NRCS dropped substantially. The largest response was for VV and HH polarizations at 20° incidence angle. Physical sampling indicated that diesel emerged to the surface of the sea ice and trended towards the tub edge and the polarimetric scatterometer was sensitive to these physical changes. This study contributes to a greater understanding of how C-band frequencies can be used to monitor oil products in the Arctic and act as a baseline for the interpretation of satellite data. Additionally, these findings will assist in the development of standards for oil and diesel fuel detection in the Canadian Arctic in association with the Canadian Standards Association Group. [ABSTRACT FROM AUTHOR]

The recent wireless communication systems require high gain, lightweight, low profile, and simple antenna structures to ensure high efficiency and reliability. The existing microstrip patch antenna (MPA) design approaches attain low gain and high return loss. To solve this issue, the geometric dimensions of the antenna should be optimized. The improved Particle Swarm Optimization (PSO) algorithm which is the combination of PSO and simulated annealing (SA) approach (PSO-SA) is employed in this paper to optimize the width and length of the inset-fed rectangular microstrip patch antennas for Ku-band and C-band applications. The inputs to the proposed algorithm such as substrate height, dielectric constant, and resonant frequency and outputs are optimized for width and height. The return loss and gain of the antenna are considered for the fitness function. To calculate the fitness value, the Feedforward Neural Network (FNN) is employed in the PSO-SA approach. The design and optimization of the proposed MPA are implemented in MATLAB software. The performance of the optimally designed antenna with the proposed approach is evaluated in terms of the radiation pattern, return loss, Voltage Standing Wave Ratio (VSWR), gain, computation time, directivity, and convergence speed. [ABSTRACT FROM AUTHOR]

The Earth Observation Satellite, EOS-4, launched by the Indian Space Research Organisation, operates in the microwave C-band (5.6 GHz), offering high-quality backscatter images for various thematic applications. In this study, we demonstrate applicability of EOS-4 data in visualizing and identifying geological features, i.e. landforms, structures and rock type variations. Through test cases, we have suggested optimization of parameters like viewing node, geometry, look angle and polarization for geological applications. In analysis of geological structures, SAR look direction and node variation are crucial, whereas for shallow and moist subsurface features, multiple polarizations may be investigated for optimum results. FRS data analysis is essential for mesoscale features like landslides and glaciers, to bring out the subtle granularities. Finally for lithological contrast identification, RGB composites and band ratios derived from the available polarization channels provides the optimum outcomes. Thus, EOS4 are aptly complementary to any optical datasets for geological feature identification and mapping. [ABSTRACT FROM AUTHOR]

The rapid and accurate detection of forest disturbances in temperate forests has become increasingly crucial as policy demands and climate pressure on these forests rise. The cloud-penetrating Sentinel-1 radar constellation provides frequent and high-resolution observations with global coverage, but few studies have assessed its potential for mapping disturbances in temperate forests. This study investigated the sensitivity of temporally dense C-band backscatter data from Sentinel-1 to varying management-related disturbance intensities in temperate forests, and the influence of confounding factors such as radar backscatter signal seasonality, shadow, and layover on the radar backscatter signal at a pixel level. A unique network of 14 experimental sites in the Netherlands was used in which trees were removed to simulate different levels of management-related forest disturbances across a range of representative temperate forest species. Results from six years (2016–2022) of Sentinel-1 observations indicated that backscatter seasonality is dependent on species phenology and degree of canopy cover. The backscatter change magnitude was sensitive to medium- and high-severity disturbances, with radar layover having a stronger impact on the backscatter disturbance signal than radar shadow. Combining ascending and descending orbits and complementing polarizations compared to a single orbit or polarization was found to result in a 34% mean increase in disturbance detection sensitivity across all disturbance severities. This study underlines the importance of linking high-quality experimental ground-based data to dense satellite time series to improve future forest disturbance mapping. It suggests a key role for C-band backscatter time series in the rapid and accurate large-area monitoring of temperate forests and, in particular, the disturbances imposed by logging practices or tree mortality driven by climate change factors. [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]

In satellite remote sensing, C-band synthetic aperture radar (SAR) sensors with the frequency of about 5.4 GHz and wavelength of about 5.5 cm interact heavily with the leaves, twigs and small stems. Hence, it is ideal for monitoring vegetation phenology, stratification of canopy closure/openness and biomass assessment of low- to medium-aboveground-biomass (AGB) density regions. Earth Observation Satellite-04 (EOS-04) is a C-band SAR mission from the Indian Space Research Organisation launched on 14 February 2022. This study presents the applications of EOS-04 data in forest phenological studies and biomass estimation in different vegetation conditions. Multi-temporal EOS-04 data were used to track the land surface phenology of tropical dry deciduous forests of Betul, Madhya Pradesh, which is mostly dominated by Tectona grandis. Phenological metrics were also derived from the tracked land surface phenology. For the mangrove forests of Sundarbans delta for two islands, namely Lothian and Dhanchi characterization in terms of canopy density and homogeneity/heterogeneity was carried out and AGB was estimated. The AGB values ranged from 29 to 241 Mg/ha, and the validation root mean square error (RMSE) was calculated to be 34 Mg/ha. EOS04 data were also used in combination with L-band ALOS PALSAR data for the forest biomass estimation in the part of Central India. Synergistic utilization of C- and L-band improves upon the individual models in terms of R2 and RMSE. L-band HV backscatter estimates AGB with a correlation coefficient of 0.49 which improved to 0.57 with the inclusion of C-band and estimates AGB with RMSE of 29 Mg/ha. This study successfully demonstrated the usability of EOS-04 for tracking land surface phenology and deriving phenological metrics from it, for the characterization of mangrove forests and it AGB estimation and for AGB estimation of forests in low-biomass regions. [ABSTRACT FROM AUTHOR]

Precise and prompt information on forest disturbances in the tropics is critical to support law enforcement and protect tropical forests. In 2023, medium resolution ALOS-2 ScanSAR data (∼100 m spatial resolution) was made available for Southeast Asia, marking the first freely accessible large-area L-Band dataset. We assessed its potential for large-area forest disturbance mapping and its combination with high-resolution C-band Sentinel-1 data (∼20 m spatial resolution). We mapped forest disturbances in Sumatra, Indonesia for the year 2021 based on ALOS-2 ScanSAR data and Sentinel-1 data separately, and subsequently combined the mapped disturbances. Forest disturbances detected by both C-band and L-band SAR using a probabilistic change algorithm were combined at the product level by merging both sets of detections. The added benefit of combining both sensors was particularly evident in higher detection rates, as indicated by an improved producer accuracy (78.9 ± 11.9 %) compared to detections based on single sensor ALOS-2 ScanSAR (40.8 ± 6.3 %) and Sentinel-1 data (63.3 ± 9.6 %). Both combined and single sensor detections showed negligible false detections. ALOS-2 ScanSAR showed advantages for overcoming limited capability of Sentinel-1 to detect large-sized disturbance events characterized by post-disturbance tree remnants, occurring at locations with large-scale agricultural clearings. The medium resolution of approximately 100 m restricts the detection capability of ALOS-2 ScanSAR data for small-scale disturbances, resulting in missed detections. ALOS-2 ScanSAR detections showed a delay of up to 17.8 days compared to detections based solely on Sentinel-1 data. Combining ALOS-2 ScanSAR and Sentinel-1-based disturbances resulted in improved detection timeliness, with an average improvement of up to 16.5 days compared to Sentinel-1-based detections. Furthermore, we observed improved detection rates for our ALOS-2 ScanSAR-based detections compared to those of the ALOS-2 ScanSAR-based JICA-JAXA Forest Early Warning System in the Tropics (JJ-FAST) forest disturbance alerting product. This suggests that the potential of ALOS-2 ScanSAR data in operational forest monitoring systems is not currently fully realized. Comparing the SAR-based disturbance detections from this study with existing optical-based forest disturbance products (GFC and GLAD-L) suggested improved detection accuracies by overcoming sensor-specific omission errors when using combined SAR and optical data. The demonstrated potential of L-Band ALOS-2 ScanSAR data for improving operational forest monitoring efforts using C-band radar and optical satellites is expected to be amplified by upcoming L-Band satellite missions like NiSAR (2024) and ROSE-L (2028), which will provide freely accessible L-Band data with higher spatial resolution.

This study presents dual polarization spectral analysis over updraft environments in thunderstorms. The composition and interaction of particle in updrafts environments are analyzed using the expansion that the spectral polarimetric provides in radar variables. Updrafts are identified using dual Doppler analysis and polarimetric signatures such as $Z_{\text{dr}}$ columns. Spectral techniques are presented to estimate the spectrum in updraft and mixed-phase environments. A separation in the spectrum of melting ice and rain was observed in the analyzed updrafts. This separation in the spectrum allows us to study the polarimetric characteristics and interaction of melting ice and rain. Furthermore, scattering simulations were carried out to validate the spectral signatures attributed to melting ice. It was found that small ice particles mixed with rain can produced similar polarimetric characteristics as the one observed in the spectral analysis. Conceptual models based on the spectral observations are presented to illustrate the interaction of ice particles with a recirculation and a vigorous updraft.

This study evaluates the maximum theoretical exposure to radiofrequency (RF) electromag- netic fields (EMFs) from a Fifth-generation (5G) New Radio (NR) base station (BS) while using four commonly used mobile applications: YouTube for video streaming, WhatsApp for voice calls, Instagram for posting pictures and videos, and running a Video game. Three factors that might affect exposure, i.e., distance of the measurement positions from the BS, measurement time, and induced traffic, were examined. Exposure was assessed through both instantaneous and time-averaged extrapolated field strengths using the Maximum Power Extrapolation (MPE) method. The former was calculated for every measured SS-RSRP (Secondary Synchronization Reference Signal Received Power) power sample obtained with a sampling resolution of 1 second, whereas the latter was obtained using a 1-min moving average applied on the applications’ instantaneous extrapolated field strengths datasets. Regarding distance, two measurement positions (MPs) were selected: MP1 at 56 meters and MP2 at 170 meters. Next, considering the measurement time, all mobile application tests were initially set to run for 30 minutes at both MPs, whereas the video streaming test (YouTube) was run for an additional 150 minutes to investigate the temporal evolution of field strengths. Considering the traffic, throughput data vs. both instantaneous and time-averaged extrapolated field strengths were observed for all four mobile applications. In addition, at MP1, a 30-minute test without a User Equipment (UE) device was conducted to analyze exposure levels in the absence of induced traffic. The findings indicated that the estimated field strengths for mobile applications varied. It was observed that distance and time had a more significant impact than the volume of data traffic generated (throughput). Notably, the exposure levels in all tests were considerably lower than the public exposure thresholds set by the ICNIRP guidelines.INDEX TERMS 5G NR, C-band, human exposure assessment, mobile applications, traffic data, maximum extrapolation method, RF-EMF.

This study introduces a new design for a low noise amplifier (LNA) consisting of two stages taking advantage of the inherent lossy properties of the input matching components. By doing this, the design balances the minimum noise figure (NF) and stability, eliminating the complexities and challenges introduced by feedback networks. Furthermore, the integration of the low-pass filter (LPF) into the design as a noise-matching network ensures improved performance across both the amplifier stages. A comprehensive analytical study is also introduced to delve deep into the relationship between critical LNA parameters, such as stability and noise figures, and the internal resistance of input-matching inductors. Two C-band LNAs are compared in terms of stability using indigenous $0.25~\mu \text{m}$ GaN technology. The designs are substantiated by fabricating two LNA MMICs for a 5–7 GHz frequency range, having a minimum NF of 1.3 dB and 1.5 dB, with a gain of 15 dB and 16 dB at 6 GHz, respectively. The study reveals that using the proposed approach, there is an overall improvement in NF of 0.2 dB within the frequency of operation. The work entails a way to remove the feedback network in the LNA leading to an improved NF.

Radio frequency interference (RFI) analysis is crucial for ensuring the proper functioning of a radio telescope and the quality of astronomical observations, as human-generated interference can compromise scientific data collection. The aim of this study is to present the results of an RFI measurement campaign in the frequency range of 4–5.8 GHz, a portion of the well-known C-band, for the Sardinia Radio Telescope (SRT), conducted in October–November 2023. In fact, this Italian telescope, managed by the Astronomical Observatory of Cagliari (OAC), a branch of the Italian National Institute for Astrophysics (INAF), was recently equipped with a new C-band receiver that operates from 4.2 GHz to 5.6 GHz. The measurements were carried out at three strategically chosen locations around the telescope using the INAF mobile laboratory, providing comprehensive coverage of all possible antenna pointing directions. The results revealed several sources of RFI, including emissions from radar, terrestrial and satellite communications, and wireless transmissions. Characterizing these sources and assessing their frequency band occupation are essential for understanding the impact of RFI on scientific observations. This work provides a significant contribution to astronomers who will use the SRT for scientific observations, offering a suggestion for the development of mitigation strategies and safeguarding the radio astronomical environment for future observational campaigns.

Miniaturization in the telecommunications field is deemed a current challenge and a critical demand in order to improve communication quality between the transmitter and the receiver while avoiding clutter issues. The main objective of this work is to design a miniature interdigital bandpass filter (IBF) using planar technology. The proposed bandpass filter is made up of three equidistant parallel-coupled lines carefully deposited on a small Rogers-5880 substrate possessing a full dimension of 10×10×1.6 mm³, a relative permittivity =2.2, and a loss tangen of 0.0009. The proposed IBF has been designed and simulated using the HFSS software, which is a simulator that studies the electromagnetic behavior of radio frequency structures using cutting-edge finite element solvers. The reached outcomes present good electrical performance in terms of insertion loss, reflection coefficient, voltage standing wave ratio (VSWR), and selectivity, making the proposed IBF suitable for integration in small electronic devices for C-band applications (4 GHz to 8 GHz). [ABSTRACT FROM AUTHOR]

This paper presents a highly integrated C-band RF transceiver front-end design consisting of two Single Pole Double Throw (SPDT) transmit/receive (T/R) switches, a Low Noise Amplifier (LNA), and a Power Amplifier (PA) for Ultra-Wideband (UWB) positioning system applications. When fabricated using a 0.25 μm GaAs pseudomorphic high electron mobility transistor (pHEMT) process, the switch is optimized for system isolation and stability using inductive resonance techniques. The transceiver front-end achieves overall bandwidth expansion as well as the flat noise in receive mode using the bandwidth expansion technique. The results show that the front-end modules (FEM) have a typical gain of 22 dB in transmit mode, 18 dB in receive mode, and 2 dB noise in the 4.5–8 GHz band, with a chip area of 1.56 × 1.46 mm2. Based on the available literature, it is known that the proposed circuit is the most highly integrated C-band RF transceiver front-end design for UWB applications in the same process. [ABSTRACT FROM AUTHOR]

This article proposes an empirical methodology for accurately estimating the relative permittivity ${\varepsilon _r}$εr of FR4 boards, which is essential for designing microstrip antennas at S and C frequency bands. As the relative permittivity of dielectric materials changes with frequency, the proposed method involves selecting a known starting value of ${\varepsilon _r}$εr for an FR4 board and then simulating the reflection coefficient S11 parameters of an antenna design. These simulated parameters are then compared to the measured S11 parameters of a fabricated antenna. A value of ${\varepsilon _r}$εr = 4.55 is accurately determined when the two S11 parameters converge close to the desired design frequency. With the FR4 ${\varepsilon _r}$εr value obtained from this methodology, a slot patch antenna is designed for a frequency of 4 GHz, obtaining a reflection coefficient of |Γ| = 0.035, a bandwidth BW = 117 MHz, and a standing wave ratio (SWR) of 1.0746. The proposed methodology can be used as a tool to estimate the ${\varepsilon _r}$εr of various substrates that are not characterized at high frequencies. [ABSTRACT FROM AUTHOR]

A novel stacked rectangular structure with surface-mounted short rectangle dielectric resonator antenna (SRSMSR) with an E-shaped microstrip feed through a wide aperture slot was investigated for C-band operation in wireless communication and tracking radar applications. The developed design uses copper for SMSR to improve return loss up to -46 dB, gain up to 10.7 dB, and an observed impedance bandwidth of 20.6% in the broad frequency range of 5.69 GHz-7.0 GHz. The 3 dB beamwidth achieved in the E-plane is 89.82°, while that in the H-plane is 24.31°. [ABSTRACT FROM AUTHOR]

Abstract A dual-port multiple-input multiple-output (MIMO) filtenna with minimal sizes of 80 × 45 mm2 is set up in this study. Each element in this MIMO filtenna is positioned orthogonally to the one next to it to improve isolation. For the MIMO element to achieve high-frequency selectivity and compact size, a frequency-reconfigurable filtenna that was created by fusing a band-pass filter and a monopole radiator was used. The suggested filtenna can switch between its C-band and X-band operating states with ease. On build the filtenna circuit, a band-pass filter based on defective microstrip structure is inserted to a circular monopole radiator. The developed filtenna operates in the C-band frequency range of 6.5–8 GHz and the X-band frequency range of 8–12 GHz. It is possible to use the X-band operating state for communication in a cognitive radio environment. Used as a decoupling structure, metamaterial structures can increase isolation to more than 40 dB across the bandwidth. The suggested MIMO filtenna system has an envelope correlation coefficient of 2.4e−6, a peak gain of 6 dBi, and an impedance bandwidth of 7.4–7.75 GHz. The MIMO filtenna is constructed and measured, and the findings of the measurement and simulation are in good agreement.

Soil freeze-thaw (FT) cycles over agricultural lands are of great importance due to their vital role in controlling soil moisture distribution, nutrient availability, health of microbial communities, and water partitioning during flood events. Active microwave sensors such as C-band Sentinel-1 synthetic aperture radar (SAR) can serve as powerful tools to detect field-scale soil FT state. Using Sentinel-1 SAR observations, this study compares the performance of two FT detection approaches, a commonly used seasonal threshold approach (STA) and a computationally inexpensive general threshold approach (GTA) at an agricultural field in New Hampshire, US. It also explores the applicability of an interferometric coherence approach (ICA) for FT detection. STA and GTA achieved 85% and 78% accuracy, respectively, using VH polarization. We find a marginal degradation in the performance of STA (82%) and GTA (76%) when employing VV-polarized data. While there was approximately a 6 percentage point difference between STA’s and GTA‘s overall accuracy, we recommend GTA for FT detection using SAR images at sub-field-scale over extended regions because of its higher computational efficiency. Our analysis shows that interferometric coherence is not suitable for detecting FT transitions under mild and highly dynamic winter conditions. We hypothesize that the relatively mild winter conditions and therefore the subtle FT transitions are not able to significantly reduce the correlation between the phase values. Also, the ephemeral nature of snowpack in our study area, further compounded by frequent rainfall, could cause decorrelation of SAR images even in the absence of a FT transition. We conclude that despite Sentinel-1’s ~80% mapping accuracy at a mid-latitude site, understanding the cause of misclassification remains challenging, even when detailed ground data are readily available and employed in error attribution efforts.

Spatial information about plant health and productivity are essential when assessing the progress towards Sustainable Development Goals such as life on land and zero hunger. Plant health and productivity are strongly linked to a plant’s phenological progress. Remote sensing, and since the launch of Sentinel-1 (S1), specifically, radar-based frameworks have been studied for the purpose of monitoring phenological development. This study produces insights into how crop phenology shapes S1 signatures of PolSAR features and InSAR coherence of wheat, canola, sugar beet. and potato across multiple years and orbits. Hereby, differently smoothed time series and a base line of growing degree days are stacked to estimate the patterns of occurrence of extreme values and break points. These patterns are then linked to in situ observations of phenological developments. The comparison of patterns across multiple orbits and years reveals that a single optimized fit hampers the tracking capacities of an entire season monitoring framework, as does the sole reliance on extreme values. VV and VH backscatter intensities outperform all other features, but certain combinations of phenological stage and crop type are better covered by a complementary set of PolSAR features and coherence. With regard to PolSAR features, alpha and entropy can be replaced by the cross-polarization ratio for tracking certain stages. Moreover, a range of moderate incidence angles is better suited for monitoring crop phenology. Also, wheat and canola are favored by a late afternoon overpass. In sum, this study provides insights into phenological developments at the landscape level that can be of further use when investigating spatial and temporal variations within the landscape.

Belirlenen frekans aralığında yüzeye gelen elektromanyetik dalgaların iletim, yansıma veya soğurma özelliği göstermesini sağlayan periyodik yapılara frekans seçici yüzeyler (FSY) denir. Çalışmada üç farklı geometrik şekle sahip FSY tasarlanmıştır. Tasarlanan yapıların temel iletim karakteristiğini bozmadan, birim hücreleri üzerinde optimizasyon çalışmaları yaparak, kullanılan parametrelerin değiştirilmesinin, s parametreleri, rezonans frekansı, bant genişliği ve maksimum soğurma değerine etkisi incelenmiştir. Cbandında (4 GHz–8 GHz) gerçekleştirilen çalışmalarda -10 dB kazanç değerinde bant genişliğini arttırabilmek için tasarlanan iki yapının üst üste birleştirilmesiyle yeni bir ultra geniş bantlı (UGB) FSY elde edilmiştir. Elde edilen yeni UGB FSY ile radar kesit alanının (RKA) azaltılması amaçlanmıştır. Tasarıma ait benzetim ve analizler CST Studio Suite 3D programı ile gerçekleştirilmiştir.

In this article, a miniature eight-port multiple-input multiple-output (MIMO) antenna array is proposed for fifth-generation (5G) sub-6 GHz handset applications. The individual antenna element comprises a radiator shaped like the Chinese character "王" (phonetically represented as "Wang") and three split-ring resonators (SRR) on the metal frame. The size of the individual antenna element is only 6.8 × 7 × 1 mm3 (47.6 mm3). The proposed antenna element has a −10 dB impedance bandwidth of 1.7 GHz (from 3.3 GHz to 5 GHz) that can cover 5G New Radio (NR) sub-6 GHz bands N77 (3.3–4.2 GHz), N78 (3.3–3.8 GHz), and N79 (4.4–5 GHz). The evolution design, the current distribution, the effects of single-handed holding, and the analysis of the parameters are deduced to study the approach used to design the featured antenna. The measured total efficiencies are from 40% to 80%, the isolation is better than 12 dB, the calculated envelope correlation coefficient (ECC) is less than 0.12, and the calculated channel capacity (CC) ranges from 35 to 38 bps/Hz. The presented antenna array is a good alternative to 5G mobile handsets with wideband operation, a metal frame, and minimized spacing. [ABSTRACT FROM AUTHOR]

Vegetation structural complexity (VSC) plays an essential role in the functioning and the stability of fire-prone Mediterranean ecosystems. However, we currently lack knowledge about the effects of increasing fire severity on the VSC spatial variability, as modulated by the plant community type in complex post-fire landscapes. Accordingly, this study explored, for the first time, the effect of fire severity on the VSC of different Mediterranean plant communities one year after fire by leveraging field inventory and Sentinel-1 C-band synthetic aperture radar (SAR) data. The field-evaluated VSC retrieved in post-fire scenarios from Sentinel-1 γ0 VV and VH backscatter data featured high fit (R2 = 0.878) and low predictive error (RMSE = 0.112). Wall-to-wall VSC estimates showed that plant community types strongly modulated the VSC response to increasing fire severity, with this response strongly linked to the regenerative strategies of the dominant species in the community. Moderate and high fire severities had a strong impact, one year after fire, on the VSC of broom shrublands and Scots pine forests, dominated by facultative and obligate seeder species, respectively. In contrast, the fire-induced impacts on VSC were not significantly different between low and moderate fire-severity scenarios in communities dominated by resprouter species, i.e., heathlands and Pyrenean oak forests. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a dual‐band complementary frequency selective surface (CFSS) with narrow stop band and large stop band. The proposed CFSS combines two simple geometries, the square loop with grid and the crossed dipole. The resonant frequencies are 2.53 and 5.38 GHz. The bandwidths of 280 MHz and 1.77 GHz were obtained, at –10 dB level, for the first and second bands, respectively. These frequencies and bands show that the structure can be applied in Wi‐Fi (2.4–2.5 GHz) and C‐band (4–6 GHz) frequencies. The simulated and measured results show that the chosen geometry has angular stability and polarization independence up to 45°. We can observe a good agreement between simulated and measured results. [ABSTRACT FROM AUTHOR]

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Monitoring snowmelt dynamics in mountains is crucial to understand water releases downstream. Sentinel-1 (S-1) synthetic-aperture radar (SAR) has become one of the most widely used techniques to achieve this aim due to its high frequency of acquisitions and all-weather capability. This work aims to understand the possibilities of S-1 SAR imagery to capture snowmelt dynamics and related changes in streamflow response in semi-arid mountains. The results proved that S-1 SAR imagery was able not only to capture the final spring melting but also all melting cycles that commonly appear throughout the year in these types of environments. The general change detection approach to identify wet snow was adapted for these regions using as reference the average S-1 SAR image from the previous summer, and a threshold of −3.00 dB, which has been assessed using Landsat images as reference dataset obtaining a general accuracy of 0.79. In addition, four different types of melting-runoff onsets depending on physical snow condition were identified. When translating that at the catchment scale, distributed melting-runoff onset maps were defined to better understand the spatiotemporal evolution of melting dynamics. Finally, a linear connection between melting dynamics and streamflow was found for long-lasting melting cycles, with a determination coefficient (R2) ranging from 0.62 to 0.83 and an average delay between the melting onset and streamflow peak of about 21 days. [ABSTRACT FROM AUTHOR]

The paper presents a compact dual-band pentagonal-shaped patch antenna, with resonating frequencies 7.6 GHz and 12 GHz, that is used for satellite communication, 5G application, and high-speed applications. The proposed antenna is designed on an FR4 substrate with an overall dimension of 16 x 16 mm where the height of the substrate is 0.8 mm. The proposed antenna contains a pentagonal-shaped patch with four circles at each corner of the patch that is used for the dual-band; in addition, the circular slot with the combination of the cross-shaped slot achieves better results. The proposed antenna has a partial ground configuration for better bandwidth and gain. The peak gain of the antenna is 8.07 dB at 12 GHz and has a 7.13 dB gain at 7.6 GHz. With its compact size and wide bandwidth capabilities, the antenna proves to be an ideal solution for mobile communication systems, satellite ground stations, and remote sensing applications across C-, X-, and Ku-bands. The proposed antenna also covers Ku used for satellite and high-speed communication. [ABSTRACT FROM AUTHOR]

A dual-port multiple-input multiple-output (MIMO) filtenna with minimal sizes of 80 × 45 mm2 is set up in this study. Each element in this MIMO filtenna is positioned orthogonally to the one next to it to improve isolation. For the MIMO element to achieve high-frequency selectivity and compact size, a frequency-reconfigurable filtenna that was created by fusing a band-pass filter and a monopole radiator was used. The suggested filtenna can switch between its C-band and X-band operating states with ease. On build the filtenna circuit, a band-pass filter based on defective microstrip structure is inserted to a circular monopole radiator. The developed filtenna operates in the C-band frequency range of 6.5–8 GHz and the X-band frequency range of 8–12 GHz. It is possible to use the X-band operating state for communication in a cognitive radio environment. Used as a decoupling structure, metamaterial structures can increase isolation to more than 40 dB across the bandwidth. The suggested MIMO filtenna system has an envelope correlation coefficient of 2.4e−6, a peak gain of 6 dBi, and an impedance bandwidth of 7.4–7.75 GHz. The MIMO filtenna is constructed and measured, and the findings of the measurement and simulation are in good agreement. [ABSTRACT FROM AUTHOR]

This paper presents the physical layer of a proprietary broadband communication system for CubeSats. The system operates in the C band (5.8 GHz), delivering at least 10 Mbps of the net user throughput. Operation at low elevation angles (and therefore low SNRs) and high Doppler shifts is made possible thanks to a sophisticated synchronization subsystem. The system can be adapted to propagation conditions experienced during a given visibility window by changing the signal bandwidth and coding rate. It is implemented using Software Defined Radio (SDR) technology. The system will be used in two missions that are scheduled for 2023 and 2024 and are planned in cooperation with the National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute" and SatRev S.A. [ABSTRACT FROM AUTHOR]

Compact printed multiple input multiple output (MIMO) antenna is reported for C-band (n79, LTE-46/47) applications. The presented twoelement MIMO antenna has a size of 27×27 mm2 and it is printed on a 0.8 mm thick, low-cost dielectric substrate (FR4). The rectangular patch consists of two parallel narrow slots on both sides of the patch. These parallel slots are used to enhance the impedance bandwidth of a proposed antenna. The antenna is fed via a 50Ω impedance feedline. The proposed antenna has partial ground that helps to get wider bandwidth. The antenna operates at a frequency of 4.42 GHz which is included in the future near radio (n79-band) 5G frequency band. Proposed antenna has a bandwidth of 2.45 GHz, and a peak gain of an antenna is 7.1 dB which is appropriate for portable C-band (n79, LTE-46/47) applications. Optimization using simulation and fabrication shows that the proposed MIMO antenna can provide requisite gain, reasonable bandwidth, and high radiation efficiency in resonant frequency bands. [ABSTRACT FROM AUTHOR]

This paper describes a substrate integrated waveguide (SIW) filter built on an Fr4-Epoxy substrate with a dielectric constant 4.4 and a height of h=1.6mm. SIW-based devices have piqued the interest of researchers in recent years due to their low loss, small size, and low cost. The goal is to simulate and realize a SIW filter for C-band applications. The designed filter is analyzed using the reflection coefficient S11 and electric field distributions. We used the HFSS simulator. According to the findings, there is a high degree of agreement between the simulated and realized filters. The results also show that the filter has a very good response. It also shows a bandwidth of 6.3GHz around the C-band frequencies. This filter's pass-band ranges from 5.39 to 6.83GHz, with an insertion loss of 4.2dB and a return loss of 45.49dB. [JJCIT 2023; 9(2.000): 166-174]

A porous 3D cross-linked conductive network pierced by multi-wall carbon nanotubes (MWCNTs) was successfully designed from zeolitic imidazolate framework-8 (ZIF-8). Zn@NPC@MWCNTs composites were tailored by the facile regulating the mass ratios and thermal annealing treatment. Due to the combination of less eddy current loss and dielectric loss together with multiple reflection attenuation caused by a unique structure. With a 10 wt% filler loading, the Zn@NPC@MWCNTs composites carbonized at 800 °C show two high reflection loss (RL) values with different thicknesses. An RL value is −53.18 dB with 4.09 mm thickness in the C-Band (4–8 GHz), and a minimum RL can reach −74.83 dB (10.8 GHz) with a matching thickness of 2.749 mm. The effective absorption bandwidth is 4 GHz (from 8 to 12 GHz, RL ≤ −10 dB), which just covers the full X-band. Low cost and easy preparation can also provide advantages to develop MOF-based materials as effective EMW absorbents.