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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.

Precise knowledge of the antenna pointing direction is a key facet to ensure the accuracy of observations from scanning weather radars. The sun is an often-used reference point to aid accurate alignment of weather radar systems and is particularly useful when observed as interference during normal scanning operations. In this study, we combine two online solar interference approaches to determine the pointing accuracy of an X-band mobile weather radar system deployed for 26 months in northern England (54.517°N, 3.615°W). During the deployment, several shifts in the tilt of the radar system are diagnosed between site visits. One extended period of time (>11 months) is shown to have a changing tilt that is independent of human intervention. To verify the corrections derived from this combined approach, quantitative precipitation estimates (QPEs) from the radar system are compared to surface observations: an approach that takes advantage of the variations in the magnitude of partial beam blockage corrections required due to tilting of the radar system close to mountainous terrain. The observed improvements in QPE performance after correction support the use of the derived tilt corrections for further applications using the corrected dataset. Finally, recommendations for future deployments are made, with particular focus on higher latitudes where solar interference spikes show more seasonality than those at mid-latitudes. [ABSTRACT FROM AUTHOR]

In this study, the quantitative precipitation estimation (QPE) capability of three X-band dual-polarization phased array radars (PAR) in Guangzhou, South China, was demonstrated, with an S-band operational dual-polarization radar as the benchmark. Rainfall rate (R) estimators based on the specific differential phase (KDP) for summer precipitation for both X-band and S-band radars were derived from the raindrop size distributions (DSDs) observed by a 2-dimensional video disdrometer (2DVD) in South China. Rainfall estimates from the radars were evaluated with gauge observations in three events, including pre-summer rainfall, typhoon precipitation, and local severe convective precipitation. Observational results showed that radar echoes from the X-band PARs suffered much more severely from attenuation than those from the S-band radar. Compared to S-band observations, the X-band echoes can disappear when the signal-to-noise ratio drops to a certain level due to severe attenuation, resulting in different estimated rainfall areas for X- and S-band radars. The attenuation corrected by KDP had good consistency with S-band observations, but the accuracy of attenuation correction was affected by DSD uncertainty and may vary in different types of precipitation. The QPE results demonstrated that the R(KDP) estimator produced better rainfall accumulations from the X-band PAR observations compared to the S-band observations. For both the X-band and S-band radars, the estimates of hourly accumulated rainfall became more accurate in heavier rainfall, due to the decreases of both the DSD uncertainty and the impact of measurement errors. In the heavy precipitation area, the estimation accuracy of the X-band radar was high, and the overestimation of the S-band radar was obvious. Through the analysis of the ZH-ZDR distribution in the three weather events, it was found that the X-band PAR with the capability of high spatiotemporal observations can capture minute-level changes in the microphysical characteristics, which help improve the estimation accuracy of ground rainfall. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a broad band A-sandwich radome wall structure based on band-pass FSS (frequency selective surface) is proposed for an airborne radar applications. The FSS structure having two square conducting rings, which are embedded on either side of core layer. The conventional and proposed FSS based radome wall is analyzed with different incidence angles (0°, 10°, 20° and 30°) for both TE and TM polarization. The radome wall structure consist of a low density Nomex honeycomb core layer sandwiched between two high density Quartz skin layers. The structure shows the percentage impedance bandwidth of 40.8 % in the frequency range from 7.8GHz to 11.8GHz with sharp roll-off characteristics. The proposed novel approach involves high frequency unit cell simulation, which is carried out using EM Simulation Tool. To understand the practical behavior of the proposed structure for radome application the conformal analysis has been also carried out, with respect to different radius. The superior EM performance of the proposed broadband novel radome wall structure makes it suitable for the design of airborne radome.

An airborne radar echo signal includes signals returned from clutter and a target; thus, simulating the signal from the clutter may be crucial for predicting and analyzing accurate radar performance. Because it can be extremely difficult and expensive to obtain real measured signal data for various scenarios, an accurate signal generation method is required. Existing weather clutter and ground clutter simulators for an X-band airborne radar are combined to simulate the echo signal when two clutters exist simultaneously. The weather clutter effect becomes more significant with increasing frequencies, such as in the X-band. The proposed simulator can generate time-do- main signals by considering the random characteristics of the clutter signal and the Doppler effect caused by the movement of aircraft and clutter. In addition, a simple scheme is proposed for generating signals from artificial structures. Finally, the finite bandwidth of the transmitted chirp signal is calculated to improve the accuracy of the generated signal. [ABSTRACT FROM AUTHOR]

Development of satellite and radar applications has been continuously studied to reach the demand in the recent communication technology. In this study, a new oval-square-shaped split-ring resonator with left-handed metamaterial properties was developed for C-band and X-band applications. The proposed metamaterial was fabricated on 9 × 9 × 0.508 mm3 size of Rogers RO4003C substrate. The proposed metamaterial structure was designed and simulated using Computer Simulation Technique (CST) Microwave Studio with the frequency ranging between 0 to 12 GHz. The simulated result of the proposed design indicated dual resonance frequency at 5.52 GHz (C-band) and 8.81 GHz (X-band). Meanwhile, the experimental result of the proposed design demonstrated dual resonance frequency at 5.53 GHz (C-band) and 8.31 GHz (X-band). Therefore, with a slight difference in the dual resonance frequency, the simulated result corresponded to the experimental result. Additionally, the proposed design exhibited the ideal properties of electromagnetic which is left-handed metamaterial (LHM) behavior. Hence, the metamaterial structure is highly recommended for satellite and radar applications. [ABSTRACT FROM AUTHOR]

In this paper, a multiband symmetrical Jerusalem cross-shaped metasurface absorber is designed, fabricated, and measured. The upper layer consists of Jerusalem cross metasurface placed over FR-4 substrate to achieve perfect absorption. The unit cell of the proposed absorber is symmetrical and periodic in the horizontal and vertical axis. The Jerusalem cross absorber gives good impedance response at five different frequencies in the X-band region. The proposed absorber gives absorptivity of 97.3%, 97%, 96.1%, 98.8%, and 97.4% at 8.82 GHz, 9 GHz, 9.25 GHz, 9.43 GHz, and 10.1 GHz. In transverse electric and magnetic field response, the absorptivity is angle insensitive up to 600. The change in absorption spectra for the proposed absorber with a change in different physical parameters, electric field distribution is presented. The measured results of the fabricated absorber are similar to the numerically investigated results. The proposed absorber can be applicable in X-band satellite and radar applications. [ABSTRACT FROM AUTHOR]

In this paper, a broad band A-sandwich radome wall structure based on band-pass FSS (frequency selective surface) is proposed for an airborne radar applications. The FSS structure having two square conducting rings, which are embedded on either side of core layer. The conventional and proposed FSS based radome wall is analyzed with different incidence angles (0o,10o, 20o and 30o) for both TE and TM polarization. The radome wall structure consist of a low density Nomex honeycomb core layer sandwiched between two high density Quartz skin layers. The structure shows the percentage impedance bandwidth of 40.8 % in the frequency range from 7.8GHz to 11.8GHz with sharp roll-off characteristics. The proposed novel approach involves high frequency unit cell simulation, which is carried out using EM Simulation Tool. To understand the practical behavior of the proposed structure for radome application the conformal analysis has been also carried out, with respect to different radius. The superior EM performance of the proposed broadband novel radome wall structure makes it suitable for the design of airborne radome. [ABSTRACT FROM AUTHOR]

Recently, most of researches concentrate on design broadband and high gain microstrip antenna with a low profile to fulfill modern communication system requirements. This paper presents a novel design of microstrip patch antenna. The design is based on the number two (Two-Shape) shape using the Computer Simulation Technology (CST) microwave studio. The novel design is operated at the X-band frequency, and it provides a very wide bandwidth which is around 25 % at the center frequency 10.25 GHz. The antenna realized gain fluctuates between 5.3-7.7 dBi over the entire X-band frequency. The antenna provides a Fan- beam radiation patterns with very low side lobe levels, which are below -10 dB in both of the E- and H-planes. Due to the simplicity and compatibility, it is believed the antenna could be of interest to the radar applications.

A pulsed chirping phased-array transceiver (TRX) is demonstrated for X-band synthetic aperture radar (SAR) application. The phased-array TRX is implemented on a single CMOS chip with beamsteering/beamforming capabilities. The chip-scale radar TRX is composed of four transmitters (TXs) and four receivers (RXs) operating at 10-GHz center frequency with 1-GHz bandwidth (BW). To achieve the wideband beamsteering with a fine angle step, the two-stage delay control in the TX is proposed, where a delay-locked loop (DLL) -based multi-phase synthesizer (MPS) is used to control the coarse true-time delay of the baseband chirp, and the active phase shifters (PS) in radio frequency (RF) path are used for fine phase tuning. Fabricated in a 65-nm CMOS technology, the TRX consumes 228 mW for each channel at a 1.2-V supply, delivering ~10.2-dBm power with <1.3-dB ripple. The delay-line test shows that the dechirped signal achieves −13-dB peak-to-sidelobe ratio (PSLR) and the phase coherence error is within ±1.2° at a chirp rate of 1 MHz/ $\mu \text{s}$. The prototype phased-array radar TRX chip is demonstrated with the antenna arrays consisting of Vivaldi antennas of 8-dBi gain, 6-GHz BW, and 6-cm pitch distance. Experiments indicate that beamsteering/beamforming up to ±60° with a step of ~1° is achieved. SAR imaging experiment is carried out based on both the two-stage beamsteering in the TXs and the digital beamforming in the RXs, proving the capability of the prototype phased-array radar TRX chip for the SAR imaging applications. [ABSTRACT FROM AUTHOR]

The paper discusses the structure of a distributed radar system for detecting and locating airborne objects. We touch the theoretical problems of designing sector surveillance radars using electronic scanning and rho-theta method. The location is performed by matching the data from two small radars. This improves the accuracy of the moving object trajectory measurements. We present implemented scenarios (parallel or serial) for the layout of two radars in a distributed measurement system based on X-band mobile radars. Mobile radars for remote registration of small airborne object movement parameters are build according to the cascaded active phased waveguide-slot antenna array technology. We discuss the main technical characteristics of radars in a distributed measurement/registration system, determining the limitations on the measurement distance and angular coverage. [ABSTRACT FROM AUTHOR]

Design of a conical-disc-backed circular-polarized Archimedean single-arm spiral antenna is presented in this paper. The antenna operation covers the X-band frequencies ranging from 8 to 12 GHz. The antenna makes use of a very simple structure having the single-arm spiral backed by a cone-shaped metallic disc to achieve high gain, circular polarization, and unidirectional symmetric radiation near the boresight. The diameter of the antenna only measures to 40 mm. The simulated and measured results show that the antenna has a very good impedance matching (better than -10 dB), good right-hand circular polarization (with an axial ratio of ≤3 dB) throughout the frequency range of interest, and offers a maximum peak gain of 11.4 dBiC. The presented S11 response and radiation pattern results also show that the antenna offers excellent performance in the X-band with no need of a balun. Antenna usefulness is also established through a detailed parametric study and comparison with a traditional flat disc structure. Compact size, simple design, wide range, and high gain make the proposed antenna design a good choice for radar, terrestrial communications, and satellite/aerospace communications applications.

An X-band dual-polarization radar (XPRAD) was deployed in Guangdong province as part of the Southern China Monsoon Rainfall Experiment (SCMREX) during the storm season in 2016. This paper presents a comprehensive assessment of XPRAD observations during SCMREX with emphasis on data processing and rainfall products. The differential phase-based attenuation correction and radar calibration using self-consistency of dual-polarization observables are presented. It is found that the standard deviation of the Zdr bias is less than 0.2 dB based on 'light rain at low angle' and 'dry aggregate snow' observations. Cross-comparison with two standard S-band China New Generation Weather Radars (CINRAD) shows that the bias of Zh has a mean value less than 1.5 dBZ and a standard deviation less than 0.5 dBZ. In addition, fifteen rainfall events that occurred during the intensive observing period (IOP) are analyzed to demonstrate the rainfall estimation performance of XPRAD. In particular, rainfall accumulations at 1-, 2- and 3-h scales derived using R(Kdp) and R(Zh, Zdr) relations are evaluated using national level rain gauge data and CINRAD-based rainfall estimation. The results show that both R(Kdp)- and R(Zh, Zdr)-based products agree well with the rain gauge observations and CINRAD estimation. The difference between R(Kdp) and R(Zh, Zdr) is not significant, although R(Kdp) shows slightly better performance than R(Zh, Zdr). [ABSTRACT FROM AUTHOR]

Despite many efforts of the radar community, quantitative precipitation estimation (QPE) from weather radar data remains a challenging topic. The high resolution of X-band radar imagery in space and time comes with an intricate correction process of reflectivity. The steep and high mountain topography of the Andes enhances its complexity. This study aims to optimize the rainfall derivation of the highest X-band radar in the world (4450 m a.s.l.) by using a random forest (RF) model and single Plan Position Indicator (PPI) scans. The performance of the RF model was evaluated in comparison with the traditional step-wise approach by using both, the Marshall-Palmer and a site-specific Z−R relationship. Since rain gauge networks are frequently unevenly distributed and hardly available at real time in mountain regions, bias adjustment was neglected. Results showed an improvement in the step-wise approach by using the site-specific (instead of the Marshall-Palmer) Z−R relationship. However, both models highly underestimate the rainfall rate (correlation coefficient < 0.69; slope up to 12). Contrary, the RF model greatly outperformed the step-wise approach in all testing locations and on different rainfall events (correlation coefficient up to 0.83; slope = 1.04). The results are promising and unveil a different approach to overcome the high attenuation issues inherent to X-band radars.

In this paper, we propose the design of and provide an analysis of, a rectangular patch antenna and its integration in a 4 element linear array. A T form power divider feeds in parallel the array elements through microstrip lines. The basic antenna has a simple structure, with dimensions of about 16×18×1.6 mm3, leading to a good bandwidth. In addition, the patch element characteristics, such as the reflection coefficient and the voltage standing wave ratio (VSWR), are improved by the insertion of a slot in the structure. The main objective of the 4 element array structure is the enhancement of the gain, which is enhanced up to 12.6 dBi. A prototype of the antenna is fabricated and tested with network analyzer. The proposed antenna has 4 resonant frequencies that define 4 bandwidths, defined by a return loss of less than -10 dB, and are: (7.62 GHz, 1250 MHz), (9.20 GHz, 330 MHz), (11.07 GHz, 940 MHz) and (15.02 GHz, 920 MHz), respectively. The simple configuration of this profile permits an easy and lowexpense fabrication process, with usability in many applications such as in radar, satellite, and wireless communications. [ABSTRACT FROM AUTHOR]

This paper present the compact power divider integrated with coupler and microstrip cavity filter for x-band surveillance radar system. These modules consist of several devices (splitter, filter and coupler) it is integrated in a single module aims to reduce the loss in the joint connectors. The bandpass filter is use microstrip cavity filter for operating on X-Band Frequency and deployed on RT/duroid 5880. The power divider and coupler is designed using quarter wavelength transformer. A theoretical analytical circuit model will be presented, from the theoretical model; a compact integrated module will be designed and simulated. The proposed compact integrated module is small in dimension and performs a compact size. The compact integrated devices design on X-Band frequency is simulated and the result is presented. [ABSTRACT FROM AUTHOR]

The single-event transient (SET) response of two different silicon-germanium (SiGe) X-band (8–12 GHz) low noise amplifier (LNA) topologies is fully investigated in this paper. The two LNAs were designed and implemented in 130nm SiGe HBT BiCMOS process technology. Two-photon absorption (TPA) laser pulses were utilized to induce transients within various devices in these LNAs. Impulse response theory is identified as a useful tool for predicting the settling behavior of the LNAs subjected to heavy ion strikes. Comprehensive device and circuit level modeling and simulations were performed to accurately simulate the behavior of the circuits under ion strikes. The simulations agree well with TPA measurements. The simulation, modeling and analysis presented in this paper can be applied for any other circuit topologies for SET modeling and prediction. [ABSTRACT FROM PUBLISHER]

In this paper, we propose the design of and provide an analysis of, a rectangular patch antenna and its integration in a 4 element linear array. A T form power divider feeds in parallel the array elements through microstrip lines. The basic antenna has a simple structure, with dimensions of about 16´18´1.6 mm3, leading to a good bandwidth. In addition, the patch element characteristics, such as the reflection coefficient and the voltage standing wave ratio (VSWR), are improved by the insertion of a slot in the structure. The main objective of the 4 element array structure is the enhancement of the gain, which is enhanced up to 12.6 dBi. A prototype of the antenna is fabricated and tested with network analyzer. The proposed antenna has 4 resonant frequencies that define 4 bandwidths, defined by a return loss of less than -10 dB, and are: (7.62 GHz, 1250 MHz), (9.20 GHz, 330 MHz), (11.07 GHz, 940 MHz) and (15.02 GHz, 920 MHz), respectively. The simple configuration of this profile permits an easy and low-expense fabrication process, with usability in many applications such as in radar, satellite, and wireless communications.

A three-port active circulator and an active quasi-circulator (QC) based on bridged-T networks (BTNs) are designed and fabricated in a standard 0.18- \mu \textm CMOS technology. The BTN provides a notch frequency response, and therefore, the circulator is practical by connecting three BTNs in a ring-type configuration. With a power consumption of 18.2 mW, the circulator achieves $6.1\sim 8$ -dB insertion loss, better than 25-dB isolation and 18.3-dB transmission ratio from 8.4 to 11.1 GHz. Furthermore, the QC based on one BTN topology can also be obtained by adding an external amplifier. With a power consumption of 18.6 mW, it achieves 7/−2-dB forward transmission gain, better than 17.3-dB isolation, and better than 15.3-dB transmission ratio at 9.9 GHz. The presented designs feature excellent performances in high isolation and transmission ratio compared with other CMOS active circulators or QCs. To the best of our knowledge, the designs are the first demonstration of three-port circulator/QC designs based on the BTN topology, and the design concept is also applicable to an $n$ -port circulator design. [ABSTRACT FROM PUBLISHER]

An X-band dual-polarization radar (XPRAD) was deployed in Guangdong province as part of the Southern China Monsoon Rainfall Experiment (SCMREX) during the storm season in 2016. This paper presents a comprehensive assessment of XPRAD observations during SCMREX with emphasis on data processing and rainfall products. The differential phase-based attenuation correction and radar calibration using self-consistency of dual-polarization observables are presented. It is found that the standard deviation of the Z d r bias is less than 0.2 dB based on ‘light rain at low angle’ and ‘dry aggregate snow’ observations. Cross-comparison with two standard S-band China New Generation Weather Radars (CINRAD) shows that the bias of Z h has a mean value less than 1.5 dBZ and a standard deviation less than 0.5 dBZ. In addition, fifteen rainfall events that occurred during the intensive observing period (IOP) are analyzed to demonstrate the rainfall estimation performance of XPRAD. In particular, rainfall accumulations at 1-, 2- and 3-h scales derived using R( K d p ) and R( Z h , Z d r ) relations are evaluated using national level rain gauge data and CINRAD-based rainfall estimation. The results show that both R( K d p )- and R( Z h , Z d r )-based products agree well with the rain gauge observations and CINRAD estimation. The difference between R ( K d p ) and R ( Z h , Z d r ) is not significant, although R ( K d p ) shows slightly better performance than R ( Z h , Z d r ) .

• Precipitation data from an X-band radar in northern Scotland are assessed. • Assessment against river flow using a distributed hydrological model brings fresh insights. • Lowest usable beam elevation is the main limit on performance in this mountainous area. • Use of dual-polarisation estimators improves performance during summer months. • The X-band radar is suited for filling gaps in the existing C-band radar network. A set of Quantitative Precipitation Estimates (QPEs) from a dual-polarisation X-band radar observation campaign in a mountainous area of Northern Scotland is assessed with reference to observed river flows as well as being compared to estimates from the UK C-band radar and raingauge networks. Employing estimation methods of varying complexity, the X-band QPEs are trialled as alternative inputs to Grid-to-Grid (G2G), a distributed hydrological model, to produce simulated river flows for comparison with observations. This hydrological assessment complements and extends a previous meteorological assessment that used point raingauge data only. Precipitation estimates for two periods over the observation campaign in 2016 (March to April and June to August) are assessed. During the second period, increased incorporation of dual-polarisation variables into the radar processing chain is found to be of considerable benefit, whereas during the first period the low height of the melting layer often restricts their use. As a result of the complex topography in Northern Scotland, the Lowest Usable Elevation (LUE) of the X-band radar observations is found to be a stronger indicator of the hydrological model performance than range from the radar. For catchments with an LUE of less than 3 km, the best X-band QPE typically performs better for modelling river flow than using an estimate from the UK C-band radar network. The hydrological assessment framework used here brings fresh insights into the performance of the different QPEs, as well as providing a stimulus for targeted improvements to dual-polarisation radar-based QPEs that have wider relevance beyond the case study situation. [ABSTRACT FROM AUTHOR]

A high-gain, wideband antenna element that covers most portions of X- and Ku-bands is essential formultimode radar applications. This letter presents an aperture-coupled stacked patch antenna for 8.75-12.25-GHz frequency band. Fixed beam tilt up to 30° in scan range can be obtained by offsetting the aperture relative to a driven patch. When there is no offset, a single antenna has broadside gain greater than 10 dBi. An antenna array (4 × 4) with fixed beam tilt is designed and validated with measurements. The prototype antenna exhibits 44% fractional bandwidth and maximum gain 20.6 dBi in the target frequency band. [ABSTRACT FROM AUTHOR]

A narrow band radar system based on a field programmable gate array is proposed for dual-mode operation.Frequency-modulated continuous-wave (FMCW) radar mode is for short-range target detection and pulse-Doppler (PD) radar mode is for long-range target detection. Precomputed codes are used to generate linear frequency modulation signals in both FMCW and PD radar mode. The bandwidths of FMCW and PD radar modes are 10 and 1 MHz. Experiments have been carried out to confirm the system operation. In FMCW radar mode, nonlinear amplitude response can be corrected by precomputed code. In PD radar mode, the RX signals have been checked in the pulse width of 4 μs with a compressed echo signal response. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:474-479, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27343 [ABSTRACT FROM AUTHOR]

Abstract: Radar precipitation estimates can improve hydrologic prediction over a range of spatial scales represented by both rural and urban basins. Flooding results from the combination of heavy precipitation and the distributed hydraulic and hydrologic characteristics of the basin. Accuracy and spatial scaling of radar estimated rainfall, and its impact at relevant hydrologic scales is an important determinant of hydrologic prediction accuracy and flood forecasting. Results of simulations using archival radar events are used to demonstrate the sources of uncertainty affecting site-specific flood forecasts within the distributed hydrologic model, Vflo. Radar data used in this analysis are derived from both S-band (NEXRAD/88D) and the Collaborative Adaptive Sensing of the Atmosphere (CASA), polarimetric X-band radars. X-band radars have the capability to provide higher spatial and temporal resolution than the conventional radars operating at S-band. However, compared to S-band, X-band radars have shorter wavelengths and suffer from attenuation, or even total extinction of the radar signal at short ranges from the radar. Degradation of precipitation mapping is a serious concern, especially in heavy precipitation over distances associated with watersheds prone to flooding. Compared to rain gauge accumulations, X-band radar polarimetric rainfall estimates were significantly degraded beyond about 15km from the radars. With rainfall input derived from X-band radars, uncertainty in runoff volume scales with watershed area as a smooth monotonically decreasing function as area increases due to averaging of random errors in the input. Relative to estimates derived from S-band radar, unreliable hydrograph response was produced using X-band polarimetric rainfall estimates as input to a physics-based distributed hydrologic model, especially for watershed areas less than about 20km2. [Copyright &y& Elsevier]

This paper describes the use of the Stable Point Network technique, a Persistent Scatterer Interferometry SAR technique, for the analysis of the Portalet landslide area (Central Pyrenees, Spain). For this purpose, different SAR datasets acquired by ERS-1, ERS-2, ENVISAT and TerraSAR-X satellites have been analysed. The use of different SAR images acquired by satellite radar sensors operating at different microwave lengths has allowed for a comparative assessment and illustration of the advantages and disadvantages of these satellites for landslide detection and monitoring. In the introduction, differential interferometry and the study area are briefly described. Then the specifics of the SPN processing and the results of the different datasets are described and compared. In Analysis of the results: the Portalet landslide area, the Portalet landslide area is introduced and the radar displacement measurements are analysed with available geo-information data. Additionally, X-band measurements are compared with those gathered by a ground-based SAR for a previous project. Finally, the most relevant conclusions of this work are discussed. [ABSTRACT FROM AUTHOR]

Novel radar satellite missions also include sensors operating in X-band at very high resolution. The presented study reports methodologies, algorithms and results on forest assessment utilizing such X-band satellite images, namely from TerraSAR-X and COSMO-SkyMed sensors. The proposed procedures cover advanced stereo-radargrammetric and interferometric data processing, as well as image segmentation and image classification. A core methodology is the multi-image matching concept for digital surface modeling based on geometrically constrained matching. Validation of generated surface models is made through comparison with LiDAR data, resulting in a standard deviation height error of less than 2 meters over forest. Image classification of forest regions is then based on X-band backscatter information, a canopy height model and interferometric coherence information yielding a classification accuracy above 90%. Such information is then directly used to extract forest border lines. High resolution X-band sensors deliver imagery that can be used for automatic forest assessment on a large scale. [ABSTRACT FROM AUTHOR]

It is an important issue not only for military purposes but also from commercial point of view, whether or not the reflective wave from an incident electromagnetic wave can be nullified. In this research, by blending conductive carbon black with the binder matrix of glass/epoxy composite, a radar absorbing structure (RAS) which can support loads and absorb the electromagnetic wave has been designed. The RAS was specially designed so as to exhibit the optimum absorptivity for X-band of (8.2–12 GHz) frequency ranges, centered at 10 GHz. Its absorbing characteristics were also investigated. Unlike other existing measurements of reflection loss using a waveguide, the reflection loss within an anechoic chamber simulating the radar cross section method of measurement was used with a plane-wave shaped incident wave. An optimized multi-layer design of RAS using the adopted material system is described in this research. [Copyright &y& Elsevier]

Phased array technology features rapid and directional scanning and has become a promising approach for remote sensing and wireless communication. In addition, element-level digitization has increased the feasibility of complicated signal processing and simultaneous multi-beamforming processes. However, the high cost and bulky characteristics of beam-steering systems have prevented their extensive application. In this paper, an X-band element-level digital phased array radar utilizing fully integrated complementary metal-oxide-semiconductor (CMOS) transceivers is proposed for achieving a low-cost and compact-size digital beamforming system. An 8–10 GHz transceiver system-on-chip (SoC) fabricated in 65 nm CMOS technology offers baseband filtering, frequency translation, and global clock synchronization through the proposed periodic pulse injection technique. A 16-element subarray module with an SoC integration, antenna-in-package, and tile array configuration achieves digital beamforming, back-end computing, and dc–dc conversion with a size of 317 × 149 × 74.6 mm3. A radar demonstrator with scalable subarray modules simultaneously realizes range sensing and azimuth recognition for pulsed radar configurations. Captured by the suggested software-defined pulsed radar, a complete range–azimuth figure with a 1 km maximum observation range can be displayed within 150 ms under the current implementation. [ABSTRACT FROM AUTHOR]

This paper presents a new configuration of a slotted waveguide antenna (SWA) array aimed at the X-band within the desired band of 9.38~9.44 GHz for shipboard marine radars. The SWA array, which typically consists of a slotted waveguide, a polarizing filter, and a metal reflector, is widely employed in marine radar applications. Nonetheless, conventional slot array designs are weighty, mechanically complex, and geometrically large to obtain high performances, such as gain. These features of the conventional SWA are undesirable for the shipboard marine radar, where the antenna rotates at high angular speed for the beam scanning mechanism. The proposed SWA array herein reduces the conventional design's size by 62% using a tapered dielectric-inset guide structure. It shows high gain performance (up to 30 dB) and obtains improvements in radiation efficiency (up to 80% in the numerical simulations) and weight due to the use of loss and low-density dielectric material. [ABSTRACT FROM AUTHOR]

Discharge forecasting is a key component for early warning systems and extremely useful for decision makers. Forecasting models require accurate rainfall estimations of high spatial resolution and other geomorphological characteristics of the catchment, which are rarely available in remote mountain regions such as the Andean highlands. While radar data is available in some mountain areas, the absence of a well distributed rain gauge network makes it hard to obtain accurate rainfall maps. Thus, this study explored a Random Forest model and its ability to leverage native radar data (i.e., reflectivity) by providing a simplified but efficient discharge forecasting model for a representative mountain catchment in the southern Andes of Ecuador. This model was compared with another that used as input derived radar rainfall (i.e., rainfall depth), obtained after the transformation from reflectivity to rainfall rate by using a local Z-R relation and a rain gauge-based bias adjustment. In addition, the influence of a soil moisture proxy was evaluated. Radar and runoff data from April 2015 to June 2017 were used. Results showed that (i) model performance was similar by using either native or derived radar data as inputs (0.66 < NSE < 0.75; 0.72 < KGE < 0.78). Thus, exhaustive pre-processing for obtaining radar rainfall estimates can be avoided for discharge forecasting. (ii) Soil moisture representation as input of the model did not significantly improve model performance (i.e., NSE increased from 0.66 to 0.68). Finally, this native radar data-based model constitutes a promising alternative for discharge forecasting in remote mountain regions where ground monitoring is scarce and hardly available. [ABSTRACT FROM AUTHOR]

Recently, the interest on snowfall remote sensing and quantitative precipitation estimation is becoming a popular topic by both the scientific and operational communities. As a matter of fact, snow plays a key role in the hydrological cycle and Earth energy budget and clearly represents a meteorological hazard that can seriously compromise human activities and properties. In this study, we used a dual-polarization X-band weather radar to quantify the near-surface liquid equivalent snowfall rate, proposing a new parameterization based on the use of radar reflectivity factor and specific differential phase shift. This effort adds to several recent works, mainly focused on S-band weather radar systems, demonstrating that the use of the radar specific differential phase shift (K dp) is able to enhance the estimation precision with respect to the more customary approaches making use of radar reflectivity factor alone. To demonstrate this concept also at X-band, some case studies were collected from December 2018 to May 2019 in the Southern Apennine Mountains in the area of Naples (Italy). They were used to compare the proposed radar based liquid equivalent snowfall rate estimations, based on Z and K dp , with reference laser-optical disdrometer time series collected in the close reference site of Montevergine observatory. Findings show that also at X band the use of K dp produces a better score between the radar-derived liquid equivalent snowfall rate and the reference one from the disdrometer. • The use of specific differential phase shift improves the radar-based estimation of snowfall rate. • Snow estimators based on equivalent radar reflectivity factor can be corrupted by melting layer effects. • In snow conditions, strong horizontal winds can corrupt laser-optical disdrometer measurements. [ABSTRACT FROM AUTHOR]

Despite many efforts of the radar community, quantitative precipitation estimation (QPE) from weather radar data remains a challenging topic. The high resolution of X-band radar imagery in space and time comes with an intricate correction process of reflectivity. The steep and high mountain topography of the Andes enhances its complexity. This study aims to optimize the rainfall derivation of the highest X-band radar in the world (4450 m a.s.l.) by using a random forest (RF) model and single Plan Position Indicator (PPI) scans. The performance of the RF model was evaluated in comparison with the traditional step-wise approach by using both, the Marshall-Palmer and a site-specific Z–R relationship. Since rain gauge networks are frequently unevenly distributed and hardly available at real time in mountain regions, bias adjustment was neglected. Results showed an improvement in the step-wise approach by using the site-specific (instead of the Marshall-Palmer) Z–R relationship. However, both models highly underestimate the rainfall rate (correlation coefficient < 0.69; slope up to 12). Contrary, the RF model greatly outperformed the step-wise approach in all testing locations and on different rainfall events (correlation coefficient up to 0.83; slope = 1.04). The results are promising and unveil a different approach to overcome the high attenuation issues inherent to X-band radars. [ABSTRACT FROM AUTHOR]