scholarly journals Untangling the Incoherent and Coherent Scattering Components in GNSS-R and Novel Applications

2020 ◽  
Vol 12 (7) ◽  
pp. 1208 ◽  
Author(s):  
Joan Francesc Munoz-Martin ◽  
Raul Onrubia ◽  
Daniel Pascual ◽  
Hyuk Park ◽  
Adriano Camps ◽  
...  
Keyword(s):  
Antenna Arrays ◽  
Fresnel Zone ◽  
Specular Reflection ◽  
Coherent Scattering ◽  
Global Navigation Satellite Systems ◽  
Dual Band ◽  
Total Power ◽  
Data Set ◽  
Coherent Component ◽  
Leo Satellite

As opposed to monostatic radars where incoherent backscattering dominates, in bistatic radars, such as Global Navigation Satellite Systems Reflectometry (GNSS-R), the forward scattered signals exhibit both an incoherent and a coherent component. Current models assume that either one or the other are dominant, and the calibration and geophysical parameter retrieval (e.g., wind speed, soil moisture, etc.) are developed accordingly. Even the presence of the coherent component of a GNSS reflected signal itself has been a matter of discussion in the last years. In this work, a method developed to separate the leakage of the direct signal in the reflected one is applied to a data set of GNSS-R signals collected over the ocean by the Microwave Interferometer Reflectometer (MIR) instrument, an airborne dual-band (L1/E1 and L5/E5a), multi-constellation (GPS and Galileo) GNSS-R instrument with two 19-elements antenna arrays with 4 beam-steered each. The presented results demonstrate the feasibility of the proposed technique to untangle the coherent and incoherent components from the total power waveform in GNSS reflected signals. This technique allows the processing of these components separately, which increases the calibration accuracy (as today both are mixed and processed together), allowing higher resolution applications since the spatial resolution of the coherent component is determined by the size of the first Fresnel zone (300–500 meters from a LEO satellite), and not by the size of the glistening zone (25 km from a LEO satellite). The identification of the coherent component enhances also the location of the specular reflection point by determining the peak maximum from this coherent component rather than the point of maximum derivative of the incoherent one, which is normally noisy and it is blurred by all the glistening zone contributions.

scholarly journals High-Efficiency, Dual-Band Beam Splitter Based on an All-Dielectric Quasi-Continuous Metasurface

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3184
Author(s):  
Jing Li ◽  
Yonggang He ◽  
Han Ye ◽  
Tiesheng Wu ◽  
Yumin Liu ◽  
...  
Keyword(s):  
Wavelength Range ◽  
Conversion Efficiency ◽  
Antenna Arrays ◽  
Beam Splitter ◽  
High Efficiency ◽  
Visible Region ◽  
Polarized Light ◽  
Dual Band ◽  
Phase Gradient ◽  
Total Transmission

Metasurface-based beam splitters attracted huge interest for their superior properties compared with conventional ones made of bulk materials. The previously reported designs adopted discrete metasurfaces with the limitation of a discontinuous phase profile. In this paper, we propose a dual-band beam splitter, based on an anisotropic quasi-continuous metasurface, by exploring the optical responses under x-polarized (with an electric field parallel to the direction of the phase gradient) and y-polarized incidences. The adopted metasurface consists of two identical trapezoidal silicon antenna arrays with opposite spatial variations that lead to opposite phase gradients. The operational window of the proposed beam splitter falls in the infrared and visible region, respectively, for x- and y-polarized light, resulting from the different mechanisms. When x-polarized light is incident, the conversion efficiency and total transmission of the beam splitter remains higher than 90% and 0.74 within the wavelength range from 969 nm to 1054 nm, respectively. In this condition, each array can act as a beam splitter of unequal power. For y-polarized incidence, the maximum conversion efficiency and transmission reach approximately 100% and 0.85, while the values remain higher than 90% and 0.65 in the wavelength range from 687 nm to 710 nm, respectively. In this case, each array can be viewed as an effective beam deflector. We anticipate that it can play a key role in future integrated optical devices.

Scalable Multibeam Antenna Arrays Fed by Dual-Band Modified Butler Matrices

2016 ◽  
Vol 64 (4) ◽  
pp. 1287-1297 ◽  
Author(s):  
Krzysztof Wincza ◽  
Kamil Staszek ◽  
Izabela Slomian ◽  
Slawomir Gruszczynski
Keyword(s):  
Antenna Arrays ◽  
Dual Band ◽  
Multibeam Antenna

A Decoupling and Matching Network Design for Dual-Band Two-Element Antenna Arrays

2021 ◽  
Author(s):  
Jinkai Li ◽  
Xiaoxi Zhang ◽  
Yaoxu Lei ◽  
Huiqing Zhai ◽  
Changyuan Liu
Keyword(s):  
Network Design ◽  
Antenna Arrays ◽  
Dual Band ◽  
Matching Network

scholarly journals A Contrast Calibration Protocol for X-ray Speckle Visibility Spectroscopy

2021 ◽  
Vol 11 (21) ◽  
pp. 10041
Author(s):  
Yanwen Sun ◽  
Vincent Esposito ◽  
Philip Adam Hart ◽  
Conny Hansson ◽  
Haoyuan Li ◽  
...  
Keyword(s):  
High Speed ◽  
Coherent Scattering ◽  
Atomic Scale ◽  
Photon Statistics ◽  
Free Electron Lasers ◽  
Data Set ◽  
X Ray ◽  
Charge Cloud ◽  
Typical Experiment ◽  
Calibration Protocol

X-ray free electron lasers, with their ultrashort highly coherent pulses, opened up the opportunity of probing ultrafast nano- and atomic-scale dynamics in amorphous and disordered material systems via speckle visibility spectroscopy. However, the anticipated count rate in a typical experiment is usually low. Therefore, visibility needs to be extracted via photon statistics analysis, i.e., by estimating the probabilities of multiple photons per pixel events using pixelated detectors. Considering the realistic X-ray detector responses including charge cloud sharing between pixels, pixel readout noise, and gain non-uniformity, speckle visibility extraction relying on photon assignment algorithms are often computationally demanding and suffer from systematic errors. In this paper, we present a systematic study of the commonly-used algorithms by applying them to an experimental data set containing small-angle coherent scattering with visibility levels ranging from below 1% to ∼60%. We also propose a contrast calibration protocol and show that a computationally lightweight algorithm can be implemented for high-speed correlation evaluation.

scholarly journals Suppression of Cross-Band Scattering in Interleaved Dual-Band Cellular Base-Station Antenna Arrays

IEEE Access ◽  
2020 ◽  
Vol 8 ◽  
pp. 222486-222495
Author(s):  
Hai-Han Sun ◽  
Bevan Jones ◽  
Y. Jay Guo ◽  
Yee Hui Lee
Keyword(s):  
Antenna Arrays ◽  
Base Station ◽  
Dual Band

scholarly journals Sensitivity of GNSS tropospheric gradients to processing options

2019 ◽  
Vol 37 (3) ◽  
pp. 429-446 ◽  
Author(s):  
Michal Kačmařík ◽  
Jan Douša ◽  
Florian Zus ◽  
Pavel Václavovic ◽  
Kyriakos Balidakis ◽  
...  
Keyword(s):  
Real Time ◽  
Elevation Angle ◽  
Mapping Function ◽  
Global Navigation Satellite Systems ◽  
Gradient Estimates ◽  
Post Processing ◽  
Data Set ◽  
Mapping Functions ◽  
Gradient Mapping

Abstract. An analysis of processing settings impacts on estimated tropospheric gradients is presented. The study is based on the benchmark data set collected within the COST GNSS4SWEC action with observations from 430 Global Navigation Satellite Systems (GNSS) reference stations in central Europe for May and June 2013. Tropospheric gradients were estimated in eight different variants of GNSS data processing using precise point positioning (PPP) with the G-Nut/Tefnut software. The impacts of the gradient mapping function, elevation cut-off angle, GNSS constellation, observation elevation-dependent weighting and real-time versus post-processing mode were assessed by comparing the variants by each to other and by evaluating them with respect to tropospheric gradients derived from two numerical weather models (NWMs). Tropospheric gradients estimated in post-processing GNSS solutions using final products were in good agreement with NWM outputs. The quality of high-resolution gradients estimated in (near-)real-time PPP analysis still remains a challenging task due to the quality of the real-time orbit and clock corrections. Comparisons of GNSS and NWM gradients suggest the 3∘ elevation angle cut-off and GPS+GLONASS constellation for obtaining optimal gradient estimates provided precise models for antenna-phase centre offsets and variations, and tropospheric mapping functions are applied for low-elevation observations. Finally, systematic errors can affect the gradient components solely due to the use of different gradient mapping functions, and still depending on observation elevation-dependent weighting. A latitudinal tilting of the troposphere in a global scale causes a systematic difference of up to 0.3 mm in the north-gradient component, while large local gradients, usually pointing in a direction of increasing humidity, can cause differences of up to 1.0 mm (or even more in extreme cases) in any component depending on the actual direction of the gradient. Although the Bar-Sever gradient mapping function provided slightly better results in some aspects, it is not possible to give any strong recommendation on the gradient mapping function selection.

scholarly journals ENVIRONMENTAL CONTROLS ON LITTORAL SAND TRANSPORT

1988 ◽  
Vol 1 (21) ◽  
pp. 92 ◽  
Author(s):  
Paul D. Komar
Keyword(s):  
Environmental Factors ◽  
Field Data ◽  
Measurement Techniques ◽  
Breaking Waves ◽  
Total Power ◽  
Sand Transport ◽  
Longshore Current ◽  
Data Set ◽  
Environmental Controls ◽  
Gravel Beaches

Quantities of sand transported along beaches are generally related to the "longshore component of wave power", F^, through the proportionality is = KF£ where l8 is the immersed-weight sand transport rate and K is a dimensionless proportionality factor. A more-generally applicable relationship is that of Bagnold, ls = K'(ECn)bvL/um where (ECn)b is the energy flux or total power of the breaking waves, y^ is the longshore current, um is the mean orbital velocity under the waves, and K' is another dimensionless coefficient. It is apparent that sediment transport rates on beaches should depend on environmental factors such as the grain diameter or settling velocity, and possibly on factors such as the beach slope or wave steepness. However, examinations of such dependencies for K and K' within the field data are hampered by problems with large random scatter within any one data set, and by systematic differences between separate studies which have employed diverse measurement techniques. Examinations of the field data for K and K' variations indicate that meaningful dependencies on sediment grain diameters and other factors cannot be established with confidence in the sand-size range. Limited data available from gravel beaches support the expected decreases in K and K' with increasing grain sizes. These data are too few in numbers to establish firm trends, but do suggest that future investigations to establish dependencies on environmental factors would be most profitably undertaken on gravel beaches. The measurements collected in recent years from sand beaches suggest revisions in average K and K' coefficients to be used in transport evaluations, but such revisions must be coordinated such that K/K' = 2.7 so as to maintain agreement with the longshore current data.

Interpretative lessons from three‐dimensional modeling

Geophysics ◽  
1982 ◽  
Vol 47 (5) ◽  
pp. 784-808 ◽  
Author(s):  
Fred J. Hilterman
Keyword(s):  
Fresnel Zone ◽  
Specular Reflection ◽  
Three Dimensional ◽  
Wave Theory ◽  
Three Dimensional Modeling ◽  
Seismic Resolution ◽  
Maximum Resolution ◽  
Dimensional Modeling ◽  
Complex Models ◽  
Concave Boundary

Three‐dimensional (3-D) seismic modeling has been accomplished by describing geologic surfaces with triangular plates and then computing the seismic response by Kirchhoff wave theory. The resulting time sections illustrate many interesting 3-D phenomena which are useful in interpreting geologic structures. Three‐dimensional resolution studies relate the concept of Fresnel zone reflection to seismic resolution. If high resolution is desired both horizontally and vertically, then not only is a dense field survey required, but also a detailed amplitude study. The dense seismic coverage is required to map the focal line of concave boundary edges, which are difficult to delineate with conventional seismic data. Additional studies on complex models, such as grabens and 3-D permeability traps, associate interpretational pitfalls to a wandering specular reflection path, that is, “side‐swipe.” In each geologic model, maximum resolution is obtained on a principal plane line (dip line). If a seismic dip line is not available, the necessity of doing 3-D migration is emphasized, even if it is a migration of the time map.

Ka-band antenna arrays with dual-frequency and dual-polarized patch elements

2016 ◽  
Vol 8 (6) ◽  
pp. 963-972 ◽  
Author(s):  
Benjamin Rohrdantz ◽  
Thomas Jaschke ◽  
Frauke K. H. Gellersen ◽  
Anton Sieganschin ◽  
Arne F. Jacob
Keyword(s):  
Antenna Arrays ◽  
Patch Antenna ◽  
Communication Systems ◽  
Satellite Communication ◽  
Circuit Board ◽  
Dual Band ◽  
Antenna Element ◽  
Dual Frequency ◽  
Ka Band ◽  
Dual Polarized

In this contribution a dual-band, dual-polarized microstrip antenna element for array applications is presented. The patch antenna is designed to operate simultaneously at around 30 and 20 GHz, the up- and downlink frequencies of modern Ka-band satellite communication systems. The antenna is smaller than half the freespace wavelength at 30 GHz to enable its utilization as array element of dual-band ground terminals. Integrating transmitter and receiver circuits allows, in turn, for a very compact active terminal solution. To minimize production cost, the design is carried out in standard multilayer printed circuit board technology. The antenna features two distinct polarization ports suitable for either dual linear or dual circular polarization if both ports are excited in quadrature. The single antenna design process is described in detail and simulation and measurement results are presented. Finally, different arrays based on this patch antenna are evaluated by simulation and measurements.

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