Elevation Scan Research Articles

A combined aperture‐coupled membrane microstrip patch antenna array

AbstractA novel lightweight L‐band combined aperture‐coupled microstrip antenna has been proposed for synthetic aperture radar (SAR) applications. The proposed antenna element is composed of only two membranes. This design innovatively integrates the coupling aperture with the radiating patch, significantly reducing the number of required dielectric layers to achieve a simplified and lightweight structure. The feed line is placed on the front side to facilitate integration with the transmit/receive (T/R) module. Simulation results demonstrate that the antenna element exhibits excellent radiation pattern performance and bandwidth. A passive antenna array utilising polyimide as the dielectric material was fabricated and measured to validate its performance. This array employs a 4‐stage Wilkinson power divider network. Measurements show that S1,1 is below −15 dB in the frequency range from 1.15 to 1.49 GHz, with a maximum efficiency of 72.87%. Additionally, an phased array antenna was fabricated and tested. This array demonstrated stable radiation pattern performance over an azimuthal scan range of and an elevation scan of . This design offers a new option for antenna modules in spaceborne SAR applications.

Intercomparison between Ground-Based and Spaceborne Radars’ Echo-Top Heights: Application to the Multi-Radar Multi-Sensor and the Global Precipitation Measurement

Abstract The accuracy and uncertainty of radar echo-top heights estimated by ground-based radars remain largely unknown despite their critical importance for applications ranging from aviation weather forecasting to severe weather diagnosis. Because the vantage point of space is more suited than that of ground-based radars for the estimation of echo-top heights, the use of spaceborne radar observations is explored as an external reference for cross comparison. An investigation has been carried out across the conterminous United States by comparing the NOAA/National Severe Storms Laboratory Multi-Radar Multi-Sensor (MRMS) system with the space-based radar on board the NASA–JAXA Global Precipitation Measurement satellite platform. No major bias was assessed between the two products. An annual cycle of differences is found, driven by an underestimation of the stratiform cloud echo-top heights and an overestimation of the convective ones. The investigation of the systematic biases for different radar volume coverage patterns (VCP) shows that scanning strategies with fewer tilts and greater voids as VCP 21/121/221 contribute to overestimations observed for high MRMS tops. For VCP 12/212, the automated volume scan evaluation and termination (AVSET) function increases the radar cone of silence, causing overestimations when the echo top lies above the highest elevation scan. However, it seems that for low echo tops the shorter refresh rates contribute to mitigate underestimations, especially in stratiform cases.

Design of Low-Profile Transmitarray Antennas With Wide Mechanical Beam Steering at Millimeter Waves

Mechanical beam steering using a single transmitarray (TA) can be a cost-effective solution for a high-gain antenna with wide-angle scanning. Elevation scanning can be achieved by a linear displacement of the feed in the focal plane parallel to the aperture of diameter D. When designing compact terminals with a short focal length F and with high gain, the aberrations caused by this mechanical movement become the main limiting factor for the maximum scanning range. This work presents a novel design method for devising the TA phase correction with an even distribution of these aberrations among all beam directions. A significant improvement in the scanning performance is achieved when compared with the conventional single-focus phase correction approach. To validate the proposed approach, we consider a TA design at the Ka-band (30 GHz) F/D <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cong ~0.34$ </tex-math></inline-formula> . A multifocal TA design was manufactured using 3-D printed unit cells. To highlight the proposed concept, the antenna configuration is stripped to the bare minimum: a perforated dielectric slab with in-plane mechanical movements in front of an open-ended standard waveguide used as feed. This antenna scans up to 50°, with a gain of 25 dBi at 30 GHz, 2.5 dB of scan loss, sidelobe level (SLL) <–10, and 1 dB bandwidth of 6.7%.

ARIEL: Passive Beam-Scanning Antenna teRminal for Iridescent and Efficient LEO Satellite Connectivity

A novel low-cost high-gain beam-steering antenna terminal topology for global data connectivity with low-earth-orbit satellite constellations in the UHF 900 MHz ISM band is reported. It is shown how a simple printed-circuit-board half-width microstrip leaky-wave antenna (LWA) with passive frequency-beam scanning capacity provides an energy-efficient scanning method avoiding more power-demanding and expensive beam-steering techniques (such as electronic scanning, mechanical rotation, or beam switching). For that, iridescent channel-agile operation and cross-layer optimization are needed. As an example, two single-element LWAs and an LWA array are designed to scan the celestial vault with an angular elevation scanning range of 130° and using the available LoRaWAN protocol channels from 902 to 928 MHz. It is reported a scanned-beam peak gain above 9 dBi for the compact printed-circuit LWA array design with 55 cm × 27 cm aperture dimensions.

Horizontal distribution of tropospheric NO2 and aerosols derived by dual-scan multi-wavelength multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in Uccle, Belgium

Abstract. Dual-scan ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of tropospheric nitrogen dioxide (NO2) and aerosols were carried out in Uccle (50.8∘ N, 4.35∘ E; Brussels region, Belgium) for 2 years from March 2018 to February 2020. The MAX-DOAS instrument operated in both UV and visible wavelength ranges in a dual-scan configuration consisting of two submodes: (1) an elevation scan in a fixed viewing azimuthal direction and (2) an azimuthal scan in a fixed low elevation angle (2∘). By analyzing the O4 and NO2 differential slant column density (dSCD) at six different wavelength intervals along every azimuthal direction and by applying a new optimal-estimation-based inversion approach (the so-called mapping MAX-DOAS technique), the horizontal distribution of the NO2 near-surface concentrations and vertical column densities (VCDs) as well as the aerosol near-surface extinction coefficients are retrieved along 10 azimuthal directions. The retrieved horizontal NO2 concentration profiles allow the identification of the main NO2 hotspots in the Brussels area. Correlative comparisons of the retrieved horizontal NO2 distribution were conducted with airborne, mobile, air quality model, and satellite datasets, and overall good agreement is found. The comparison with TROPOMI observations from operational and scientific data products reveals that the characterization of the horizontal distribution of tropospheric NO2 VCDs by ground-based measurements and an adequate a priori NO2 profile shape in TROPOMI retrievals lead to better consistency between satellite and ground-based datasets.

Radar-Based, Storm-Scale Circulation and Tornado-Probability Tendencies Preceding Tornadogenesis in Kansas and Nebraska

This study analyzes the behavior of storm-scale circulations preceding initial tornadogenesis in 179 Kansas and Nebraska storms. Manually determined assessments of radar data for storm-scale circulations preceding the tornadoes are performed as far back in time prior to the tornado as a circulation is apparent, with average rotational velocity (Vrot), circulation diameter, and circulation clarity documented for the 0.5° elevation scan. These data are simultaneously combined with an indication of environmental conditions (as represented by the significant tornado parameter) to determine the tornado probability at each of these times based on a recently developed probabilistic model. By aggregating these parameters in time-range bins, subsequent statistical analyses portray the bulk variability of circulation characteristics and tornado probabilities preceding tornadogenesis. The blended approach for assessing tornado potential yields a stronger relative increase in tornado probabilities leading up to tornadogenesis than the sub-component of average Vrot; this is especially true within 15 min before tornadogenesis. Additionally, significant tornadoes are associated with more substantial increase in tornado probabilities preceding tornadogenesis compared to weak tornadoes, and smaller lead time to tornadogenesis for weak tornadoes. Also, a cycling pattern may appear in velocities prior to significant tornadoes, along with a relative decrease in pretornadic circulation diameter, especially for significant tornadoes. These findings are intended to highlight some of the behaviors of storm-scale circulations and their corresponding environments, which can be used to reinforce meteorologists’ tornado threat assessment. Extending this work to encompass more convective-mode variability, null cases, and geographic expanse will be necessary for more overarching applicability.

Wideband Circularly Polarized Phased Array Antenna System for Wide Axial Ratio Scanning

This paper proposes the wideband circularly polarized (CP) phased array antenna system for wide axial ratio scanning. For mobile satellite communication, the low profile CP antenna with a wide axial ratio scanning region in wide frequency bandwidth is necessary, but the antenna with the required axial ratio performance is rarely reported. In this paper, the proposed CP phased array antenna system with an axial ratio control scheme has a wide axial ratio scanning region in the wide frequency bandwidth. In the proposed axial ratio control scheme, the amplitude and phase of the received signals are controlled to compensate for the difference between dual polarizations. The proposed antenna system is designed at 5.8 GHz and has a fractional frequency bandwidth of 20%. In a simulation, the axial ratio is under 1 dB at the elevation scanning region from -60∘ to 60∘ at every 360∘ azimuth angle in the operating frequency bandwidth. For validation, the 1x8 CP phased array antenna system was implemented. The measured axial ratio is under 2 dB at the elevation scanning region from -57∘ to 57∘ in the operating frequency bandwidth.

Study on Radar Echo-Filling in an Occlusion Area by a Deep Learning Algorithm

Radar beam blockage is an important error source that affects the quality of weather radar data. An echo-filling network (EFnet) is proposed based on a deep learning algorithm to correct the echo intensity under the occlusion area in the Nanjing S-band new-generation weather radar (CINRAD/SA). The training dataset is constructed by the labels, which are the echo intensity at the 0.5° elevation in the unblocked area, and by the input features, which are the intensity in the cube including multiple elevations and gates corresponding to the location of bottom labels. Two loss functions are applied to compile the network: one is the common mean square error (MSE), and the other is a self-defined loss function that increases the weight of strong echoes. Considering that the radar beam broadens with distance and height, the 0.5° elevation scan is divided into six range bands every 25 km to train different models. The models are evaluated by three indicators: explained variance (EVar), mean absolute error (MAE), and correlation coefficient (CC). Two cases are demonstrated to compare the effect of the echo-filling model by different loss functions. The results suggest that EFnet can effectively correct the echo reflectivity and improve the data quality in the occlusion area, and there are better results for strong echoes when the self-defined loss function is used.

A Neural-Network Quality Control scheme for improved Quantitative Precipitation Estimation accuracy on the UK weather radar network

AbstractIn this work, we present a new Quantitative-Precipitation-Estimation (QPE) quality-control (QC) algorithm for the UK weather radar network. The real-time adaptive algorithm uses a neural network (NN) to select data from the lowest useable elevation scan to optimize the combined performance of two other radar data correction algorithms: ground clutter mitigation (using CLEAN-AP) and vertical profile of reflectivity (VPR) correction. The NN is trained using 3D tiles of observed uncontaminated weather signals that are systematically combined with ground-clutter signals collected under dry weather conditions. This approach provides a way to simulate radar signals with a wide range of clutter contamination conditions and with realistic spatial structures while providing the uncontaminated “truth” with respect to which the performance of the QC algorithm can be measured. An evaluation of QPE products obtained with the proposed QC algorithm demonstrates superior performance as compared to those obtained with the QC algorithm currently used in operations. Similar improvements are also illustrated using radar observations from two periods of prolonged precipitation, showing a better balance between overestimation errors from using clutter-contaminated low-elevation radar data and VPR-induced errors from using high-elevation radar data.

Comparative analysis of cylindrical and planar aesa in 3d suveillance radar.

A modern rotating 3D surveillance radars scan azimuth by mechanical rotation, and scan elevation using Active Electronic Scanning Array (AESA) in Multi Beam Receive Mode (MBM). Radars with fixed cylindrical AESA and four-sided prismatic antenna, with 4 flat AESA, scan azimuth electronically, without mechanical rotation. The most significant advantage of electronic scanning is the possibility of Multi-mode operation: surveillance targets in the far zone and targeting targets in the near zone. However, electronic scanning also brings problems. A main beam of planar AESA spreads and lateral lobes increase when the radiating direction increases. An original arrangement of shifted array to reduce lateral lobes has been proposed. The cylindrical array has a constant shape of pattern during azimuth scanning. But, for both prismatic and cylindrical AESA, the beam deforms during scanning in vertical plane, so limits the elevation scan. Also, the complexity and price of fixed AESA is significantly higher compared to the rotating one. In order to enable the selection of the optimal solution for a specific application, the comparative analysis of advantages and disadvantages for cylindrical, prismatic and rotating AESA is done. The original configuration of the cylindrical AESA for Very Fast Scanning in Near-zone has been proposed.

Phased array weather radar for heavy precipitation measurements with high resolution

AbstractA new Phased Array Radar (PAR) system for meteorological application has been developed by Toshiba Corporation and Osaka University under a grant of NICT, and installed in Osaka University, Japan in 2012. The PAR system developed has the unique capability of scanning the whole sky with 100 m and 10 to 30‐second resolution up to 60 km. The system adopts the digital beam forming technique for elevation scanning and mechanically rotates the array antenna in azimuth direction within 10 to 30 seconds. The radar transmits a broad beam of several degrees with 24 antenna elements and receives the back scattered signal with 128 elements digitizing at each element. Then, by digitally forming the beam in the signal processor, the fast scanning is realized. After the installation of the PAR, SIP project has started to develop a new PAR with polarimetric capabilities.

Concentric Ring Array Synthesis for Low Side Lobes: An Overview and a Tool for Optimizing Ring Radii and Angle of Rotation

A comprehensive review on the approaches for synthesizing low side lobe concentric ring array (CRA) antennas is given. An Iterative Convex Optimization (ICO) based array layout synthesis technique is proposed for peak side-lobe level (PSLL) minimization over a given circular field-of-view in steerable uniform-amplitude concentric ring array (UA-CRA) antennas. For a given number of rings and number of uniformly-distributed elements in each ring, the ICO algorithm optimizes the ring radii and angle of rotation, with possible constraints on the minimum element separation and largest array size. As compared to the existing UA-CRA synthesis techniques, the proposed method presents unique features as it combines the capability of optimization of angle of rotation of the rings and PSLL minimization for multiple elevation scan angles in a computationally-efficient and easy-to-solve procedure. Through numerical design examples, it is demonstrated how the ICO technique can be effectively used (i) to synthesize sparse UA-CRA topologies generating low PSLL steerable beams, and (ii) to assess and improve the PSLL suppression performance of various known optimization algorithms. Based on the UA-CRA topologies synthesized via competitive methods in the recent literature, a new set of improved array topologies are presented.

Validation of TROPOMI tropospheric NO2 columns using dual-scan multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in Uccle, Brussels

Abstract. Ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of aerosols and tropospheric nitrogen dioxide (NO2) were carried out in Uccle (50.8∘ N, 4.35∘ E), Brussels, during 1 year from March 2018 until March 2019. The instrument was operated in both the UV and visible wavelength ranges in a dual-scan configuration consisting of two sub-modes: (1) an elevation scan in a fixed viewing azimuthal direction (the so-called main azimuthal direction) pointing to the northeast and (2) an azimuthal scan in a fixed low elevation angle (2∘). By applying a vertical profile inversion algorithm in the main azimuthal direction and a parameterization technique in the other azimuthal directions, near-surface NO2 volume mixing ratios (VMRs) and vertical column densities (VCDs) were retrieved in 10 different azimuthal directions. The dual-scan MAX-DOAS dataset allows for partly resolving the horizontal distribution of NO2 around the measurement site and studying its seasonal variations. Furthermore, we show that measuring the tropospheric NO2 VCDs in different azimuthal directions improves the spatial colocation with measurements from the Sentinel-5 Precursor (S5P), leading to a reduction of the spread in validation results. By using NO2 vertical profile information derived from the MAX-DOAS measurements, we also resolve a systematic underestimation in S5P NO2 data due to the use of inadequate a priori NO2 profile shape data in the satellite retrieval.

Highly Efficient 30 GHz 2x2 Beamformer Based on Rectangular Air-Filled Coaxial Line

This article introduces a low loss beamformer with a capability of 2-D scanning in elevation and azimuth directions at 30 GHz for 5G applications. The proposed beamformer is based on the broadband and highly efficient rectangular air-filled coaxial line. The beamformer is fed by four standard waveguides (WR-28) as the input ports. Correspondingly, each of the input ports using specific transitions is connected to the coaxial beamformer network. Ultimately, the coaxial transmission lines, in the radiating part of the beamformer, feed a $2\times 2$ waveguide antenna array. The structure is aptly called a waveguide–coaxial–waveguide beamformer. The total dimensions of the fabricated prototype are 60 mm $\times60$ mm (corresponding to $6\lambda \times 6\lambda$ ). The beamformer is able to generate four fixed beams, one in each quadrant at an elevation angle of 25° from the broadside to the array axis. The results demonstrate that the proposed passive beamformer has a radiation efficiency greater than 90% over the frequency bandwidth (BW) of interest. Good stability of the radiation pattern and maximum gain over the desired BW were achieved while maintaining the sidelobe level of less than 20 dB.

Fluorescence Scheimpflug LiDAR developed for the three-dimension profiling of plants.

This work proposes a novel fluorescence Scheimpflug LiDAR (SLiDAR) technique based on the Scheimpflug principle for three-dimension (3D) plant profile measurements. A 405 nm laser diode was employed as the excitation light source to generate a light sheet. Both the elastic and inelastic/fluorescence signals from a target object (e.g., plants) can be simultaneously measured by the fluorescence SLiDAR system employing a color image sensor with blue, green and red detection channels. The 3D profile can be obtained from the elastic signal recorded by blue pixels through elevation scanning measurements, while the fluorescence intensity of the target object is mainly acquired by red and green pixels. The normalized fluorescence intensity of the red channel, related to the chlorophyll distribution of the plant, can be utilized for the classification of leaves, branches and trunks. The promising results demonstrated in this work have shown a great potential of employing the fluorescence SLiDAR technique for 3D fluorescence profiling of plants in agriculture and forestry applications.

Analysis of a Precipitation System that Exists above Freezing Level Using a Multi-Parameter Phased Array Weather Radar

An X-band multi-parameter phased array weather radar (MP-PAWR) was developed in 2017. The scan concept of the MP-PAWR is electronic scanning in elevation by combining fan beam transmissions and pencil beam receptions with digital beam-forming techniques and mechanical scanning along the azimuth. The MP-PAWR realized three-dimensional (60 km in radius and 15 km in height) observations without gaps of 30 s. Although the MP-PAWR is supposed to be suitable for observations of rapidly changing convective systems, it can be advantageous for observations of stratiform rainfall because of continuous vertical pointing observations and its ability to apply the Velocity Azimuth Display (VAD) method with a constant radius for a vertical profile of dynamic parameters such as divergence and deformation. In this study, a precipitation system that existed mainly above the freezing level (in this case, it was approximately 5 km in height) observed from 14:00 to 17:00 Japan Standard Time on 6 September 2018 was analyzed using MP-PAWR data. The averaged area of the vertical profile of Z, and the Doppler velocity with fixed elevation showed a stationary structure with time. The average differential reflectivity factor (ZDR) profile with fixed elevation angles showed values that were close to zero and increased with height. Similar characteristics were shown in the average Specific Differential Phase (KDP) profile. Vertical pointing data, especially for Z, ZDR, and Doppler velocity, were utilized when the echo passed over the radar site, and the Doppler velocity showed the acceleration of fall speed below the freezing level. The vertical profile of divergence with a fixed radius was calculated using the VAD method, and the vertical velocity was calculated using the fall speed profile from the vertical pointing data and by assuming the vertical velocity at the cloud base was zero. The results indicate that the updraft region corresponds to higher ZDR and KDP regions.

A Novel Method of Radar Antenna Scan Pattern Recognition Using Visibility Graph

Radar antenna scan has a great influence on reconnaissance targets, interference decision-making, and electronic support measures. In this paper, we propose a recognition methods of antenna scan pattern based on visibility graph, including circular scan, sector scan, helical scan, raster scan, conical scan, phased array scan, phased array azimuth scan and circular elevation scan. We have mapped the radar scans pattern, the azimuth and elevation curves of various scan pattern and the signal variation of the EW receiver. Moreover, the related features are extracted from the visibility graph and the seven radar scan patterns are classified by five kinds of classifiers. Simulation experiments verify the efficiency of the algorithm.

Techniques and Thresholds of Significance for Using WSR-88D Velocity Data to Anticipate Significant Tornadoes

Significant tornadoes (EF2+) make up a very small percentage of the total United States tornado events, but produce the overwhelming majority of tornado fatalities. Identifying significant tornado events in a shortfused warning environment has been a particular focus of the United States National Weather Service’s severe weather program in recent years, with the goal of reducing the loss of life from significant events to the greatest extent possible. This study aims to further this effort by identifying and quantifying the skill of key signals present in Weather Service Radar-1998 Doppler velocity data in the minutes prior to the onset of significant tornado damage. When separated by storm mode, several radar velocity signals are identified that show operationally useful skill in differentiating between significant and weak/nontornadic events in supercells—with lead time. The highest skill scores are achieved by combining maximum volumetric rotational speed and depth of the storm’s mesocyclone, as well as the overall change in rotational speed in the final minutes prior to the onset of significant damage. Very little, if any, predictive skill was found when only the lowest elevation scan was considered, including more frequent supplementary scans in between full volumetric scans. The same signals that showed noteworthy skill for supercells failed to discriminate between significant and weak/nontornadic events in quasi-linear convective Systems and bow echo/mesoscale convective vortex events.

2-D Beam Scanning With Cylindrical-Leaky-Wave-Enhanced Phased Arrays

Directive pencil beams scannable in both elevation and azimuth are obtained through a planar phased array placed inside a Fabry–Perot cavity. The key element of the proposed approach is the exploitation of a conical element pattern (EP) with high directivity in elevation, obtained through the excitation of a dominant, weakly attenuated cylindrical TM leaky wave of azimuthal order $n = 0$ by means of a simple coaxial probe. Then, a highly reduced number $N$ of such sources are arranged to form a phased array radiating directive pencil beams. Beam-angle reconfigurability with continuous scanning both in azimuth and elevation inside a wide solid angular range is achieved by varying the array phasing and the operating frequency. An investigation on the features of truncated cylindrical leaky waves is first developed to properly characterize the EP. Then, conventional array theory is exploited to calculate the pattern of the entire array. The radiation efficiency is also evaluated accounting for the spurious surface wave related to the undesired excitation of the quasi-TEM mode. The proposed array design provides a simple and inexpensive innovative solution for obtaining a high-gain pencil beam continuously scanning in the 3-D space without suffering gain losses. In the presented implementation, the elevation angular scan, which is generally constrained by the wideband capability of the feeding system, by the requirements on the sidelobe level, and by the cutoff of the relevant leaky mode, ranges from about 21° to about 68°. Possible applications are envisaged for the next generation of wireless power transfer devices, for advanced radar and surveillance systems, earth observation, as well as for ceiling-mounted indoor localization and tracking.

PRINTED DIPOLE 8-BEAM ANTENNA ARRAY WITH CHART-FORMING MATRIX BUTLER ON CONNECTED STRIP LINES

The results of the analysis of the printed 8-beam antenna array with an operating frequency of 2.2 GHz are presented. Charting devices made on the basis of the Butler matrix are widely used in modern telecommunication and radar systems and complexes. Forming in space a fan of independent radiation patterns, such arrays provide both scanning in azimuth and elevation and switching several transmitters to different directions. This ensures a high efficiency of a multipath planar phased antenna array, and reduces its overall dimensions. To test the features of the implementation of the 8-input Butler matrix, an eight-beam dipole phased array antenna was modeled. The results of the system analysis and computer simulation showed that it is possible to print the antenna with acceptable performance.