scholarly journals Primary beam effects of radio astronomy antennas – II. Modelling MeerKAT L-band beams

2021 ◽  
Vol 502 (2) ◽  
pp. 2970-2983
Author(s):  
K M B Asad ◽  
J N Girard ◽  
M de Villiers ◽  
T Ansah-Narh ◽  
K Iheanetu ◽  
...  
Keyword(s):  
Software Tool ◽  
Sparse Representations ◽  
Primary Beam ◽  
Electromagnetic Simulation ◽  
Zernike Polynomials ◽  
Jones Matrix ◽  
Cross Polarization ◽  
Science Operations ◽  
Spectral Behaviour ◽  
L Band

ABSTRACT After a decade of design and construction, South Africa’s SKA-MID precursor MeerKAT has begun its science operations. To make full use of the widefield capability of the array, it is imperative that we have an accurate model of the primary beam of its antennas. We have taken available L-band full-polarization ‘astro-holographic’ observations of three antennas and a generic electromagnetic simulation and created sparse representations of the beams using principal components and Zernike polynomials. The spectral behaviour of the spatial coefficients has been modelled using discrete cosine transform. We have provided the Zernike-based model over a diameter of 10 deg averaged over the beams of three antennas in an associated software tool (EIDOS) that can be useful in direction-dependent calibration and imaging. The model is more accurate for the diagonal elements of the beam Jones matrix and at lower frequencies. As we get more accurate beam measurements and simulations in the future, especially for the cross-polarization patterns, our pipeline can be used to create more accurate sparse representations of MeerKAT beams.

scholarly journals DETECTION OF MARINE VESSELS BASED ON VARIATION OF DEGREE OF POLARIZATION

2018 ◽  
Vol IV-5 ◽  
pp. 311-316
Author(s):  
G. K. Dashondhi ◽  
K. M. Buddhiraju
Keyword(s):  
Satellite Images ◽  
Speckle Noise ◽  
Vital Role ◽  
Degree Of Polarization ◽  
False Alarms ◽  
Cross Polarization ◽  
Maritime Surveillance ◽  
L Band ◽  
Sar Imagery ◽  
Marine Vessels

<p><strong>Abstract.</strong> For improving security of any country, satellite images are playing vital role. Vessels detection using SAR imagery is one of the primary requirements for maritime surveillance. In this paper, the algorithm used for vessels detection has four parts. The first part includes pre-processing to reduce speckle noise, second part helps in the reduction of cross polarization by real and complex rotation of the coherency matrix, third part derives a new parameter called variation of degree of polarization (VD) and fourth one is a post processing part to connect region and fill gaps using morphological operation. The proposed algorithm is tested on ALOS PALSAR1 (space borne L band) and UAVSAR (Airborne L band) datasets and yielded promising results with a relatively few false alarms.</p>

scholarly journals Sequential 90° Rotation of Dual-Polarized Antenna Elements in Linear Phased Arrays with Improved Cross-Polarization Level for Airborne Synthetic Aperture Radar Applications

2021 ◽  
Vol 13 (8) ◽  
pp. 1430
Author(s):  
Diego Lorente ◽  
Markus Limbach ◽  
Bernd Gabler ◽  
Héctor Esteban ◽  
Vicente E. Boria
Keyword(s):  
Synthetic Aperture Radar ◽  
Phase Distribution ◽  
Synthetic Aperture ◽  
Main Beam ◽  
Cross Polarization ◽  
L Band ◽  
Dual Polarized ◽  
German Aerospace ◽  
Polarization Level ◽  
Aperture Radar

In this work, a novel rotation approach for the antenna elements of a linear phased array is presented. The proposed method improves by up to 14 dB the cross-polarization level within the main beam by performing a sequential 90° rotation of the identical array elements, and achieving measured cross-polarization suppressions of 40 dB. This configuration is validated by means of simulation and measurements of a manufactured linear array of five dual-polarized cavity-box aperture coupled stacked patch antennas operating in L-Band, and considering both uniform amplitude and phase distribution and beamforming with amplitude tapering. The analysis is further extended by applying and comparing the proposed design with the 180° rotation and non-rotation topologies. This technique is expected to be used for the next generation L-Band Airborne Synthetic Aperture Radar Sensor of the German Aerospace Center (DLR).

scholarly journals Multi resonance patch antenna with multiple slits

2020 ◽  
Vol 2 (2) ◽  
pp. 119-125
Author(s):  
Merjem Begovic ◽  
Şehabeddin Taha İmeci
Keyword(s):  
Reflection Coefficient ◽  
Electric Field ◽  
Parametric Study ◽  
Patch Antenna ◽  
Simulation Program ◽  
Electromagnetic Simulation ◽  
Gap Size ◽  
Cross Polarization ◽  
Dielectric Thickness ◽  
Fabrication Tolerances

In this paper we have presented new design of multi resonance patch antenna with multiple slits. Slits are located on the three sides of the designed antenna. It is simulated in a planar 3D electromagnetic simulation program, called Sonnet Software, designed on the Aluminum (96%) substrate and operates at three frequencies with reflection coefficient (S11) values lower than -10 dB. Values for the operating frequencies are 4.14, 5.52, 9.24 GHz. Electric field theta polarized gains for these three frequencies are; 8.09, 8.35 and 8.39 dB’s respectively. Cross polarization levels are well below -10 dB. A parametric study was conducted by changing the gap size and the dielectric thickness. As a result of the parametric study, it is seen that fabrication tolerances of the antenna are good enough.

scholarly journals Primary beam effects of radio astronomy antennas – I. Modelling the Karl G. Jansky Very Large Array (VLA) L-band beam using holography

2019 ◽  
Vol 485 (3) ◽  
pp. 4107-4121 ◽  
Author(s):  
K Iheanetu ◽  
J N Girard ◽  
O Smirnov ◽  
K M B Asad ◽  
M de Villiers ◽  
...  
Keyword(s):  
Radio Astronomy ◽  
Primary Beam ◽  
Large Array ◽  
Very Large Array ◽  
L Band

Compact back-scattered electrons' energy analyzer for standard SEM

1994 ◽  
Vol 52 ◽  
pp. 488-489
Author(s):  
S. Likharev ◽  
A. Kramarenko ◽  
V. Vybornov
Keyword(s):  
Depth Resolution ◽  
High Energy ◽  
Primary Beam ◽  
Layer By Layer ◽  
Energy Analyzer ◽  
High Energy Part ◽  
Small Window ◽  
Energy Part ◽  
Wide Range ◽  
High Voltage Supply

At present time the interest is growing considerably for theoretical and experimental analysis of back-scattered electrons (BSE) energy spectra. It was discovered that a special angle and energy nitration of BSE flow could be used for increasing a spatial resolution of BSE mode, sample topography investigations and for layer-by layer visualizing of a depth structure. In the last case it was shown theoretically that in order to obtain suitable depth resolution it is necessary to select a part of BSE flow with the directions of velocities close to inverse to the primary beam and energies within a small window in the high-energy part of the whole spectrum.A wide range of such devices has been developed earlier, but all of them have considerable demerit: they can hardly be used with a standard SEM due to the necessity of sufficient SEM modifications like installation of large accessories in or out SEM chamber, mounting of specialized detector systems, input wires for high voltage supply, screening a primary beam from additional electromagnetic field, etc. In this report we present a new scheme of a compact BSE energy analyzer that is free of imperfections mentioned above.

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