Concepts for Next-Generation Spaceborne Precipitation Radar
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precipitation radar TRMM↗
Engineering topics
Rahmat-Samii, Y.
Publications and source records attributed to Rahmat-Samii, Y..
System Concept for the Next-Generation Spaceborne Precipitation Radars
In the paper, we will present a system concept for a second-generation spaceborne precipitation radar (PR-2) for operations at the Low Earth Orbit (LEO).
precipitation radar TRMM↗
Large Deployable-Mesh Antenna System for Ocean Salinity and Soil Moisture Sensing
A concept has been studied for remote sensing of sea surface salinity and soil moistute from space using a large deployable mesh antenna system.
microwave remote sensing mesh antenna ocean salini↗
Noise Temperature and Gain Loss Due to Paints and Primers: A Case Study of DSN Antennas
In achieving high performance for reflector antennas, it has been noted that it is essential to carefully assess the roles of surface paints and primers.
Noise↗
A Large-Antenna Microwave Radiometer-Scatterometer Concept for Ocean and Land Sensing
Microwave radiometry and scatterometry are established techniques for surface remote sensing applications.
radiometer scatterometer remote sensing antenna oc↗
Advanced Microwave Radiometry and Scattorometry Approaches for Surface Hydrology
In this study we have examined techniques and technology options for achieving desired microwave system performance (high spatial resolution and accuracy) using low-mass deployable antennas.
Microwave radiometry Scatterometry Hydrology Ocean↗
Anomalous Results from PO Applied to Reflector Antennas: The Importance of Near Field Computations
It is the purpose of this paper to demonstrate that the typical approach based on the far field pattern of the feed would result into erroneous result and special care must be exercised to obtain the correct result.
reflector↗
Design and Near-Field Measurement Performance Evaluation of the SeaWinds Dual-Beam Reflector Antenna
This paper presents the design and performance evaluation of a lightweight, composite material, elliptical-aperture, parabolic-reflector antenna.
reflector SeaWinds resonant frequency antenna RF p↗
Design and Near-Field Measurement Performance Evaluation of the Sea Winds Dual- Beam Reflector Antenna
This paper presents the design and performance evaluation of a lightweight, composite material, elliptical-aperture, parabolic-reflector antenna. The performance characterization is obtained using the cylindrical near-field measurement facility at JPL as shown. The reflector has been designed and calibrated for the SeaWinds spaceborne scatterometer instrument. The instrument operates at Ku-band and is designed to accurately measure wind speed and direction over Earth's ocean surface. The SeaWinds antenna design requires two linearly polarized independent beams pointed at 40 deg.and 46 deg. from nadir as shown. The inner beam, pointed at 40 deg. from nadir, is horizontally polarized with 1.6 in x 1.8 in required beamwidths in the elevation and azimuth planes, respectively. The outer beam, pointed at 46 deg. from nadir, is vertically polarized with 1.4 in x 1.7 in required beamwidths. Noteworthy, the reflector boresight axis is pointed at 43 deg. from nadir. Both beams are required to have the first sidelobe level below -15 dB relative to the peak of the beam.
Hussein, Z.↗
Soil Moisture Pathfinder: A Low-Cost Passive Spaceborne System Using Inflatable Structures
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inflatable antennas↗
On the Accurate Calibration of the SeaWinds Radar Antenna: A Cylindrical Near-Field Measurement Approach
The radar antenna for the SeaWinds scatterometer will be of the multipolarized, multi- incidence angle, conical scanning design. It will measure echos from the sea surface to derive both the speed and direction of winds. To calibrate this radar, measurement error models are used to define the effects of near-field measurement bias errors on antenna gain and far-field radiation patterns.
SeaWinds↗
On the Accurate Calibration of the SeaWinds Radar Antenna: A Cylindrical Near-Field Measurement Approach
This paper demonstrates the utility of a cylindrical near-field measurement approach for the SeaWinds radar antenna calibration. Both generalized measurement error models and measured tests on a standard gain horn and NASA Scatterometer instrument antenna have been performed to achieve and verify the desired calibration accuracy. A comparison between far-field measured data and those obtained from cylindrical near-field measurements was found in excellent agreement.
spaceborne↗
A Massively Parallel Computation Strategy for FDTD: Time and Space Parallelism Applied to Electromagnetics Problems
In this paper, we present a novel strategy for incorporating massive parallelism into the solution of Maxwell's equations using finite-difference time-domain methods. In a departure from previous techniques wherein spatial parallelism is used, our approach exploits massive temporal parallelism by computing all of the time steps in parallel.
Maxwell's↗
Experimental code verification results for reflector antenna distortion compensation by array feeds
Electronic compensation of reflector surface distortion using array feed with individual amplitude and phase control of the array elements is becoming increasingly attractive because of the recent advances in monolithic microwave integrated circuit (MMIC) technology. An algorithm has been developed previously using the concept of focal plane conjugate field matching in the receive mode and a computer code has been generated that predicts the proper excitation coefficients for the elements of the reflector feed array to compensate the effects of reflector surface distortion. This paper presents the results of an experimental study to verify the above compensation algorithm and in general to demonstrate the effectiveness of the array feed compensation technique.
Zaman, A. J.↗
More About Lens Antenna For Mobile/Satellite Communication
Report presents additional details of design of proposed phased-array antenna described in "Lens Antenna for Mobile/Satellite Communication" (NPO-16948). Intended to be compact and to lie flat on top of vehicle on ground. Transmits and receives circularly polarized radiation in frequency ranges of 821 to 825 MHz and 860 to 870 MHz. Transmitting and receiving beams electronically steerable to any of 48 evenly spaced directions to provide complete azimuth coverage, and would be fixed, but wide, in elevation, to provide coverage at elevation angles from 20 degrees to 60 degrees.
Rahmat-Samii, Y.↗
Array Feed To Compensate For Distortion In Antenna
System partly restores desired far-field radiation pattern. Adaptive array feed for paraboloidal-reflector antenna helps compensate for effects of slow changes in shape of reflecting surface. Counteracts distortion by illuminating reflector with wave fronts that have "opposite" distortion.
Rahmat-Samii, Y.↗