Watt Veruttipong

Beam-waveguide antenna performance predictions with comparisons to experimental results

An overview of a NASA/JPL antenna project, with specific focus on the methodology used to predict the microwave performance of a 34-m-diameter beam-waveguide (BWG) reflector antenna, designated DSS 13, is given. Microwave performance predictions are given, as well as a summary of test results for the antenna, which has Cassegrain and centerline BWG operating models at X-band (8.450-GHz) and Ka-band (32-GHz) frequencies. Predictions were used to identify critical and poorly understood areas needing further study and diagnostic testing, and assisted in planning, scheduling, and evaluating the final results of a detailed test program. Predictions were assembled for all known losses that contribute to antenna performance degradation. It was found that predictions and experimental results agreed reasonably well for beam-peak gain and corresponding efficiency, and for several (but not all) noise temperatures. >

Scanning properties of large dual-shaped offset and symmetric reflector antennas

The scanning properties of shaped reflectors, both offset and circularly symmetric, are examined and compared to conic section scanning characteristics. Scanning of the pencil beam is obtained by lateral and axial translation of a single point source feed. The feed is kept pointed toward the center of the subreflector. The effects of power spillover and aperture phase error as a function beam scanning are examined for several different types of large reflector design including dual-offset, circularly symmetric large f/D, and smaller f/D dual reflector antenna system. It is shown that the Abbe-sine condition for improved scanning of an optical system cannot, inherently, be satisfied in a dual-shaped reflector system that is shaped for high gain and low feed spillover. The gain loss, with scanning, of a high-gain shaped reflector pair is demonstrated to be due to both aperture phase error loss and power spillover loss. >

Gaussian beam and physical optics iteration technique for wideband beam waveguide feed design

A novel approach is demonstrated which involves iterating Gaussian beam and beam waveguide (BWG) parameters to obtain a wideband BWG feed. The result is further improved by making a comparison with the physical-optics result and repeating the iteration. The basic goal was to design a BWG feed system with good performance from 2 to 32 GHz, utilizing mirror sizes of 20 lambda at the low frequency. The BWG antenna performance (e.g. gain, efficiency, noise temperature) at S, X, and Ka-bands is presented. It is noted that higher-gain horns are needed for higher frequencies.<<ETX>>

A technique for computation of noise temperature due to a beam waveguide shroud

The authors present a relatively simple technique used to compute a real BWG (beam waveguide) system noise temperature by combining analytical techniques with data from experimental tests. Specific expressions and parameters for X-band BWG noise computation are obtained for NASA Deep Space Network (DSN) BWG antennas. These expressions are also valid for various conditions of the BWG feed systems, including horn sizes and positions, and mirror sizes, curvatures, and positions.<<ETX>>

Beam aberration correction technique for a BWG antenna

A technique for a real-time beam aberration correction scheme for deep space uplink and downlink communications is presented. This technique provides a closed-form relationship between the beam aberration angles and the corresponding feed displacement for a reflector antenna with a beam waveguide (BWG) or multiple reflector system. This algorithm will enable one to accurately predict the movement of the feed in real time for a known beam deviation while the antenna is tracking a spacecraft. It is also useful to determine the feed offset position needed to correct for the beam deviation due to an imperfect antenna mechanical structure, and subreflector and mirror misalignments for a complex multiple reflector system.

A new technique for vernier pointing of a beam-waveguide antenna

This paper presents a new and simple approach for the Ka-band vernier pointing of a 34 m beam-waveguide (BWG) antenna (also applicable to a 70 m antenna). In this study, rotation of a BWG flat mirror, located at the elevation axis, is used to scan the beam instead of using the very large tipping structure of the antenna. The rotation of a BWG flat minor at another location is also investigated. The advantages of scanning the drastically smaller mirror with a less precise mechanism will be discussed. RF performance predictions will be presented.<<ETX>>

Design of a correcting plate for compensating the main reflector distortions of a dual shaped system

The authors present a method of synthesizing a correcting flat plate that compensates for the main reflector distortions of a dual shaped system. The dual shaped reflector system, synthesized for high gain, has a main reflector diameter of 32.8m (not including a noise shield). The time and space slowly varying surface distortions in the main reflector are due to gravitational and thermal effects and reduce the antenna gain. The correcting plate is nominally flat and part of a beam waveguide. It is designed by geometrical optics (GO) to be distorted so as to have a virtual point caustic for the GO rays reflected off the flat plate (in receiving mode).<<ETX>>

Multi-step Ka/Ka dichroic plate with rounded corners for NASA's 34m Beam Waveguide antenna

A multi-step Ka/Ka dichroic plate (Frequency Selective Surface (FSS)) is designed, manufactured and tested for use in NASAs Deep Space Network (DSN) 34m Beam Waveguide (BWG) antennas. The proposed design allows ease of manufacturing and ability to handle the increased transmit power (reflected off the FSS) of the DSN BWG antennas from 20kW to 100 kW. The dichroic is designed using HFSS and results agree well with measured data considering the manufacturing tolerances that could be achieved on the dichroic.

Gaussian beam iteration technique for a wideband multiple reflector design

The Gaussian beam technique has become increasingly popular for a multiple reflector design. This paper demonstrates a new design approach by iterating Gaussian beam and reflector parameters simultaneously at various frequencies to achieve a wideband multiple reflector system. The result can be further improved by comparing it with physical optics results and repeating the iteration.

Compensation of gravity-induced structural deformations on a beam-waveguide antenna using a deformable mirror

At the NASA Deep Space Network (DSN) Goldstone Complex, located in the Mojave Desert in California, a 34-meter-diameter beam-waveguide (BWG) antenna, DSS-13, was constructed, and has become an integral part of an advanced systems program and a test bed for technologies being developed to introduce Ka-band (32 GHz) frequencies into the DSN. The antenna efficiency at 32 GHz was found to depend significantly on the elevation angle, i.e., it decreased from 45% to 35% as the elevation angle changed from 45 degrees to 20 degrees. This elevation angle dependence is due to the deformation of the main reflector caused by the resulting change in gravitational force applied to the antenna structure. A method for compensating the gravity-induced structural deformations in a large ground-based beam-waveguide antenna is presented. A deformable flat plate (DFP) is installed at the M6 mirror location in the beam-waveguide optics.