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Introducing AnToolsÓ for Windows

Figure 1 AnTools Plot Window

Overview

AnTools (Antenna Tools) is a reflector antenna analysis program that runs under Microsoft Windows 3.1 and higher. It is designed to be a productivity-enhancement application for people involved in the design, manufacture and installation of reflector antennas. AnTools does the following:

In AnTools the antenna can be defined and the results interpreted both in pictures and data tables. The pictures are useful in visualizing the antenna optics and to interpret broad error patterns, while tables of input and derived data provide a more quantitative feel for the results. Often combinations of pictures and tables leads to the deepest understanding.
 
 

Applications

AnTools was designed to be as versatile as possible in order to satisfy the needs of antenna analysts, designers, fabricators, installers and measurers. The paragraphs below describe some of the ways that the program can be useful.
 
ANTENNA OPTICS LAYOUT: Designing an antenna often involves tradeoffs involving the feed pattern, subreflector blockage, tooling which exists for specific curvatures, etc. The Antenna Optics design window allows the user to vary each of the parameters in order to arrive at an optimized solution. Instant feedback is provided numerically and graphically as shown in Figure 2 with a properly scaled schematic representation of the current options, showing the primary shape, subreflector shape, primary vertex, primary focus, secondary focus and (optionally) coordinate axes. The numerical data includes primary diameter, subreflector diameter, primary focal length, F/D ratio, prime focus half angle, secondary focal length, subreflector offset from the prime focus, Cassegrain feed half angle, magnification factor, hyperbola eccentricity, magnified F/D ratio, hyperbola construction constants A and B. Parameters at the same level of detail are provided for all available antenna types.

STRUCTURAL ANALYSIS POST-PROCESSOR: When antenna structures are analyzed for the effects of the environment including gravity, wind and thermal loads, the deformed antenna shape is available to the analyst. AnTools can use these data to predict antenna performance including RMS accuracy, pointing error and required subreflector position adjustment. The analyst can use this feedback to optimize the design.

ANTENNA INSTALLATION: Large reflectors are often initially aligned using a vertex-mounted theodolite and a calibrated drill tape which follows the surface curvature. If the target coordinates are determined from the theodolite angles, AnTools can tell the installer how far each target must be adjusted to bring the surface into spec. Constant thickness offsets can be used to account for the target heights. 

Figure 1 Antenna Optics Layout
 
Figure 2 Antenna Optics Layout

QUALITY CONTROL/ASSURANCE: Small reflectors or panels fabricated by a plastic layup, aluminum spinning or machining are often measured using a Coordinate Measuring Machine (CMM). AnTools can use the CMM output data to create a complete and professional QC/QA inspection report including numerical tables of results, graphical representations of the measurement locations on the dish, and the surface profile as shown in Figures 1 and 3. A surface map of the errors often leads to an understanding of the manufacturing problems which may be compromising accuracy.

DESIGN OF ARRAY RECEIVER ANTENNAS: Some specialized radar antennas and radio telescopes place an array of receivers at the secondary focal plane near the primary vertex in order to expand the effective beamwidth of the antenna. By displacing the feed (receiver) location in a Cassegrain or Gregorian antenna configuration, AnTools will determine the resulting beamshift, path length errors and near-field phase plane error map. The regularly spaced grid of path length errors from each of the array feeds can be superimposed if desired to determine the effects of combining signals.

ANTENNA PATTERN PREDICTION: AnTools analyzes the near-field path length errors. These can be used as input to a post-processor which determines the far-field patterns through Fourier transformations. Path length errors for the full antenna assembly are available in a regularly-spaced grid interpolated from the data supplied. Near-field path length data can easily be converted into phase errors. By combining phase with the amplitude (illumination) at each grid point, the far-field pattern can be calculated. (For this application AnTools only performs the pre-processing tasks.)
 
 

Program Structure and Operation

AnTools consists of 21 windows. The top-level ones are accessed from the drop-down menu at the top of the main window. The top-level windows perform the following tasks, which are introduced below and described in more detail in the AnTools User’s Guide:

Main Program Windows

OPTICS LAYOUT (required): The definition of a project must start with the optics, or geometry, layout. The choices are parabola, hyperbola, ellipse, sphere, prime focus antenna, Cassegrain antenna and Gregorian antenna. The contours of each of these reflectors may optionally be biased from the defining polynomial equation. All optics layouts are fully axi-symmetric. However, offset reflectors and antennas can be analyzed as long as their components (primary, secondary, feed and subreflector) are consistent with the parent optics parameters defined here. The map shown in Figure 1 is an example of an offset reflector.

BOUNDARIES AND MEASUREMENT SELECTIONS (optional): The boundaries of each of the reflectors (primary and secondary for Cassegrain and Gregorian antennas) is selected. Boundary files are created and displayed in a picture box. Measurement data may be read in here or in the measurement window described next. The measurements may be displayed in the picture box, and reference points and those selected for "skip-at-analysis" may be selected here.

MEASUREMENTS (required): Surface measurements for the primary, secondary, feed and subreflector are read in here and displayed in tabular format. Reference points and "skip-at-analysis" points are selected here. If measurements are defined in the "BOUNDARIES…" window above, the use of this window is not required.

ANALYSIS (optional): Once the antenna is defined by its geometry and measurement data, the bestfitting analysis takes place. Up to 6 degrees of freedom least squares analyses are performed and the statistical and tabular results displayed. For antenna assemblies (prime focus, Cassegrain and Gregorian), measurement data from any or all of the components may be included in the analysis. Illumination taper in dB may be varied.

PLOTTING (optional): The results of the latest analysis may be plotted in a picture box as shown in Figures 1 and 3. Surface plots and contour plots are available. The plot size and surface plot viewing position may be selected.
 
PREFERENCES (optional): The default settings may be changed in this window. These include the project title, the start-up window, the timer delay, the deviation magnification factor, and the maximum number of surface measurements.

VIEWING FILE NAMES (optional): Up to 13 different data files may be used during program operation. Some of them are user files read in by the program, such as surface measurements, and others are created by the program. A list of these file names with descriptions may be viewed only. 

VIEWING DATA (optional): Up to 9 different data sets in tabular form may be viewed (simultaneously if desired). These include measurements, boundary coordinates, bias shaping, results of bestfitting and required surface adjustments.

PRINTING (optional): Tabular data may be printed as a report with headers and page numbers, or filed as such or in tab-delimited format for import to any of the popular spreadsheets. Pictures of the reflector boundaries with measurement points, and surface errors plots may be printed. 

 

Figure 2 Surface Plot of Residual Path Length Errors
 
Figure 3 Surface Plot of Residual Path Length Errors

Using Projects

Antenna definitions (optics layout, reflector geometry, measurements, reference points, etc.) may be saved for future reference as project files for future reference and updating. A default project may be selected which loads with AnTools.
 
 

Units of Measure

No particular linear units of measure are used. Results are reported in terms of the values supplied in measurements. It is the responsibility of the user to be consistent. Deformations, offsets and adjustments are magnified by 10n, where n may be defined by the user. The default value is n=3 so that measurement data provided in inches displays deformations in thousandths (mils), and measurements in millimeters give deformations in microns (mm).

All angular measurement data is given in radians, and results are shown as radians x 10n as described above. For example, if n=3 then angular deformations (beamshifts) are given in milliradians.
 
 

Coordinate System

A right-handed Cartesian (XYZ) coordinate system is used throughout the program. For the optics layout as shown in Figure 2, X is into the paper (not shown), Y is up and Z is along the antenna boresight axis from the primary vertex to the focal point. For single dishes, the positive Z direction is positive away from the reflector surface. This results in nominally positive Z coordinates for the parabolas, ellipses and spheres, but negative coordinates for hyperbolas.

For the standard panel shapes in the Boundaries window, the X axis is along the panel centerline.
 


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