This paper describes a software based receiver post
processor that corrects circularity and gain errors in
coherent receivers. The receiver post processor
additionally provides range gating capabilities, signal
quality estimation, mixer non-linearity detection and
various display functions. This paper will
concentrate primarily on the identification of
circularity errors by the receiver post processor.
A New Wideband Dual Linear Feed for Prime Focus Compact Ranges
Authors: Ray Lewis, James H. Cook, Jr.
Publication: AMTA 1991
Copyright Owner: NSI-MI Technologies
Performance trade-offs are Investigated between the use of
clustered waveguide bandwidth feeds and the use of one multioctave
bandwidth single aperture feed in a prime focus compact
range for dual linear polarization. The results show that feed
structure may be used for advantage for the particular test
requirements of compact range systems for Radar Cross
Section Measurement.
Applications of Portable Near-Field Antenna Measurement Systems
Author: Greg Hindman
Publication: AMTA 1991
Copyright Owner: NSI-MI Technologies
Portable near-field measurement systems can provide
significant flexibility to both large companies seeking
to increase their antenna test capabilities, and small
companies looking for their first investment in a test
range. There are many unique applications for
portable near-field antenna measurement systems in
addition to their use for standard antenna
performance measurements. Some additional
applications include flightline testing, anechoic
chamber quiet zone imaging, and EMI testing.
Many of NSI's near-field systems have been portable
designs, capable of being set up in a small lab or
office and easily relocated. Key features required for
a portable system are rapid setup, simplicity of use,
low cost, and accuracy. This paper will be focused on
practical experience with installing, calibrating, and
operating portable near-field measurement systems. It
will also cover tradeoffs in their design, and usage in
a variety of applications.
Measurement Receiver Error Analysis for Rapidly Varying Input Signals
Author: 0. M. Caldwell
Publication: AMTA 1991
Copyright Owner: NSI-MI Technologies
An assessment of instrumentation error sources and their
respective contributions to overall accuracy is essential for
optimizing an electromagnetic field measurement system.
This study quantifies the effects of measurement receiver
signal processing and the relationship to its transient
response when performing measurements on rapidly
varying input signals. These signals can be encountered
from electronically steered phased arrays, from switched
front end receive RF multiplexers, from rapid mechanical
scanning, or from dual polarization switched source
antennas.
Numerical error models are presented with examples of
accuracy degradation versus input signal dynamics and the
type of receiver IF processing system that is used.
Simulations of far field data show the effects on amplitude
patterns for differing rate of change input conditions.
Criteria are suggested which can establish a figure of merit
for receivers measuring input signals with large time rates
of change.
Measurement System Performance Considerations for Planar Near-Field Scanning Applications
Author: J. H. Pape
Publication: AMTA 1991
Copyright Owner: NSI-MI Technologies
This paper describes measurement system performance parameters that were considered during the design phase of a planar near-field measurement range for Spar Aerospace Limited. All aspects of the planar near-field measurement system are addressed. These include; instrument selection, scanner interface hardware, system controller/computer hardware, software for data collection, near-field to far-field transformation, data analysis, networking and system configuration. The Scientific-Atlanta Model 2095 Microwave Measurement System with its near-field options is used as the basis for meeting the Spar requirement. The various data collection parameters of the Model 2095 are described with special emphasis on how the factors relate to near-field requirements such as fixed grid sampling. Examples of typical test scenarios are presented as an aid in exploring detailed data collection system timing.
Near-Field Measurement Experience at Scientific-Atlanta
Author: Doren W. Hess
Publication: AMTA 1991
Copyright Owner: NSI-MI Technologies
The experience with near-field scanning at Scientific-Atlanta began with a system based upon a analog computer for computing the two-dimensional Fourier transform of the main polarization component. When coupled with a phase/amplitude receiver and a modest planar near-field scanner this system could produce far-field patterns from near-field scanning measurements. In the 1970’s it came to be recognized that the same advances, which made the more sophisticated probe-corrected planar near field measurements possible, would enable conventional far-field range hardware to be used on near-field ranges employing spherical coordinates. In 1980 Scientific-Atlanta first introduced a spherical near-field scanning system based upon a minicomputer already used to automate data acquisition and display. In 1990, to meet the need of measuring complex multistate phased-array antennas, Scientific-Atlanta began planning a system to support the high volume data requirement and high speed measurement need represented by this challenge. Today Scientific-Atlanta is again pursuing planar near-field scanning as the method of choice for this test problem.
Probe - Correction Coefficients Derived From Near-Field Measurements
Author: Gregory F. Masters
Publication: AMTA 1991
Copyright Owner: NSI-MI Technologies
Probe correction is necessary in near-field
measurements to compensate for non-ideal
probes. Probe compensation requires that the
probe’s far-field pattern be known. In many
cases direct far-field measurements are
undesirable, either because they require
dismantling the probe from the near-field range
set-up or because a far-field range is not
available. This paper presents a unique method
of deriving probe-correction coefficients by
measuring a probe on a near-field range with an
“identical” probe and taking the square root of
the transformed far-field. This technique, known
as the “Probe-square-root” method can be
thought of as self-compensation. Far-field
compensations are given to show that this
technique is accurate.
