Home' RTCA Documents for Review : DO-213A Change 1 Contents Appendix C
DO-213A Change 1
© 2018 RTCA, Inc.
Radome performance measurements require a qualified test range that simulates the actual
operation of the radome as installed over the antenna system on the aircraft.
The radome/antenna positioner system used should locate the test antenna within the
radome at the same location as in the aircraft installation. The gimbal sequence should
consider the order of the actual antenna system in the aircraft installation. For sidelobe
level measurements, evaluate the reflectivity level of the range and relate it to the sidelobe
level requirements in Paragraph 2.2.2.
The radome performance requirements for Transmission Efficiency, Sidelobe Level, Beam
Width, and Beam Deflection in Subsection 2.2 are defined as far-field quantities, or with a
single plane wave incident on the combination of radome and system antenna.
Traditionally, radome-measurement ranges directly illuminated the radome and system
antenna with a plane wave using either a far-field or a compact range. There are other
configurations like the near-field approach that can also produce valid results, and this
section attempts to specify the needs of the measurement without constraining the
The requirements for accuracy of the test range should be evaluated based on the
applications to which the test measurements are being applied.
Direct Plane-Wave Illumination
This method includes traditional far-field and compact ranges. Other geometries (such as
a lens, an array of range antennas, or other mechanism) may also produce a plane wave of
the required quality. This method provides direct measurement of the far-field quantities
needed to evaluate the radome.
The quality of the approximated plane wave presented to the test article is of primary
importance. The following specifications apply to any test range that presents the test
article with an approximated plane wave.
The traditional far-field criterion of R ≥ 2D2/λ represents a quadrature phase taper of 22.5°
over a diameter D, where R is the separation between the range antenna and the system
antenna. This is considered a reasonable approximation to a plane wave for the purposes
of antenna-pattern testing. Stray signals in the range will result in additional ripple on top
of that phase taper.
Earlier versions of DO-213 permitted shorter distances than 2D2/λ (by a factor of four) in
certain circumstances, yielding a quadrature phase taper of 90° over the diameter D. This
level of phase distortion is known to induce notable errors in a measured antenna pattern,
especially on or near the main beam. Many experts in related RF-measurement disciplines
have questioned the validity of radome testing with that much phase taper, and thus in
revision A of DO-213 that has been reevaluated.
A compact range uses a large reflector to convert a spherical wave into a plane wave in a
relatively short distance, typically producing negligible phase curvature over the test zone.
The finite size of the reflector, however, induces ripple on the test-zone field. Typical
compact-range specifications call for ±5° of phase ripple over the test zone.
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