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highly automated, so that workshop personnel not
familiar with RF testing can easily do RTCA/DO-213
compliant testing. Test reports are generated fully
automatic.
Since the design is based on standard antenna / radome
test technologies, the advanced user can perform a
multitude of tests beyond what is defined in the
RTCA/DO-213. Thus this facility also presents a sound
investment for future standards and applications.
2. Facility Overview
Figure 1. shows the ORBIT/FR near field radome test
facility for nose-mounted radomes. The near field probing
surface is spherical. The positioning is realized with a fast
rotating azimuth positioner (30 rpm), which carries the
Device Under Test (radome, radar antenna on gimbal
positioner, aircraft bulkhead, where applicable), and an
elevation arm. Note that the orientation of the facility is
such that the aircraft “flies” to the zenith of the facility.
Figure 1. General overview of test facility
The test facility chamber outside dimensions are approx.
5.7 m x 5.2 m x 3.9 m (W x L x H), with a pit for the
azimuth positioner of 0.7 m deep. Thus it can be easily
installed right in the radome workshop. Access inside the
facility is through a large double leaved door of 4.0 m x
3.3 m (W x H). Typically the chamber is build as a
shielded, self supporting structure, so that there is no
interaction / disturbance from the radar signals inside the
facility with the outside world and vice versa. The inside
of the chamber is installed with 200 mm pyramidal
absorbers everywhere. In those areas of the floor where
people have to be for installation purposes, so-called
walk-on absorbers are installed.
Figure 2. The facility “as built”
All the instrumentation is mounted in a rack inside the
test chamber, right next to the elevation positioner. The
system is controlled through Fiber Optic LAN by either a
computer directly next to the facility, or optionally any
other computer connected to the same network.
The RF system is based on a network analyzer. For
Production testing and After Repair Testing, typically a
single frequency is used (e.g. 9.35 GHz), for
Qualification Testing multiple frequencies between 9.3
and 9.5 GHz are used. The RF probe on the elevation arm
is a dual linear polarized single choke circular probe.
Figure 3. Radar antenna under the radome
Facility temperature control is through one inlet into and
one outlet out of the test chamber, and can either be
connected to the building air conditioning supply or a
separate unit just for this facility. Note that the absolute
temperature does not need to be as strictly controlled as
the temperature variation during one measurement (+17
to +28 deg C versus ± 2 deg).
The radar antenna is mounted on the gimbal positioner,
which has a travel of ± 88 deg in azimuth and ± 33 deg in
elevation (relative to the aircraft). An automated linear
translation of approx. 8 mm (representing ¼ λ in X-band)
is installed between the radar antenna and the gimbal.
Note that RTCA/DO-213 requires the transmission
measurements to be done in two antenna positions
separated by ¼ λ in the boresight direction.
The entire gimbal unit is installed on a vertical slide
which allows to position the unit at the correct position
inside the radome. In addition this allows to lower the
radar antenna below the radome mounting surface, so that
it is protected while a new radome is being installed.
Figure 4. Radar antenna in low position for easy radome
mounting
The facility is designed to be able to handle a multitude of
different radomes with a minimum of operator
adjustments. For this purpose, each different size of
radome is mounted on its own support plate, made out of
a light weight fibre reinforced plastic honeycomb
sandwich structure. Thus it can easily be adapted to
include the aircraft bulkhead or to include the real
aircrafts interface (hinges, latches, screws), or any other
means to position and hold the radome. Since the
radomes are supported by these plates and point upright,
the loads on the interfaces are relatively small.
The plates are coded such that it is not possible to move
the antenna inside the radome to a position which would
allow the antenna to hit the radome. Also the interface
between the support plate and the azimuth positioner is
designed such that the radome is automatically mounted
correctly in radial and axial directions.
In this way most radomes can be mounted and
dismounted by just two or three people who carry the
　
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