Measurements of ADMIRALS RTO at 322 GHz in a Hologram-Based Compact Antenna Test Range
See Compact antenna test ranges web page for the structure of the hologram and experimental set-up.
ADMIRALS RTO Tests
The ADMIRALS representative test object (RTO) was constructed by EADS Astrium for comparison of potential antenna testing methods at mm- and sub-mm wavelengths. The diameter of the ADMIRALS RTO main reflector is 1.5 m. The diameter of the quiet-zone extent had to be larger than that.
The required hologram was made from three 1 m × 3 m pieces, which were joined together to form the final 3 m × 3 m hologram structure. The patterns were exposed with a laser on the photosensitive resist on top of the copper layer of the hologram material (17 µm copper on 50 µm Mylar). Chemical wet etching was used for processing the slots to the copper layer.
A vacuum table was used to support the hologram pieces and to keep them firmly in place during the cutting of the edges and the actual joining. Figure 1 shows the hologram surrounded by absorber walls.
Fig. 1 The 3 m × 3 m hologram for the ADMIRALS RTO tests.
The tests of the ADMIRALS RTO were carried out in the large test hall of the High Voltage Institute at Aalto (that time TKK) during summer 2003. The layout of the CATR, i.e., its orientation in the hall and the position of the installed absorbers were carefully designed in order to avoid reflections and minimize the amount of needed absorbers.
Antenna Positioner and Linear Scanner
Fig. 2 Antenna Positioner and Linear Scanner
A high-accuracy antenna positioner was built by modifying the pedestal of an old anti-aircraft gun.The realized positioner is capable of rotating the antenna from -12° to +90° in elevation and full 360° in azimuth. The estimated repeatability in azimuth direction was 0.004°. The positioner has variable speed AC drives in both rotation directions.
The quiet-zone field of the CATR was probed with a planar scanner to verify the quality of the plane wave. The scanner has a 2-metre linear stage that allows rotation to fixed positions so that horizontal, vertical, and both diagonal scans could be made.
The antenna positioner and linear scanner were constructed by the Laboratory of Machine Design at TKK (currently also part of Aalto University).
Measured Azimuth Pattern of the ADMIRALS RTO
The radiation pattern of the RTO was measured in angular ranges of −85°…+85° in azimuth direction.
Fig. 3 Radiation pattern of the RTO
The general agreement between the measured results and the results obtained by EADS Astrium in their reflector CATR is good.
Contact person: Juha Ala-Laurinaho