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Operation
The performance of the 3159 antenna in a SAC depends on several factors. These include the overall size of the
chamber, the effectiveness of the absorber treatment on all surfaces, especially those close to the antenna and the
ground, height above the ground and size of the ferrite layout (if used) below the antenna. The variation in the VSWR
performance can be seen in the following three examples of installations of the 3159 in chambers of various sizes, with
different absorber treatments.
The chamber example shown in Figure 4 shows the effect of the 3159 antenna positioned at heights of 2.3 m and 3.3 m
above a large ferrite grid on the chamber floor. The antenna is being used to illuminate a large DUT. In this installation the
antenna was mounted on a custom driven positioner, with metallic structural components, which were known to impact
antenna performance at the upper frequencies
In the Figure 5 installation, the antenna is positioned at a height of 2 m above a ferrite grid in a fairly standard sized full
vehicle 10 m EMC chamber.
In the Figure 6 installation, the antenna is positioned at a height of 2 m and at a distance of 2 m from the field probe above
a reflective ground plane. As can be seen from the measurements, the trends in the measured VSWR changes with
installation conditions, since most test installations will be different from an ideal far field setup, it is expected that there
could be significant deviations from ideal antenna performance.
The E-field performance of the antenna should be measured as part of the installation setup. The plots below show some
of the variations seen in EMC installations where ferrite tiles were positioned below the antenna, and with a reflective
ground. Figure 7 shows the performance of the antenna with the full set of extensions when positioned in a small 3m
chamber and 7kW transmit power, with and without ferrites below the antenna. Figure 8 shows the same antenna in the
same chamber with the ferrite grid below the antenna but without the extension elements. This setup most closely
resembles the use of the antenna in a small EMC chamber.
Figure 4: Measured VSWR in a very large SAC at 2.3m and 3.3m height above ferrites tiles
