Hi Kevin Antennas that have a significant length, and construction, such as a wide band Bilog made by Schaffner/Chase, are marked where their centers are and that is where all range distances should be measured from! It is my understanding that this phase center is a compromise as it "moves" for different frequencies! However, using any other location will effect calibration data (probably only significant with emissions), but can also have an effect of the antennas beam width coverage when doing immunity! For example, the special immunity bilog antennas (IE X wing) have a fairly narrow horizontal beam width, which is worst at about 300MHz. So, even at 3 meters distance there may be a 1-2 dB loss of field at the edges of a 1.5m plane at 300MHz. If one moves the antenna closer (for example by measuring from the rear) then this can only get worse! Regards Tony LARCTEC Marketing Colorado
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