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Antenna measurement

Question asked by e4411a on Jun 25, 2007
Latest reply on Jun 26, 2007 by Dr_joel

I am using a VNA for radiation pattern measurements in an anechoic chamber. To get a better dynamic range I reduced the IF bandwidth. However when I do this,I am facing a small issue . For an antenna I am getting the following results:
-37 dB for co polarization and -44dB for cross polarization with an IF bandwidth of 1kHz. However with a higher IF BW, these jump to  about -42 and -55 respectively.
So it appears that I "lost" on my cross-pol ratio while trying to improve the dynamic range.  Is this expected? and if so how do I set the correct IF bandwidth.