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Antennas suitable for radiation pattern measurements

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VR4V6E39

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conducting antenna pattern

Hi, I was wondering if someone could tell me whether a biconical antenna as a transmitter would be suitable for conducting antenna pattern measurements? My confusion comes from the fact that for such antennas (and for frequencies less than 1GHz) the physical size would be rather large, and hence the far-field criteria would not be met if it was conducted in a chamber of 5m maximum length?
 

VR4V6E39

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So does that mean they are not suitable for conducting antenna pattern measurments?

Whats the minimum sufficent gain required for the transmit antenna?
 

Kohi_boy

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I would recommend to have a narrow beamwidth so as not to illuminate the surrounding.
 

biff44

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If you are making pattern measurements in the great outdoors, it is not so critical. If you are making pattern measurements in a chamber or room, then you do not want reflections off the walls confusing your gain vs azimuth readings, so you want a small, higher gain antenna, with very low back/side lobes.
 

VR4V6E39

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Measurements will be conducted in a chamber and therefore yess I will need very narrow beam antennas I agree, but with low frequencies (<GHz) high gain antennas are not acheivable and what I wanted to know is what sort of gain or beamwidth should I be looking for?
 

biff44

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http://www.ce-mag.com/99ARG/Williams97.html

For RF part 15 tests I have observed at certified test houses, they use antennas that look like these:
http://www.ahsystems.com/catalog/logperiodic.php

The will do one set of readings, and then rotate the antenna 90 degrees to get the other polarization. They will often have these mounted on a motor driven mast that allows them to raise and lower the antenna with respect to the floor height.

Added after 2 hours 13 minutes:

Of course, there is such a thing as near field and far field. Since many antennas at RF frequencies are physically large, you have to have a chamber that is big enough to be outside of the near field if you want an accurate gain measurement!
 

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