RF Shielded Rooms and Antenna Types

[Maxwell077]

Hi everyone,

I want to learn something..

I knew that there are laboratories or facilities for testing purposes and they have anechoic chambers or rf shielded rooms for testing purposes. They're trying to do radar cross-section calculation, EMC-EMI tests, mobile phone tests etc...

Do you know that what kind of antenna types are used in these facilities? For eq: which antenna type is suitable for radar cross-section calculation.. Please give some detail information.
Does the type of antenna completely dependent or independent from facilitiy shielding(anechoic or shielded)
What is the main point choosing of antenna type these kind of facilities?

Regards...

I.A

 

[jiripolivka]

Dear Ilgaz:
Anechoic chambers are used as an attempt to a free space. It is not exactly a free space; the wall reflectivity is frequency dependent. In principle, any antenna operating at a frequency for which the chamber parameters are calibrated can be tested inside. Large aperture antennas like parabolic dishes generate their main lobes far away in the free space, so in the limited chamber volume it is impossible to measure it. Experts developed the "near-field" method so such antennas can be evaluated inside of the chamber. Then by FFT (Fourier transform) the "real" radiation pattern is calculated. With some minor deviations, it is generally accepted.
For the radar cross-section test in an anechoic chamber, a small-aperture antenna like a horn is preferred. RCS objects may be scaled for the test.