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NSIFAQsTopicsFarFieldSystems

FAQ Topics

Far-field Systems FAQ

1. In the NSI data sheet for the NSI-800F-20 using the az/el positioner (NSI-SC-5665), there is no information about the limits for the dimensions of the AUT (only the limit of 25 kg). Can I measure antennas up to 1 m in diameter?

2. Is far-field testing possible with an NSI-700S-30, 50, 60 or 70 scanner?



1. In the NSI data sheet for the NSI-800F-20 using the az/el positioner (NSI-SC-5665), there is no information about the limits for the dimensions of the AUT (only the limit of 25 kg). Can I measure antennas up to 1 m in diameter?

We don't state a limit for the dimensions of the AUT. In principle, providing the mass and centre of gravity for the AUT defines the bending moment and is the only limitation. Within these limits you are essentially able to mount as large an antenna as is practical (adherence to far-field criteria, quiet-zone illumination, AUT stiffness, i.e. flexure, and clearance from the walls, ceiling and floor are obviously still limiting factors here). However, a larger AUT would perhaps imply a larger centre of gravity offset (remember the 25 kg at 200 mm limit of this stage) which would impose a practical limit. Normally the customer needs to provide an AUT mount to hold the AUT up on the az/el stage but this is something that the customer would fabricate themselves as it is AUT dependant and can be something as simple as a dielectric column. The reason we state a maximum AUT size on our other spherical, mostly roll-over-azimuth systems, is that they employ an L-bracket within the design of the AUT positioner. This means the distance between the top roll axis and the (absorber on the) base of the L-bracket is fixed at the time of manufacture, and it is this which imposes the size constraint on the diameter of the AUT. (This is for polar mode acquisitions. However, long thin antennas can still be mounted on these stages in an equatorial measurement mode as shown in: http://ww2.nearfield.com/Sales/datasheets/NSI-700S-50.htm)

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2. Is far-field testing possible with an NSI-700S-30, 50, 60 or 70 scanner?

The NSI-700s-30, 50, 60 & 70 scanners are comprised of two separate parts, a roll over azimuth AUT positioner and a probe mount. As such, and within reason, the separation between these can be chosen arbitrarily. However, the consequence of an increased range length is firstly an increase in the RF path length, and an accompanying degradation in the system signal to noise ratio and secondly, an increase in the size, and therefore the cost, of the chamber. If the customer wishes to increase the AUT to probe separation NSI would be pleased to provide a quote for the necessary RF system engineering and any additional amplifiers, etc that may be required. NSI offers a far-field software option to address this requirement.

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