Near Field Antenna Range

The Near Field Range (NFR) Antenna Measurement system at BTP Systems consists of a 12’ wide by 12’ high measurement zone capable of testing from 1 GHz to 50 GHz with a dynamic range of 95 dB.  This is accomplished by utilizing an MI-Technologies MI-3000 data acquisition system along with an Agilent N5264A Series 50 GHz PNA-X, two Agilent N5183A MXG Analog Signal Generators, and an Agilent 85320B-H50 Reference Mixer Module with distributed amplifiers, allowing for both planar and cylindrical tests. The range itself is comprised of a temperature controlled 26’x 23’x 22’ (length/width/height) room with an interior lining of sheet metal fully covered with 8” pyramidal absorber for improved shielding, isolation and elimination of undesired reflections and multipath effects.  The scanning plane was laser positioned and aligned to a 0.0017-in. root-mean-square (RMS) scanning plane flatness with a 6’ by 5’ section aligned to a 0.0009 RMS flatness for higher frequency testing.  For reference, NASA’s Near Field Range boasts of a 0.004-in. RMS scanning plane flatness (https://aos.grc.nasa.gov/main/test-facilities/near-field-range/).  

 

  Indoor Near Field Antenna Range

Measurement Zone

120 by 120 inches
Frequency Range 1 to 50 GHz
Aperture Size 2 to 120 inches
Weight Limits 10,000 lbs.
VSWR 2.0:1 (typical)
Polarization Isolation 35dB (typical)
Extraneous Signal -80 (typical)
Dynamic Range 95 dB
Environmental Control full HVAC +/- 2 degF

 

Near feild antenna ranges are ideally suited for testing phased array antennas.  By using hologrpahic back projection, amplitude and phase details of each element become visible.  To prove out this capability, BTP tested a Ku weather radar slotted array antenna, picutured below.

We placed a piece of metallic tape over one of the slots.  A typical far field antenna plot shows some asymmetry in the sidelobes but the cause is not clear.

By performing a back projection of the near field data, the amplitude and phase clearly show the blocked element.  This level of troubleshooting can prove highly valuable.