Theory
NEAR-FIELD
11
Near-field vs Far-field
Any antenna can be successfully measured on either a near-field or far-field range, with appropriate
implementation. There are significant cost, size, and complexity details which will lead to a
recommendation of one type over the other. In general, far-field ranges are a better choice for lower
frequency antennas and where simple pattern cut measurements are required, and near-field ranges are a
better choice for higher frequency antennas and where complete pattern and polarization measurements
are required.
Each measurement type has additional sub-types which have certain advantages and disadvantages, and
this makes generalized comparisons between near-field and far-field techniques difficult. One common
advantage cited for near-field measurement techniques is that testing can be accomplished indoors,
eliminating problems due to weather, electromagnetic interference, security concerns, etc. however the
same advantages can be quoted for indoor far-field measurements using anechoic chambers and compact
ranges. Cost of facility implementation is a critical determining factor in range selection. Far-field
ranges are often considered to be less expensive than near-field ranges. When considering the value
of the real-estate required for an outdoor far-field range, the situation may reverse. An indoor far-field
compact range would typically cost 3-4 times more than a planar near-field range capable of testing the
same size aperture, due to the larger chamber size required and cost of the compact range reflectors.
The following table summarizes some general tradeoffs to help you in your selection criteria. Many of
the characterizations are difficult to make without caveats, and there will certainly be exceptions.
Antenna engineers are a creative group and, over the years, have certainly developed innovative ways
to maximize the use of their test ranges to get acceptable results. Your NSI sales representative can help
you evaluate the tradeoffs further.
Reprinted with the permission of Nearfield Systems Inc.
