Antenna measurement
Testing antennas to characterize gain, pattern, impedance, and efficiency.
Antenna measurement techniques are used to test antennas to ensure they meet specifications or to characterize their performance. Typical parameters measured include gain, bandwidth, radiation pattern, beamwidth, polarization, and impedance, all of which are essential for effective communication. The antenna pattern, which describes the response of the antenna to a plane wave from a given direction or the relative power density of a transmitted wave, is a key characteristic; for reciprocal antennas, the transmit and receive patterns are identical.
- Far field distance formula
- 2D²/λ, where D is the widest diameter of the antenna and λ is the wavelength
- Near field scanning distance
- 3 to 10 times the wavelength
- Maximum near field sample spacing
- λ/2
- Compact range surface accuracy
- less than 0.001λ
- Typical compact radiation measurement ro
- 4 × 4 × 3 m
Lore & Background
The first antenna measurement technique developed was the far-field range, where the antenna under test (AUT) is placed in the far-field of a range antenna. The far-field distance, or Fraunhofer distance, is considered to be 2D²/λ, where D is the widest diameter of the antenna and λ is the wavelength; separating the AUT and the standard receiving antenna by this distance reduces detectable phase variation enough for a reasonably accurate estimate of the far-field pattern. The IEEE antenna measurement standard (IEEE-Std-149-1979) suggests setups for far-field ranges and ground-bounce ranges.
Reader's Guide
Antenna measurement techniques are significant because they enable the characterization of antennas across a wide range of frequencies and sizes. Far-field ranges, while simple, require large distances for large antennas, leading to the development of near-field techniques that measure the field close to the antenna (typically 3 to 10 times its wavelength) and then transform the data to predict the far-field pattern. Compact ranges use a reflector to create a plane-wave-like field near the AUT, making them suitable for microwave and millimeter wave frequencies where the far-field distance is large, though the reflector requires precision surface accuracy (typically less than 0.001λ) and edge treatment to avoid diffracted waves. For small antennas in wireless and IoT devices, compact radiation measurement systems operate in standard laboratory environments without a dedicated anechoic chamber, using a narrow-beam measurement antenna and narrow receiver bandwidth to suppress reflections, enabling measurement of radiation patterns, total radiated power (TRP), gain, efficiency, and effective radiated power (ERP) in rooms as small as 4 × 4 × 3 m.
Did You Know?
- Near-field measurements are typically taken at distances of 3 to 10 times the wavelength from the antenna.
- The compact antenna test range (CATR) was invented by Richard C. Johnson at the Georgia Tech Research Institute.
- The IEEE antenna measurement standard is document IEEE-Std-149-1979.
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