Correct measurement of the antennas is a very important part of their design phases. Because it is often very difficult to analytically calculate the properties of the complex antenna structures, the physical measurement techniques and test results are required for the verification of the simulated design data. Antenna measurements can be performed in such different environments like indoor test sites and outdoor sites. For example, anechoic chambers are indoor test sites, while Open Area Test Sites(OATS) are outdoor sites. In this context, the test range and test setup should be chosen correctly for the best and reliable antenna measurements.
The most important antenna parameters that can be measured are listed as below:
- Input impedance
- Radiation Pattern (Magnitude & Phase)
- Power Handling
For the indoor antenna tests in an anechoic chamber, enough testing area is required to provide the far-field region. The far-field region is ensured by separating the distance, d≥(2D^2)⁄λ, far enough between the reference antenna and the antenna under test (AUT). D is the maximum dimension of the radiating part of the antenna, λ is the wavelength in the working frequency band. On the other hand, sometimes it is impossible to provide far-field region in an indoor range, and so near-field antenna measurement is performed. In this type of measurement, near-field to far-field (NF/FF) transformation is needed by using some analytical methods. In addition to this, the application of the antenna to be tested necessitates directly near-field measurements.
Antennas should be tested firstly in a reflection-free environment to see and evaluate their ideal electromagnetic performance. Afterwards, more realistic test & measurement field may be created for test purposes with respect to the real working conditions of the antenna. For example, the input impedance value of the antennas is varied by the obstacles and reflective objects inside the testing environment.
The antenna pattern or radiation pattern is defined as “the spatial distribution of a quantity that characterizes the electromagnetic field generated by an antenna” in IEEE Standard for Definitions of Terms for Antennas (IEEE Std 145™-2013).
Three-dimensional antenna pattern measurement is not practical, so two-dimensional pattern is measured in the principal E- and H-planes. 2D antenna pattern measurements are performed for varying elevation angle (0≤θ≤π) with a fixed azimuth angle, and also for varying azimuth angle (0≤φ≤2π) with a fixed elevation angle.
An example for Antenna 3D radiation pattern with normalized values is shown below:
The fundamental test instruments for the antenna measurements are Vector Network Analyser, Spectrum Analyser, RF/Microwave Signal Generator, Reference Antennas, Mechanical or Electro-Mechanical positioner for the angle adjustment, Data Analysis & Post-Processing tools.
Testups provides antenna testing and measurement services in a suitable anechoic chamber with all necessary test tools and equipment. In addition, Testups can also provide antenna test and measurement services with its wide international testing facilities network.
All the fundamental antenna parameters listed above are measured and reported as per customer requirements. All types of antenna tests are performed and reported according to the “IEEE Standard Test Procedures for Antennas – IEEE Std 149™-1979 (R2008)” unless otherwise specified.
“IEEE Standard for Definitions of Terms for Antennas – Redline,” in IEEE Std 145-2013 (Revision of IEEE Std 145-1993) – Redline , vol., no., pp.1-92, 6 March 2014.
“IEEE Standard Test Procedures for Antennas,” in ANSI/IEEE Std 149-1979 , vol., no., pp.0_1-, 1979, doi: 10.1109/IEEESTD.1979.120310.