Antenna Test Range basics | Antenna Range Types
This page covers antenna range basics and mentions antenna range types which include near field and far field antenna test ranges.
As we know antenna is the device used as electromagnetic (EM) transformer.
It is used to send and receive EM Waves to/from the air.
Following are the parameters need to be evaluated for RF antenna.
• Input Impedance
• Frequency range
• Radiation Efficiency
• Radiation Pattern
Antenna test range is required in order to test and measure above mentioned antenna
parameters. Selection of antenna test range depends on following parameters.
• RF Antenna specifications as listed above
• Mechanical specifications of antenna e.g. size, volume, weight
• Accuracy of antenna measurement to be done
The perfect antenna measurement depends on monitoring and control of following parameters
other than the right antenna range selected as per need.
• Incident field phase variation
• Incident field amplitude vatiation
• Interference due to reflections
Antenna test range used for radiation pattern measurement consists of following sub systems.
• Positioning and control: AUT is installed on positioner and is tested in receiving mode. It is rotated using control unit and pattern measurement is captured.
• Receiver: It is other equipments used for capturing the RF signal and used to vary different axis for measurement.
• Signal source:It is used to provide RF signal for remote AUT. It is fixed on the ground floor.
• Recording and processing: Positioner placed at test antenna side is used for this purpose.
Antenna Range Types
Following are the types of antenna ranges:
• Outdoor far-field antenna range
• Indoor far-field test antenna range
• Compact antenna test range
• Near-field antenna Range
Near-field antenna Range
The figure-1 depicts near field antenna range. The distance or range from antenna upto 2*D2/λ is known as nearfield distance. Here D is the aperture diameter of AUT (Antenna Under Test) and λ is the operating wavelength.
This antenna test ranges are usually used to test antenna indoors in small space. It uses small RF probe on one side and the AUT (Antenna Under Test) on the other side. The distance or seperation between the two is about 4 to 10 wavelength long. Either RF probe is scanned and AUT is kept fixed or AUT is moved and RF probe is kept fixed during measurement. During the measurement both amplitude and phase information is collected at discrete points as determined.
Based on scanning method, there are three types of near field methods viz. planar, cylindrical and spherical.
Compact antenna test range
The figure-2 depicts compact antenna test range. This is supplement to traditional farfield antenna range. The testing carried out in farfield can also be done in compact antenna test range.
The advantage of such test range is testing is done in indoor anechoic chamber. This will avoid all the weather and security related concerns while testing. One can avoid interference generated by other sources with the use of shielding chamber. This facility is very convenient for R & D engineers due to its compact size.
Indoor far-field antenna test range
The figure-3 depicts indoor far field antenna test range. The distance or range from antenna above 2*D2/λ is known as farfield range or distance. Anechoic chamber is used heer. There are three main entities in this antenna range viz. receiver front end, signal source and positioner. Antenna Under Test (AUT) is located on positioner. Polarization control is available with source antenna. control room is connected to both the ends of antenna range using cables or links. As entire equipments are located indoorand enchoic chamber is used the test facility is known as indoor far-field range.
Outdoor far-field antenna range
The figure-4 depicts outdoor far field antenna range. The test system consists of test antenna with receiver front end and positioner,source antenna and outdoor enclosure. The outdoor enclosure protects the setup from weather and temperature effects. The receiver portion is remotely controlled using control console. Both sides are fixed on tower or supporting structure opposite to each other.