Meaning
Microwave measurement laboratories use highly stable antennas with mathematically predictable radiation patterns to calibrate test systems. The device known as a standard gain horn consists of a flared waveguide structure designed to provide a precise, repeatable gain over a specific frequency band. Because its geometry is highly controlled, its electrical performance can be calculated with high precision.
It is the primary reference antenna used in radio frequency test chambers.
Antenna Reference
Test engineers require a known standard to determine the absolute gain of an antenna under test. When utilizing a standard gain horn, the device is mounted on a positioner to act as either the transmitter or receiver in a calibrated path. The measured power is compared to the calculated power to determine the system response.
This comparison eliminates variables associated with the test environment itself.
Chamber Calibration
Over-the-air test chambers must be characterized regularly to ensure the accuracy of the measurements performed within them. For this procedure, a standard gain horn is placed in the center of the quiet zone to measure the path loss of the chamber. The test system scans the frequency range of interest and records the received power at each frequency step.
This dataset forms the calibration table used to correct all subsequent measurements of active devices. Using a standard gain horn ensures that the path loss values are traceable to national metrology standards and are free from structural resonance effects.
Accuracy Factor
Measurement uncertainty depends heavily on the mechanical stability and surface finish of the reference antenna. A standard gain horn is typically constructed from gold-plated or silver-plated brass to prevent corrosion and minimize conductor losses. The precise dimensions of the horn flare must be maintained to prevent changes in the phase center of the antenna.
This physical stability ensures that the gain remains constant over many years of laboratory use.
