Whitepaper
Considerations when Selecting an Antenna for an RF Immunity Test System
This brief technical paper from Com-Power Corporation outlines the key factors beyond frequency range that engineers must evaluate when choosing an antenna for RF immunity testing. Test distance is addressed first, showing mathematically that required amplifier power scales with the square of the test distance, meaning a change from one to three meters demands nine times the power. VSWR is then explained as a measure of impedance mismatch between the antenna and feed cable, with high VSWR causing significant power reflection and the need for increased drive power to achieve the required field strength. Physical antenna size is flagged as a concern in chamber environments, where long antenna elements can interact with walls or the ceiling and degrade field uniformity. Antenna gain over isotropic (expressed in dBi) is presented as a key figure of merit that directly reduces the power needed to generate a target field strength, though excessively narrow beam widths can complicate uniform illumination of the calibration plane. Return loss, the dB expression of the reflection coefficient, is explained as a complementary metric to VSWR where higher values indicate better impedance matching.