Antenna Factor
Understanding Antenna Factor
Antenna factor is essential for EMI compliance measurements. EMC regulations specify limits in field strength (dBuV/m or V/m), but the measurement instrument reads voltage (dBuV). The antenna factor bridges these two domains.
Antenna Factor Equation
- E (dBuV/m) = V (dBuV) + AF (dB/m)
- Where V is the voltage measured by the spectrum analyzer (corrected for cable loss).
- AF is the antenna's calibrated conversion factor at each frequency.
Typical Antenna Factors
| Antenna Type | Frequency | AF Range |
|---|---|---|
| Biconical | 30-300 MHz | 10-25 dB/m |
| Log-periodic | 200-1000 MHz | 15-30 dB/m |
| Horn | 1-18 GHz | 20-40 dB/m |
Frequently Asked Questions
What is antenna factor?
Antenna factor converts between electric field strength (V/m) and voltage at the receiver (V). AF = 20log(E/V). Used for EMI compliance measurements: E(dBuV/m) = V(dBuV) + AF(dB/m). Provided by calibration certificate.
Why is antenna factor important for EMC?
EMC regulations specify limits in field strength (V/m or dBuV/m). Measurement instruments read voltage (dBuV). Without the correct antenna factor, the measured voltage cannot be converted to field strength, and compliance cannot be determined.
How is antenna factor calibrated?
Antenna factor is determined by comparing the test antenna against a reference antenna of known characteristics (standard antenna method), or by using three antennas of unknown characteristics (three-antenna method). Calibration is traceable to national standards.