Technical data
Table Of Contents
- EMC Measurement Application Measurement Guide
- Table of Contents
- 1 EMC Measurements
- 2 Conducted Emissions Measurements
- 3 Radiated Emissions Measurements
- A: Line Impedance Stabilization Networks (LISN)
- B: Antenna Factors
- C: Basic Electrical Relationships
- D: Detectors Used in EMI Measurements
- Glossary of Acronyms and Definitions
30
Antenna Factors
Field Strength Units
Field Strength Units
Radiated EMI emissions measurements measure the electric field. The field strength is
calibrated in dBμV/m. Field strength in dBμV/m is derived from the following:
P
t
= total power radiated from an isotropic radiator
P
D
= the power density at a distance r from the isotropic radiator (far field)
P
D
= P
t
/4πr
2
R = 120mΩ
P
D
= E
2
/R
E2/R = P
t
/4πr
2
E = (P
t
x 30)
1/2
/r (V/m)
Far field
1
is considered to be >λ/2π
Antenna factors
The definition of antenna factors is the ratio of the electric field in volts per meter
present at the plane of the antenna versus the voltage out of the antenna connector.
NOTE Antenna factors are not the same as antenna gain.
1. Far Field is the minimum distance from a radiator where the field becomes a planar wave.