Field Strength Calculation
Below is a calculation tool to help determine the actual field Strength or power density (in V/M) at a given distance with a known antenna gain.
This calculation tool will assist:
EMC Field Strength Tools
Enter values and calculate. All calculations are based on free space conditions (impedance of 377 ohm).
1 Field Strength & Power Density
Inputs: Power (W), Gain (dBi or linear), Distance (m)
Numeric gain is linear ratio (e.g., 7 dBi ≈ 5.01 linear).
Field Strength
— V/m
Power Density
— W/m²
Formula
$$E\,(\mathrm{V/m})=\frac{\sqrt{30*P*10^{G_{\mathrm{dBi}}/10}}}{R}$$
$$S\,(\mathrm{W/m^2})=\frac{E^{2}}{\eta},\qquad \eta=377\ \Omega$$
* All calculations are based on free space conditions (impedance of 377 ohm)
2 Required Amplifier Power
Inputs: Desired field (V/m), Gain (dBi or linear), Distance (m)
Numeric gain is linear ratio (e.g., 7 dBi ≈ 5.01 linear).
Required Amplifier Power
— Watts
Formula
$$P\,(\mathrm{W})=\frac{\big(E\,R\big)^{2}}{30* 10^{G_{\mathrm{dBi}}/10}}$$
* This calculation helps determine required power to produce a desired field intensity using antenna gain and separation distance.
* All calculations are based on free space conditions (impedance of 377 ohm)
* All calculations are based on free space conditions (impedance of 377 ohm)
3 Required Antenna Gain
Inputs: Power (W), Required field (V/m), Distance (m)
Required Antenna Gain
— dBi
Formula
$$G_{\mathrm{dBi}}=10*log_{10}\!\left(\frac{\big(E\,R\big)^{2}}{30*P}\right)$$
* Calculate the required antenna gain using the maximum system power, desired field intensity and separation distance.
* All calculations are based on free space conditions (impedance of 377 ohm)
* All calculations are based on free space conditions (impedance of 377 ohm)