Power Density Calculator
Calculate far-field power density, E/H field strengths, FCC/ICNIRP frequency-dependent MPE exposure margins, FSPL, and far-field boundary limits.
7
Inputs
Live
Math
3
Related
Enter parameters and click Calculate to view results
Formula & Theory
S = EIRP / (4πR²) | E = √(S · η₀) | H = E / η₀ | R_ff = 2D² / λ | FSPL = 20log10(d_km) + 20log10(f_MHz) + 32.44This formula is used to calculate antenna parameters for power density calculator.
Overview
Power Density helps you calculate design values for a rf conversion project from Input Mode (0: Direct EIRP in Watts, 1: Tx Power dBm + Antenna Gain dBi), Power Input (EIRP [W] if Mode 0 | Tx Power [dBm] if Mode 1), Antenna Gain (Used only if Mode = 1), Center Frequency (f), Distance from Antenna (R) [Boresight Axis], Largest Antenna Aperture Dimension (D), Custom MPE Limit (Set 0 to Auto-Calculate via FCC Rules). Calculate far-field power density, E/H field strengths, FCC/ICNIRP frequency-dependent MPE exposure margins, FSPL, and far-field boundary limits. Use the result to make an informed first design decision before choosing hardware, setting dimensions, or evaluating the RF system in its final environment.
Input Guide
Enter Input Mode (0: Direct EIRP in Watts, 1: Tx Power dBm + Antenna Gain dBi), Power Input (EIRP [W] if Mode 0 | Tx Power [dBm] if Mode 1), Antenna Gain (Used only if Mode = 1), Center Frequency (f), Distance from Antenna (R) [Boresight Axis], Largest Antenna Aperture Dimension (D), Custom MPE Limit (Set 0 to Auto-Calculate via FCC Rules) exactly in the units shown by this power density. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Input Mode (0: Direct EIRP in Watts, 1: Tx Power dBm + Antenna Gain dBi).
- Power Input (EIRP [W] if Mode 0 | Tx Power [dBm] if Mode 1) — use W / dBm.
- Antenna Gain (Used only if Mode = 1) — use dBi.
- Center Frequency (f) — use MHz.
- Distance from Antenna (R) [Boresight Axis] — use m.
- Largest Antenna Aperture Dimension (D) — use m.
- Custom MPE Limit (Set 0 to Auto-Calculate via FCC Rules) — use mW/cm².
Output Guide
The results describe the calculated power density values for the inputs you entered. Check each value against the available space, selected components, feed system, and operating conditions before making a final design decision.
How This Calculator Works
The Power Density uses S = EIRP / (4πR²) | E = √(S · η₀) | H = E / η₀ | R_ff = 2D² / λ | FSPL = 20log10(d_km) + 20log10(f_MHz) + 32.44. Supply Input Mode (0: Direct EIRP in Watts, 1: Tx Power dBm + Antenna Gain dBi), Power Input (EIRP [W] if Mode 0 | Tx Power [dBm] if Mode 1) (W / dBm), Antenna Gain (Used only if Mode = 1) (dBi), Center Frequency (f) (MHz), Distance from Antenna (R) [Boresight Axis] (m), Largest Antenna Aperture Dimension (D) (m), Custom MPE Limit (Set 0 to Auto-Calculate via FCC Rules) (mW/cm²) in the displayed units, then use the calculated values as the first engineering target for this rf conversion design or analysis.
Design Notes
This rf conversion calculation is based on S = EIRP / (4πR²) | E = √(S · η₀) | H = E / η₀ | R_ff = 2D² / λ | FSPL = 20log10(d_km) + 20log10(f_MHz) + 32.44. Real-world accuracy depends on factors such as material properties, losses, mounting, nearby conductors, ground interaction, feed-line effects, and construction tolerance. Confirm the final system with measurement or simulation.
Build and Tuning Notes
Apply the power density result as an initial target, then validate it in the intended installation. Keep the physical layout and feed arrangement consistent while testing, change one parameter at a time, and record the measured outcome before making another adjustment.
Frequently Asked Questions
What does the Power Density calculate?
Calculate far-field power density, E/H field strengths, FCC/ICNIRP frequency-dependent MPE exposure margins, FSPL, and far-field boundary limits. The calculation provides an initial design value based on Input Mode (0: Direct EIRP in Watts, 1: Tx Power dBm + Antenna Gain dBi), Power Input (EIRP [W] if Mode 0 | Tx Power [dBm] if Mode 1) (W / dBm), Antenna Gain (Used only if Mode = 1) (dBi), Center Frequency (f) (MHz), Distance from Antenna (R) [Boresight Axis] (m), Largest Antenna Aperture Dimension (D) (m), Custom MPE Limit (Set 0 to Auto-Calculate via FCC Rules) (mW/cm²).
Which inputs are needed for the Power Density?
Enter Input Mode (0: Direct EIRP in Watts, 1: Tx Power dBm + Antenna Gain dBi), Power Input (EIRP [W] if Mode 0 | Tx Power [dBm] if Mode 1) (W / dBm), Antenna Gain (Used only if Mode = 1) (dBi), Center Frequency (f) (MHz), Distance from Antenna (R) [Boresight Axis] (m), Largest Antenna Aperture Dimension (D) (m), Custom MPE Limit (Set 0 to Auto-Calculate via FCC Rules) (mW/cm²) using the displayed units. Each value directly affects the calculated result, so confirm the unit and operating conditions before running the calculation.
How accurate is this power density?
It follows S = EIRP / (4πR²) | E = √(S · η₀) | H = E / η₀ | R_ff = 2D² / λ | FSPL = 20log10(d_km) + 20log10(f_MHz) + 32.44. It is accurate for the formula assumptions, but installed performance can change because of materials, loss, environment, mounting, nearby objects, and measurement uncertainty.
What should I do after using the Power Density?
Compare the result with the practical constraints of your rf conversion system, then validate the completed design with appropriate measurement equipment or simulation.
Alex Warren
B.Sc. in Electrical & Electronic Engineering (EEE)
Alex specialises in antenna design and wave propagation. His expertise helps ensure these calculators present practical RF concepts, useful design estimates, and clear engineering guidance for students, HAM operators, and wireless professionals.