Antenna Radiation Calculator

Calculator inputs

Mode

Directivity converts to gain using efficiency.

Frequency (MHz)

Example: 900, 2400, 5800.

Distance r (m)

Used for FSPL, S, E, and H values.

Transmit power

Watts convert to dBm internally.

Antenna gain (dBi)

Used when mode is Gain.

Directivity (dBi)

Used when mode is Directivity.

Efficiency (%)

Typical ranges are 40 to 90 percent.

TX feedline loss (dB)

Coax or waveguide insertion loss.

TX mismatch loss (dB)

Enter 0 if unknown.

Other TX losses (dB)

Filters, splitters, connectors, radome.

Receiver gain (dBi)

Set 0 for isotropic receiver.

Receiver losses (dB)

Cable, filter, and connector losses.

Largest antenna dimension D (m)

Used for far-field estimate: 2D^2/lambda.

S limit (W/m^2)

Set 0 to disable check.

E limit (V/m)

Set 0 to disable check.

Formulas used

These are standard engineering relations for free-space and far-field behavior.

EIRP (dBm) = Ptx(dBm) + Gt(dBi) - Ltx(dB)
Efficiency gain: G(dBi) = D(dBi) + 10*log10(eta), where eta is 0..1
FSPL (dB) = 32.44 + 20*log10(f_MHz) + 20*log10(d_km)
Friis received power (dBm) = EIRP(dBm) + Gr(dBi) - FSPL(dB) - Lrx(dB)
Power density S = EIRP(W) / (4*pi*r^2)
E-field magnitude E = sqrt(30*EIRP(W)) / r
H-field magnitude H = E / 377
Fraunhofer distance Rff = 2*D^2 / lambda, and lambda = c/f

How to use this calculator

Enter frequency and distance. Use meters for distance.
Enter transmit power in watts or dBm.
Select Gain mode or Directivity plus efficiency.
Add realistic TX and RX losses for better accuracy.
Optionally enter antenna size for a far-field check.
Optional limits can flag results for quick review.
Press Compute. Download CSV or PDF when ready.

Example data table

Scenario	f (MHz)	r (m)	Ptx	Gt (dBi)	Ltx (dB)	Approx FSPL (dB)
WiFi point-to-point	2400	100	1 W	14	2	~80.0
Sub-GHz link	900	1000	20 dBm	6	1	~91.5
5 GHz backhaul	5800	500	30 dBm	23	2	~101.7

FSPL values are rounded for illustration. Use the calculator for exact results.

Technical article

1) Why EIRP is the starting point

EIRP combines transmitter power, antenna gain, and transmitter losses into one number. It is the best single indicator of how strongly an antenna system radiates in its maximum direction. Engineers use EIRP to compare systems with different radios and antennas fairly.

2) Loss budgeting improves realism

Cable insertion loss, connector loss, filter loss, and mismatch loss reduce delivered power. A 2 dB loss means only about 63% of the power reaches the antenna. Including these values prevents optimistic results and makes compliance checks more meaningful.

3) Free-space path loss and distance scaling

FSPL increases with both frequency and distance. For example, at 2400 MHz and 100 m, FSPL is about 80 dB. At 900 MHz and 1 km, it is about 91.5 dB. These numbers explain why higher frequencies usually need more gain for the same range.

4) Received power using Friis

The Friis relation links EIRP, receive antenna gain, and FSPL to estimate received power. It is widely used in link budgets. When receiver-side cable losses exist, subtracting them keeps the received estimate aligned with actual radio input power.

5) Power density and field strength metrics

Power density S is expressed in W/m^2 and is often used for exposure assessment. The electric field magnitude E in V/m is derived from EIRP under far-field conditions. These metrics help compare emissions against limits and design separation distances.

6) Far-field validation matters

Far-field assumptions are typically valid beyond the Fraunhofer distance, Rff = 2D^2/lambda. Larger antennas and higher frequencies increase Rff. Entering the largest antenna dimension lets the calculator warn when the chosen distance may be near-field.

7) Engineering use cases

This calculator supports WLAN planning, point-to-point links, outdoor RF assessments, and educational labs. It can also support quick sensitivity checks by varying gain, frequency, or distance. Export options help preserve calculations for audits and documentation.

8) How to interpret results professionally

Use EIRP and FSPL for link feasibility, then review received power against receiver sensitivity. For safety analysis, review S and E using realistic losses and antenna size. If the far-field check warns, treat E and H estimates as approximations only.

FAQs

1) What does EIRP represent?

EIRP is the equivalent isotropic radiated power. It combines transmitter power, antenna gain, and transmitter losses into a single value that indicates maximum directional radiation strength.

2) When should I use directivity and efficiency?

Use it when you know directivity from geometry or simulation and want realistic gain. Efficiency accounts for losses like conductor and dielectric loss, lowering gain relative to directivity.

3) Are E and H always accurate?

E and H are far-field approximations. If your distance is below the Fraunhofer distance, the near-field can dominate and these simple expressions may not represent the real field distribution.

4) Why do I need cable and connector losses?

Losses reduce power delivered to the antenna and power delivered to the receiver input. Even 1 to 3 dB can noticeably change EIRP, received power, and exposure metrics.

5) What units should I use for distance?

Use meters. The calculator converts to kilometers internally for FSPL and keeps field calculations in standard SI units for power density and field strength.

6) How is received power computed?

Received power uses the Friis transmission equation in dB form: Pr = EIRP + Gr - FSPL - receiver losses. It is best for line-of-sight free-space assumptions.

7) What do the limit checks do?

Limit checks compare the computed S and E against your entered thresholds. If a limit is set to 0, that check is skipped to avoid accidental false failures.