Calculator Input Form
Example Data Table
Use these sample values to test the calculator and compare different engineering approaches for the same concept.
| Scenario | Inputs | Approx. Directivity | Approx. dBi |
|---|---|---|---|
| Panel antenna from beamwidth | Azimuth 30°, Elevation 24°, Constant 41253 | 57.30 | 17.58 dBi |
| Dish from aperture | 5800 MHz, Area 0.18 m², Aperture efficiency 70% | 591.80 | 27.72 dBi |
| Measured intensity case | Umax 3.5 W/sr, Prad 0.42 W | 104.72 | 20.20 dBi |
Formula Used
D ≈ K / (HPBWaz × HPBWel)Use degrees for both beamwidth values. A common constant is
41253.
D = (4πAe) / λ²Ae = Aphysical × ηapertureλ = c / f
D = (4πUmax) / PradThis method is useful when measured radiation intensity and total radiated power are available.
D(dBi) = 10 log10(D)ΩA = 4π / DGain ≈ ηradiation × D
How to Use This Calculator
- Select the calculation method matching your available design or measurement data.
- Enter operating frequency if wavelength-dependent calculations are needed or desired.
- Provide radiation efficiency to estimate gain from directivity.
- For beamwidth mode, enter azimuth and elevation half-power beamwidth values.
- For aperture mode, enter physical area and aperture efficiency.
- For power mode, enter maximum radiation intensity and total radiated power.
- Submit the form to display results above the form, including dBi and beam solid angle.
- Use the CSV and PDF buttons to export the visible result block.
Frequently Asked Questions
1) What is antenna directivity?
Directivity measures how strongly an antenna concentrates radiated power in its strongest direction compared with an isotropic radiator using the same total radiated power.
2) How is gain different from directivity?
Directivity ignores internal losses. Gain includes radiation efficiency, so gain is usually lower than directivity for real antennas.
3) When should I use the beamwidth method?
Use it when you know the antenna half-power beamwidths but do not have detailed field measurements or effective aperture information.
4) Why does frequency matter in aperture mode?
Frequency sets wavelength, and wavelength appears squared in the aperture formula. Higher frequency often increases directivity for the same effective aperture.
5) What does beam solid angle mean?
Beam solid angle represents the angular spread of the antenna pattern in steradians. Smaller beam solid angle generally means higher directivity.
6) Can directivity be below one?
An ideal isotropic radiator has directivity exactly one. Practical antennas are usually one or higher in their main direction when evaluated correctly.
7) Is higher directivity always better?
No. Higher directivity narrows coverage. It helps point-to-point links and radar, but wider patterns are often better for broad-area coverage.
8) Which units are used here?
Beamwidth is in degrees, beam solid angle is in steradians, frequency is in megahertz, area is in square meters, and power is in watts.