Calculator Inputs
Formula Used
The calculator first converts frequency into wavelength.
λ = c / f
Then it estimates parabolic dish gain.
G = η × (πD / λ)²
The result in dBi is:
G(dBi) = 10 × log10(G)
Surface loss is estimated with the Ruze factor.
R = e-(4πσ / λ)²
Net gain subtracts feed, cable, pointing, polarization, radome, and atmospheric losses.
Net gain = real gain - total losses
The 3 dB beamwidth estimate is:
Beamwidth ≈ 70 × λ / D
How to Use This Calculator
- Enter the physical dish diameter and select its unit.
- Enter the operating frequency and select the correct unit.
- Add aperture efficiency. Use 55 to 70 percent for many practical dishes.
- Enter surface RMS error when reflector accuracy matters.
- Add known feed, cable, pointing, polarization, radome, and atmospheric losses.
- Enter transmit power if you want EIRP output.
- Enter system noise temperature if you want G/T output.
- Press calculate. The result appears above the form.
- Use the CSV or PDF buttons to save the result.
Example Data Table
| Example | Diameter | Frequency | Efficiency | Added loss | Real gain | Net gain | Beamwidth |
|---|---|---|---|---|---|---|---|
| Small Ku dish | 0.75 m | 12.2 GHz | 62% | 1.2 dB | 37.275 dBi | 36.075 dBi | 2.2935° |
| C band station | 2.4 m | 4 GHz | 65% | 0.9 dB | 38.103 dBi | 37.203 dBi | 2.186° |
| Microwave link | 0.6 m | 18 GHz | 58% | 1.5 dB | 38.487 dBi | 36.987 dBi | 1.9431° |
Dish Antenna Gain Guide
A dish antenna focuses radio energy toward one direction. This focused pattern gives more signal than a simple radiator. The gain depends on dish diameter, frequency, and efficiency. A larger reflector captures more energy. A higher frequency also raises gain because the wavelength becomes shorter.
Why gain matters
Gain helps estimate link strength for satellite, microwave, Wi-Fi backhaul, radar, and radio astronomy work. It tells how strongly the dish concentrates power. The result is usually shown in dBi. This means gain compared with an ideal isotropic antenna. Engineers use dBi because it fits link budgets and path loss equations.
Main input factors
Diameter is the physical size across the reflector. Frequency sets the wavelength. Efficiency accounts for feed blockage, spillover, illumination taper, surface errors, and manufacturing limits. Real dishes rarely reach perfect efficiency. Many practical dishes use values between 55% and 70%. Precision antennas can be higher.
Loss and surface control
Total loss reduces usable gain. Cable loss, radome loss, polarization mismatch, and pointing errors can all lower the final value. Surface accuracy also matters at high frequency. A rough reflector scatters energy. The Ruze correction estimates this loss from surface RMS error and wavelength. It is very useful for microwave and millimeter wave dishes.
Beamwidth and aperture
Beamwidth shows how narrow the main lobe is. A narrow beam gives stronger focus but needs better aiming. Effective aperture shows the useful collecting area after efficiency is applied. These values help compare antennas with different shapes, feeds, and operating bands.
Planning advice
Use measured data when available. Calculator results are estimates. They are best for early design, equipment comparison, field checks, and education. For critical links, add fade margin and check manufacturer antenna patterns. Also confirm local rules before transmitting. A clean gain estimate still needs safe installation, stable mounting, and accurate alignment.
Common use cases
Satellite television installers use gain to match dish size with weak signals. Amateur radio operators use it for moonbounce and narrow microwave contacts. Network designers use it for long point-to-point paths. Researchers use it to compare receiving sensitivity. In every case, small errors in frequency, size, or efficiency can change the final dBi result. Save each run for later project comparison.
FAQs
What is dish antenna gain?
Dish antenna gain shows how strongly a reflector focuses radio energy in one direction. It is usually given in dBi, which compares the dish with an ideal isotropic radiator.
Why does frequency affect gain?
Higher frequency means shorter wavelength. For the same dish diameter, a shorter wavelength increases the diameter-to-wavelength ratio. This raises gain and narrows beamwidth.
What efficiency should I use?
Many practical dishes use 55% to 70%. Poor feeds or rough surfaces can be lower. Precision antennas with good feeds can be higher.
What is Ruze surface loss?
Ruze loss estimates gain reduction caused by reflector surface error. It becomes more important when wavelength is short, such as microwave and millimeter wave operation.
What is net usable gain?
Net usable gain is real dish gain after subtracting added losses. It is often better for link budgets than raw dish gain alone.
Why is beamwidth useful?
Beamwidth estimates how narrow the main antenna beam is. Narrow beams give stronger focus, but they require more accurate aiming and stable mounting.
Can I use this for satellite links?
Yes. It is useful for early satellite link planning. For final designs, compare results with measured antenna data and full link budget requirements.
What is EIRP?
EIRP means equivalent isotropic radiated power. It combines transmitter power and net antenna gain to estimate radiated strength in the main beam.