What is antenna gain?

Antenna gain is the ratio of radiation intensity in the peak direction to the intensity of an isotropic (omnidirectional) radiator fed with the same power. It is expressed in dBi (decibels relative to isotropic).

How do you calculate antenna gain from aperture?

G = η × (4π × A) / λ², where A is the physical aperture area, λ is wavelength, and η is aperture efficiency (typically 0.55–0.70 for dishes).

What is the gain of a half-wave dipole?

A half-wave dipole has a gain of 2.15 dBi (1.64 linear). It is the practical reference antenna, and gains expressed in dBd are relative to a dipole.

What is the difference between dBi and dBd?

dBi is gain relative to an isotropic antenna. dBd is gain relative to a half-wave dipole. dBi = dBd + 2.15. Always check which reference is used in datasheets.

Effective Isotropic Radiated Power: EIRP = P_transmit × G_linear, or EIRP_dBm = P_tx_dBm + G_dBi. It represents the apparent power an isotropic antenna would need to produce the same peak signal.

How does frequency affect gain for a fixed dish?

Gain increases with the square of frequency for a fixed aperture: G ∝ f². Doubling frequency adds 6 dB of gain because the aperture captures more wavelengths.

What is aperture efficiency?

Aperture efficiency η is the ratio of effective aperture to physical aperture: η = Ae/A. It accounts for illumination taper, spillover, blockage, and surface errors. Typical values: 0.55–0.70 for dishes, 0.50–0.80 for horns.

G/T (gain-to-noise-temperature ratio, in dB/K) is a figure of merit for receive systems. Higher G/T means better sensitivity: G/T_dB = G_dBi − 10×log10(T_system).

What gain do I need for a 10 km point-to-point link?

Depends on frequency, data rate, and receiver sensitivity. For 5.8 GHz: FSPL ≈ 128 dB. With 30 dBm Tx, 20 dBi antenna each side, received power ≈ 30 + 20 − 128 + 20 = −58 dBm — well above typical −80 dBm sensitivity.

Antenna Gain Calculator – dBi, Effective Aperture, EIRP & G/T

Antenna Parameters

G = 4π A_e / λ²

📐 Effective Aperture Area (Aₑ)

The area of the antenna that captures incoming signal energy

0.00110 m²

〜 Wavelength (λ)

Wavelength of the signal (λ = c / f)

0.0011 m

📻 Frequency (Optional) — Auto-fills λ

Enter frequency to calculate wavelength automatically

0.1100 GHz

Gain (Linear)

3490.66

Gain (dBi)

35.43 dBi

Aperture (Aₑ)

0.25 m²

Wavelength (λ)

0.030 m

Very High Gain Antenna

ℹ️

Antenna gain increases with larger aperture area (Aₑ) and decreases with the square of wavelength (λ). At higher frequencies (shorter λ), the same dish provides more gain.

⚙️ Calculation Steps

Determine the effective aperture area (Aₑ) in m².

Determine the wavelength (λ) in meters. Use λ = c / f if frequency is known.

Apply the formula: G = 4π × Aₑ / λ²

Convert to dBi if needed: G_dBi = 10 × log₁₀(G)

Compare against reference table for antenna type classification.

📊 Live Calculation

Step 1 — Aperture Area

Aₑ = 0.2500 m²

Step 2 — Wavelength

λ = 0.0300 m

Step 3 — Linear Gain

G = 4π × 0.25 / 0.03² = 3490.66

Step 4 — Gain in dBi

G_dBi = 10 × log₁₀(3490.66) = 35.43 dBi

📋 Quick Reference — Antenna Types

Antenna Type	Frequency Range	Typical Gain (dBi)	Typical Use
Isotropic Antenna	All	0 dBi	Reference standard
Dipole Antenna	100 MHz – 1 GHz	2 – 3 dBi	AM/FM, general purpose
Yagi-Uda Antenna	100 MHz – 1 GHz	6 – 15 dBi	TV reception, amateur radio
Log-Periodic Antenna	100 MHz – 3 GHz	7 – 12 dBi	Broadband reception
Horn Antenna	1 – 100 GHz	10 – 25 dBi	Microwave links, radar
Patch Antenna	1 – 10 GHz	6 – 12 dBi	GPS, WiFi, mobile devices
Parabolic Dish	1 GHz – 100 GHz	20 – 50+ dBi	Satellite comms, radar
Phased Array	1 – 100 GHz	25 – 50+ dBi	Radar, 5G base stations

Antenna Gain Calculator — Complete Guide to dBi, Aperture & EIRP

This antenna gain calculator computes gain in dBi and linear from effective aperture area, wavelength, and aperture efficiency using the fundamental formula G = η × 4πA / λ². It also calculates EIRP, effective aperture, and provides a common antenna gains reference table — everything you need for link budget analysis, antenna selection, and RF system design.

Key Gain Formulas

Parameter	Formula	Unit
Gain from aperture	G = η × (4π × A) / λ²	linear
Gain in dBi	G_dBi = 10 × log₁₀(G)	dBi
Wavelength	λ = c / f = 3×10⁸ / f	metres
Effective aperture	A_e = η × A_physical	m²
EIRP	EIRP = P_tx × G or P_dBm + G_dBi	W or dBm
G/T ratio	G/T = G_dBi − 10×log₁₀(T_sys)	dB/K
dBi ↔ dBd	dBi = dBd + 2.15	—

Common Antenna Gain Reference

Antenna Type	Gain (dBi)	Gain (linear)	Typical Use
Isotropic (theoretical)	0	1.0	Reference only
Short dipole / rubber duck	1.5	1.4	Handheld radios
Half-wave dipole	2.15	1.64	Reference (0 dBd)
Quarter-wave monopole	5.15	3.28	Vehicle, base station
Patch / microstrip	5–9	3–8	Wi-Fi, RFID, IoT
Yagi-Uda (5-element)	8–10	6–10	TV, amateur, P2P
Horn antenna	10–25	10–316	Feeds, radar, test
1 m dish @ 10 GHz	~38	~6300	Satellite, microwave
3 m dish @ 12 GHz	~48	~63000	Earth station

Worked Examples

📡 Example 1 — 0.6 m Parabolic Dish at 5.8 GHz, η = 0.60

GivenD = 0.6 m → A = π(0.3)² = 0.2827 m², f = 5.8 GHz → λ = 0.0517 m, η = 0.60

Step 1A_e = 0.60 × 0.2827 = 0.1696 m²

Step 2G = 4π × 0.1696 / (0.0517)² = 2.1356 / 0.002673 = 798.9

Step 3G_dBi = 10 × log₁₀(798.9) = 29.0 dBi

ResultGain = 29.0 dBi | HPBW ≈ 70×0.0517/0.6 = 6.0° — good for outdoor P2P

📶 Example 2 — EIRP of a 30 dBm Transmitter with 12 dBi Antenna

GivenP_tx = 30 dBm (1 W), G = 12 dBi

Step 1EIRP = 30 + 12 = 42 dBm

Step 2In watts: 10^(42/10) / 1000 = 15.85 W

ResultEIRP = 42 dBm = 15.85 W — check against regulatory limit (e.g., 36 dBm for 5 GHz)

Gain vs Frequency for Fixed Aperture

Frequency	λ (m)	Gain (1 m² dish, η=0.6)
1 GHz	0.300	22.2 dBi
2.4 GHz	0.125	29.8 dBi
5.8 GHz	0.052	37.5 dBi
10 GHz	0.030	42.2 dBi
28 GHz	0.011	51.2 dBi
60 GHz	0.005	57.8 dBi

Practical Applications

Link budget: Gain at both ends directly sets received power: P_rx = P_tx + G_tx − FSPL + G_rx.
Regulatory compliance: EIRP limits (e.g., FCC Part 15, ETSI EN 302 502) constrain the product of transmit power and antenna gain.
Satellite earth stations: High-gain dishes (35–50 dBi) compensate for the huge FSPL to geostationary orbit (~200 dB at Ku-band).
Radar: G² appears in the radar range equation — doubling gain extends detection range by ~1.4×.
5G mmWave: Small apertures at 28–60 GHz still deliver 25–35 dBi thanks to the short wavelength.

Frequently Asked Questions

Can an antenna amplify a signal?

An antenna doesn't add energy — gain means it concentrates existing energy in a narrower beam. Higher gain = more energy in the forward direction, less to the sides and rear.

How does dish size affect gain?

Gain scales with the square of diameter: G ∝ D². Doubling the dish diameter quadruples the gain (+6 dB) and halves the beamwidth.

Related Calculators

Antenna Beamwidth Calculator — HPBW, FNBW, directivity, beam pattern
Antenna Aperture Efficiency — effective vs physical aperture
Attenuation Calculator — dB, FSPL, cable loss, link budget
ADC Calculator — resolution, SNR, ENOB