Does higher gain mean the antenna radiates more power?

No. An antenna is a passive device (excluding active antennas with integrated amplifiers). It cannot create power. Higher gain means the antenna concentrates the available power into a narrower beam, increasing the intensity in that direction at the expense of reduced radiation in other directions. A 20 dBi dish antenna does not produce 100 times more power than an isotropic antenna. It takes the same power and focuses it into a beam about 10 degrees wide, making the signal 100 times stronger in that narrow direction. The total radiated power is unchanged (minus ohmic losses). Think of it like a flashlight versus a bare bulb: same battery, different beam pattern.

What is the difference between dBi and dBd?

dBi references an isotropic radiator (a theoretical point source that radiates equally in all directions). dBd references a half-wave dipole, which has 2.15 dBi of gain. Therefore dBi = dBd + 2.15. A Yagi antenna with 10 dBd gain has 12.15 dBi gain. Manufacturers sometimes specify gain in dBd to make the number look more impressive (a 10 dBd antenna sounds better than a 12.15 dBi antenna). Always check the reference and convert to a consistent unit before comparing antennas. IEEE and most engineering specifications use dBi. Amateur radio traditionally uses dBd.

How does antenna size relate to gain?

For aperture antennas (dishes, horns), gain is directly related to the physical aperture area and the aperture efficiency: G = 4 pi eta A / lambda^2, where eta is the aperture efficiency (typically 0.5 to 0.7) and A is the physical area. Doubling the diameter quadruples the area and increases gain by 6 dB. For a 1-meter dish at 10 GHz (lambda = 3 cm): G = 4 pi times 0.6 times 0.785 / 0.0009 = 6,580 = 38.2 dBi. At 30 GHz with the same dish: the gain triples to 47.7 dBi. This is why satellite antennas can be small at Ku/Ka-band: the shorter wavelength provides the same gain with a smaller dish.

Antenna Tech

Antenna Gain

A cellular base station with a 120° sector antenna at 18 dBi gain concentrates its transmit power into a 120° horizontal and 7° vertical beam. Compared to an isotropic radiator, the signal is 63 times stronger in the beam direction. No extra power was created; the antenna simply redirected energy that would have gone sideways and backward into the forward beam. This is antenna gain: the ability to trade coverage angle for intensity. Every 3 dB of additional gain halves the beamwidth and doubles the effective radiated power in the main beam direction, extending the coverage range by about 40% (since power falls as distance squared).

Category: Antenna Tech

Unit: dBi (isotropic ref)

Formula: G = η × D

Gain Across Antenna Types

Antenna Type	Gain (dBi)	Beamwidth	Size (at 2.4 GHz)	Application
Isotropic (theoretical)	0	360° all planes	N/A	Reference only
Half-wave dipole	2.15	78° (E-plane)	62 mm	Omnidirectional base
Quarter-wave monopole	5.2	78° (E-plane)	31 mm + ground	Handheld, vehicle roof
Patch (single element)	6 to 8	70 to 90°	40 × 40 mm	WLAN, GPS, IoT
Sector (base station)	15 to 18	65 to 120° H, 5 to 7° V	250 × 1200 mm	Cellular macro
Parabolic dish (0.6 m)	30 to 34	3 to 5°	600 mm diameter	PtP microwave, satellite
Phased array (64 elements)	24 to 30	10 to 15° (steerable)	300 × 300 mm	5G mmWave, radar

Gain from aperture:
G = 4πηA / λ²
where η = aperture efficiency (0.5 to 0.7), A = physical area

Gain from beamwidth (approximate):
G ≈ 26,000 / (θ_H × θ_V) (degrees)

Gain = Directivity × Efficiency:
G(dBi) = D(dBi) + 10·log(η_rad)
A dipole has D = 2.15 dBi and η ≈ 98%, so G = 2.15 + (−0.09) = 2.06 dBi

Common Questions

Frequently Asked Questions

Does higher gain mean more power?

No. Antennas are passive. Higher gain concentrates existing power into a narrower beam. 20 dBi = 100× stronger in the beam direction but at the cost of reduced radiation elsewhere. Total radiated power is unchanged (minus ohmic losses).

dBi vs. dBd?

dBi references isotropic. dBd references a dipole (2.15 dBi). dBi = dBd + 2.15. A "10 dBd" antenna is 12.15 dBi. Always convert to the same reference before comparing. IEEE uses dBi; amateur radio uses dBd.

How does size relate to gain?

For aperture antennas: G = 4πηA/λ². Doubling diameter quadruples area and adds 6 dB. Higher frequency = more gain for the same dish size (shorter λ in the denominator). A 1 m dish: 38 dBi at 10 GHz, 48 dBi at 30 GHz.

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