Antenna Gain Calculator

Yes, but with an important caveat: gain comes from narrowing the beam, so you must aim the antenna carefully. Replacing a 2 dBi omnidirectional antenna with a 12 dBi Yagi gives you 10 dB of extra signal - equivalent to a 10x increase in transmitter power or roughly tripling the range in free space. However, the Yagi has a beam only 30-40 degrees wide, so both ends of the link must point at each other. For fixed point-to-point links this is straightforward. For mobile or broadcast applications where coverage area matters, a high-gain antenna can actually hurt performance by leaving gaps in coverage.

Several real-world factors subtract from the rated figure. Impedance mismatch between the antenna and feedline causes some power to reflect rather than radiate, reducing effective gain. Cable losses between the transmitter and antenna consume power before it even reaches the radiating element. Polarization mismatch between transmit and receive antennas (for example, vertical vs. horizontal) can cost 3-20 dB. Nearby structures detune the antenna and alter its pattern. And many datasheets are measured in an anechoic chamber with an ideal feed, conditions that rarely exist in a real installation.

EIRP (Equivalent Isotropic Radiated Power) is referenced to an isotropic radiator, while ERP is referenced to a half-wave dipole and is therefore 2.15 dB lower than EIRP for the same installation. The FCC uses EIRP for most regulatory limits because it is unambiguous. For example, a transmitter putting out 23 dBm through 2 dB of cable loss and a 5 dBi antenna has an EIRP of 23 - 2 + 5 = 26 dBm.

Half-wave dipole: 2.15 dBi. Three-element Yagi: 7-8 dBi. Patch/microstrip: 5-8 dBi. Horn: 10-25 dBi. Parabolic dish: 20-45 dBi. A phased array scales with the number of elements: doubling the elements adds 3 dB. The trade-off is inescapable - higher gain means a narrower beam and a smaller coverage area.

G/T (gain-to-noise-temperature ratio) is the figure of merit for receive-only systems such as satellite dishes and radio telescopes. A higher G/T means the system can detect weaker signals. Pointing a dish at a warmer part of the sky raises the system noise temperature T and degrades G/T even though the gain G has not changed.