Antenna gains are sometimes specified as Gd and sometimes as Gi. What do these gain terms mean? Open


Antenna gain is specified in some different ways that are confusing. The first is Gain referenced to an isotropic radiator (G subscript i) which is an antenna that radiates omni directionally and equally in all directions. A dipole antenna in this specification has a gain of about 3 dB Gi. However,an isotropic radiator doesn't exist in the real world. Any efficient antenna has more gain than an isotropic radiator. Even a simple 1/4 wave whip antenna has a gain of 3dB Gi. Since it radiates its power only above the ground plane, or into half free space it has a Gi of 3 dB. 

The other way of specifying the gain of an antenna is referenced to a dipole (or G sub d ). Obviously a dipole has a gain of 0 dB or unity referenced to Gd. The dipole is just referenced to a dipole. 

As an example, our ALP600 log periodic antenna has a gain of 4 dB Gd or 4 dB better than a dipole. If we wanted bigger, more impressive numbers, we would just rate it at 7db Gi. 

The ALP600 is more directional than a dipole of course, in fact 4 dB more directional. Gain is always proportional to directionality. Most of the directionality is in the vertical plane or up and down. The horizontal plane, left to right, which concerns you, is +- 60 degrees or 120 degrees total for a gain equal or better than a dipole.

Posted 3 years agoby LectroAdmin

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