To: All Subject: Need sanity check for one point of antenna theory Here goes:
The gain of any antenna is referenced to a theoretical isotropic radiator. A half wave resonant dipole (in free space) has a gain of 2.15 dB over an isotropic source; hence it's rated at 2.15 dBi. A quarter wave, end fed, monopole rod, erected normal to an infinite ground plane, displays a field pattern equal to one lobe, or one half, of the pattern formed by the dipole antenna. The ground plane serves as an image, or mirror, of the other half of this resonant system. So, the monopole directs the radiant energy into only one hemisphere (above the ground plane), at the expense of no radiation into the other hemisphere (below the ground plane). From the vantage point of those observers located above the ground plane, the monopole creates a field with twice the power of a dipole. And, since twice the power is a 3 dB increase, then the gain of a quarter wave ground plane rod is 3 dBd, or 5.15 dBi. Uhhhh, right? -------------------------- Ed Price [email protected] Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 List-Post: [email protected] Date: 07/16/97 Time: 16:56:26 --------------------------
