For a monopole antenna, the Earth – ground - reflects part of the waves, and it seems that they are coming from an image antenna – the other part of the dipole.

GP antenna mechanism of work

GP antennas do exactly that. Since we position antennas the highest we can, there must be a conductive element that acts as a reflective ground. For this purpose we can use an approximation of the ideal ground with 4 rods, each of the length of ¼ wavelength.

Impedance of the antenna will depend on the angle of the rods that imitate ground. Horizontal rods will give 35Ω, vertical “sleeve” will give as predicted (like vertical dipole) 75 Ω, and at the angle of approximately 40°, we will get the desired 50Ω.

GP antenna impedance

02 radiation pattern03 radiation pattern

 

Radiation pattern of the GP antenna

Data Table

 02

Construction

6m, FM and 2m

Construction Instructions are only for Registered Users. Please Register.

GP antenna 2m

06 GP Photo

Photos of a finished and mounted GP antenna for 2m band

 

70cm

Note that this same design can be used for 2m, however the above method is better in every aspect.

Construction Instructions are only for Registered Users. Please Register.

07 GP Photo

Photo of a finished and mounted GP antenna for 70cm band


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