Chapter 8

Antenna placement and groundplane:
Groundplane is the term used to describe the reflective effect on RF signal when an antenna is placed on a piece of steel. When an antenna radiates energy (signal) it will radiate energy in all directions. Some energy will be radiated towards the ground; hence a substantial portion energy is wasted. Radio frequency microwaves cannot penetrate steel and when an antenna is placed on steel, the energy that radiates towards the ground is reflected by the steel to the air. This effect has a profoundly beneficial effect on signal range. An effective groundplane should be at least 1 wavelength wide; this is a little greater than 14 inches for the cellular communication frequencies.

There are several popular locations to mount cellular antennas. The best location is the center of a vehicle roof where it is unobstructed and has a large metal surface (groundplane) under it.

A second choice would be a mirror mount, fender mount or pole-mount using a thru-hole type antenna that passes through a metal mounting bracket. When this type of mounting is used it is recommended that an antenna with a built-in groundplane is used. Antennas with coils, symmetrical horizontal protrusions and other methods are designed for use in places where a metal groundplane is unavailable. An antenna with a built in groundplane will be effective if it is designed well.

A third and very popular mounting type is known as on-glass. This type of antenna mounting configuration is the least efficient of all. This type of antenna does not have the benefit of groundplane and transfers the signal by an electrical phenomenon that is called capacitive coupling. There is signal loss between the antenna and the coupling box on the inside of the glass hence this type of antenna configuration will have inferior performance when compared to the same antenna with same antenna cable that is connected directly to the co-ax cable. It is important to understand that an antenna's gain number and type of antenna mast (radiator) is less significant than how it is connected and where it is placed.