Antenna tidbits everyone needs to know

Antenna tidbits


Antennas are not as complicated as many people make them out to be. There are certain laws of physics that come into play. There is no answer for the question “What is the best antenna?”.  It all depends on what you want it to do for you.

I have a list of what I call tidbits about antennas that might help explain a few things.


First of all no antenna can radiate the power supplied to it in all directions. It just is not possible. However if there was such an antenna and it could do that then it could be used as a baseline or reference to compare all other antennas to.

Any real antenna would radiate more energy in some directions than this reference antenna and less energy in other directions. Using mathematics we can calculate what the strength of a signal would be if it was radiated from such an antenna and then we could measure the signal strength from a real antenna and compare the two. 

That is exactly what we do! We can also calculate the signal strength from real antennas also. It’s more precise if we pretend we are out in free space and nothing is around to affect the radiation. If we do this either by calculations or going out into space we find that a simple half wave dipole has a gain in some directions and a loss is other directions when compared to the ideal antenna that radiated equal in all directions. The dipole in free space has a gain of 2.14 dB over this ideal antenna, but only directly broad side to the dipole. 

We have named this ideal fictional antenna an isotopic antenna. The dipole in free space is said to have 2.14 dBi gain. That means 2.14 dB gain over an isotopic antenna. In free space it does not matter if the dipole is horizontal or vertical, but here on earth it makes a big difference. 

The radio wave from a horizontal dipole has a horizontal Electric field while from a vertical the Electric field is perpendicular to the earth. The earth reflects the two waves very differently.

The earth reflections normally do not add in phase with the direct radiation from a vertical but they do from a horizontal antenna. That almost always gives the horizontal antenna an advantage over the vertical. With the horizontal the height above the ground really matters when determining gain. With the vertical that does not matter so much if at all.

The bottom line is that the free space gain of a dipole of 2.14 dB increases by about 6 dB due to ground reflections. This fact is in the antenna handbooks but is often overlooked by many. 

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