Looking At Antenna Patterns

One of the most useful things anyone can have to work with when you deal with antennas is the determination of expected signal patterns. The patterns are usually calculated in a perfect environment, over a perfectly conducting ground with no other conductors in the field to cause any distortion. However, in the real world this is not a normal situation, but for the purpose of experimentation this type of approach is adequate.

Patterns can be displayed in either horizontal or vertical display, but even some folks have a difficult time figuring out where the viewpoint is located. For the vertical pattern, the viewpoint is along the Y-axis as shown by line A in the diagram below. This axis is on the ground and you are usually located at right angles to the antenna off the ends of a dipole for instance. The horizontal pattern is viewed from straight above line B. In all the patterns you seen in antenneX and other publications, the patterns are all marked off in degrees with 0 degrees directly in front of the antenna and 180 degrees directly behind the antenna for the horizontal pattern. Vertical patterns are marked off in the same way with 0 degrees and 180 being on ground level and 90 degrees being straight up.

Patterns are also marked off with decreasing size circles and marked with numbers in dB that usually get larger as the circles get smaller. These numbers enable you to see how much signal drop takes place in the pattern nulls with reference to the maximum, which is the gain of the antenna. The patterns here also show the angle above the horizon that the pattern was measured. Vertical patterns also show nulls and peaks and you will see what angles the maximum radiation takes place. This will give a good idea of how good a DX antenna would be. The lower the angle of radiation the better the DX antenna.

The part of the pattern sticking out the most is called the major lobe and the smaller ones are called minor lobes. It is possible to have two equal sized major lobes, such as in the case of bi-directional antennas like a dipole. Sometimes there are antennas that produce a pattern with four major lobes, much in the shape of a four-leaf clover.

In the antenneX articles, as you may have noticed, there are numerous 3D patterns produced by a computer program. Many times seeing what the antenna looks like in 3D will give a better understanding of how the antenna should work and how its radiated or received signal behaves.

There are many more details to be determined from an antenna pattern calculation and this little discussion has only touched the surface to give a basic explanation of what may be found by looking at the various patterns.

Originally posted on the AntennaX Online Magazine by Richard Morrow, K5CNF

Last Updated : 12th March 2024