The Effects Of Angle Of Antenna Height Radiation And Gain

The Effects of Angle of Antenna Height

Radiation and Gain

The effects of antenna height on gain and angle of radiation has been the subject of discussions for many years. Many pages have been written about what happens to an antenna when you increased its height above ground. So, to shed a little light on the subject, we will take two antennas and see what happens as the height is increased in quarterwave increments. The antennas used in this case will be a 1/2 wave vertical antenna on 10 meters and a 1/2 wave 10 meter dipole. Both antennas are resonant on 28.5 MHz.

The Vertical

We will first take the vertical antenna and look at its patterns. Figure Vertical-1 is the vertical radiation pattern of this antenna.

Figure Vertical-2 is the three-dimensional pattern of this antenna. This is a typical circular pattern of a vertical antenna and shows the deep null directly overhead.

Click here to look at Graph-1. The angle of radiation of the antenna can be seen to change as a height of the antenna is increased by one quarter wavelength. At ground level, the radiation angle is 20 degrees and decreases to three degrees at 144 feet (43.9m). View Graph-2 which shows how as the height is increased, the gain increases. The gain of this antenna starts out at minus 1.8 dB and increases to 4.5 dB at 144 feet. Now click for Graph-3 which is a combination of the previous two graphs, and displays all of the parameters.

Sorry but the Graphs mentioned above were not backed up – MD0MDI.

The Dipole

The next antenna we will examine will be the 10 meter dipole. The diagram Figure Dipole-1, is of the antenna at 16 feet above ground, and the diagram Figure Dipole-2 is the vertical radiation pattern of this antenna.

Again, Sorry No Graphs!

Graph-4 is the graph of gain versus height as the height is increased from 16 feet (4.9m) to 144 feet. You see, both from the figures and graph, at 16 feet the gain is 4.56 dB which increases to 5.8 dB at 144 feet. This is an increase in signal strength of 1.24 dB. This is very little increase in signal strength for such a great increase in height. Graph-5 is height versus radiation angle. At 16 feet, the radiation angle is 30 degrees above the horizon and as the antenna height is increased to 144 feet, the angle has decreased to three degrees. Graph-6 is gain versus radiation angle and be compared easily on this graph.

Graph-7 is a comparison of radiation angles of the dipole and the vertical antenna. It can be seen that the vertical antenna starts out with a much lower angle of radiation than the dipole. As height is increased, the angle of radiation of the dipole begins to catch up to the vertical antenna and at 112 feet, the radiation angle is the same. From this point, the angle of radiation of the two antennas is the same, varying only slightly until they reach the maxim height, 144 feet. At this height, the two antennas are only 1.55 dB apart. This is not a significant amount and under normal conditions on 10 meters, would barely be noticeable.

Graph-8 is a gain comparison of the dipole versus the vertical antenna. It can be seen that the vertical starts off at a loss compared to the dipole, but by the time both antennas reach maximum height, the difference is very slight at only 1.55 dB. Of course, the dipole has the advantage of being directional and the vertical does not. The horizontal pattern of both antennas does not change much as a height is increased. However, the vertical patterns of both show evidence of many lobes being created by reflection of in phase and out of phase energy from the ground. This can be seen in Figure Vert-3 and in Figure Dipole-3, but the major lobes of both antennas can be seen easily seen at the extremely low angle presented in the diagrams.

The conclusion to be reached is that height can make a difference in both radiation angle and gain. However, the change in height of the horizontal polarized antenna seems to make little difference in gain, but a fairly large amount of difference in radiation angle. The vertical antenna started out at zero gain, but caught up to the dipole rapidly. The vertical also started out having a much lower angle of radiation than the dipole. This is an advantage, even though it had less gain than the dipole at the lower altitude. The amount of difference in gain between the two antennas is not a significant amount. Therefore, it is easy to conclude that for a horizontal antenna such as a dipole, height has a minimal effect on gain. However, increasing height of the dipole has a far greater effect on radiation angle. The vertical antenna is a different story, as increases in heights appear to affect both radiation angle and gain more than more than the dipole.

So the effects of height does affect the performance of an antenna, but, how much depends on the type of antenna and its polarization. Keep in mind these antennas were analyzed under ideal conditions, clear of any surrounding conductors that could cause interference.

For those who are interested, the 10 meter band was used in our examples to keep the dimensions and heights within reason. Besides, with the sunspots heading towards a maximum, ten meters will really start to open more and more for DX contacts. Later on, there will be another article on the effects of height on the lower frequency antennas.

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

Last Updated : 22nd April 2024