Vertical antennas form a widely used form of radio antenna. Used in a number of specific areas, their properties enable them to provide performance that horizontal or other antennas are unable to provide.
In view of their properties, vertical antennas are used in many areas from medium wave broadcasting, to mobile communications and many other applications.
Vertical antenna properties
The properties and advantages of vertical antennas enable them to be used in a variety of different areas.
Some of the vertical antenna properties and advantages include:
- Omnidirectional radiation pattern: Single element vertical antennas exhibit an omnidirectional radiation pattern in the horizontal plane. This means that the signal will spread out equally in all directions.
- Vertically polarised radiation: Having a vertical element, or elements, these antennas radiate vertically polarised signals. This is an advantage when the signal is being received by other vertically polarised antennas.
- Propagation considerations: Vertically polarised radiation has some advantages for lower frequency propagation modes. For example ground wave propagation, used for LF and some MF transmissions is often better when a vertically polarised antenna is used. For HF the propagation modes mean that signals of either polarisation may be used. There are some studies that indicate that horizontally polarised low angle radiation is better for long distance communications if the antenna can provide a sufficiently low angle of radiation, i.e. a vertical antenna may produce more low angle radiation, but horizontally polarised radiation may on some occasions provide better results..
- Provides low angle of radiation: The signal that emanates from a vertical antenna tends to have a low angle of radiation. Accordingly there is less at higher angles, i.e. directed towards the sky, and more that can be received by other terrestrial stations. It also has advantages for long distance ionospheric communications where a low angle of radiation will assist in gaining additional distance. Some vertical antennas are designed to increase the low angle radiation, further reducing the level at higher angles and thereby providing additional gain over a vertical dipole or quarter wave vertical.
- Space occupied: The space occupied by a vertical antenna is normally less than that occupied by an equivalent horizontally polarised antenna. Some vertical antennas use a ground plane and the space occupied by this will need to be taken into consideration to gain a complete view.
- Ease of mounting: Vertical antenna types are normally easy to mount, requiring a single mounting at the base.
- Windage: In some instances the wind resistance of a vertical antenna may be less than that of a horizontally mounted equivalent. Figures need to be checked for each instance.
Grounding vertical antennas
Many vertical antennas are what are termed monopole antennas and require the use of a ground for their proper operation.
The ground can implemented in one of two main ways:
- Physical earth connection: The most obvious method is to make a physical connection to the earth using ground rods and the like.
Note on antenna RF grounding:
Grounding an antenna can be key to its operation, particularly if it is a vertical monopole antenna where the ground forms part of the antenna.
Read more about antenna RF ground.
- Ground plane system: It is also possible to simulate a ground system using what is termed a ground plane. This is often made up from a number of typically quarter wavelength radials.
Note on antenna ground plane:
Apart from using a direct connection to ground, it is also possible to use a 'simulated' ground consisting of a conducting plate or a number of radials. The advantage of this scheme is that it can be raised above the real ground to improve the coverage.
Read more about antenna ground plane.
Vertical antenna types
There are many different types of vertical antenna that have been designed and are in common use. Some of the more popular are mentioned below:
- Quarter wave vertical: The quarter wave vertical antenna type is one of the most popular forms of vertical antenna. It is easy to construct, it can be made to be very robust and provides a good level of performance. This form of antenna requires the use of a connection to ground (connection as short as possible), or a ground plane. This increases the space required and windage of the antenna.
- Five eighths wave vertical: This form of vertical antenna is popular in many instances because it is able to provide gain over a quarter wave vertical, focussing more power in a plane closer to the horizontal. As such it is used in many applications. Like the basic quarter wave vertical, this antenna also needs a ground plane against which to operate.
- J pole antenna : This type of vertical antenna is a convenient for of vertical antenna. It provides some gain over a quarter wave vertical and has the advantage that it does not require any radials or some form of ground plane against which to operate.
- Vertical dipole: The vertical dipole is used in some instances to provide a robust form of vertical antenna. It has the advantage that it does not require any radials, but does require to be a minimum of a half wavelength long.
Vertical antennas are able to operate particularly well in many instances. Utilising their advantages means that the best can be made of what they have to offer, but against this the disadvantages should also be considered as well.
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