# V Beam Antenna Basics

## The V beam antenna (not to be confused with the inverted V) is a form of long wire antenna sometimes used on the HF bands to provide gain and directivity.

The V beam antenna, not to be confused with the inverted V antenna is a form of antenna based around long wire technology that is occasionally used on the HF bands to provide good levels of gain.

The antenna gets its name from the fact that two long wire elements are arranged in a V shape, and it can provide some very good levels of gain.

This type of antenna is not widely seen these days, especially with the fall in use of HF radio communications, but it can be used where a fixed direction of radiation is required.

Sometimes where space is not an issue the V beam antenna is an ideal option, providing very high levels of gain, and where several lengths of wire can be erected in a radial fashion, the direction can be switched by connecting in the required legs of the antenna.

## V antenna concept

It is well known that if the length of a wire antenna is extended so that it becomes long compared to the wavelength, typically a few wavelengths, then the lobes of the maximum radiation progressively tend towards the axis of the wire.

It can be seen that as the length of a single wire is increased the major lobes align progressively with the axis of the wire. This increases further as the length increases further.

Gain and Angles for Major Lobes on Long Wire Antennas
Length (λ) Angle of main lobe Gain (dBd)
1 54° 0.4
42 1.0
2 36° 1.5
33° 1.8
3 30° 1.8
4 26° 3.3
5 22° 4.2
6 20° 5.0
8 18° 6.4
10 16° 7.4

Notes:
• The gain of the major lobes is measured in decibels compared to a dipole, dBd.
• The figures are given for the major lobes as shown in the diagrams above.
• Apart from the major lobe, there are also minor ones with less gain.

The reason that this occurs may not be totally intuitive, but it arises from the phases of the waveform on the antenna. These add and subtract at different angles.

## V beam antenna

The V beam antenna consists of two wires extending out from the apex in a V shape. It is fed at the apex, typically with open wire feeder as the impedance is normally quite high.

The V beam antenna utilises the lobes of the end fed wires and uses two wires angled apart so that the main lobes of the wires reinforce each other to provide a directive beam antenna.

The lobes thata re not within the main axis tend to be out of alignment with each other and they tend to cancel, although as with any antenna, there will be minor lobes away from the main radiation beam.

The beam antenna in this form has a bidirectional radiation pattern, radiating equally in both directions as indicated on the diagram.

The directivity and gain of these antenas depends upon the length of the legs in terms of their wavelength and the apex angle as the lobes need to conicide to reinforce the main radiation along the axis of the antenna.

Under ideal conditions, good levels of gain can be achieved and the table below summarises the length of the antenna legs as well as the apex angle and the maximum gan likely to be seen.

Gain and Angles for Major Lobes on Long Wire Antennas
Leg length (λ) Gain (dB) Angle of apex (degrees °)
1 3 108
2 4.5 70
3 5.5 57
4 6.5 47
5 7.5 43
6 8.5 37
7 9.3 34

The feed impedance of the antenna at the apex point is high and as a result the antenna is best fed with an open wire form of feeder - 600Ω would be a good choice. It can be as high as 2000Ω or so for short beams, but 800 - 1000Ω in longer ones.

This feeder can be matched to the more usual 50Ω feed systems and output impedances of transmitters and receivers using a tuning / matching unit as the open wire feeder is likely to have a high VSWR level itself.

In terms of the masts, the mast at the feed point is often made to be the highest and the remote ends are often lower as this saves on cost.

it is worth noting that if a V beam is designed for use on one particular frequency or band, then it can normally be used very successfully on higher frequency bands. The radiation pattern and lobes from the individual wires will changes as the number of wavelengths along the wire changes with the frequency, but the general bidirectional radiation pattern along the axis of the antenna will remain albeit with some changes.

In an ideal world, the antenna operates best if it is at a height of one wavelength at the main frequency of operation, but this can obviously be difficult to achieve. Lower heights can still give very satisfactory results, although the low angle radiation is reduced a little.

Although the V beam is not viable for many situations these days, various antennas of this form have been used very successfully by people and organisations with sufficient land and space. They provide high levels of gain and if multiple legs can be erected, these can be switched in as required to give the required beam orientation.