V antenna
A V antenna is a directional antenna that serves as a transmitting and receiving antenna in the frequency range from approx. 1 MHz to approx. 1 GHz. It belongs to the group of long-wire antennas and was invented by Lindenblad in 1928 and described in a patent in 1930 by Philip Staats Carter at the Radio Corporation of America (RCA).
Structure and description
With the V-antenna, the V-shaped arrangement of two horizontal long-wire antennas increases the directional effect and the antenna gain . This creates a bidirectional directional antenna (effective in two directions). The gain of a V antenna is around 3 dB higher than that of a single wire of the same length, provided that the optimal spread angle alpha has been selected.
With increasing leg length, the antenna gain in the main beam direction increases, and at the same time the bundling of the beam becomes sharper. The optimal spread angle depends on the leg length; it becomes smaller with increasing leg length. With a V antenna, the leg length is relatively uncritical. The angle of spread is very critical, especially with large leg lengths. The spread angle causes the main lobes in the directional diagram of the two antenna branches to be in phase.
The following empirical relationship applies to the calculation of the spread angle:
- α = angle of spread
- λ = wavelength
- l = leg length (length of the individual wires)
The main beam direction of the antenna is in the direction of the bisector. The elevation angle of the radiation is relatively small. The V antenna is therefore particularly suitable for the high-frequency shortwave bands.
The V antenna is fed in a voltage curve, which is why it has a high-resistance input impedance. Multi-band operation is possible when using a coordinated feed line. In single-band operation, it is more advantageous to feed the antenna via an unmatched feed line, via a closed quarter-wave stub line. With large leg lengths, the input resistance is approx. 600 Ω .
Completed V antenna
A closed V-antenna is a directional antenna which is used as a transmitting and receiving antenna in the frequency range from approx. 1 MHz to approx. 1 GHz. It belongs to the group of long-wire antennas and was described in 1933 by Philip Staats Carter in a patent (PS Carter - US 2,099,296 - 1933).
3 masts and 2 terminating resistors are required to set up the antenna. The earthing of the terminating resistors is critical, as their distance from the earth normally corresponds to the height of the mast. The grounding problem can be solved by using an artificial earth. The artificial earth is formed from λ / 4 long wires that are connected to the terminating resistors. However, this makes the antenna more frequency-dependent or narrower band. In multi-band operation, separate λ / 4 lines are required for each band.
The adapted, symmetrical feed line of the closed V antenna has a wave impedance of approx. 450 Ω to 600 Ω. The closed V antenna can be excited using any length 50 Ω coaxial cable . For this, a feed point is at the toroidal - Balun 9: used 1: 1 to 12th
Completed inverted V antenna
A closed inverted V antenna , also: half rhombus antenna , is a directional antenna that serves as a transmitting and receiving antenna in the frequency range from approx. 1 MHz to approx. 1 GHz. It belongs to the group of long wire antennas and was described in 1929 by E. Bruce in a patent (E. Bruce - US 1,899,410 - 1929).
Closed inverted V antennas are mainly used in the form of vertically constructed, obtuse-angled V-radiators. The vertical construction has the advantage that only one central mast is required and that the terminating resistor can be directly earthed. In this version the antenna is mixed polarized. The main radiation runs unidirectionally (effective on one side) in the direction of the antenna end terminated with the terminating resistor.
As with the open version of the inverted V antenna, the optimal spread angle α depends on the leg length l. The values for the closed version of the inverted V antenna are roughly the same. The optimal terminating resistance is approximately 600 Ω. It has the same value as the impedance of the antenna. The impedance depends only slightly on the frequency. This also results in an input impedance of around 600 Ω. The input impedance is real over a very large frequency range.
A typical area of application of the closed inverted V antenna are e.g. B. Scatter Measurements.
literature
- Rothammels Antennenbuch , DARC Verlag GmbH, Baunatal 2002, ISBN 3-88692-033-X , p. 248f, p. 257f
- Rothammels Antennenbuch , DARC Verlag GmbH, Baunatal 2002, ISBN 3-88692-033-X , pp. 257f
- Rothammels Antennenbuch , DARC Verlag GmbH, Baunatal 2002, ISBN 3-88692-033-X , pp. 258f.