Antennas for transmitting DAB signals are similar to other broadcast transmitting antennas, but the dielectric strength has to be increased.
If DAB transmitting antennas shall be installed on existing antenna supports, very often the problem appears that there is no free space nor load capacity reserves on the masts.
Some typical examples shall demonstrate how DAB transmitting antennas can be realized without additional load of the antenna support.

1. Antenna types for DAB in Band III (223-240 MHz)

1.1 Omnidirectional antenna for installation at the top of a mast
If the top of a mast is free, a very good omnidirectional antenna can be installed with vertical dipoles. In order to achieve a gain of 6 dB, 4 dipoles can be installed one above the other, if a fibre glass tube is used as carrying element. The near field of these omnidirectional antennas should be kept free of conducting obstacles, as otherwise the input impedance will be influenced and the radiation diagrams may be drastically changed.

1.2 Vertical dipole row for side mounted installation on a mast
The influence of the mast can be controlled, if a defined reflector is positioned in direction to the mast. Picture 1 shows such an antenna, where two dipoles are connected and are fed via a 2-way splitter installed in the reflector tube.

1.3 Single polarized dipole panels
Dipole panels with vertical dipoles in front of a reflector screen have been used for a long time, and by interconnecting them to antenna groups omnidirectional diagrams and differently formed directional diagrams can be created.

1.4 Double polarized dipole panels
Dipole panels with horizontal and vertical dipoles have been used for a long time to produce slant or circular polarisation in the FM broadcasting.

If the construction is transfered to the band III range (see picture 2 above), it is also possible to put different signals on the dipoles (i.e. TV on the horizontal and DAB on the vertical radiators), as they are well decoupled (about 40 dB) if the reflector symmetry to the main axes is kept.
Such an antenna system which can transmit TV and DAB signals simultaneously, loads a mast only little more than does an antenna for only one polarization, as the fixing and reflector screens are commonly used.
The dimensioning can be optimized in such a way that similar radiation patterns result for both polarizations.

2. Antenna types for DAB in the L-Band (1452-1492 MHz)

2.1 Omnidirectional antenna for the installation on top of a mast
For omnidirectional antennas dipoles are installed one above the other in a fibre glass tube . According to the higher frequency the dimensions are considerably smaller than in band III. 2.2 Vertically polarized dipole panels
The vertically polarized dipole panels are so small that the whole arrangement of dipoles and reflector screen can be housed in a flat weather-protected case (see picture 3).

Dipole panels are availabe with half wave beam widthes of the horizontal diagram of 65ø to 160ø. In order to increase the gain, pairs of dipoles are installed one above the other, and the installation and interconnection is done inside the weather-protected case so that the antenna group looks like one unit.

3. Antenna systems for DAB

3.1 Extension of a TV transmitting antenna to a TV-DAB antenna
The broadcasting station Merkur had a normal antenna for channel 7. There was no space for an additional DAB antenna, as the mast was completely covered with antennas.By exchanging the present antennas against double-polarized dipole panels (as described in item 1.4) - keeping the feeder network and the fixing construction - a DAB transmitting antenna could be realized easily (see picture 4). 

Without changing the radiation pattern for TV, an own directional diagram for DAB was created by optimizing the feeding of the vertical dipoles. 3.2 Multi-panel DAB TV transmitting antenna
In the lower part of a mast a TV emergency antenna was planned. This free capacity can be used to realize a TV DAB transmitting antenna, if double polarized dipole panels are used. The diameter of the space reserved at the mast is so big that in case of a normal arrangement of 4 panels per bay deep minima of up to 7 dB would result in the horizontal diagram.Therefore a multi-panel arrangement was designed with eight dipole panels per bay which provides good horizontal diagrams even for a big mast diameter of 2 m (see picture 5).

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KATHREIN-Werke KG Rosenheim
last update 14.03.2000