Telecommunications – Transmitter – Diversity
Patent
1996-04-09
1998-11-24
Louis-Jacques, Jacques H.
Telecommunications
Transmitter
Diversity
455524, 455562, H03C 702, H04B 102, H04B 702
Patent
active
058421173
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an antenna system for small basic or base transmitter-receiver stations of a communications system for mobile radio operators of the type wherein each base transmitter-receiver station is for a system having at least two transmission channels and two associated reception channels, wherein transmitters and receivers of each base transmitter-receiver station operate on separate frequencies, and with at least two antennas which are embodied for redundant reception, or of the type wherein each base transmitter-receiver station is for a system with at least one transmission channel and one reception channel associated with this transmission channel, wherein the transmitter and receiver of the base transmitter-receiver station operate on separate frequencies, with at least two antennas which are embodied for redundant reception.
Antenna systems of this kind have been disclosed for use in mobile radio communication systems. One of these antenna systems is based on a three-antenna solution, see FIG. 1, wherein one of the antennas is used exclusively as a transmitting antenna, wherein the channels to be transmitted are combined by means of diplexers or coupler networks and are fed into the transmitting antenna. The two other antennas are used only for receiving, wherein each antenna receives all channels and wherein the antennas are affixed so that the reception of the antennas is independent and consequently the desired redundancy is guaranteed.
Another known antenna system uses only two antennas, see FIG. 2, wherein the one antenna is used as a combined transmitting and receiving antenna and the other is used exclusively as a receiving antenna for the redundant reception of the channels operated. The transmission and reception signals of the combined antenna are separated by a corresponding diplexer. In this embodiment, the transmission channels are also to be combined via combination networks of frequency filters or couplers before they are supplied to the antenna.
The combination networks which are necessary for this have a few fundamental disadvantages. Combination networks which are based on filters allow only a minimal channel spacing, for example three times the channel raster (600 kHz to 200 kHz). Despite the use of high quality dielectric resonators, these filters additionally have a not inconsiderable attenuation, e.g., up to 2.5 dB at 1850 MHZ. As a rule, these filters are tuned to a fixed channel frequency and can only be re-tuned to other channel frequencies with a coupled mechanical drive. This process therefore does not allow a rapid change of channel frequencies as is often desired in modern systems. FIG. 3 shows a channel combination network with filters, and it can be clearly seen how large and complex a system of this kind, with monitoring and tuning control, turns out to be.
In contrast, combination networks based on hybrids are very compact, permit a very narrow channel spacing, and also allow a rapid change of channel frequencies in the system, since tuning is no longer necessary. However, they have a systemrelated high transmission loss: In the four-channel combination network with 3 dB couplers according to FIG. 4, a power loss of more than 6 dB is obtain ed for each channel.
A further disadvantage of the known antenna systems consists in that when feeding a plurality of transmission signals to a transmitting antenna, intermodulation signals are produced which can impair the functioning of the system. The probability that these intermodulation products end up on the frequency bands of reception channels increases exponentially with the number of transmission channels fed in. Furthermore, the interference output also increases very sharply with the number of transmission channels. With the two-antenna embodiment (FIG. 2), this turns out to be particularly disadvantageous because in this case the signals reach the reception amplifier without isolation, while with the three-antenna embodiment according to FIG. 1, an antenna decoupling of ap
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Cluse Dieter
Rosenberg Uwe
Ant Nachrichtentechnick GmbH
Arthur Gertrude
Louis-Jacques Jacques H.
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