EP0227005B1 - Transmitting device comprising two microwave transmitters radiating different frequencies with different radiation patterns - Google Patents

Description

The invention is based on a transmission device according to the preamble of the main claim.

It is known to interconnect two or more RF transmitters that operate on different transmission frequencies via crossovers with a common antenna so that the individual transmitters are decoupled from one another via the crossovers and do not influence one another (VHF-FM / Am transmission systems for Radio, Info No. 3-012 D1 by Rohde & Schwarz, pages 30 to 33; TELECOMMUNICATIONS AND RADIO ENGINEERING, volume 28/29, No. 6, June 1974, pages 45 to 48; REVIEW OF THE ELECTRICAL COMMUNICATION LABARATORY; Volume 18, No. 3/4, March / April 1970, pages 179-202). This means, for example, that two or more radio transmitters operating on frequencies in the FM radio range from 87.5 to 100 MHz can use a common antenna and broadcast their program with the same radiation pattern in the same coverage area. In recent times, the expansion of the FM radio range by the band between 100 and 108 MHz has created the need to delimit the transmitters to different coverage areas. For example, the same or very close frequencies in the new band range from 100 to 108 MHz were assigned to transmitters that are directly in neighboring countries work. For a transmitter working in this area in the border area, an antenna with omnidirectional radiation pattern can no longer be used, as was previously the case in the 87.5 to 100 MHz range, but an antenna with a specified directional radiation pattern must be used for this, so that only its own coverage area is covered and the transmitter operating on the same frequency in the neighboring country is not disturbed.

It is obvious to use two separate antenna systems for this purpose, as is known in shortwave transmitters, in which several separate shortwave antennas of different designs and radiation directions are set up side by side, which can be fed by several shortwave transmitters with different power and frequency simultaneously or in succession . In the present case, it would be obvious to install two separate antenna systems on the same mast or possibly even to nest them (e.g. according to Meinke-Grundlach, Taschenbuch der Hochfrequenztechnik, Springer Verlag Berlin, 1968, p. 597). With this solution, however, the individual antenna systems would have to be decoupled from one another, which would be very complex and expensive, especially since only antenna systems are suitable for this which are different from one another for the required mutual decoupling, that is to say have different polarization, for example.

It is therefore an object of the invention to provide a transmission device which, with a simple antenna system, enables the transmissions of two or more radio frequency transmitters, in particular VHF radio transmitters, to be emitted not only with a different transmission frequency but also with a different radiation diagram.

This object is achieved on the basis of a transmission device according to the preamble of the main claim by its characterizing features. Advantageous further developments result from the subclaims.

In the transmission device according to the invention, one and the same antenna is used not only for radiating the transmissions from several high-frequency transmitters at different transmission frequencies, but also with a different radiation pattern, for which purpose only the individual fields of the common antenna are divided into two or more separate groups and each combined in a separate feed cable will. Using known crossovers and power distributors, these groups can then be interconnected with the transmitters in such a way that, for example, one transmitter in the FM radio range transmits 87.5 to 100 MHz on any frequency as before with an omnidirectional diagram, while a second transmitter emits, for example, in the range from 100 to 108 MHz with a predetermined directional beam diagram. This allows the antenna system to be constructed very simply and in a space-saving manner, since only a single antenna is used for different radiation patterns. It is even possible to retrofit a known transmitter antenna, which consists of several antenna fields arranged around a mast and in several levels one above the other and which is operated as an omnidirectional antenna for the previous FM radio range from 87.5 to 100 MHz Modify cables and divide them into groups so that an additional transmitter with a corresponding directional diagram can be operated in the new range from 100 to 108 MHz, for which it is only necessary to set up additional high-frequency crossovers between the transmitters. The solution according to the invention is much simpler and cheaper than the obvious measure to use two separate transmit antennas. The measure according to the invention is not only for the FM radio range of Advantage but can also be applied to TV antennas or the like. However, because of the relatively large space requirement of FM radio antennas, the invention is particularly suitable for this.

The crossover and power distribution arrangement for mutually decoupled interconnection of the transmitters with the feed lines for the antenna groups can be made from known crossovers (for example according to pages 30 to 33 of the Rohde & Schwarz publication mentioned above) and also power distributors known per se, which divide the distribution as desired Output power of the transmitter on two or more outputs in a predetermined power sharing ratio allow to be put together. Known neutral points (page 31 of the Rohde & Schwarz publication mentioned above) can be used for this purpose, however, which however presuppose that all transmitters only work on a fixed predetermined transmission frequency. If a broadband solution is desired, directional couplers (page 32 of the Rohde & Schwarz publication) are preferably used, which is particularly advantageous for VHF radio broadcasting systems. Instead of neutral points or directional couplers, other known non-reactive parallel circuits can also be used for frequency division, as described, for example, in Meinke-Grundlach, 3rd edition 1968, pages 1441-1451.

The costs of directional couplers are essentially determined by the band filters arranged between the directional couplers of the narrowband input, by means of which the power of the is reflected by the second transmitter and, after addition in the second directional coupler, is fed to the antenna group provided for this purpose. According to an advantageous development of the invention according to subclaims 5 to 7, a crossover and power distribution arrangement is therefore proposed which is particularly simple in construction and, above all, can also be produced at low cost, since the number of bandpass filters used is one Minimum is limited.

The invention is explained in more detail below with the aid of schematic drawings using several exemplary embodiments.

Fig. 1 shows a transmission device according to the invention using a known directional coupler transmitter switch W, which consists of two directional couplers R, two band filters F tuned to the same frequency and a terminating resistor K and which has a narrowband input C, a broadband input B and a common output Z. . The first transmitter S1 operating on a frequency f1, for example in the range 100 to 108 MHz, is connected to the narrowband input C, the second transmitter S2 operating on a frequency f2, for example in the frequency band 87.5 to 100 MHz, is via a 1: 1 power distributor V. on the one hand connected to the broadband input B of the switch W and on the other hand to the feed line L2, which is connected to the group G2 of the antenna. In the exemplary embodiment shown, the antenna consists of four antenna fields A1 to A4, which are arranged in a rectangle around an antenna mast and preferably still above one another in a plurality of antenna levels (see, for example, antenna to the side 34 to 35 of the R&S publication specified above). The antenna fields A1 and A2 are combined to the antenna group G2, the other two antenna fields A3 and A4 to the group G1, which is connected to the output Z of the switch W via the feed line L1. The group G2 would emit isolated radiation with a directional diagram D2, the group G1 with a directional diagram D1 in the opposite direction. The same half of the transmission power N2 of the transmitter S2 is fed to the two antenna groups G1 and G2 via the distributor V and the switch W, which results in the omnidirectional radiation pattern D3. The bandpass filters F of the switch W are tuned to the frequency f1 of the transmitter S1, so that the full transmitter power N1 of the transmitter S1 is fed via the narrowband input C to the output Z and thus only to the group G1, the transmitter S1 therefore only radiates with the directional diagram D1 from. A predetermined directional beam diagram D1 is thus achieved for the transmitter S1 via one and the same antenna, while an omnidirectional diagram D3 is produced for the transmitter S2. The two transmitters are mutually decoupled via the switch.

Fig. 2 shows a solution with two directional couplers W1 and W2 using two power distributors V1 and V2. The distributor V1 has a distribution ratio of 1: 4, the distributor V2 again has a distribution ratio of 1: 1. With this arrangement, the transmitter S2 again feeds half the power into the antenna groups G1 and G2, and this transmitter S2 therefore emits again with an omnidirectional diagram D3. The transmitter S1, on the other hand, feeds the first group G1 with a fifth of the total power N1 via the distributor V1 and the switches W1 and W2, while the groups G2 are fed with 4/5 of the power N1. This creates a flattened one Directional diagram D1, which mainly emits via group G2, but partly with 1/5 of the power also via group G1 in the opposite direction.

In this way, the most varied radiation patterns for the two transmitters S1 and S2 can be put together by means of corresponding power distributors and corresponding division of the antenna fields into combined groups. It is of course also possible, for example, to combine the antenna fields A1, A2 and A3 into a group and to use the antenna field A4 only as a second group. Any other division is also conceivable. Of course, the invention can also be used with antennas consisting of fewer or more than four antenna fields arranged around a mast. The division of the fields arranged one above the other in several levels can also be carried out in different ways in the individual antenna groups, so that not only the horizontal diagram but also the vertical diagram of the antenna can be selected differently in the individual groups.

Since the transmitter S2 feeds the broadband input B of the directional coupler, it can also operate in a known manner by means of additional switches connected in cascade (pages 33 of the R&S publication) in the specified frequency band on several different frequencies, which are then all emitted with the omnidirectional diagram D3 .

For certain tasks it may also be desirable to operate multiple transmitters with more than two different radiation patterns. For example, if three different transmitters are to emit with three different radiation patterns, all that is necessary is that to divide existing antenna fields into three groups so that these alone or in combination with each other each result in the three desired radiation patterns. These three different antenna groups then only have to be interconnected with the transmitters via appropriate switches and distributors in such a way that, despite mutual decoupling of the transmitters, these each feed those antenna fields which give the desired radiation diagrams. In this way, more than three antenna groups can of course also be formed. It is also possible to interconnect three or more transmitters with a corresponding number of switches with two or more antenna groups, the number of possible combinations for transmitters and different assigned radiation patterns is arbitrary and depends only on the type of division of the antenna fields into groups and the type of the switches used. By suitable selection of the filters F in the crossovers, it is also possible, for example, to connect two transmitters operating at relatively close adjacent frequencies via the narrowband input C, as a result of which the number of crossovers can be reduced for the interconnection of several transmitters. This could be achieved, for example, by appropriately wide bandpass filters or high or low pass filters.

The power distributors V are of a known type, in the simplest case they are power transformers with a corresponding transformation ratio. The transmission ratio can be chosen as desired and depends only on the desired power distribution among the antenna groups, i.e. on the desired radiation pattern.

The manufacturing costs of a directional coupler switch W used in the exemplary embodiments according to FIGS. 1 and 2 are essentially determined by the bandpass filters arranged between the directional couplers. According to a development of the invention, crossovers and power distribution arrangements are therefore shown in the exemplary embodiments according to FIGS. 3 to 5, which are particularly simple and inexpensive in construction and in which the number of bandpass filters used is limited to a minimum.

3 shows a crossover and power distribution arrangement with which a transmitter S1 transmitting at frequency f1 feeds two antenna groups G1 and G2 with such a power distribution that a first predetermined radiation diagram (for example D1 according to FIG. 2) results, while the second transmitter S2 operating on a frequency f2 (f2 may not only be equal to f1) feeds the same antenna groups G1 and G2 with such a power distribution that a second different predetermined radiation pattern (for example D3 according to FIG. 2) results for S2 . The antenna groups G1 and G2 are again combined from different antenna fields of a single transmitting antenna.

The transmitter S1 is connected to the input 1 of a first directional coupler R1, which acts as a power distributor and is terminated at its output 3 via a resistor K with the correct wave resistance. This directional coupler R1 (3 dB coupler) divides half of the power N1 of the transmitter S1 via the outputs 2, 4 into the inputs of two bandpass filters F, the center frequency of which is matched to the transmission frequency f1 are. The outputs of these two narrow-band band filters F are each connected to the connections 2, 4 of two further 3 dB directional couplers R2 and R3 by dual power distributors V3 and V4. The power split ratio of the two distributors V3 and V4 is chosen as desired with n1: 1, so that any power distribution of the power N1 of the transmitter S1 between the two antenna groups G1 and G2 is possible. The power N1 initially divided via the directional coupler R1 is thus added again in the directional couplers R2 and R3 in the respective outputs 3 of these directional couplers and thus distributed to the antenna groups G1 and G2 with the selected power division ratio n1. The power N2 of the transmitter S2 is fed to the broadband inputs 1 of the two directional couplers R2 and R3 via a further dual power distributor V5 with the power division ratio n2: 1, this power N2 reaches the filters F, since these are not tuned to the frequency f2 are, the power is reflected there and added again in a manner known per se in the two directional couplers R2 and R3 and fed back to the antenna groups G1 and G2 with the selected power distribution n2 via the output 3 of these directional couplers. The power N1 and N2 of the two transmitters S1 and S2 on the antenna groups G1 and G2 is thus available in the selected power division ratio for the radiation of the desired radiation diagram.

The power distributors V used are preferably designed for the VHF range with a simple λ / 4 transformers after the branch point. Because of the necessary plug connections, all transformation line sections are chosen to be somewhat longer than λ / 4 for the band center frequency. To prevent the power of the transmitter S2 with the frequency f2 across the branches of the power distributors V3 and V4 to the other antenna group, which would lead to a falsification of the power division between the two antenna groups G1 and G2, it is appropriate to use the reactance at the junction points of the power distributors V3 and V4 to make this transmission frequency f2 equal to zero or very small. For this purpose, the line length between the branch point of these distributors and the filter outputs for this frequency f2 is chosen approximately λ / 4.

FIG. 4 shows the distribution of the powers of two transmitters S1 and S2 onto two different radiation diagrams, which in this case each result as a sum diagram of three individual diagrams which are formed by three different antenna groups G1, G2 and G3. By appropriate selection of the distribution of the powers N1 and N2 among these three antenna groups G1, G2 and G3, any radiation idagrams optimal for the respective application can be set for the two transmitters S1 and S2.

4, the power N1 is again divided into two filters F via a directional coupler R1, but the outputs of these filters F are connected to the inputs 2, 4 of three further directional couplers R2 via a triple power distributor V6 or V7, R3 and R4 connected. The power N1 of the transmitter S1 is therefore divided with a predetermined power division ratio n1 ': n1: 1 of the triple power distributors V6 and V7 between the three antenna groups G1, G2 and G3. To avoid crosstalk, these triple distributors V6 and V7 are again like distributors V3 and V4 dimensioned. The power N2 of the transmitter S2 is fed in at the broadband input via a further triple power distributor V8 and is fed to the broadband inputs 1 of the three directional couplers R2, R3 and R4 with a division ratio n2 ': n2: 1; G1, G2 and G3.

5 shows a crossover arrangement for dividing the transmitter powers of three transmitters S1, S2 and S3 operating at different frequencies f1, f2 and f3 onto two antenna groups G1 and G2. Via a first directional coupler R1 with two downstream filters F1 tuned to the frequency f1 and two downstream dual power distributors V9 and V10 of any power sharing ratio, the power N1 of the transmitter S1 is divided between the two antenna groups G1 and G2, in a corresponding manner the power N2 of Transmitter S2 via a directional coupler R4 and downstream band filters F2 of the center frequency f2 and distributors V11 and V12 via the directional couplers R5 and R6, which are interconnected with the directional couplers R2 and R3 of the first switch, divided between the antenna groups G1 and G2. The power N3 of the third transmitter S3 is again fed via the broadband input and the series-connected directional couplers R2, R3, R5 and R6 to the antenna groups G1 and G2 in accordance with the selected power sharing ratio of a dual power distributor V13. With this arrangement according to FIG. 5, it is difficult to make the reactances for the frequencies f2 and f3 zero at the branching points of the power distributors V9, V10. In this case, it is sufficient to make the reactance at these branch points zero for a medium frequency between the two frequencies f2 and f3.

By a corresponding combination of the circuit measures according to FIGS. 4 and 5, several transmitters could also be divided into several different antenna groups. It is essential that the number of filters required for the switches used is reduced to a minimum. The filters of such switches are the most expensive because of their high performance, but the directional couplers and distributors used can be implemented relatively easily and cheaply.

Claims (7)

1. Transmission device for emitting the initial output (N1,N2) from two or more high-frequency transmitters (S1,S2) operating on different transmission frequencies (f1,f2) via a single aerial composed of several aerial fields (A1 to A4) accommodated on the same mast and coupled to each other, characterised by the fact that for the transmitter (S1,S2) to radiate with different radiation patterns (D1,D2) the aerial fields (A1 to A4) of the individual aerials are collected together in two or more aerial groups (G1,G2), these aerial groups (G1,G2) are each connected to separate supply lines (L1,L2) and these supply lines (L1,L2) are connected, via a frequency separating filter and power distribution arrangement (W,V) with the transmitters (S1,S2) in such a way that one transmitter (S1) feeds the aerial groups (G1,G2) with a power distribution which produces a primary predetermined radiation pattern (D1), whilst the second transmitter (S2) feeds the aerial groups (G1,G2) with a different power distribution, which produces a second predetermined radiation pattern (D3) which at least in part matches the first radiation pattern (D1).
2. Transmission device as per claim 1, characterised by the fact that the frequency filter and power distribution arrangement comprises at least one directional coupler filter (W) and at least one power distributor (V).
3. Transmission device as per claim 2 for two transmitters and two aerial groups, characterised by the fact that the frequency filter and power distribution arangement comprises only one directional coupler filter (W) and only one power distributor (V), whereby one transmitter (S1) only feeds one aerial group (G1) with the whole of its output (N1) and the other transmitter (S2) feeds the same aerial group (G1), via the power distributor (V) and the directional coupler filter (W), with part (1/2 N2) of its output and the aerial group (G2), only via the power distributor (V) with the other part (1/2 N2) of its output (Figure 1).
4. Transmission device as per claim 2 for two transmitters and two aerial groups, characterised by the fact that the frequency separating filter and power distribution arrangement comprise two directional coupler filters (W1,W2) and two two-way power distributors (V1,V2) whereby one transmitter (S1) feeds, via the first power distributor (V1) and the two directional coupler filters (W1,W2) both aerial groups (G1,G2) with the first power distribution, giving a predetermined radiation pattern (D1), whilst the second transmitter (S2) feeds the same aerial groups (G1,G2) via the second power distributor (V2) and the two directional coupler filters (W1,W2) with a second power distribution which produced a second predetermined radiation pattern (D3) (Figure 2).
5. Transmission device as per claim 2 for two transmitters and two aerial groups, characterised by the fact that the frequency separating filter and power distribution arrangement comprises three directional couplers (R1,R2,R3), three two-way power distributors (V3,V4,V5) and two band filters (F) adjusted to the frequency (f1) of the first transmitter (S1), whereby the first directional coupler (R1) distributes the output (N1) of the first transmitter (S1) between the two filter entries, the two filter exits are connected via two of the power distributors (V3,V4) each with one of the decoupled entries (2,4) of the other two directional couplers (R2,R3) and at the joint exit (3) of the third and fourth directional coupler (R2,R3) the other two separate aerial groups (G1 and G2) are connected (Figure 3).
6. Transmission device as per claim 2 for two transmitters and three aerial groups, characterised by the fact that the frequency separating filter and power distribution arrangement comprises four directional couplers (R1 to R4), three three-way power distributors (V6,V7,V8) and two band filters (F) adjusted to the transmission frequency (f1) of the first transmitter (S1), whereby the output (N1) from the first transmitter (S1) distributed via the first directional coupler (R1) and the band filters (F) is distributed through the first two three-way distributors (V6,V7) to the second, third and fourth directional couplers (R2,R3,R4), whilst the output (N2) of the scond transmitter (S2) is distributed through the third three-way distributor (V8) also to these three directional couplers (R2,R3,R4), and the three aerial groups (G1,G2,G3) are each connected to the exits (3) of these directional couplers (R2,R3,R4) (Figure 4).
7. Transmission device as per claim 2 for three high-frequency transmitters and two aerial groups, characterised by the fact that the frequency separating filter and power distribution arrangement comprises six directional couplers (R1 to R6), five two-way power distributors (V9 to V13) and two band filters (F1, F2) adjusted to the frequency (f1) of the first transmitter (S1) and two to the frequency of the second transmitter (S2) (Figure 5).

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