EP0435752A1 - A wide band diplexer, especially for decameter waves - Google Patents

Abstract

The aim of the invention is to make it possible to benefit from the advantages of multichannel antennas when such an antenna is coupled to two transmitters by one diplexer. To do this, the length of the line segments (L1-L4, L1'-L4') of the diplexer can be modified by means of switches (C1, C2, C1', C2') whose contacts are arranged in series within the diplexer line segments. Application, in particular, to decameter wave diplexers. <IMAGE>

Description

The present invention relates to a diplexer for broadband antenna and, in particular, for antenna operating in HF that is to say at frequencies ranging from 3 to 30 MHz.

In broadcasting, to transmit the same program on two frequencies of neighboring channels and with the same radiation characteristics, in order to be sure of reaching a given geographical area, it is known to use a diplexer which performs the paralleling of two transmitters on the same antenna while avoiding, or at least making very weak, the coupling between the two transmitters.

The diplexers currently used are designed to perform the diplexing on two given channels at a given frequency in each channel. Broadband, "multi-channel" antennas, developed for more than ten years therefore lose much of their interest if they are used with such diplexers.

The object of the present invention is to avoid this drawback by giving the possibility of using the same diplexer for different transmission frequencies of the two transmitters, which will therefore require the use of a "multi-channel" broadband antenna.

The subject of the present invention is a diplexer, the length of the line elements of which it is composed is adjustable, as defined by claim 1.

• - la figure 1 un schéma d'un diplexeur selon l'art antérieur,
• - les figures 2 et 3, des schémas de diplexeurs selon l'invention,
• - la figure 4, une partie d'un autre diplexeur selon l'invention

Other objects and other characteristics will appear with the aid of the description below and of the figures relating thereto which represent:

• FIG. 1 a diagram of a diplexer according to the prior art,
• FIGS. 2 and 3, diagrams of diplexers according to the invention,
• - Figure 4, part of another diplexer according to the invention

In the various figures, the corresponding elements are designated by the same references. In addition, it should be noted that, for problems of space and readability, the proportions have not always been respected in the figures.

FIG. 1 is a schematic view showing a diplexer according to the prior art which receives signals at two distinct frequencies F and F ′ respectively on a first and a second access, A1, A2, and delivers them to an antenna A connected to a third access A0. In the example described F is greater than F ′ so that, in what follows and in claims F and F ′ will be respectively called high frequency and low frequency and the frequencies around F and F ′ will be respectively called high frequencies and low frequencies.

The access A1 receiving the signal at the frequency F is connected to the access A0 to which the antenna A is connected by a line which two separate connection points M and N separate into three sections of line: a section L connects the point M at access A1, a section L1 connects points M and N and a section L2 connects point N to access AO. In addition, two sections of line L3, L4, arranged in derivation, connect the points M and N respectively to the ground.

Similarly, access A2 receiving the signal at frequency F ′ is connected to access AO by a line which two separate connection points M 'and N' separate into three line sections: a section L 'connects point M 'at the access A2, a section L1 ′ connects the points M' and N 'and a section L2 ′ connects the point N ′ to the antenna access, A0; moreover two sections of line L3 ′, L4 ′ connect points M 'and N' respectively to ground.

The diplexer according to FIG. 1 comprises a diplexer proper constituted by the line sections L2, L4, L2 ′, L4 ′. The lengths of these sections are respectively λ ′ / 4, λ ′ / 2, λ / 4, λ / 2, where λ and λ ′ are the wavelengths corresponding to F and F ′; these values are theoretical values but the real values are very close.

The diplexer according to FIG. 1 also includes two impedance matching circuits constituted respectively by the sections 1L, L3 and L1 ′, L3 ′. Indeed, for example on the low frequency channel, the introduction, in N ', of the line section L4 ′ leads to a mismatch; to readjust the antenna A with its line L4 ′, to the nominal impedance, it is necessary to place in M ′ the short-circuited line L3 ′. The length of the section L3 ′ is very close to that of the section L4′ and therefore of λ / 2; the length of the section L1 ′ depends on the antenna impedance, seen in N ′ and on the line impedance of L2 ′. Similarly, in the adaptation circuit constituted by the sections L1 and L3, the line section L3 has a length of the order of λ ′ / 2 and the length of L1 depends on the antenna impedance seen from N and the line impedance of L2.

It is also known to use diplexers corresponding substantially, from the point of view of the lengths of line sections, to the diplexer according to FIG. 1, but in which the line sections L3, L4, L3 ′, L4 ′ are no longer short -circuited by earthing at one of their ends but are open at this end; it is also known to use diplexers in which one of the two channels, for example the low frequency channel, has short-circuited lines while the other channel has open lines. But it should be noted that, generally, for lines where high powers circulate, that is to say in the case of using transmitters of 100 kW and more, open line diplexers are generally not used to avoid radiation and Corona effects; they can however be used, despite these drawbacks, when the ratio of the extreme frequencies of use is of the order of 2 or greater than 2.

A circuit, like that of FIG. 1, can only operate with two predetermined values respectively for F and F ′.

FIG. 2 shows how the diplexer according to FIG. 1 can be modified to allow it to operate on four distinct values for its low frequency F ′ and four distinct values for its high frequency F. FIG. 2 corresponds to a study of a diplexer intended to be associated with a multi-channel, broadband antenna, designed for the five bands of 11, 13, 15, 17, 21 MHz; the bandwidths are defined as follows according to international standards:
11 MHz band = from 11.65 to 12.05 MHz = 3.43% from 11.65
13 MHz band = from 13.6 to 13.8 MHz = 1.47% of 13.6
band 15 MHz = from 15.1 to 15.6 MHz = 3.31% of 15.1
band 17 MHz = from 17.55 to 17.9 MHz = 1.99% of 17.55
21 MHz band = from 21.45 to 21.85 MHz = 1.86% of 21.45.

To be able to use all the possibilities of this antenna, the low frequency channel of the diplexer according to FIG. 2 has been provided for ability to couple a transmitter working in the 11, 13, 15 and 17 MHz bands to the antenna while the high frequency channel has been designed to couple a transmitter working in the bands of 13, 15, 17 and 21 to the antenna MHz, which allows the antenna to work in the following pairs of bands: 11-13, 11-15, 11-17, 13-15, 13-17, 13-21, 15-17, 15-21 and 17-21; it should be noted that the pair 11-21 is not used because, the frequency ratio between the two bands being very close to 2, it is difficult to prevent harmonics 2 of the 11 MHz band from disturbing the 21 MHz band.

To allow these different operations, the diplexer of FIG. 2 has the same line sections L, L ′, L1, L1 ′, L2, L2 ′, L3, L3 ′, L4, L4 ′, as that of FIG. 1, in a similar arrangement, but the length of the line sections can be modified so that the diplexer can be adjusted according to the frequencies F and F ′ indicated above. To this end, the low frequency channel, that is to say in the channel which conducts the frequency signal F ′ to the antenna A, and the high frequency channel each comprise two switches: C1, C2 for the high channel frequencies, C1 ′, C2′ for the low frequency channel. Each switch is a rotary switch with two wafers with four pads per wafer, such as the pads P11 to P14 and P15 to P18 for the first and second wafer of the switch C1; a slider is associated with each wafer, such as the sliders J11 and J12 for the switch C1, which correspond to the wafers carrying the pads P11 to P14 and P15 to P18 respectively. The first of the two wafers of each switch has its pads in the connection between the two accesses A1, A2, and the successive pads of each first wafer are interconnected by sections of line; thus the pads P11 to P14 of the switch C1 are in series in this connection, thanks to line sections K11, K12 and K13 which respectively connect the pads P11 and P12, P12 and P13, P13 and P14. The second of the two wafers of each switch has its successive pads connected by sections of lines; thus the pads P15 to P18 of the switch C1 are connected by sections K16, K15, K14 disposed respectively between the pads P15 and P16, P16 and P17, P17 and P18.

The cursor of the first wafer, such as the cursor J11 of the switch C1, is connected to one of the two extreme pads of the second wafer while the other end pad and the slider of this wafer are connected to ground. The line sections relating to the switch C2, as well as the sliders and the pads of this switch, have been designated in FIG. 2 by adding 10 to the figure of the corresponding element relating to the switch C1, this is how the section K22 of switch C2 corresponds to section K12 of switch C1. Furthermore, to facilitate the understanding of FIG. 2, as well as that of FIG. 3, the line sections of the first wafers, that is to say the sections such as K21, which are in series between the accesses A1, A2, have been drawn in the form of rounds while the sections of the second wafers of the switches have been drawn in the form of slots.

In the position they occupy in FIG. 2, the four cursors of the high frequency channel determine a structure according to FIG. 1, in which the points M and N are the movable ends of the cursors of the first wafers of the switches C1 and C2 and in which the line sections L1, L2, L3, L4 of FIG. 1 are respectively constituted by the sections going from the block P13 to the block P23, from the block P23 to the access AO, from the block P13 to the ground including the section K14, and from stud P23 to ground including the section K24. The position occupied by the sliders of switches C1 and C2 is that which is provided when the signal F ′, on port A2, is in the 15 MHz band. By moving the four sliders of the switches C1 and C2 simultaneously by one pad on the right (in the sense of a displacement in FIG. 2), or by one pad on the left, or by two pads on the left, the diplexer is set for a signal on access A2 whose frequency F ′ is respectively in the band of 17, 13 and 11 MHz.

Similar comments could be made with respect to switches C1 ′, C2 ′ of the low frequency channel, which are identical to those of the high frequency channel and the pads of the wafers of which are wired with line sections of which only the length is different by compared to the high frequency channel. It should be noted that the position of the cursors of the low frequency channel corresponds to a working signal, on the access A1, located in the 17 MHz band, while a displacement of all the cursors of the switches C1 ′ and C2′by one pad to the left, or one pad to the right, or two pads to the right would correspond to a working signal, on access A1, located respectively in the bands of 21, 15 and 13 MHz.

The lengths of the sections, such as K11 and K25, are determined by considering a diplexer according to FIG. 1 in which the position of the points M, N, M ′, N 'would be adjustable according to the operating bands and in which the length of the short-circuited sections L3, L4, L3 ′, L4 ′ would also be adjustable. Thus, four positions are defined for each of these points and four lengths for each short-circuited section; the length of the sections such as K11 and K25 can then be determined by simple subtractions taking into account the line lengths which constitute, for example, the cursor J1 of the switch C1 in series with the link going from this cursor to the pad P18 of the second wafer from the same switch. The lengths of the line sections between the two switches of the same channel are average lengths determined as a function of the antenna impedance at the average frequency of the frequencies of use.

For the sake of simplification, the conductive lines of the various attached figures have been represented by a single line, of course these are symmetrical lines, of the kind of two-wire lines, or asymmetrical, of the kind of coaxial lines. Thus the example according to FIG. 2 was produced in two-wire lines, which amounts to saying that, to be complete, FIG. 2 should include lines represented by two parallel lines, double cursors with two parallel arms and double pancakes with two superimposed sets of four studs each.

FIG. 3 is the diagram of an embodiment of a diplexer according to the invention associated with a multi-channel, broadband antenna, A, working in the bands of 13, 15, 17 and 21 MHz. In this figure, which corresponds to Figure 2 but with pancakes with three studs, only the marks relating to the antenna, A, and the access points, AO, A1, A2 have been marked so as not to overload the drawing and allow d '' indicate the lengths in meters of the different line sections.

In this embodiment the high frequency channel, that is to say the one corresponding to access A1, was designed to work in bands of 15, 17 and 21 MHz, while the low frequency channel has been designed to work in the bands of 13, 15 and 17 MHz.

The length of the sections in series between the line of access A1 and that of access A2 are respectively 1 -1.6 - 2.16 - 0.5 - 0.8 - 3.46 - 4.21 - 0.56 - 0.7 - 1 - 1.47 meters. As for the four branch line elements, they each comprise three sections of line in series; the length of these sections, from the cursors relating to the first wafers (that is to say to the wafers relating to the sections in series between the accesses A1 and A2) is 6.92 - 1.5 and 1 meter in the high frequency channel and 8.42 - 1.13 and 1.45 meters in the low frequency channel.

• - utilisation d'une antenne multicanaux d'impédance d'entrée étale à 150 ohms et de ROS (rapport d'onde stationnaire, standing-wave ratio ou SWR dans la littérature anglo-saxonne) au maximum égal à 2,
• - lignes symétriques 300 ohms
• - découplage entre les voies hautes et basses fréquences au moins de 30 dB ce qui, avec des émetteurs de 500 kW, laisse au plus 500 W dans la voie découplée, valeur tout à fait acceptable, qui n'empêche pas la mise en service du second émetteur branché sur le diplexeur lorsque le premier est déjà en fonctionnement.

The diplexer which served as an example for the embodiment according to FIG. 3 has the following characteristics:

• - use of a multichannel antenna with input impedance spread at 150 ohms and ROS (standing wave ratio, standing-wave ratio or SWR in Anglo-Saxon literature) at most equal to 2,
• - balanced lines 300 ohms
• - decoupling between the high and low frequency channels of at least 30 dB which, with 500 kW transmitters, leaves at most 500 W in the decoupled channel, a completely acceptable value, which does not prevent the commissioning of the second transmitter connected to the diplexer when the first is already in operation.

FIG. 4 shows a study of a switch of the type of the switch C1 of FIG. 2, when the line L3 has its end in open circuit and not to ground as in FIGS. 1 to 3. In this case the structure of the first wafer, with its cursor J11, remains unchanged. On the other hand, the second wafer with its cursor J21 is modified so that the line sections K14, K15, K16 have no electrical contact with the rest of the diplexer when they are not used; for this purpose the second wafer has studs, Q11, Q12, Q13, with two separate terminals and a cursor B with three branches B1, B2, B3 each cut by an isolator S1, S2, S3; the cursor B makes it possible to join the two terminals of the pad Q11 or of the pads Q11, Q12 or of the pads Q11, Q12, Q13 or of no pad; this cursor moves like the cursor J12 in FIG. 2 between four positions and its positions are linked to those that takes cursor J11 from the first cake. Thus, from the position they occupy in FIG. 4, the cursors J11 and B can be moved together either from one position to the right, or from one or two positions to the left, so as to modify the setting of the diplexer as a function of the low operating frequency chosen.

The present invention is not limited to the examples described, thus in particular that it applies to the case of diplexers intended to operate on a number of bands other than three or four, both at high frequencies and at low frequencies and, possibly for a different number of bands in high frequencies than that in low frequencies; it suffices that the two switches of a channel have the number of positions corresponding to the number of possible bands of the other channel.

Similarly, it is possible, for example with two-wire lines, to use switches with sliding cursors and even to control the movement of the cursors by a motor controlled by the selected operating bands and by measurement results carried out on the diplexer. In the case of FIG. 4, that is to say in the case of diplexers with open lines, the sliding cursor loses its interest as regards the second wafer which is relative to a line in open circuit, given that the cursor must stop at the two terminals of the same pad.

Claims (4)

Diplexer for coupling two transmitters in parallel to the same broadband antenna (A), comprising three ports (AO, A1, A2) intended respectively for connecting the two transmitters and the antenna and, between each transmitter ports (A1 , A2) and antenna access (AO), a line (L, L1, L2; L ′, L1 ′, L2 ′) with two separate connection points (M, N; M ′, N ′) and , in derivation, from the two connection points respectively, two line sections (L3, L4; L3 ′, L4 ′), characterized in that it comprises first adjustment means (J11, J21) for adjusting the position of each connection point in the line where it is located and second adjustment means (J12, J22; B) for adjusting the length of each section of branch line. Diplexer according to claim 1, characterized in that the first adjustment means are constituted, between each transmitter access (A1, A2) and the antenna access (AO), by two successive groups of n pads (P11- P14, P21-P24), where n is an integer at least equal to 2 and by two cursors (J11, J21) associated respectively with the two groups, and whose moving ends constitute the two connection points (M, N; M ′ . NOT'). Diplexer according to claim 1, characterized in that the second adjustment means are constituted, for each of at least two of the branch sections, by a group of m successive studs (P15-P18; P25-P28) where m is a integer at least equal to 2, arranged in the section of the branch under consideration, and by a cursor (J12; J22) allowing to ground one of the m studs. Diplexer according to claim 1, characterized in that the second adjustment means consist, for each of at least two of the branch sections, by p studs (Q11, Q12, Q13), with p positive integer, with two separate terminals electrically separated, arranged in series in the section of the branch considered, and by a cursor (B) to connect electrically from 0 to p of the studs.

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