FR2912557A1 - DEPHASING SYSTEM FOR RADIANT ELEMENTS OF AN ANTENNA - Google Patents

Abstract

The present invention relates to a phase shift system comprising at least one body (21) having at least one electrically conductive surface, an electrically conductive supply line (22) disposed on the body (21) and comprising at least two parallel segments along a longitudinal axis BB and at least three ports (23, 24a-24e, 25a-25e), a movable dielectric device (26) disposed above the supply line (22), characterized in that the device ( 26) comprises at least two distinct sections (26a-26e) of dielectric material, able to move independently along the longitudinal axis BB.

Description

Phase shift system for radiating elements of an antenna

  The invention relates to a longitudinal displacement phase shifter comprising a dielectric material for applying a phase shift to radiating elements, or groups of radiating elements. The invention is intended to be used in particular to radiating elements belonging to antennas for the base stations of the cellular communication networks (GSM, UMTS, etc.) but also to any other type of application using phase shifters. . The phase shift aims to detach the direction of the main lobe of the antenna, and thus achieve antennas with dynamic misalignment, or otherwise called variable tilt antennas. Phase shifters are passive systems, that is to say having no electronic components, making it possible to apply a relative phase difference between different accesses of a radio frequency power supply network. There are several major families of phase shift systems according to their mechanical mode of operation. On the one hand the rotary systems (for example described in US-6,850,130 or JP-09-246,846), wherein one or more metal parts provide the connection between various conductive lines. These metal parts provide an ad hoc coupling between the conductive lines most often in the form of a contactless connection, that is to say where a capacitive effect between two metal parts ensures an RF coupling between the lines. However the coupling between lines has the disadvantage that these systems can hardly have good performance over a wide frequency band without the need to make compromises harmful to the coupling losses, so the overall efficiency of the phase shift system. Another disadvantage of these systems is that it is difficult to multiply the conductive lines that will be connected to the radiating elements. Finally this type of system has a large footprint. On the other hand cross-displacement systems (for example described in EP-1 215 752), where a low-loss, high-dielectric material is used to create a relative phase shift between two radiating elements. The supply lines of the radiating elements are connected in series. The movement is transversal to the supply line of the various radiating elements. Each of the phase shifts adds up to each other until the last radiating element is energized.

  The disadvantage of this system is that it is appropriate to set in motion each of these phase shifters, while they are quite physically distant from each other. Furthermore these phase shifters are placed along the longitudinal main axis of the antenna, and dividers are interposed between them, resulting in a large length of the system, particularly when seeking to obtain a significant phase shift of the antenna (especially up to 20 and beyond). This length causes difficulties in respect of the tolerances imposed. Finally, the longitudinal displacement systems (for example described in US Pat. No. 5,949,303 or WO-02 / 35,651) in which a material of high dielectric constant and low loss is used to create a relative phase shift between two radiating elements, or two groups of radiating elements, an antenna. The material is inserted near the conductive line which may be planar stripline or microstrip structure. The speed of propagation of the signal flowing on this conductive line is reduced as the dielectric constant of the material is high, the thickness of the piece of dielectric material is substantial, and this piece is placed so as to cut the current lines that lie between the power lines and the earth. The major disadvantage of this system is that it requires a large enough area to be activated, since the piece of dielectric material must move linearly from one end of the system to the other in the longitudinal direction. The limits of the displacement of the part therefore limit the amplitude of phase shift of the system. Another disadvantage is that it is necessary to use several phase shifters to obtain a complete network supply structure for an antenna. WO-02/35 651 discloses a monobloc phase shifter, moving in one piece, consisting of a single piece of dielectric material which is apertured in a manner adapted to the different conductive lines. This device does not allow independent control of the different conductive lines. The object of the present invention is to eliminate the drawbacks of the prior art, and in particular to propose a mechanically stable and mechanically compact low-loss longitudinal displacement phase shifting system which makes it possible to obtain a phase shift which varies continuously. . The object of the present invention is a phase shift system comprising at least: - a body having at least one electrically conductive surface, - an electrically conductive supply line disposed on the body and having at least two parallel segments along a longitudinal axis and at least three accesses, - a mobile dielectric device disposed above the supply line, to the invention according to the invention comprises at least two separate sections of dielectric material, capable of moving independently along the longitudinal axis. According to a preferred embodiment, each section has areas located respectively at each end of the section for the impedance transformation. According to one variant, the impedance transformation zones have recesses. According to another variant, the impedance transformation zones are separated by a central zone made of solid dielectric material. According to yet another variant, the central areas of the sections have different lengths. Preferably the dielectric material is selected from a plastic material and a ceramic material. Advantageously, the displacement of the sections is achieved by means of a gear or a pivoting rod. The system according to the invention may further comprise means for guiding the longitudinal displacement of the sections. According to one embodiment, the supply line further comprises a first portion for the impedance transformation and a second portion for the current division, these portions being connected to the segments. The invention also relates to an antenna comprising a phase shift system according to one of the preceding claims.

  The phase shift system according to the invention is a passive system (that is to say having no active electronic component) and reciprocal, that is to say able to function as well as divider in the summator vis-à-vis different access.

  The main advantage of the present invention is the possibility of independently controlling the phase differences between two radiating elements of an antenna. The system of the invention is thus applicable to an unlimited number of radiating elements. In addition it leaves the possibility of making non-linear phase shifts between the elements, that is to say to provide independent control phase shifts applied in pairs on the radiating elements. Another advantage of the invention is to allow a wide choice of the inclination value of the antenna. Indeed, the system according to the invention makes it possible to achieve inclinations of large antenna beams that can reach and even exceed 20.

  In addition, this system has the advantage of being modifiable so that it can be adapted to be used on different frequency bands. Consequently, the possible inclination range of the antenna beam is limited only by the dielectric material used (the higher the dielectric constant of the material, the wider the inclination range) and the length of the antenna , which is naturally important in the case of panel-type antennas. Other objects, features and advantages of the present invention will emerge from the following description of a particular embodiment, given of course by way of illustration and not limitation, and in the accompanying drawing in which: - Figure 1 is a diagram simplified diagram of the phase shift system according to the invention, - Figure 2 shows an exploded schematic view of a first embodiment of a phase shift system according to the invention, - Figure 3 shows the system of Figure 2, a assembled in a position corresponding to the minimum phase shift of the antenna, - Figure 4 is an oblique perspective view of the body of the system of Figure 2, - Figure 5 is a top view of the power supply line. FIG. 6 is an oblique perspective view of the dielectric body of the system of FIG. 2; FIG. 7 is a diagrammatic illustration of the displacement of the dielectric sections by means of FIG. 8 is a schematic illustration of the displacement of the dielectric sections by means of a pivoting rod, FIG. 9, similar to FIG. 3, shows the system according to the invention in a centered position, FIG. 1 shows the phase shift system according to the invention, comprising a power supply line 11 placed between two dielectric devices 12, the assembly being disposed between two conductive bodies 13. In the embodiment of the invention illustrated on FIG. Figures 2 and 3, the phase shift system comprises the following components superimposed in a direction AA: - a body 21 with a conductive surface; a power supply line 22 which comprises: a plurality of parallel conducting segments 22a-22e in the direction BB intended to supply the radiating elements; at least three accesses, for example here a central access 23 and several access points 24a; 24e 20 and 25a-25e placed respectively at the two ends of the segments 22a-22e, - a portion devoted to impedance matching, - a portion devoted to the distribution of the power to the different accesses; a device 26 made of dielectric material comprising a plurality of independent sections 26a-26e which are interposed between the electrical line 22 and the conductive body 21; by a mechanical translation, the dielectric sections 26a-26e can be moved in the direction B-B to independently change the coverage respectively of the segments 22a-22e of the line 22; - Guiding means 27 and possibly additional mechanical parts to facilitate the sliding movement of the dielectric sections 26a-26e. The body 21, in the embodiment shown in FIG. 4, consists, at least on the surface, of a conductive material. In the case of a triplate type construction as is the case here, the body is provided with two parallel conductive planes 21a and 21b; in the case of a microstrip-type construction, a conductive line and a conducting plane acting as a ground plane suffice. The body 21 is made in the form of an aluminum block, whether folded, molded or machined. The body could equally well be made of other materials such as brass, copper, or any other alloy having similar properties. The body can also be made in other forms than that shown here. The body 21 carries an input 23 and outputs 24a-24e and 25a-25e connected to the supply line 22. The accesses are here in the form of several connectors 24a-24e and 25a-25e, but they could also be realized in the form of direct links to the radiating elements by means of coaxial cables, or by extending the segments of the microstrip or stripline feed line. The input 23 is here represented in central position, but it could also be placed on one of the sides of the body 21. The minimum access number is therefore three, and there are only congestion constraints. physical that can limit the number, without this number being limited to an even or odd number. The power supply line 22 stripline type, shown in Figure 5, is made in one piece and composed of several conductive segments 22a-22e. The supply line 22 is obtained by perforation of a brass sheet 1 mm thick, but it could equally well be made with a different material having good electrical conductivity, and in the form of a circuit said PCB (for Printed Circuit Board in English). In the form illustrated here, the input 23 of the supply line 22 communicates with an access area 50. The next portion 51 of the supply line 22 is used to allow a correct impedance transformation between the input 23 and the number N of connections to be output with N 2 (here N = 10), for example by a Klopfenstein type progressive impedance transformation. The portion 51 is extended by the portion 52 which is used to allow division or summation in power vis-à-vis the various accesses 50, 53a-53e and 54a-54e. Indeed the conductive segments 22a-22e do not necessarily have the same amplitude of operation. In this case the outputs 53a-53, 54-54e all have different amplitudes. The conductive segments 22a-22e are arranged rectilinearly and parallel to each other. In doing so, efforts will be made to keep the segments 22a-22e as far as possible so as to minimize the coupling between them. The width of the conductive segments 22a-22e is adapted to respect the desired input and output impedance, generally 60 Ohms. Typically the conductive segments 22a-22e may have a width of the order of 7.35 mm and a thickness of about 1 mm, when the stripline supply line 22 is inscribed between two spaced planes of mass 21a and 21b. of 7 mm. FIG. 6 shows the device 26 made of solid dielectric material which comprises a fixed part 60 placed above the portion 51 of the power supply line 22, and a plurality of sections 26a-26e which are movable and can be move independently of each other. Each dielectric section 26a-26e comprises a central zone 61 made of solid dielectric material; the central areas are identical except for their length. Sections 26a-26e are made of plastic, such as polyester polypropylene (PPS RYTON) having a dielectric constant of the order of 4 to 6. Although more expensive and requiring greater accuracy, it is also possible to use a ceramic-like material as a dielectric material whose dielectric constant Cr is of the order of 10. Each dielectric section 26a-26e has two zones 62a and 62b, located respectively at each end of the sections 26a-26e, which serve for the transformation of the dielectric material. impedance of the feed line 22 stripline. An impedance transition must be made between the part of the supply line 22 which is surrounded by air, and the part where the supply line 22 is between the solid body 21 and the central zone 61 of a 26a-26e section of the dielectric device 26. In the embodiment shown here as an example, the impedance transformation function is provided through the creation of recesses 63 in the dielectric material of the end zones 62a, 62b of each section 26a-26e of the dielectric device 26. These recesses 63 have been represented here by rectangular holes, but they can of course have any other shape depending on the expected result. In order to obtain a suitable impedance transformation between the part of the supply line 2 which is surrounded by air, and the part where the supply line 2 is surrounded by dielectric material, the appropriate modification of the dielectric material of the sections 26a-26e can be determined by calculation or by simulation starting from an equivalence of the dielectric medium composed of localized elements, that is to say envisaged as the succession of discrete elements R, L and C.

  According to another embodiment of the embodiment, the zones 62a, 62b providing the impedance transition can be obtained by virtue of the use of quarter-wave sections having different thicknesses, thus making it possible to carry out the impedance transition between the part of the supply line 2 located in an environment consisting of air, the portion of this line 2 whose environment is filled with dielectric material. An important advantage of the invention is that the dielectric device of the phase shift system is realized by means of several sections 26a-26e. The displacement of each of these sections can thus be controlled separately and thus the phase difference between elements is obtained at least by pair of radiating elements of the antenna. The guiding means 27 consist of a dielectric material, in particular the same material as that used for the dielectric device 26, so that the conductive sections 26a-26e of the power supply line 22 through which they pass not undergo any change of environment. These means 27 can be made in multiple ways. In the embodiment proposed here, spacers 27a-27e are used to allow the guiding of sections 26a-26e when they slide longitudinally. For example, a gear or a rod can help move the sections; in this case the speed of movement of the connected sections is identical. Another solution is to move the sections perfectly independently, for example using stepper motors or independent linear actuators. The displacement of the dielectric sections 26a-26e above the conductive segments 22a-22e is carried out respecting rules that depend on the use of the phase shift system. In the particular case where a linear and progressive phase shift between the radiating elements of the antenna is necessary, such as 10, then 20, then 50, etc., the sections 26a-26e move independently and maintaining between they a constant displacement gap. For example, if section 26a moves 20mm, section 26b should move 40mm, section 26c should be 60mm, and so on.

  The displacement of the dielectric sections 26a-26e can be realized in different ways. The synchronous displacement of the dielectric sections 26a-26e can be carried out in particular by means of a gear, comprising an even number of toothed wheels, or of a pivoting rod.

  The displacement by a gear 70 is shown in FIG. 7. A gear system 70, including two gears 70a and 70b, is illustrated here for moving the dielectric sections 71, 72 therebetween. A main dielectric section 71 is moved in a direction 73, while an associated section 72 moves parallel to the section 71 and in the same direction 74 through the gear 70. The displacement by a pivoting rod is shown in FIG. 8. A rod 80 pivots in a direction of rotation 81 around a mechanical axis 82 which is not fixed on the dielectric device 26. Each dielectric section 83a-83d of the phase shift system is connected to the rod 80 by means of a pivot 84a-84d. The pivots 84a-84d must be able to accompany the movement of rotation of the rod 80 by sliding. This solution is simple to implement mechanically, but may require the presence of oblong holes in the body 1 to allow the sliding of the pivots 84a-84d.

  The operation of the phase shifting system according to the invention has been studied in two different mechanical configurations: when the system 90 is in the centered position as shown in FIG. 9, and when the dielectric sections 26a-26e are aligned and shifted by 20 mm between them, which corresponds to the position equivalent to a minimum inclination of the antenna, as shown in Figure 3. The results of the simulations show that the phase shift system according to the present invention can be advantageously incorporated into a concept of together of an antenna, to obtain performance of the same level in the current conditions of use, and with the possibility of accessing angles of inclination of the antenna much higher than current solutions. The present invention is not limited to the embodiments that have been explicitly described, but it includes the various variants and generalizations that are within the abilities of those skilled in the art.

Claims (10)

  A phase shift system comprising at least one body (21) having at least one electrically conductive surface, an electrically conductive supply line (22) disposed on the body (21) and having at least two parallel segments along an axis. longitudinal BB and at least three ports (23, 24a-24e, 25a-25e), - a dielectric device (26) movable disposed above the feed line (22), characterized in that the device (26) has at least two distinct sections (26a-26e) of dielectric material, capable of moving independently along the longitudinal axis BB.   2. System according to one of claims 1 and 2, wherein each section (26a-26e) has areas (62a, 62b) respectively at each end of the section (26a-26e) for impedance transformation.   The system of claim 2, wherein the impedance transforming regions (62a, 62b) have recesses (63).   The system of claim 3 wherein the impedance transforming regions (62a, 62b) are separated by a central region (61) of solid dielectric material.   The system of claim 4, wherein the central areas (61) of the sections (26a-26e) have different lengths.   6. System according to one of the preceding claims, wherein the displacement of the sections (26a-26e) is achieved by means of a gear (70) or a pivoting rod (80).   7. System according to one of the preceding claims, wherein the dielectric material is selected from a plastic material and a ceramic material.   8. System according to one of the preceding claims, further comprising a means (27) for guiding the longitudinal displacement of the sections (26a-26e). 10   9. System according to one of the preceding claims, wherein the supply line (22) further comprises a first portion (51) for the impedance transformation and a second portion (52) for the current division, the portions being connected to the segments (22a-22e).   10. Antenna comprising a phase shift system according to one of the preceding claims.