EP1956675A1

EP1956675A1 - Phase-shifting system for radiating elements of an antenna

Info

Publication number: EP1956675A1
Application number: EP08101406A
Authority: EP
Inventors: Jean-Pierre Harel; Nicolas Cojean; René Grone
Original assignee: Alcatel Lucent SAS
Current assignee: Alcatel Lucent SAS
Priority date: 2007-02-08
Filing date: 2008-02-08
Publication date: 2008-08-13
Anticipated expiration: 2028-02-08
Also published as: FR2912557B1; FR2912557A1; EP1956675B1

Abstract

The subject of the present invention is a phase-shifting system including at least one body (21) which has at least one electrically conductive surface, an electrically conductive feed line (22) placed on the body (21) and including at least two segments (33a-33e, 34a-34e) which are parallel along a longitudinal axis B-B and at least three access points (23, 24a-24e, 25a-25e), a movable dielectric device (26) placed above the feed line (22), characterized in that the device (26) includes two distinct sections (26a-26e) made up of dielectric material, which are capable of moving independently along the longitudinal axis B-B.

Description

The present invention relates to a device for longitudinally displaced phase-shifting, including a dielectric material, used for phase-shifting radiating elements, or groups of radiating elements. The invention is intended to particularly be used for radiating elements that belong to antennas for base stations of cellular communication networks (GSM, UMTS, etc.), but also for any other type of application that implements phase-shifters. The purpose of phase-shifting is to adjust the direction of an antenna's main lobe, thereby attaining dynamic-tilt antennas, otherwise known as "adjustable-tilt antennas."
Phase-shifters are passive systems, meaning that they do not include electronic components, enabling them to apply a relative shift in phases between different access points of a radio frequency feed network. There are several major families of phase-shifting systems, depending on their mechanical operation method.
Firstly, there are rotating systems (such as described in US 6,850,130 and JP 09,246,846 ), in which one or more metallic parts are used to link various conductive lines. These metallic parts perform ad hoc coupling between the conductive lines, most commonly in the form of a contact-free connection, i.e. one in which a capacitive effect between two metallic parts couples the lines using RF.
However, the disadvantage of coupling lines together is that these systems may have difficulty achieving good performance over a wide frequency band without requiring that unwanted compromises be made with regard to coupling losses, and therefore to the overall effectiveness of the phase-shifting system. Another disadvantage of these systems is that it is difficult to add more of the conductive lines that will be linked to the radiating elements. Finally, this sort of system is significantly bulky.
Secondly, there are transverse movement systems (such as described in EP1215752 ), in which a material with a high dielectric constant and low dielectric loss is used to create relative phase-shifting between two radiating elements. The feed lines for radiating elements are installed serially. The movement is transversal with respect to the feed lines of the various radiating elements. Each phase shift is added to the total, until the final radiating element is being fed.
The disadvantage of this system is that each of these phase-shifters should be set in motion, although they are fairly distant physically from one another. Furthermore, these phase-shifters are placed along the primary longitudinal axis of the antenna, and the splitters are interspersed between them, which leads to the system being very long, particularly when significant phase-shifting is sought for the antenna (especially to 20° and beyond). This length makes it difficult to comply with the required tolerance.
Finally, there are longitudinal movement systems (such as described in US5,949,303 or WO/2002/035651 ), in which a material with a high dielectric constant and low dielectric loss is used to create relative phase-shifting between two radiating elements, or two groups of radiating elements, of an antenna. The material is inserted near the conductive line, which may be planar in structure, in the form of a stripline or microstrip. The propagation velocity of the signal that runs through this conductive line is reduced to a greater extent if the material's dielectric constant is higher, if the thickness of the dielectric material part is greater, and if the part is placed so as to cut off the lines of current running between the feed lines and the ground.
The major disadvantage of this system is that it requires a fairly high surface area to be activated, because the part made of dielectric material must move in a linear fashion from one end of the system to another, in a longitudinal direction. The limits to the part's movement thus limit the system's phase-shifting amplitude. Another disadvantage is that it is necessary to use multiple phase-shifters in order to achieve a complete feed-line structure for an antenna feed network.
The document WO/2002/035651 describes a monoblock phase-shifter, which moves as one piece and is made up of a single part made of dielectric material; it is given holes suitable for various conductive lines. This device does not allow the various conductive lines to be controlled independently.
The goal of the present invention is to eliminate the disadvantages found in the prior art, and particularly to disclose a low-loss longitudinal-movement phase-shifting system that is mechanically compact and stable, and that enables continuously varying phase-shifting.
The subject of the present invention is a phase-shifting system containing at least:

a body which has at least one electrically conductive surface,
an electrically conductive feed line placed on the body, including at least two segments which are parallel along a longitudinal axis and at least three access points,
a movable dielectric device placed above the feed line.

In the invention, the device includes at least two distinct sections made of dielectric material, which are capable of moving independently along the longitudinal axis.
In a preferable embodiment, each section has areas located respectively at each end of the section, enabling impedance transformation.
In one variant, the impedance transformation areas possess recesses.
In another variant, the impedance transformation areas are separated by a central area made completely of dielectric material.
In yet another variant, the central areas of the sections have different lengths.
Preferably, the dielectric material selected is either a plastic material or a ceramic material.
Advantageously, the movement of the sections is achieved using a gear or a pivoting rod.
The system of the invention may additionally comprise a means for guiding the longitudinal movement of the sections.
In one embodiment of the invention, the feed line further includes a first portion for impedance transformation, and a second portion for dividing the current, with these portions being connected to the segments.
Another subject of the invention is an antenna that includes a phase-shifting system based on one of the preceding claims.
The phase-shifting system of the invention is a system that is passive (meaning that it contains no active electrical components) and reciprocal, meaning that it is suitable for functioning as either a "splitter" or a "combiner" with respect to the various access points.
The main advantage of the present invention is the ability to independently control the phase shifts between two radiating elements of an antenna. The system of the invention is thereby applicable to an unlimited number of radiating elements. Furthermore, it allows for the ability to attain non-linear phase shifts between the elements, meaning ensuring independent control of the phase shifts that are applied in pairs to the radiating elements.
Another advantage of the invention is that it makes possible a broad range of values for the antenna's inclination. In the system of the invention, it is even possible to attain high antenna beam inclinations, which may reach and even exceed 20°.
Furthermore, this system has the advantage of being modifiable, so that it can be adapted to be used along different frequency bands.
Consequently, the possible range of inclinations for the antenna's beam are limited only by the dielectric material used (the higher the material's dielectric constant, the wider the range of inclinations) and by the length of the antenna, which is naturally significant for panel antennas.
Other subjects, characteristics, and advantages of the present invention will become apparent from the following description of one particular embodiment, which naturally is given for illustrative purposes and is non-limiting, and from the attached diagram, in which:

Figure 1 is a simplified diagram of the phase-shifting system of the invention,
Figure 2 represents an exploded schematic view of a first embodiment of one phase-shifting system of the invention,
Figure 3 shows the system of Figure 2, once 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 electrical feed line of the system in Figure 2,
Figure 6 is an oblique-perspective view of the dielectric body of the system of Figure 2,
Figure 7 is a schematic illustration of the movement of the dielectric sections using a gear,
Figure 8 is a schematic illustration of the movement of the dielectric sections using a pivoting rod,
Figure 9, analogous to Figure 3, shows the system of the invention in a centered position,

Figure 1 shows the phase-shifting system of the invention, including one electrical feed line 11 placed between two dielectric devices 12, with the entire assembly being placed between two conductive bodies 13.
In the embodiment of the invention depicted in Figures 2 and 3, the phase-shifting system includes the following components, overlaid along a direction A-A :

a body 21 with a conductive surface;
an electrical feed line 22 that comprises:
- multiple conductive segments 22a-22e which are parallel along direction B-B, intended to feed the radiating elements,
- at least three access points, here for example as one central access point 23 and several access points 24a-24e and 25a-25e placed respectively on both ends of segments 22a-22e,
- a portion dedicated to the impedance transformation,
- a portion dedicated to distributing power to the various access points;
- a device 26 made of dielectric material that includes several independent sections 26a-26e interspersed between the electrical line 22 and the conductive body 21; through mechanical translation, the dielectric sections 26a-26e may move along direction B-B so as to independently modify the respective coverage range of segments 22a-22e of line 22;
- guiding means 27 and potentially additional mechanical parts to make it easier for the dielectric sections 26a-26e to slide.

The body 21, in the embodiment depicted in Figure 4, is made up of a conductive material, at least on its surface. For a "stripline" construction such as the one shown here, the body is equipped with two parallel conductive planes 21a and 21b; for a "microstrip" construction, a conductive line and a conductive plan acting as a "ground plane" are sufficient. The body 21 is constructed in the form of an aluminum block, which may have been bent, molded, or machined. The body may just as easily be created from other materials, such as brass, copper, or any other alloy with similar properties. The body may also be constructed in shapes other than the one depicted here.
The body 21 has an input 23 and outputs 24a-24e and 25a-25e linked to a feed line 22. The access points are shown here in the form of several connectors 24a-24e and 25a-25e, but they may also be constructed in the form of direct links to the radiating elements using coaxial cables, or by lengthening the segments of the "microstrip" or "stripline" feed line. The input 23 is depicted here in the central position, but it may also be placed on one of the sides of the body 21. The minimum number of access points is therefore three, and only physical form-factor constraints may limit the number of them, except that this number is additionally limited to being an even or odd number.
The "stripline" electrical feed line 22, depicted in Figure 5, is constructed as a single part, and is made up of several conductive segments 22a-22e. The feed line 22 is obtained by perforating a brass plate 1 mm thick, but it may also be constructed with a different material with good electrical conductivity, as well as in the form of a printed circuit board.
In the form depicted here, the input 23 of the feed line 22 communicated with an access point area 50. The portion 51 following the feed line 22 is used to enable proper impedance transformation between the input 23 and the number N of output connections available, with N ≥2 (here N = 10), such as with a progressive Klopfenstein impedance taper.
The portion 51 is extended by portion 52, which is used to enable the splitting or combining of current for the various access points 50, 53a-53e and 54a-54e. Indeed, the conductive segments 22a-22e do not necessarily have the same operating amplitude. In the present case, the outputs 53a-53, 54-54e all have different amplitudes.
The conductive segments 22a-22e are arranged in a rectilinear fashion, and are parallel to one another. During construction, an effort will be made to spread apart the segments 22a-22e if possible, so as to minimize coupling between them. The width of the conductive segments 22a-22e is suitable for attaining the desired input and output impedance, which is generally 60 Ohms. Typically, the conductive segments 22a-22e may be about 7.35 mm wide for a thickness of 1 mm, when the "stripline" feed line 22 is etched between two ground planes 21a and 21b spaced 7 mm apart.
Figure 6 depicts the device 26 made entirely of dielectric material, which includes a fixed portion 60, placed above the portion 51 of the electrical feed line 22, and several sections 26a-26e which are movable and can move independently of one another. Each dielectric section 26a-26e includes a central area 61 made entirely of dielectric material; the central areas are identical, except for their length. The sections 26a-26e are constructed of plastic, such as polyphenylene sulfide (PPS RYTON©), which has a dielectric constant of about 4 to 6. Although it is more expensive and requires greater precision, a ceramic material may also be used as a dielectric material whose dielectric constant ε_r is about 10.
Each dielectric section 26a-26e includes two areas 62a and 62b, respectively located at each end of the sections 26a-26e, which serve to transform impedance along the "stripline" feed line 22. Impedance transition must occur between the part of the feed line 22 which is exposed to air and the part where the feed line 22 is completely between the body 21 and the central area 61 of one section 26a-26e of the dielectric device 26. In the embodiment shown here as an example, the impedance transformation function is handled by the creation of recesses 63 in the dielectric material at the end areas 62a, 62b of each section 26a-26e of the dielectric device 26. These recesses 63 have been depicted here as rectangular holes, but they may naturally have any other form depending on the discounted result. For the purpose of achieving suitable impedance transformation between the part of the feed line 2 which is exposed to air, and the part where the feed line 2 is surrounded by dielectric material, the appropriate modification of the dielectric material of the sections 26a-26e may be determined through calculation or simulation, based off an equivalence of the dielectric material made up of localized components, i.e. foreseen as the succession of discrete RLC components.
In another embodiment, the areas 62a, 62b that handle impedance transition may be achieved using quarter-wave sections with different thicknesses, thereby allowing impedance transition between the part of the feed line 2 located in an environment made up of air, and the part of that line 2 whose environment is filled with dielectric material.
A significant advantage of the invention is that the phase-shifting system's dielectric device is made up by means of several sections 26a-26e. The movement of each of these sections may be controlled separately, and in this manner, phase-shifting between elements is achieved at least for pairs of antenna radiating elements.
The guiding means 27 are made of a dielectric material, particularly the same material as that used for the dielectric device 26, so that the conductive sections 26a-26e of the electrical feed line 22 that they cross do not suffer any change of medium whatsoever. These means 27 may be constructed in multiple ways. In the embodiment disclosed here, struts 27a-27e are used in order to guide the sections 26a-26e when they slide longitudinally. A gear or rod, for example, may help the sections move; in this case, the speeds at which the linked sections move are identical. Another solution is to move the sections completely independently, such as by using stepper motors or independent linear actuators.
The dielectric sections 26a-26e above the conductive segments 22a-22e move while obeying rules that depend on the usage of the phase-shifting system In one specific situation, in which linear, progressive phase-shifting between the radiating elements of an antenna is necessary, such as 10°, then 20°, then 50°, etc., the sections 26a-26e move independently, while maintaining a constantly moving distance between one another. For example, if section 26a moves 20 mm, section 26b must move 40 mm, section 26c 60 mm, and so on.
The dielectric sections 26a-26e may be moved in various ways. The dielectric sections 26a-26e may, in particular, be moved in a synchronized fashion by means of a gear that includes an even number of toothed wheels, or by means of a pivoting rod.
Gear-based movement 70 is depicted in Figure 7. Shown here is a gear-based system 70, comprising two toothed wheels 70a and 70b for moving the dielectric sections 71, 72 with respect to one another. A main dielectric section 71 is moved in one direction 73, while a related section 72 moves in parallel with the section 71 and in the same direction 74 owing to the gears 70.
Pivoting-rod-based movement is depicted in Figure 8. A rod 80 pivots along a direction of rotation 81 around a mechanical axle 82, which is not fixed onto the dielectric device 26. Each dielectric section 83a-83d of the phase-shifting system is linked to the rod 80 by means of a pivot 84a-84d. The pivots 84a-84d must be capable of sliding to accompany the rotational movement of the rod 80. This solution is simple to implement mechanically, but it may require that oblong holes be present in the body 1 so that the pivots 84a-84d can slide.
The operation of the phase-shifting system of the invention has been studied in two different mechanical configurations:

when the system 90 is in a centered position as depicted in Figure 9, and
when the dielectric sections 26a-26e are aligned and are shifted 20 mm away from one another, which corresponds to the equivalent position of a minimal antenna inclination, as depicted in Figure 3.

Simulation results show that the phase-shifting system of the present invention may advantageously be incorporated into a full antenna concept, to attain the same level of performance under current conditions of use, and furthermore, with the ability to reach antenna inclination angles much greater than current solutions.
The present invention is not limited to the embodiments that have been explicitly described; rather, it includes any variations and generalizations within the reach of a person skilled in the art.

Claims

A phase-shifting system, including at least
- a body (21) which has at least one electrically conductive surface,

- an electrically conductive feed line (22) placed on the body (21) and including at least two segments (33a-33e, 34a-34e) which are parallel along a longitudinal axis B-B and at least three access points (23, 24a-24e, 25a-25e),

- a movable dielectric device (26) placed on the upper side of the feed line (22),
characterized in that the device (26) includes at least two distinct sections (26a-26e) made of dielectric material, which can move independently along the longitudinal axis B-B.
A system according to one of the claims 1 and 2, in which each section (26a-26e) possesses areas (62a, 62b) located respectively at each end of the section (26a-26e), enabling impedance transformation.
A system according to claim 2, in which the impedance transformation areas (62a, 62b) possess recesses (63).
A system according to claim 3, in which the impedance transformation areas (62a, 62b) are separated by a central area (61) made entirely of dielectric material.
A system according to claim 4, in which the central areas (61) of the sections (26a-26e) are of different lengths.
A system according to one of the preceding claims, in which the sections (26a-26e) move by means of a gear (70) or a pivoting rod (80).
A system according to one of the preceding claims, in which the dielectric material is selected from among a plastic material and a ceramic material.
A system according to one of the preceding claims, further comprising guiding means (27) to guide the longitudinal movement of the sections (26a-26e).
A system according to one of the preceding claims, in which the feed line (22) further includes a first portion (51) for impedance transformation and a second portion (52) for dividing the current, with the portions being connected to the segments (22a-22e).
An antenna comprising a phase-shifting system according to one of the preceding claims.