Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/18—Phase-shifters
  • H01P1/184—Strip line phase-shifters

Definitions

• Phase shifter capable of continuous phase variation
• the present invention relates to the variable phase shifters of antenna networks usable in particular in the base stations of cellular radiocommunication networks of the GSM or UMTS type for example.
• the antenna networks equipping the stations basic must be able to radiate directional beams orientable in elevation, typically from 0 ° to -10 ° relative to the horizon line.
• the antenna networks are located at the top of pylons or buildings, a reduction in the deflection angle between 0 ° and -10 ° makes it possible to reduce the range on the ground of radiated radio waves.
• These antenna arrays are generally formed by a vertical alignment of elementary sources spaced apart by a distance (p) forming the pitch of the array which is a multiple, generally less than 1, of the wavelength of the median frequency of the frequency band to be covered.
• the elementary sources are supplied according to a linear phase distribution law, two adjacent sources being phase-shifted by:
• ⁇ o is the angle of depointing of the beam compared to the horizon.
• the variation of ⁇ by an adjustable phase shift means induces a beam deflection of an angle ⁇ o.
• ⁇ o 0.9 ⁇
• ⁇ o -10 °
• the phase shift ⁇ is worth approximately 56.3 °.
• the amplitude of the phase shift ⁇ is typically 60 ° but, if necessary, it can reach 90 ° approximately.
• Beam defocusing can be done manually by tilting the antenna or automatically from a ground remote control. These adjustment modes depend to a large extent on the technology implemented in the production of the phase shifters. It is known to orient the beam of the electromagnetic wave radiated by an array of antennas to use phase-shifting devices with ferrite or else phase-shifting devices with PIN diodes. For the realization of antenna arrays, these devices have the particularity that they allow a remote adjustment of the beam depointing angle by applying an appropriate bias current on the ferrites or PIN diodes, but they do have the disadvantages of having non-linearities and of being a generator of intermodulation noise in multi-carrier transmission.
• phase shifters with metal-on-metal friction or alternatively phase shifters comprising a triplate structure comprising an electrically conductive track composed of several non-aligned segments, the segments being covered in whole or in part by at least one blade in dielectric material moving between two conductive planes along the electrical track.
• telescopic coaxial phase shifters with metal-on-metal friction have the drawback of being sensitive to corrosion and of exhibiting micro non-linearities at high powers which are essentially due to contact resistances.
• phase shifters with a triple plate structure
• the variable overlap of the conductive track by the dielectric plates modifies the electrical length of the conductive track, which produces a mismatch thereof and generally makes this type of phase shifter unsuitable for supplying antenna arrays. with high phase shift.
• the phase excursion can however be improved by adding, for example to the ends of the conductive track, segments of determined length which cancel out the mismatches produced by the dielectric coatings.
• this type of embodiment greatly increases the size of the phase shifters and makes them difficult to use in antenna networks of the GSM or UMTS type.
• this embodiment requires the installation, at the level of each phase shifter of the network, of devices for controlling the movement of the dielectric plates, which further increases their bulk, and limits their use to networks comprising only '' a reduced number of antennas.
• the object of the invention is to provide a phase shifting device capable of continuous variation by single mechanical control having a low insertion loss and operating in a wide frequency band with a view to being integrated for example into a network of radiating elements. aligned to form a directional beam antenna.
• the invention proposes, for this purpose, a phase shifter, comprising two plates of dielectric material, mounted to slide in a chosen direction inside a metal case, and sandwiching a main metal segment, to form a phase shift cell whose terminals are at the ends of the main segment.
• the main segment comprises two conductive sections, substantially parallel, spaced from each other both transversely and longitudinally relative to the chosen direction, with a conductive connection between them, while the plates dielectric have openings, defining movable windows, variably uncovering the sections, depending on the sliding of the dielectric plates in the housing, which at the same time modifies the phase shift between the terminals of the cell.
• each of the windows may be equal to the length of a section increased by a length slightly greater than the half-length of the conductive link in projection on the chosen direction. This characteristic makes it possible to maintain invariable the electrical length and the impedance of the conductive link whatever the position of the dielectric plates and the phase characteristics depend only on the covering of the first and second sections by the windows.
• phase shift cell can be obtained for lengths of the sections less than 0.12 times the working wavelength of the cell and for a length of the conductive link less than 0.25 times the length d working cell wave.
• the phase shifter may comprise, between the dielectric plates and the housing, an arrangement with slits and guide rod, suitable for jointly delimiting the excursion of the two sliding plates.
• the phase shifter comprises a group of at least two main segments, substantially parallel to the chosen direction and connected in series to form a multiple phase shift cell whose terminals are at the free ends of the main segments, while the plates dielectrics have openings, defining movable windows, for each section of each main segment.
• This arrangement of the invention makes it possible to directly control the orientation of the wave beam emitted by the antenna array by performing a single movement of the dielectric plates.
• This movement can be carried out by means of a single electric motor of the "Step by Step" type, for example remotely controlled, which facilitates focusing.
• the phase shifter may further comprise at least two groups of main segments connected in series, mounted symmetrically with respect to a plane perpendicular to the chosen direction, to form two phase shift cells having a common terminal and two opposite terminals located at the ends of the groups.
• the phase shifter may include an assembly defined by at least two groups of main segments connected in series and placed side by side to form two phase shift cells having a common terminal and two extreme terminals located at the ends of these groups.
• the invention allows the production of antenna networks with a phase shifting block distributor, the distributor block being composed of two sets of main segments connected in series, mounted symmetrically with respect to a plane perpendicular to said chosen direction.
• the proposed phase shifter device makes it possible to produce relatively large phase shifts in a small footprint while having a low insertion loss and good impedance matching in a wide frequency band. Another advantage is that it has very good linearity in phase adjustment.
• the impedance matching is better than 1.3 of ROS in each of the frequency bands and for any position of the phase shifter.
• the linearity of the phase shifts measured as a function of displacement of the plates and the frequency is excellent, the non-linearity is better than +/- 5 ° in the frequency band.
• the insertion losses are extremely low of the order of 0.13 dB for a double cell generating a phase shift of 60 ° in the frequency band of 2 GHz.
• FIG. 1A represents a top view along section I-I of an elementary phase shift cell according to the invention.
• FIGS. 1B and 1C respectively represent views along the sections AA and BB of FIG. 1A.
• Figure 1D shows a view along section II-II of Figure 1B.
• FIG. 2 shows an embodiment of the conductive track of the phase shift cell shown in FIGS. 1A, 1B, 1C, and 1D
• FIG. 3 represents a top view of a phase shifter comprising two elementary cells in cascade according to the invention.
• FIG. 4 represents a top view of a symmetrical distribution phase shifter formed by two elementary cells according to the invention.
• FIG. 5 represents a top view of a distributor phase shifter formed by three elementary cells in cascade according to the invention.
• FIG. 6 represents a top view of a symmetrical phase-shifting distributor block formed of elementary cells in cascade according to the invention.
• FIGS 7, 8, 9 show distribution modes of phase shifting devices according to the invention in antenna arrays.
• FIG. 10 represents a top view of a phase shifting block distributor according to a particular embodiment of the invention.
• the elementary phase shift cell which is represented in FIGS. 1A, 1B, 1C and 1D comprises a main segment sandwiched between two plates of dielectric material 2 and 3, of relative permittivity ⁇ r greater than 1.
• the plates 2 and 3, here in shape of rectangular parallelepiped, are kept adjusted one against the other inside a metal case 4, in which they slide in the longitudinal direction of the case between two open ends thereof.
• central line 1 of the phase shifter.
• central line covers in principle several main segments.
• the conductive housing 4 is formed by a U-shaped base 5 which serves as a guide for the dielectric plates 2 and 3 and by a conductive closure plate 6 in the form of a cover.
• the large dimension of the base 5 defines the direction of movement of the plates.
• To allow the displacement of the dielectric plates 2 and 3 in the housing these are crossed by a rod 7 guided by two longitudinal slots gl and g2 facing each other in the base 5 and the cover 6.
• the length of the slots gl and g2 limits the amplitude of movement of the plates 2 and 3.
• the simultaneous driving of the dielectric plates 2 and 3 can be carried out by means of one or more rods not shown, integral with the rod 7 and actuated either manually or with the aid of an electric motor.
• the central line is composed, as shown more particularly in FIG. 2, of several sections SI, Tl, T2, T3, S2.
• the sections SI and S2 constitute the entry and exit lines of the phase shift cell.
• the inputs and outputs can be reversed in a reciprocal phase shifter, consequently, an input or an output can be considered indifferently as a terminal of the phase shifter.
• the sections Tl and T2 intermediate between the sections SI and S2 are in extension in two parallel directions xx 'and yy'. They are offset relative to each other, and interconnected by a conductive link in the shape of a 90 ° elbow forming the section T3. It is mainly on the sections T1, T2 and T3 that the phase shift cell is formed.
• the dielectric plates 2 and 3 have openings defining movable windows f 1, f2 and f '1 of generally substantially rectangular shape.
• Each window fl, f2 and fl has an opening in one plate, and, substantially opposite, an opening in the other plate (as a variant, a window could be defined by an opening in only one of the two plates) .
• the windows fl, f2 are aligned respectively with the active sections T1 and T2 and are dimensioned so as to cover them partially or entirely depending on the position of the dielectric plates 2 and 3 in the housing 4.
• the Tl and T2 sections also have a substantially rectangular general shape.
• the window f 1 is aligned with a part of the output section S2 of the central line 1. It should be noted that the window f 1 is used only for cascading the cell with another cell as will appear in the following of the description, it is therefore not necessary for embodiments requiring only a phase shift cell.
• the respective width of the windows and their respective length are at least equal to those of the corresponding sections.
• the rectangular shape of the windows substantially matches that of the corresponding sections.
• the outgoing signal at (S) is out of phase (delayed) with respect to the incoming signal at (E).
• This phase shift depends, in a substantially proportional manner, on the surface of the sections T1 and T2 covered by the dielectric plates or, in an equivalent manner, on the displacement of the dielectric plates 2 and 3 materialized by the distance (d) which separates the straight edges of the windows. fl and f2 and the straight end edges of the corresponding sections T1 and T2.
• the minimum position of the phase shifter corresponds to d ⁇ O
• "1" being the predefined common length of the sections Tl and T2 so that the maximum travel of the phase shifter is equal to the common length "1" of said sections.
• the maximum achievable phase shift is substantially proportional to "1".
• the role of the windows f 1 and f2 practiced in the dielectric plates is to cover over a distance a part of the sections Tl and T2 by discovering F other part of these same sections over a distance d-1.
• the covered part of the sections Tlet T2 is surrounded by the dielectric medium of dielectric constant ⁇ r greater than 1 and the uncovered part bathes in F air of dielectric constant equal to 1 in the manner of a suspended line.
• the length of the window f2 is such that the section T2 can be completely ventilated in the minimum position of the phase-shifting module which is obtained for d ⁇ O and that the bent part of the section T3 at the end of the section T2 is also ventilated in this position.
• the length of the window f2 is at least equal to a length f as indicated in FIG. 2 comprising the length 1 of the section T2 increased by a length corresponding to the part of the section T3 falling at the end from the window.
• This part has a length slightly greater than the half length of the conductive link (T3) in projection on the direction of movement of the plates and includes a certain longitudinal length, a bend and finally a certain transverse length. It is the same for the window fl with respect to the sections Tl and SI.
• the electrical length and the impedance of the section T3 connecting the sections Tl and T2, one part of which is in the air and the other part is embedded in the dielectric are kept invariable regardless of the position of the plates dielectric 2 and 3.
• only the electrical properties of the active sections Tl and T2 are variable depending on the position of the dielectric plates 2 and 3 and all the other sections or connecting sections such as T3, SI and S2 retain their initial properties when adjusting the cell phase.
• the dielectric plates 2 and 3 are guided in the slide formed in the base 4 in cooperation with the slots gl and g2 and the drive rod 7.
• the width of a window is substantially equal to the width of a corresponding section of line. However, it may be slightly higher or lower without this having any consequence on the proper functioning of the phase shift cell.
• the material of the dielectric plates is chosen for its good radioelectric and mechanical qualities. By way of nonlimiting example, polyethylene or polytetrafluoroethylene may be used, which are well known for their good qualities of sliding and of tangent of loss at radio frequencies.
• the active sections are not aligned on the same axis.
• the axis offset is greater than the width of the windows so that the adjacent windows do not overlap.
• the length 1 of the active sections T1 and T2 is short compared to the working wavelength, for example equal to one tenth of the wavelength, and the respective widths W1, W2 are preferably substantially equal. However for impedance adaptation needs the widths W1 and W2 may differ slightly.
• the widths and lengths of the active sections determine the maximum phase shift achievable by the phase shift cell.
• the section T3 connects the two sections Tl and T2 together and has at least two elbows, these elbows not necessarily being straight.
• the characteristic impedance Zc of the section T3 and its equivalent electrical length ⁇ substantially determine the state of adaptation of impedance with respect to the impedances Zo of the input and output lines of the phase shifter, these generally being 50 Ohms .
• the impedance Zc determines the width of the section. Approximately these quantities are determined by the following relationships:
• phase shifter has a relative passband close to 25%, ie a frequency band between 1700MHz and 2200MHz for a standing wave ratio (ROS) of less than 1.2.
• ROS standing wave ratio
• the sections T1 and T2 In a triplate of 4.6mm thickness for example with a track of 0.2mm thickness, the sections T1 and T2 would have a width of 3.9 mm and the section T3 a width of 3.2 mm in the constant dielectric 2.3 or 6mm in the air.
• the precise definition of the section T3 with a view to obtaining a good impedance adaptation in the frequency band can be treated more generally taking into account the actual topology of the circuit, by means of a software tool for Appropriate CAD dedicated to microwave circuits, such as for example the software marketed under the name ADS by the company AGILENT or the software marketed under the designation SERENAD by the company ANSOFT Corporation.
• a software tool for Appropriate CAD dedicated to microwave circuits such as for example the software marketed under the name ADS by the company AGILENT or the software marketed under the designation SERENAD by the company ANSOFT Corporation.
• the impedance matching at input and at output can also be improved by the addition of matching circuits performing for example one or more quarter wave transformations.
• the relation (4) shows that the phase shift is proportional to the length 1 covered by the dielectric plates 2 and 3 and that it varies substantially linearly as a function of the displacement d of the dielectric plates 2 and 3, which facilitates the adjustment or the calibration of the phase shifter.
• the relation (4) also shows that the phase shift is proportional to the frequency.
• the relation (4) also makes it possible to estimate the phase shift achievable with an elementary cell comprising three sections T1, T2 and T3 of the type described above.
• the phase shift can be close to 30 ° using dielectric substrates with a constant close to 2, which is advantageous in terms of bandwidth and in terms of radio frequency losses.
• FIG 3 where the elements homologous to those of Figures 1A to 1D bear the same references shows a top view of the phase shifter with the cover removed, comprising two elementary cells in cascade comprising a central line, composed of four sections referenced T1, T2, T '1, T'2, of identical lengths, the sections of odd indices being aligned on the axis xx "and the sections of even indices being aligned on the axis yy'.
• the sections Tl and T2 form the first cell and the sections T'1 and T'2 form the second cell, these two cells constituting a double phase shift cell.
• the dielectric plates 2 and 3 have four windows fl, £ 2, f 1, f 2, covering respectively all or part of the sections Tl, T2, T'1, T'2.
• the phase shift obtained is 2 ⁇ , or twice that of a basic cell ⁇ .
• the connection between the two cells is by means of line sections whose properties s electrical remain invariable depending on the position of the plates 2 and 3 of the phase shifter. This embodiment is easily generalized to obtain a multiple phase shift cell composed of three or more elementary cells.
• FIG. 4 shows a top view of a symmetrical phase shifter comprising an input E and two outputs SI and S2 whose phases are conjugate, that is to say equal and opposite signs, the phase shift sections on either side of a median plane PP ', perpendicular to the direction of movement of the plates, comprising a double cell of the type shown in FIG. 3.
• This phase shifter can for example be used to excite antenna arrays of the type represented in FIGS. 8 and 9.
• the structure of the central line 1 is symmetrical with respect to the plane PP ', so that a displacement d of the plates 2 and 3 to the left of this plane for example, the fact that the active sections of the section on the right are exposed to dielectric, with equal surface area discovered and covered respectively.
• the two signals do indeed have equal and opposite phases and the maximum phase difference between the two signals is equal to the phase difference achievable by two elementary cells in cascade, that is to say substantially 2 ⁇ , ⁇ being. the maximum phase shift for a cell.
• the equalization of the phases simply consists in lengthening, not shown in FIG. 4, the output line SI with an electrical length equivalent to the phase shift ⁇ .
• such a symmetrical distributor phase shifter can be made from multiple cells in place of double cells.
• FIG. 5 shows a top view of a phase shifter comprising a common input E and three outputs SI, S2, S3, phase shifted relative to each other of the same phase shift, generated by double cells, assumed to be identical, of the type shown in FIG. 3.
• These double cells are connected in series and placed side by side to form two phase shift cells.
• the central line 1 is folded in a zigzag each branch of the zigzag corresponding to a double cell section.
• the output SI is phase-shifted by a quantity ( ⁇ o + 2 ⁇ ) relative to the input E
• the output S2 is phase-shifted by ( ⁇ l + 2 ⁇ ) relative to the output SI
• the output S3 is phase shifted by ( ⁇ 2 + 2 ⁇ ) with respect to the output S2
• ⁇ o, ⁇ l, ⁇ 2 being the residual phase shifts corresponding to the paths traveled by incoming wave in E to reach the respective outputs for a given position of the phase shifter taken as reference .
• each branch of the zigzag can have a multiple cell.
• the zigzag is not limited to three branches. This principle can therefore be generalized for any number of outputs.
• This phase shifter can be used to make a symmetrical distributor phase shifter. For the sake of clarity, only the left part of the distribution phase shifter is shown in FIG. 5.
• This symmetrical distribution phase shifter can for example be used in the network antenna architecture diagram shown in FIGS. 8 and 9.
• FIG. 6 represents a distributor phase-shifting block comprising an input E and ten outputs respectively referenced SI, S2 S5, Sl, S-2, S-5.
• the outputs have two by two conjugate phases and the input power is distributed in an unbalanced manner between the ten outputs.
• phase shifts are obtained by means of two separate blocks 8 and 9 of dielectric plates 2 and 3, disposed on either side of the median plane PP 'and moving together by means of a not dephased phase shifter adjustment mechanism.
• the parts of the conductive tracks 10 located in the space between the two removable blocks 8 and 9 and at the ends of the blocks are held in sandwich by two facing plates 11 made of insulating material, foam for example with very low loss and a dielectric constant close to that of air. Examples of embodiments of antennas organized in a uniform array which may include phase shifters according to the invention are shown in FIGS. 7 to 9.
• n l, 2, .... N
• the amplitude of the phase shift on the last source which is equal to (N-1) ⁇ can become very large if N is large.
• the size of the phase shifters limits this embodiment to a very limited number of sources.
• Figure 8 shows the same network of sources but this time supplied in series so that the phase shifts are cumulative from one source An to the next and that the phase distribution law is linear along the network.
• each node of the network has three branches, an input branch and two output branches and it is possible to easily achieve a determined law of power distribution on the radiating sources, for example in order to produce a diagram shaped radiation or having a low level of secondary lobes.
• the circuit consisting of phase shifters and power division nodes can advantageously be produced in the form of a single box which is both distributor and phase shifter or, at least if the space available does not allow it. not, of a reduced number of such boxes. Such a box which may be of the type described in FIGS.
• phase shifts will include an input and several outputs supplying the elementary sources A-2, Al, A0, Al, A2. It will also be equipped with means for adjusting the phase shifters. It will be noted that in the diagram in FIG. 8, the phase shifts are symmetrical with respect to the entry point M of the network, the phase shifts are positive towards the top and are negative towards the bottom of the point M. This arrangement is only a particular advantageous case from a practical point of view, the entry point of the network can indeed be positioned at any location on the network, the main thing is that the phase shift between two successive sources is equal to ⁇ . Thus, as shown in FIG. 9, the network is formed by an even number of sources with a feed point M positioned in the center of the network, which provides symmetrical phase shifts as in Figure 2.
• FIG. 10 represents a phase shifting block distributor, according to a particular embodiment of the invention, in which the housing 4 comprises 2 compartments 4a and 4b aligned and connected together by a coaxial cable 30 having a characteristic resistance generally of 50 ohms.
• Each compartment comprises a set of phase shift cells having a common terminal and extreme terminals situated at the lateral ends of the compartments.
• each compartment comprises four double phase-shift cells of the type of FIG. 3.
• the compartments 4a and 4b in particular have substantially identical dimensions.
• the distributor phase shift block shown in FIG. 10 has a common input E and 9 outputs SI to S5 and S-2 to S-5. These inputs / outputs are generally adapted to an impedance
• the connection of the input / output cables on the housing 4 is carried out by means of input / output cable supports 20, 21, 22 and 23, of conductive material, fixed to the lateral ends of each compartment by screwing onto the housing .
• the housing is in particular metallic.
• compartment 4a is provided with an input / output cable support 20 on its left lateral end and an input / output cable support 21 on its right lateral end.
• compartment 4b is provided with an input / output cable support 22 on its left lateral end and an input / output cable support 23 on its right lateral end.
• the coaxial cable 30 connects the cable support 22 of compartment 4a to the cable support 23 of compartment 4b.
• the output SI keeps the same fixed phase shift taken as a 0 ° reference.
• phase shifts are obtained by means of two pairs of separate blocks ⁇ 8, 9 ⁇ and ⁇ 8 ', 9' ⁇ , symmetrical with respect to an axis (P ⁇ P ⁇ ) perpendicular to the chosen direction.
• Each block consists of dielectric plates 2 and 3.
• the pair of blocks ⁇ 8,9 ⁇ is located in the compartment 4a and the pair of blocks ⁇ 8 ', 9' ⁇ is located in compartment 4b.
• the phase shift is modified by a guide rod 7 integrated into the housing 4 and passing through each compartment 4a and 4b.
• the guide rod 7 is directed in the chosen direction defined above and is integral with the dielectric plates 2, 3.
• the housing 4 according to this embodiment of the invention is a metal housing, for example aluminum, manufactured by an extrusion process.
• Dielectric plates 2 and 3 can be made by molding.
• phase-shifting block of given length L is more complex than the manufacture of a phase-shifting block with two compartments of length L / 2 that is twice as small. It follows that the structure of the housing 4 in two compartments 4a and 4b, as described above, simplifies the manufacture of the phase shifter compared to the embodiments described above.
• the mounting of the phase-shifting block can be achieved by threading each pair of blocks ⁇ 8.9 ⁇ (respectively ⁇ 8 ', 9' ⁇ ) in the corresponding compartment 4a (respectively 4b).
• the mounting of the phase shift block according to this embodiment is also simplified compared to the embodiments described above.
• phase shifter described with reference to FIG. 10 also makes it possible to eliminate the direct connection of input / output cables to the housing 4 (ie the direct contacts between the coaxial sheath and the housing) thanks to the introduction of the supports of cables and therefore the number of potential sources of passive intermodulation products (IMP).
• IMP passive intermodulation products
• the phase shifter according to the invention is used, in particular, for the creation of arrays of depointable beam antennas, by displacement of the plates 2 and 3.
• the input / output terminals then form connection points of elements d antennas.
• the invention is not limited to the embodiments described. These include different possibilities of symmetry that it is possible to arrange differently by deleting unnecessary elements if necessary.
• the invention covers all the variant embodiments that a person skilled in the art may envisage.

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