Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q1/00—Details of, or arrangements associated with, antennas
  • H01Q1/36—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith
  • H01Q1/38—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith formed by a conductive layer on an insulating support
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q1/00—Details of, or arrangements associated with, antennas
  • H01Q1/36—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith
  • H01Q1/362—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith for broadside radiating helical antennas
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q11/00—Electrically-long antennas having dimensions more than twice the shortest operating wavelength and consisting of conductive active radiating elements
  • H01Q11/02—Non-resonant antennas, e.g. travelling-wave antenna
  • H01Q11/08—Helical antennas

Definitions

• the field of the invention is that of wide bandwidth antennas with a hemispherical or quasi-hemispherical radiation pattern. More specifically, the invention relates to helical antennas of this type.
• the antenna of the invention finds applications in particular in the context of mobile satellite communications between fixed users and / or mobiles of any type, for example aeronautical, maritime or terrestrial.
• satellite communication systems are implemented, or are currently under development (for example the INMARSAT, INMARSAT-M, GLOBALSTAR (registered trademarks) systems, ).
• These antennas are also of interest in the deployment of personal communication systems (PCS) by geostationary satellites.
• PCS personal communication systems
• the aim of these systems is to provide land users with new communications services (multimedia, telephony) via satellites.
• new communications services multimedia, telephony
• geostationary or moving satellites they provide global ground coverage. They must be similar to terrestrial cellular systems in terms of cost, performance and size.
• the antenna located on the user's terminal is a key element from the point of view of the reduction in size.
• the very different incidences of the signals received or transmitted require the antennas to have a radiation diagram with hemispherical or quasi-hemispherical coverage.
• the polarization must be circular (left or right) with a ratio of less than 5 dB in the useful band. More generally, the invention can find applications in all systems requiring the use of a wide band and circular polarization.
• the antennas must indeed have the above characteristics either in a very wide bandwidth, of the order of 10% or more, or in two neighboring sub-bands corresponding respectively to reception and to l 'program.
• a quadrifilar helical antenna is formed by four radiating strands.
• This antenna called the printed quadrifilar helix antenna (HQI)
• HQI printed quadrifilar helix antenna
• Dual-layer HQI antennas These antennas are formed by the concentric "nesting" of two coaxial resonant quadrifilar helices, electromagnetically coupled. The assembly functions as two coupled resonant circuits, the coupling of which deviates the resonant frequencies.
• a two-layer resonant quadrifilar helical antenna is thus obtained, according to the technique described in FR - 89 14952.
• This technique has the advantage of requiring a single supply system, and of allowing dual band or broadband operation.
• the radiating strands are printed on a thin dielectric substrate, then wound on a cylindrical support transparent from the radioelectric point of view.
• the four strands of the propeller are open or short-circuited at one end and electrically connected at the other end.
• This antenna requires a supply circuit, which ensures the excitation of the different antenna strands by signals of the same amplitude in phase quadrature.
• This function can be performed using 3dB -90 ° coupler structures and a hybrid ring.
• the assembly can be made in printed circuit and placed at the base of the antennas. A simple but bulky supply is thus obtained.
• the antenna (including its feed) be of the smallest possible size and weight, and that it have the lowest possible cost.
• an objective of the invention is to provide a resonant helical antenna having a wide bandwidth, which can cover, for example, the transmission band and the reception band of a communication system.
• an objective of the invention is to provide such a helical antenna having a large bandwidth (greater than that obtained according to the prior art) in each sub-band, when two sub-bands are provided.
• Another objective of the invention is to provide such an antenna whose dimensions, performance and cost are acceptable for portable terminals of terrestrial cellular systems.
• Another object of the invention is to provide a reduced size antenna while having broadband operation.
• An objective of the invention is also to provide an antenna relatively simple to manufacture, and therefore of low cost. Yet another objective of the invention is to provide a technical alternative to the solutions of the prior art.
• a helical antenna comprising at least one helix formed by at least two radiating strands, at least one of the radiating strands being associated with a parasitic strand of width less than or equal to the radiating strand (s) so as to widen the bandwidth of the antenna.
• the helical antenna is remarkable in that each of the parasitic strands is connected to ground.
• the operation of the antenna and in particular of the parasitic strands is optimized.
• the helical antenna is remarkable in that the radiating strands and the parasitic strands are printed on a substrate. In this way, the helical antenna can be produced according to a manufacturing method that is simple, effective and low cost.
• the antenna is remarkable in that each of the radiating strands is associated with a parasitic strand of width less than or equal to the radiating strand.
• a selfic behavior corresponding to a radiating strand and in particular to its length
• a global capacitive behavior corresponding to the association of a radiating strand and a parasitic strand and dependent on the distance between these two strands and the ratio between their width
• the parasitic strand preferably being of small width.
• the helical antenna is remarkable in that the ratio between the width of each of the parasitic strands and the width of the associated radiating strand is less than or equal to 0.15.
• the performance of the antenna is optimal, in particular in the bands close to 1 GHz.
• the helical antenna is remarkable in that each of the parasitic strands is positioned relative to the associated radiating strand so as to optimize the coupling between the parasitic strand and the associated radiating strand.
• a parasitic strand and the associated radiating strand are positioned so as to optimize the bandwidth, a coupling optimum being, if it exists, dependent on the distance separating them.
• the antenna has a better adaptation.
• the helical antenna is remarkable in that each of the parasitic strands is more distant from the associated radiating strand than from at least one of the other radiating strands.
• an optimization of the coupling between the parasitic strand and the associated radiating strand is often obtained by moving the parasitic strand away from the associated radiating strand; thus, the further the parasitic strand and the associated radiating strand are, the wider the radiation band of the antenna.
• the helical antenna is remarkable in that each of the parasitic strands is parallel to the radiating strand with which it is associated.
• the two strands are parallel if their longitudinal center lines are parallel.
• the two strands are considered to be parallel if one of the following three conditions is met: their longitudinal median lines are parallel; or their tangent lines outside and / or inside in the direction of the length are parallel; or
• each of the segments forming the parasitic strand is parallel to an associated segment of the radiating strand.
• each of the parasitic strands and associated radiating strands have a capacitive effect.
• the helical antenna is remarkable in that each of the parasitic strands has substantially the same length as the radiating strand with which it is associated.
• the antenna is relatively simple to produce (and in particular simpler than if the ground connection at one end of the parasitic strand was made, for example, in the middle of the cylinder).
• the helical antenna is remarkable in that one of the ends of each of the radiating strands is connected by a conductive link to one of the ends of the radiating strand with which the parasitic strand is associated.
• the parasitic strands and the associated radiating strands can be etched on the same side of the substrate, the other side of the substrate then being available for another use (for example, for etching additional strands or another helical antenna ).
• the helical antenna is remarkable in that one of the ends of each of the radiating strands is connected by coupling to one of the ends of the radiating strand with which the parasitic strand is associated.
• the helical antenna is remarkable in that the radiating strands are printed on a first face of a substrate and in that the parasitic strands are printed on a second face of the substrate.
• the helical antenna is remarkable in that at least one parasitic strand and a radiating strand close to the radiating strand with which the parasitic strand is associated overlap.
• the distance between a parasitic strand and the associated radiating strand is greater than that separating two neighboring radiating strands. This makes it possible in particular to obtain more margin for the adjustment of the coupling between a parasitic strand and the associated radiating strand and therefore to find more easily a optimum for improving the bandwidth.
• the helical antenna is remarkable in that the end of the radiating strands not connected to a parasitic strand is connected to a line of attack of a supply circuit.
• the operation of the antenna is optimized.
• the helical antenna is remarkable in that at least one of the propellers is a quadrifilar propeller, comprising four strands.
• the opening of the antenna is very wide, the radiation diagram being almost hemispherical.
• the helical antenna is remarkable in that the radiating strands forming a helix all have the same dimensions and in that the parasitic strands all have the same dimensions.
• the strands have the same current distribution 90 ° out of phase.
• the helical antenna is remarkable in that at least one of the radiating and / or parasitic strands is formed of at least two segments, the winding angles of at least two of the segments being different and determined randomly or pseudo-randomly using global optimization means.
• the helical antenna is remarkable in that at least one of the radiating and / or parasitic strands has a variable width, varying regularly and monotonously between a maximum width and a minimum width. In this way, the adaptation of the antenna is simplified, an additional adjustment parameter being available for this adaptation.
• the helical antenna is remarkable in that the radiating strands have a length substantially different from a multiple of the wavelength corresponding to the average frequency of the antenna transmission band, divided by 4.
• Figures 1 and 2 illustrate a quadrilateral helical antenna of known type, with conventional strands of constant width, respectively when the propeller is developed (Figure 1) and when it is wound on a cylindrical support ( Figure 2);
• - Figure 3 is an example of a propeller according to the invention, in its developed form;
• - Figure 4 shows a front view of the propeller of Figure 3, wound on its cylindrical support;
• FIG. 5 illustrates an example of ROS measured at the input of a strand for an antenna according to the invention
• FIG. 6 is a Smith chart representing the input impedance of an antenna according to the invention.
• FIG. 7a and 7b illustrate a variant of the invention according to which radiating strands and associated parasitic strands are coupled by being printed on two opposite faces of a substrate;
• FIG. 8 shows an example of an antenna according to a variant of the invention according to which radiating strands are of variable width;
• Figures 9a and 9b show an example of an antenna according to another variant of the invention having radiating strands forming a broken line.
• Figures 1 and 2 show a conventional quadrilateral helix antenna, as already discussed in the preamble. It includes four strands 11, 11 4 in length
• the antenna requires a supply circuit which excites the different strands by signals of the same amplitude and in phase quadrature.
• This function can be obtained from 3dB -90 ° coupler structures and a hybrid ring, made in printed circuit and placed at the base of the antennas.
• FIG. 3 shows an example of a propeller 30 according to the invention, in its developed form.
• the HQI antenna 30 therefore has 4 regularly radiating strands 31, 31 4 regularly spaced, printed on a substrate 32 and of width equal to Wa.
• the four strands 31, to 31 4 are folded back on themselves at one of their ends respectively 36, to 36 4 each forming a parasitic strand respectively 34, to
• the parasitic strands 34, to 34 4 have a width W br less than the width, W a , of the radiating strands in order to guarantee a broadband operation of the antenna.
• the parasitic strands 34, to 34 4 are connected to the ground 35 at the end opposite the end respectively 36, to 36 4 .
• the width, W br , of parasitic strands and the width, W a , of radiating strands are constant.
• the antenna 30 is then wound on a cylindrical support, as illustrated in FIG. 4, which presents a front view of the antenna wound on its cylindrical support.
• the antenna produced and illustrated with reference to FIGS. 3 and 4 has the following characteristics:
• Length of the strands 0.83 ⁇ where ⁇ represents the wavelength corresponding to the average frequency of the transmission band (this length having been chosen to optimize the opening of the antenna); - Diameter: 0.18 ⁇ ; Distance d: 9 mm; Width W br : 1.95 mm - Ratio of strand widths WW br : 8.
• Winding angle 50 °.
• the antenna band widens as the distance d increases.
• the parasitic strand is therefore close to the neighboring radiating strand.
• there is an optimum bandwidth as a function of the distance between a parasitic strand and the associated radiating strand.
• FIG. 5 makes it possible to view the ROS 52 measured as a function of the frequency 50 (expressed in GHz in the figure) measured at the input of a radiating strand for the antenna 30 illustrated with reference to FIGS. 3 and 4, the others being charged under 50 ⁇ .
• the antennas are measured at the central frequency FI equal to 1.5 GHz.
• the HQI antenna with folded strand according to the invention, an adaptation of the HQI antenna is obtained which is less than ⁇ 10 dB over the interval going from 1.27 GHz to 1.65 GHz, ie a bandwidth which reaches 26%.
• the HQI antenna has a significant increase in bandwidth.
• the folded printed quadrifilar helical antenna each parasitic strand of which is connected to ground, allows transmission and / or reception in a wide passband or in two different sub-bands, each having a wide passband.
• the technique of the invention therefore gives a non-negligible increase in bandwidth.
• a printed quadrilateral helical antenna operating in a wide bandwidth and / or in two different sub-bands each having a wide bandwidth, and the height of which is reduced.
• FIG. 6 is a Smith chart representing the input impedance 60 of an antenna according to the invention standardized at 50 Ohms.
• FIG. 7a presents an example of a propeller 70 according to a variant of the invention, in its developed form.
• the HQI antenna 70 therefore comprises 4 regularly radiating conductive strands 71, 71 4 , spaced regularly, printed on a first face of the substrate 72 and of width equal to W a .
• the four strands 71, 71 4 are connected at one end to the lines of attack of the supply circuit 73.
• Parasitic strands 74, 74 4 are printed parallel to the radiating strands on a second face of the substrate 72 opposite the first face.
• the parasitic strands 74, 74 4 are connected to ground 75 at one of their ends respectively 71, 71 4 .
• Each of the parasitic strands 74, 74 4 is coupled by its end respectively 75, to 75 4 not connected to the ground 75, to the end not connected to the supply of the strand respectively 71, to 71 4 with which it is associated.
• the parasitic strands 74, to 74 4 have a width W br less than or equal and, preferably much less (in a ratio W br W a less than 0.15), to the width, W a , of the radiating strands in order to guarantee a broadband operation of the antenna.
• W br width of parasitic strands
• W a width of radiating strands
• the distance separating a parasitic strand and the associated radiating strand is not limited by the distance separating two radiating strands.
• the distance between a parasitic strand and the radiating strand can be greater than the distance separating two radiating strands.
• the coupling between a parasitic strand and the associated radiating strand and therefore the bandwidth can then be improved. We then have more possibilities in the search for optimum coupling.
• FIG. 7b illustrates in detail the end 751 of the radiating strand 711 coupled to the parasitic strand 741.
• each of the parasitic strands and the associated radiating strand overlap on either side of the substrate 72 over a distance E between 0 and the distance d separating the parasitic strand from the associated radiating strand.
• the other characteristics of the antenna 70 (winding around a cylindrical support, dimensions of the strands and of the antenna, etc.) being similar to that of the antenna 30 of FIGS. 3 and 4, they will not be described further. .
• FIG. 8 shows an example of antenna 80 according to a variant of the invention according to which radiating strands 81, 81 4 are of variable width.
• Each of the radiating strands 81, to 81 4 is connected by one of its ends to a parasitic strand 84, to 84 4 .
• the object of this embodiment is in particular to obtain an HQI antenna 80 making it possible to further broaden the bandwidth and / or to allow better adaptation of the antenna 80 (the variation in the width of the band being an additional parameter usable for adaptation).
• This is obtained in varying the width of the radiating strands along the helix.
• the ends of the radiating strands have a different width W a and W a2 respectively .
• the variation of the width can be: regular according to a linear law, exponential, double exponential, in staircase ... or not regular.
• the width of the parasitic strands is constant and each of the parasitic strands is parallel to a longitudinal center line of the associated radiating strand (illustrated, for example, by the line 87 corresponding to the strand 81,).
• each of the radiating strands of the antenna 80 has a minimum width W a , equal to 2mm and a maximum width W a2 equal to 16 mm.
• the characteristics of the antenna 80 being similar to those of the antenna 30 illustrated with reference to FIGS. 3 and 4, they will not be described further.
• the parasitic strands of a helical antenna are coupled and not directly connected to radiating strands of variable width, similar to the strands 81, 81 4 of the antenna 80 (according to a similar coupling to that of the radiating and parasitic strands of the antenna 70).
• the width of the parasitic strands is variable, the longitudinal center lines of each of the parasitic strands and of the associated radiating strand are parallel.
• the parasitic strands are parallel to one of the sides of the radiating strands.
• a parasitic strand parallel to an adjacent radiating strand makes it possible, in particular, to move this parasitic strand away from the associated radiating strand while bringing it closer to the adjacent strand thus increasing the capacitive effect and the bandwidth of the antenna.
• FIG. 9a shows an example of antenna 90 according to another variant of the invention having radiating strands 91, to 91 4 forming a broken line.
• Each of the radiating strands 91, to 91 4 is connected by one of its ends to a parasitic strand 94, to 94 4 .
• Each radiating strand 91, to 91 4 (or at least some) of the HQI antenna is broken down into a limited number of segments. From the mathematical expressions linking the geometrical parameters of a helical antenna, it can be seen that a modification of the winding angle influences the pitch of the antenna, and therefore the axial length. Thus it is possible to give a different winding angle for each segment. The height can thus be reduced. Setting up different winding angles can be compared to a change in the pitch of the antenna.
• the winding angle ⁇ is also a parameter influencing the radiation pattern of an HQI antenna (opening angle at 3dB, ellipticity ratio). This is why, to choose the different suitable angles ⁇ , a global optimization program such as simulated annealing or the genetic algorithm can be used.
• the synthesis is performed on the radiation patterns in main and cross polarization by introducing a template defined by the amplitude levels and the opening angles -3dB desired.
• this template allows perfect control of the opening angles at -3dB, as well as the rejection of the polarization therefore reverses the ellipticity ratio.
• the variables to be optimized are the different winding angles of the strands of the HQI antenna. The algorithm will give the angles ⁇ , optimum.
• Each of the radiating strands 91, to 91 4 of the antenna 90 presented opposite FIG. 9a is divided for example into eight segments of length,, identical.
• the radiating strands 91, and parasitic 94, and in particular the segments which make up the radiating strand 91, are illustrated in more detail with reference to FIG. 9b.
• the parasitic strand 94 is parallel to an inner tangent 97 (that is to say located between the radiating strand 91, and the associated parasitic strand 94,) of the radiating strand 91,.
• one or more parasitic strands are parallel to an external tangent (that is to say located on the side opposite to the parasitic strand) of the associated radiating strand (which makes it possible to bring the parasitic strand closer to a strand adjacent neighbor) or a center line of the associated radiating strand.
• one or more parasitic strands form a broken line.
• each of these parasitic strands comprises the same number of segments as the associated radiating strand and each of the segments of the parasitic strand has the same length and is parallel to a corresponding segment on the associated radiating strand (thus, in addition to a different width, the parasitic strand and the associated radiating strand have the same shape), which makes it possible to position a parasitic strand very close to an adjacent radiating strand.
• the parasitic strands of a helical antenna are connected by coupling (and not directly) to radiating strands forming a broken line similar to the coupling link presented opposite the figures 7a and 7b.
• the width of the parasitic strands can take any value less than that of an associated radiating strand and preferably of the order of an eighth of that of an associated radiating strand.
• the invention can be applied to any type of helical antenna, and not only to quadrilateral antennas.
• the strands do not all have identical dimensions.
• the antenna is printed flat, then wound on a support to form the antenna.
• the substrate intended to receive the printed elements can be produced directly in its final cylindrical shape. In this case, the printing of the strands and of the supply structure is carried out directly on the cylinder.
• the antenna of the invention also lends itself to the production of antenna arrays.
• the technique of the invention is compatible with techniques aimed at reducing the size of the antenna, such as in particular that proposed in the patent application in patent document FR-0011830, in the name of France Telecom (helical antenna with variable pitch) or to increase the bandwidth, for example, according to a technique proposed in patent document FR-0011843, in the name of France Telecom (helical antenna with width strands variable).
• the presence of variable pitch and / or the variation in width can be applied to all the strands, or selectively to some of them.

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• Details Of Aerials (AREA)
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• Variable-Direction Aerials And Aerial Arrays (AREA)

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• 2002
  • 2002-09-20 FR FR0211696A patent/FR2844923B1/fr not_active Expired - Fee Related
• 2003
  • 2003-09-19 US US10/528,516 patent/US7525508B2/en active Active
  • 2003-09-19 AU AU2003298989A patent/AU2003298989A1/en not_active Abandoned
  • 2003-09-19 AT AT03797356T patent/ATE384346T1/de not_active IP Right Cessation
  • 2003-09-19 WO PCT/FR2003/002774 patent/WO2004027930A1/fr active IP Right Grant
  • 2003-09-19 DE DE60318725T patent/DE60318725T2/de not_active Expired - Lifetime
  • 2003-09-19 EP EP03797356A patent/EP1540768B1/de not_active Expired - Lifetime

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