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
  • H01Q1/362—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 antennas with a large bandwidth having a good left and / or right circular polarization in the useful band. More specifically, the invention relates to helical antennas of this type intended in particular and without limitation to equip different types of positioning systems and / or terrestrial and / or satellite communications requiring the use of separate frequency bands and therefore, the use of multiband antenna to cover all of these different systems and / or communication standards.
• the antenna according to the invention finds particular applications in the context of mobile satellite communications between fixed users and / or mobiles of any type, for example aeronautical, maritime or terrestrial, or in the fields service broadcasting and / or satellite positioning.
• GPS for "Global Positioning System” or “Global Positioning System” which corresponds to the position American satellite originally developed for the military field
• GLONASS Russian system
• GALILEO European GALILEO system
• the printed quadrifilar helix antennas known from the prior art have characteristics very similar to those mentioned above. These antennas are formed of four radiating strands that can be made or not in printed technology. When made in such printed technology, the strands are printed on a thin dielectric substrate (FIG. 1) and then wound on a radially transparent cylindrical support, as illustrated in FIG. configuration, the antenna used requires a power circuit that can ensure the excitation of different printed strands by means of signals of the same amplitude and which are in phase quadrature. Such a function can be performed from 3dB-90 ° coupler structure and a hybrid ring. This assembly can be made in printed circuit and can be positioned at the base of the antennas.
• antennas are also of interest in the deployment of personal communications systems (PCS) by geostationary satellites. These systems are intended to provide terrestrial users with new communications services (multimedia, telephony) via satellites. With the help of geostationary or moving satellites, they make it possible to obtain a global terrestrial coverage. They must be similar to terrestrial cellular systems in terms of cost, performance and size. Thus, the antenna located on the user's terminal is a key element from the point of view of reducing the size.
• PCS personal communications systems
• the very different incidences of signals received or emitted require the antennas to have a hemispherical or quasi-hemispherical coverage pattern.
• the polarization must be circular (left or right) with a ratio of less than 5 dB in the useful band, while offering good performance on several bands that can be selected on an octave, so that the antenna according to the invention can answer indifferently to several standards of mobile communications, GSM, GPRS, UMTS for example.
• the invention can find applications in all systems requiring the use of several bands and obtaining a polarization circular. It is already known from patent FR-89 14952 in the name of the same applicant as the present application, a type of antenna particularly suitable for such applications.
• This antenna called printed quadrifilar helix antenna (HQI)
• HQI printed quadrifilar helix antenna
• Broadband or bi-band operation can be achieved by using 2-layer HQI antennas.
• These antennas are formed by the concentric "nesting" of two coaxial, electromagnetically coupled, quadrifilar resonant propellers. The assembly functions as two coupled resonant circuits, the coupling of which separates the resonance frequencies.
• a two-layer resonant quadrifilar helix antenna is thus obtained, according to the technique described in FR-89 14952.
• This technique has the advantage of requiring a single power system, and allowing dual band and wideband operation, up to 15%.
• a quadrifilar antenna is thus formed of four radiating strands.
• An exemplary embodiment is described in detail in the document "Analysis of quadrifilar resonant helical antenna for mobile communications", by A. Sharaiha and C. Terret (IEE - Proceedings H, 140, 4, August 1993).
• the radiating strands are printed on a dielectric substrate of small thickness, and then wound on a cylindrical support that is transparent from the radio point of view.
• the four strands of the helix are open or short-circuited at one end and electrically connected at the other end.
• a wider band operation is then obtained by varying the width of the strands along the helix regularly or not, which allows to obtain accordingly a wide-band variable width resonant quadrifilar helix antenna, up to 14%, according to the technique described in the patent FR-00 11843 entitled "variable-width helix antenna".
• an object of the invention is to provide a quadrilateral helical antenna with circular polarization having good performance on several bands of frequencies that can be selected on an octave and can cover the transmission and reception band of a set different communication and / or positioning systems, so as to respond to and / or adapt to several standards of communication and / or positioning systems.
• an object of the invention is to provide such a helical antenna that is resonant in a wide frequency range over at least two distinct bands, with radiation patterns that remain constant.
• Another object of the invention is to provide such an antenna whose dimensions, performance and cost are adapted (therefore at least similar) to the portable terminals of terrestrial cellular systems.
• a further object of the invention is to provide such an antenna using a compact power supply system and not necessarily disposed at the base of the antenna.
• Another object of the invention is to provide characteristics that are close to or better than those of double helix antennas (more complex to produce) with a single helix. 4. Main features of the invention
• a helical antenna comprising or less a helix formed of at least two radiating conductive strands, at least one of which one of the conductive strands advantageously extends into at least two sub-strands separated by a slot of predetermined height and width, said slot being connected in at least one point to a current belly.
• a helical antenna comprising or less a helix formed of at least two radiating conductive strands, at least one of which one of the conductive strands advantageously extends into at least two sub-strands separated by a slot of predetermined height and width, said slot being connected in at least one point to a current belly.
• different geometries of strands and / or sub-strands and / or slots may be envisaged for the invention in terms of the constraints related to the dimensioning of the antenna and / or related to the sizing in frequency bands in reception and / or or in transmission required by the antenna to be implanted.
• An additional advantage according to the invention concerns the possibility of being able to place the slot on the conductive strands, preferably at the point where the current is maximum, which eliminates the positioning constraints of the power supply source at the base of the the antenna as imposed by the known systems of the prior art.
• each of the slots is of variable width, depending on the width of the frequency range to be made accessible to the antenna in reception and / or transmission.
• the slit widths can also be fixed in a predetermined manner as needed.
• the helical antenna comprises at least two slots having different widths.
• the sub-strands are of variable width.
• the width or the width of the variable width varies monotonically between a maximum width and a minimum width.
• the widths of the strands can also be fixed and determined according to the needs.
• the widths of said one or more strands and / or of said one or more slots of variable width vary regularly.
• the width of the slots and / or conductive sub-strands may follow a law belonging to the group comprising: linear laws, exponential laws, exponential double laws, step laws.
• the widths of said one or more strands and / or of said one or more slits of variable width vary non-uniformly.
• the sub-strands adjacent to a slot have respectively different heights, so as to allow the resonance of the antenna in at least two distinct frequency bands.
• the helical antenna according to the invention the sub-strands adjacent to a slot are folded over a predetermined height towards the side opposite to the slot.
• At least one of the helices is a quadrifilar helix comprising four conductive strands.
• the conductive strands are printed on a flexible dielectric substrate. This technique, known per se, allows a simple and effective implementation of the invention.
• the conductive strands are spaced apart on the substrate by intervals of predetermined width.
• the dimensions of the conductive strands are determined so as to provide a relatively wide bandwidth spectrum, so as to be able to benefit from the multiband function in a band of width greater than 8% for a ROS less than 2.
• the slots are placed between the high end and a position where the current is highest on each of the conductive strands.
• the number of slots separating each of the conductive strands is determined according to the number of distinct frequency ranges in which the antenna must be able to operate, so as to provide a multiband operation.
• the antenna thus obtained has a larger bandwidth (in one or more subbands) than the conventional antenna, with strands of constant width, hereinafter referred to as a reference antenna, without increasing the manufacturing complexity or the cost price.
• FIG. 3 gives a description of the conventional current of an HQI antenna with a wavelength close to (3 ⁇ / 4);
• FIG. 4 illustrates a slotted tri-band HQI antenna, in its coiled antenna / developed antenna configuration;
• FIG. 5 shows a comparison of the evolution of the reflection coefficient curve in dB between a conventional HQI antenna known from the prior art and a slotted bi-band HQI antenna
• Figures 6 and 7 show the radiation patterns in the context of a two-band antenna with slots, in circular polarization, at different frequencies
• Fig. 8 shows an illustration for a slit tri-band antenna of the evolution of the coefficient of reflection versus frequency curve compared to a conventional HQI antenna
• FIG. 9 shows the radiation patterns of a tri-band antenna with circular polarization slots obtained relative to three resonant frequencies of the antenna
• FIG. 10 finally proposes an illustration for a quad band antenna with slots of the evolution of the curve of Frequency reflection, compared to a conventional HQI antenna.
• Figure 11 gives an example of a tri-band antenna, the sub-strands separated by slots extending the main strand in the form of a trident.
• Figure 12 gives an example of a dual-band antenna, the sub-strands separated by slots extending the main strand in the form of a fork.
• FIG. 13 gives an example of a two-band antenna whose sub-strands separated by slots are folded partially along the main strand.
• FIGS. 1a and 1b show a conventional quadriliform helix antenna, as already discussed in the preamble, which comprises four strands 1O 1 to 1O 4 of length 12 and width d (FIG. These radiating strands are printed on a dielectric substrate 11 of small thickness then wound on a cylindrical support 12 radially transparent (Figure Lb), of radius r, of circumference c and axial length 11, and description of the conventional current of an antenna HQI of length close to ⁇ (alpha) being the angle of winding or elevation of the antenna.
• the antenna requires a power supply circuit which ensures the excitation of the different strands by signals of the same amplitude and in phase quadrature.
• This function can be obtained from 3dB coupler structures -
• the antenna is of small dimensions (weight, volume, ...) and moreover, that it has the lowest possible cost, in coherence with the constraints of corresponding markets.
• the bandwidth of this type of antenna is generally of the order of 6% to 8% for an ROS less than two.
• the antenna configuration presented in FIGS. 13 and 14 makes it possible to reduce as much as possible the height of the antennas to be developed and integrated into the new generation mobile terminals. Indeed, in such a geometrical configuration of the antenna, the sub-strands are folded over a predetermined height which may be more or less important. This trick offers another advantage of not impairing the quality of reception and / or transmission of the antenna in the targeted frequency bands. It is also simple and inexpensive to implement on a large scale in terms of manufacturing antennas according to the invention.
• the invention particularly aims a circular polarization quadrifilar helix antenna with good performance on several bands that can be selected on an octave.
• This antenna can in particular meet a multitude of standards in the field of positioning systems and / or mobile communications.
• a multiband HQI antenna thus consists of 4 conductive strands (20 1 to 20 4 ) printed on a flexible dielectric substrate 21, regularly spaced, of width Wa.
• each strand separated by the slot or slits 22 give rise to two or more sub-strands 24 of fixed or variable widths and different heights thus allowing the resonance at several frequencies.
• FIG. 23 of the slot 22 must be placed at a current belly 30 to allow multiband operation, as shown in Figure 3.
• the antenna is then wrapped around a transparent support to obtain the antenna in its operating state .
• Figures 2 and 3 show an example of HQI antenna with a slot 22 corresponding to a dual-band operation. More precisely, FIG. 3 gives a description of the conventional current of an HQI antenna with a wavelength close to (3 ⁇ / 4). For example, for a given resonance frequency, the entire antenna can radiate on a single sub-strand.
• FIG. 4 shows the geometry of the antenna according to the invention for a multiband operation, in this case for a tri-band operation.
• FIGS 5 to 10 show examples of multi-band operation of the antenna according to the invention.
• FIGS. 5 to 9 show an example of dual-band operation of an antenna according to the invention, for an antenna designed according to a preferred embodiment and having a strand length 0.83 ⁇ 0 , diameter 0.18 ⁇ 0 .
• FIG. 5 compares the evolution of the reflection coefficient measured at the input of one of the four conducting strands (2O 1 to 2O 4 , FIG. 2) as a function of frequency, the other strands being loaded under 50 ⁇ , for a dual-band slot antenna according to the invention (solid line 51) and for a conventional HQI antenna according to the known techniques of the prior art (dashed line 52).
• F1 I.3GHz
• F2 1.45GHz
• HQI according to the prior art it was possible to obtain a single adaptation of the HQI antenna less than -2OdB on a single bandwidth 55, for a center frequency of 1.3GHz.
• the HQI antenna according to the invention makes it possible to obtain radiation diagrams which are equivalent in the two bandwidths (53 and 54) to the diagrams obtained for a conventional antenna with a wide aperture and good Rejection of the reverse bias in the aperture.
• This new approach according to the invention therefore advantageously to extend the possibilities of using such antennas and to adapt the communication systems they equip to several types of communication standards, which goes against the prejudices of the person skilled in the art.
• FIG. 8 shows a tri-band operation of an antenna according to the invention and having the same geometrical parameters as in the aforementioned two-band embodiment, the strands having always a length of 0.83 ⁇ 0 and a diameter of 0.18 ⁇ 0 .
• Fl I.22GHz
• F2 1.48GHz
• F3 1.68GHz
• an adaptation of the HQI antenna of less than -1OdB on three bands (81, 82, 83) is observed.
• the radiation patterns are equivalent in bandwidths to the diagrams obtained for a conventional antenna with always a wide aperture and a good quality of polarization, as illustrated in FIG. 9 for the frequency values F1, F2 and F3 of FIG. 8.
• FIG. 9 for the frequency values F1, F2 and F3 of FIG. 8.
• the multi-band quadrupole slotted printed antenna antenna makes it possible to obtain in a wide frequency range one operating in two or more bandwidths with radiation diagrams that remain constants, which consequently allows a new adaptability of the communication systems covered by the invention to several standards, unlike the existing technical solutions of the prior art.
• FIGS. 11 to 14 which give examples of geometrical configuration of the sub-strands of the antenna. More precisely, FIGS. 11 to 14
• FIGS. 13 and 14 respectively show examples of tri-band and dual-band antennas for which sub-strands (110) separated from one or more slots (111) extend the main strand (112) under the shape of a trident ( Figure 11) or a fork ( Figure 12).
• Such a configuration has the advantage of being able to apply in a technically relatively easy manner a current belly directly and optimally to the upper end (113) of the main strand (112).
• the antenna variants envisaged in FIGS. 13 and 14 have the main objective of enabling a substantial reduction in the height of the antenna. This reduction in height is allowed by folding the sub-strands (110) along the main strand (112), either partially as illustrated in Figure 13, or over most of its length, as shown in Figure 14.
• the dual-band antenna cited as a detailed example of implementation has the following characteristics:
• Length of the first strand 166 mm; - Length of the second strand: 156 mm;
• Radius of the antenna 18 mm; Angle of winding or elevation: 50 °; Widths of the strands: 16 mm; Depth of the slot: 36 mm; - Width of the slot: 8 mm; Permittivity of the substrate on which the strands are reported: 2.2;
• Thickness of the substrate on which the strands are reported 0.127 mm.
• the technique of the invention therefore gives a significant increase in the number of bandwidth ranges made accessible. This produces a printed quadrifilar helix antenna operating in several bandwidths. By also varying the width of the strands, it also becomes possible to increase the bandwidth of the antenna without reducing strand lengths.
• the strands, and / or the sub-strands, and / or the slits do not all have identical dimensions.
• the antenna is printed flat, then wound on a support to form the antenna.
• the substrate for receiving the printed elements can be made directly in its final cylindrical form. In this case, the printing of the strands is performed directly on the cylinder and the point of connection with a current belly is determined in coherence with the number of bandwidths to be accessed by the antenna
• the antenna of the invention also lends itself to the realization of antenna arrays.

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• 2004
  • 2004-10-25 FR FR0411373A patent/FR2877148B1/fr active Active
• 2005
  • 2005-10-24 EP EP05801356.6A patent/EP1805848B1/de not_active Not-in-force
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