WO2000049677A1

WO2000049677A1 - Radio station antenna with circular polarisation

Info

Publication number: WO2000049677A1
Application number: PCT/FR2000/000266
Authority: WO
Inventors: Thierry Lucidarme
Original assignee: Nortel Networks Sa.
Priority date: 1999-02-17
Filing date: 2000-02-04
Publication date: 2000-08-24
Also published as: FR2789807B1; FR2789807A1

Abstract

The invention concerns a radio station comprising means for processing radio signals, and several antennae (1, 2) respectively associated with hybrid polarising couplers (31, 32). Each polarising coupler has at least one input (A1 or B1, A2 or B2) connected to processing means and two outputs (C1 and D1, C2 and D2) connected to the antenna associated therewith such that when said outputs deliver two quadrature radio signals respectively in response to a transmission signal received on one of the two polarising coupler inputs, the antenna associated therewith generates two orthogonal electric field components forming a circular polarised wave. The processing means for the radio signals comprise at least a receiver (R1) arranged to combine several input radio signals obtained from the hybrid polarising couplers respective inputs. The antennae are arranged so as to radiate towards diametrically opposite sectors.

Description

RADIO STATION WITH CIRCULAR POLARIZATION ANTENNA

The present invention relates to a radio station, usable in particular as a base station in cellular radiotelephony systems.

More particularly, the invention relates to a radio station, comprising several antennas respectively associated with hybrid polarization colors, each polarization coupler having at least one input connected to radio signal processing means comprising at least one receiver and two connected outputs to the antenna which is associated with it so that when said outputs respectively deliver two radio signals in quadrature in response to a transmission signal received on one of the two inputs of the polarization coupler, the antenna which is associated with it generates two orthogonal electric field components forming a circularly polarized wave.

Document FR 2 746 991 discloses an arrangement of antennas in a radio station, the antennas emitting a circularly polarized field. On reception, the waves picked up to produce the processed signals are linearly polarized. The receiver provides spatial diversity and linear polarization diversity processing to combat channel fading. In order to separate the transmission and reception paths, the antennas of the radiocommunication stations are associated with duplexers. In the case of circular polarization antennas of the type described in FR 2 746 991, these duplexers are connected between the antenna and the polarization coupler.

EP 0 449 492 and "Base Station / Vehicular Antenna Design Techniques Employed in High-Capacity Land Mobile Communications System "(Y. Yamada et al, Review of the Electrical Communications Laboratories, Vol. 35, No. 2, March 1, 1987, pages 115-121), WO 96/28944 and WO 97/37441, disclose a base station comprising antennas which are distributed according to a geometrical configuration determined so as to emit a circularly polarized field.

Documents WO 96/28944 and WO 97/37441 further disclose reception means which are intended to ensure a diversity of circular polarization processing.

The object of the present invention is in particular to propose other arrangements of antennas in radio stations, in order to obtain good reception performance and / or to simplify its design and implementation. To this end, in a radio station of the type indicated in the introduction, the receiver is arranged to combine several radio input signals obtained from respective inputs of the hybrid polarization couplers, and the antennas are arranged so as to radiate towards diametrically opposite sectors.

Thanks to this simple station design, the receiver processes several signals picked up in diametrically opposite sectors, these signals being obtained by mixing, in the hybrid couplers, different components of the electric field picked up by the antenna. This results in a certain smoothing of the disturbances which can affect these components, and therefore a lower sensitivity of the receiver to these disturbances.

At least one of the hybrid polarization couplers preferably has two inputs, from which two radio input signals are supplied respectively to the receiver, the receiver then being arranged to provide diversity processing based on said input radio signals. Another form of polarization diversity in reception is thus obtained. This version advantageously makes it possible to combat the effects of fading, in particular when the propagation medium creates relatively little diversity.

When one or more duplexers are required, each of them can be connected between an input of the polarization coupler, an input of the receiver and the radio signal source. This provides greater flexibility in the design and choice of antennas. In particular, the duplexer can be placed in the main housing of the radio station rather than with the antenna outside. In particular embodiments: the radio station comprises two other receivers each receiving two respective input radio signals, a first division means connected between an input of one of the hybrid polarization couplers and first respective inputs of the two receivers , and a second division means connected between an input of another hybrid polarization coupler and respective second inputs of the two receivers;

- The radio station comprises at least one radio signal source delivering said transmission signal to an input of a polarization coupler.

Other features and advantages of the present invention will appear in the following description of nonlimiting exemplary embodiments, with reference to the accompanying drawings, in which: - Figure 1 is a diagram of a radio station according to the invention having a transceiver unit; - Figure 2 is a diagram of a radio station according to the invention having two antennas and a transceiver unit;

- Figure 3 is a diagram of an alternative embodiment of the station of Figure 2;

- Figure 4 is a diagram of a radio station according to the invention having an antenna and two transceiver units;

- Figure 5 is a diagram of a radio station according to the invention having two antennas and two transceiver units;

- Figure 6 is a diagram of a radio station according to the invention having two antennas and four transceiver units. With reference to all of FIGS. 1 to 6, the radio stations according to the invention described here by way of example comprise either an antenna 1 or two antennas 1 and 2. Each antenna is for example constituted by two coplanar dipoles PI , P2 oriented perpendicular to each other. For example, the dipole PI can be placed horizontally and the dipole P2 vertically.

Each antenna 1, 2 is associated with a respective hybrid polarization coupler 3ι, 3 ₂ . Each of these couplers 3ι, 3 ₂ has two inputs Al, A2 and Bl, B2 and two outputs, one Cl, C2 attacking the dipole PI of its associated antenna 1, 2, the other Dl, D2 attacking the dipole P2 its associated antenna 1, 2.

Each polarization coupler 3ι, 3 ₂ is chosen so that it produces two radio signals in quadrature on its two outputs Cl and Dl, C2 and D2. For this purpose, hybrid couplers, known as couplers, are used. "Branchline", as in patent application WO 97/37440 to which reference may be made.

The components delivered by the outputs Ci and Di of the coupler 3 are thus always in quadrature with respect to each other, so that when they respectively attack the dipoles PI, P2 of the associated antenna, the latter generates two orthogonal electric field components forming a circularly polarized wave. The left or right direction of the circular polarization depends on that of the inputs Ai, Bi of the coupler from which the transmitted signal comes. We consider for example the case where a signal attacking the input Ai of the coupler 3 _X generates a wave with left circular polarization (PCG), while a signal attacking the other input B _x of the coupler 3 generates a wave with circular polarization right (PCD).

In the embodiment shown in Figure 1, where the radio station comprises an antenna 1 associated with a hybrid polarization coupler 3 _X , the polarization coupler 3ι has its input Al connected, via a duplexer 4χ , to a source or transmitter of radio signal Tl forming part of a transceiver unit TRI, and its input B1 connected to an input FI of a receiver RI forming part of said transceiver unit. In order to ensure treatment of circular polarization diversity, the duplexer 4 ₁ supplies a second radio signal to another input El receptor RI radio signal. The duplexer 4ι, associated with the polarization coupler 3ι, separates the transmission and reception paths.

This arrangement of the duplexer provides the advantage over the arrangement which is adopted in the radio stations of the type described in WO 97/37440, to be able to house the transceiver unit, together with the duplexer 4 _lr in the main box 6 of the radio station, which is shown in dotted lines in FIG. 1, l antenna 1 and the hybrid coupler 3 _X then being external to this box. As a result, the installer of the station will be much more free when it comes to the design and choice of antennas. He may also choose to integrate the duplexer into a microwave circuit providing other functions, such as filtering, in order to limit the cost of the radio stage.

In the exemplary embodiment shown in FIG. 2, the radio station comprises another antenna 2 which is similarly associated with another hybrid polarization coupler 3 ₂ 'The antennas 1 and 2 are arranged so as to radiate towards the same space sector.

In the assembly of FIG. 2, the polarization coupler 3ι always has its input Al connected this time directly to the radio signal source Tl, and its input Bl connected to the input El of the receiver RI. The polarization coupler 3 ₂ , meanwhile, has its input A2 connected by a coaxial cable to the input FI of the receiver RI. Its other input B2 is connected to a resistor 10 for the adaptation of impedance. The presence of the two antennas 1 and 2 in the radio station makes it possible to combine the advantages of a spatial diversity and a circular type polarization diversity in the two input signals of the receiver RI. This is due to the fact that the radio signals supplied to the inputs El, FI of the receiver RI come from non-homologous inputs Bl, A2 of the polarization couplers. In the variant of FIG. 3, the signals processed by the receiver RI come from homologous inputs Bl, B2 of the two couplers so that the diversity processing applied by the receiver Ri only provides spatial diversity, possibly associated with a gain in directivity.

The arrangement of FIG. 2 or 3 is advantageous in the sense that there is no longer any need for a duplexer to separate the transmission and reception paths. However, depending on the performance of the coupler used and the standing wave rate of the antenna in the direction of circular polarization used on transmission, filters not shown, less bulky and expensive than duplexers, may be provided upstream El and FI inputs of the RI receiver, in order to eliminate the coupling components with the powerful transmission signal.

In the embodiment shown in FIG. 4, the radio station comprises a single antenna 1 associated with a polarization coupler 3ι, and two transceiver units TRI, TR2, with a radio signal source Tl, T2 and a diversity receiver RI, R2. The advantages described above can be fully obtained for the two transmission / reception units TRI, TR2.

In the assembly shown, the inputs Al and Bl of the polarization coupler 3ι are respectively connected to the radio signal sources Tl, T2 by means of a corresponding duplexer 4ι, 4 ₂ . The input Al of the polarization coupler 3χ is also connected by a coaxial cable, via the duplexer 4ι, to an input II of a division module 5ι which is incorporated in the main housing 6 of the radio station and which is by example a “Wilkinson” type coupler, while the other input Bl of the 3χ coupler is further connected by a coaxial cable, via the duplexer 4 ₂ , to an input 12 of a division module 5 ₂ which is identical to the module 5 _X. The division module 5ι has two outputs Gl, Hl, one of which, Gl, is connected to the input E2 of the receiver R2 and the other, Hl, is connected to the input El of the receiver RI. The division module 5 ₂ also has two outputs G2, H2, one of which, G2, is connected to the input F2 of the receiver R2 and the other of which, H2, is connected to the input Fl of the receiver RI. This embodiment has the additional advantage of obtaining, with only one antenna 1, a gain in polarization diversity for each of the two receivers RI and R2. Again, the duplexers can be housed in the main box 6 of the station.

The exemplary embodiment shown in FIG. 5 combines the advantages of the embodiments shown respectively in FIGS. 2 and 4. In this example, there are two antennas, but no duplexers. The inputs A1 and B2 of the polarization couplers 3χ and 3 ₂ are connected directly to the radio signal sources Tl and T2. The other inputs B1 and A2 of these polarization couplers are, for their part, connected respectively to division modules 5χ and 5 ₂ which are for example of the same type as those mentioned above. The division module 5 _ι has its outputs Gl, Hl connected respectively to the input El of the receiver RI and to the input E2 of the receiver R2, while the division module 5 ₂ has its outputs G2, H2 respectively connected to the input F1 of the receiver RI and at the input F2 of the receiver R2. This embodiment thus provides a gain in diversity, spatial and polarization, for each of the two receivers RI and R2 if the two antennas radiate towards the same sector of space. An arrangement such as that of FIG. 5 can also be used in elongated cells such as those which run along railway tracks or road axes. In this case, the two antennas 1, 2 are arranged head to tail, so as to radiate towards two diametrically opposite sectors.

It is also noted that in this example, the installer of the station has the option of choosing the option of a gain in directivity at reception instead of a gain in polarization diversity. For this, it will suffice, for example, to reverse the connection of the coaxial cable which connects the input A2 of the coupler 3 ₂ to the output 12 of the division module 5 ₂ with the connection of the coaxial cable which connects the input B2 from the polarization coupler 3 ₂ to the radio signal source T2.

In the example shown in FIG. 6, the radio station comprises two antennas 1, 2 associated respectively with two polarization couplers 3χ and 3 ₂ , two duplexers 4χ and 4 ₂ , four transceiver units TRI, TR2, TR3 and TR4 and two division modules 5'ι and 5 ' ₂ . The division modules 5'ι and 5 ' ₂ have a structure similar to that of the division modules 5χ and 5 ₂ mentioned above, with the difference that they respectively have four outputs G'I, H' 2, J'I , K '1 and G'2, H'2, J'2, K' 2 instead of two outputs. They can for example each consist of three “Wilkinson” couplers arranged in two stages. The inputs Al, Bl of the polarization coupler 3ι are connected respectively to the radio signal sources Tl, T2, while the inputs A2, B2 of the polarization coupler 3 ₂ are connected respectively to the radio signal sources T3, T4. The duplexer 4ι is connected between the input Al of the coupler of polarization 3χ, the radio signal source Tl and the input I'I of the division module 5'ι, while the duplexer 4 is connected between the input B2 of the polarization coupler 3 ₂ , the radio signal source T4 and input I'2 of the division module 5 ' ₂ - The four outputs G'I, H'1, J'I, K' 1 of the division module 5'ι are respectively connected to the inputs E4 of the receiver R, E3 of the receiver R3, E2 of the receiver R2 and Fl of the receiver RI, while the four outputs G'2, H'2, J'2, K '2 of the division module 5' ₂ are connected respectively to the inputs El of the receiver RI , F2 of the R2 receptor, F3 of the R3 receptor and F4 of the R4 receptor. It is thus possible with this embodiment to further increase the gain in polarization diversity for the four receivers RI, R2, R3 and R4 compared to what it was in the embodiment shown in FIG. 5. One can also envisage, in a manner analogous to what has been described above, to obtain a gain in directivity for this embodiment, by differently connecting the coaxial cables which respectively connect the polarization couplers 3χ, 3 ₂ respectively to the radio signal sources Tl, T2 and T3, T4.

It goes without saying that the embodiments which have been described above have been given for purely indicative and in no way limitative, and that numerous modifications can be easily made by those skilled in the art without departing from the scope. of the invention.

Thus, a person skilled in the art could adopt antennas whose geometry differs from that shown for antennas 1 and 2, provided that these make it possible to generate two orthogonal electric field components in response to two radio signals in quadrature. Furthermore, it could use various known types of polarization couplers.

Claims

1. Radio station, comprising several antennas (1, 2) respectively associated with hybrid polarization couplers (3ι, 3 ₂ ), each polarization coupler having at least one input (Al or Bl, A2 or B2) connected to means radio signal processing comprising at least one receiver (RI) and two outputs (Cl and Dl, C2 and D2) connected to the antenna associated with it so that when said outputs respectively deliver two radio signals in quadrature in response to a transmission signal received on one of the two inputs of the polarization coupler, the antenna associated with it generates two orthogonal electric field components forming a wave with circular polarization, in which the receiver is arranged to combine several signals radio input obtained from respective inputs of the hybrid polarization couplers and in which the antennas (1, 2) are arranged so as to radiate towards diam sectors very opposite.

2. Radio station according to claim 1, in which at least one of the hybrid polarization couplers (3ι, 3) has two inputs (Al, Bl), from which two radio input signals are respectively supplied to the receiver (Ri) and in which the receiver is arranged to provide diversity processing on the basis of said radio input signals.

3. Radio station according to claim 1 or 2, comprising two receivers (RI, R2) each receiving two respective input radio signals, a first division means (5ι) connected between an input (Al or Bl) of one of hybrid polarization couplers and respective first inputs (E1, E2) of the two receivers, and a second dividing means (5 ₂ ) connected between an input (A2 or B2) of another hybrid polarization coupler (3 ₂ ) and respective second inputs (F1, F2) of the two receivers.

4. Radio station according to claim 3, comprising two other receivers (R3, R4) each receiving two respective input radio signals, one of these two signals being supplied by the first division means (5ι) and the other of these two signals being provided by the second dividing means (5).

5. Radio station according to any one of claims 1 to 4, comprising at least one radio signal source (Tl) delivering said transmission signal to an input (Al or Bl) of a polarization coupler (3ι).

6. Radio station according to claim 5, comprising at least one duplexer (4ι) connected between the input (Al or Bl) of the polarization coupler (3ι) to which said transmission signal is delivered, an input (El or Fl ) of the receiver (Ri) and the radio signal source (Tl).

7. Radio station according to claim 6, in which the radio processing means and the duplexer (4 _X ) are housed in a main housing of the radio station, each antenna (1, 2) and each hybrid polarization coupler (3ι, 3 ₂ ) being external to said main housing.

8. Radio station according to claim 7, characterized in that the duplexer (4ι) is incorporated into a radio circuit further incorporating part of the radio processing means.