EP0689301A1 - System of omnidirectional antennae having angular and polarisation diversity - Google Patents

Abstract

The system includes first and second antennae (1,2) which are unidirectional in first and second directions respectively defined by two orthogonal planes (B,C). The first and second directions are orthogonal and a radiation diagram which is sensitive to an omnidirectional radiation diagram is formed by a bidirectional radiation diagram in a third plane (A) orthogonal to the first and second planes. The first antenna is rectangular and formed from strip metal and is on top of the second, ferrite antenna (2). The two vertical sections of the rectangular antenna provides two radiation patterns in a first plane (B). the horizontal sections of the rectangular antenna provide two radiation patterns in a second orthogonal plane (C) The ferrite antenna provides a radiation pattern in the third orthogonal plane (A). Each antenna output passes to a switch (3) which is connected to a receiver. Switching between antennae allows transmission or reception in any three dimensional angle and any polarisation. <IMAGE>

Description

The invention relates to a system of omnidirectional transmitting-receiving antennas with angular diversity and polarization, usable on transceivers or simple portable receivers, used in paging.

In paging systems, such as the RDS system for " Radio Data System " in Anglo-Saxon language, digital data for managing or using this network are broadcast on the carrier wave of a modulation broadcasting signal. frequency of band II. The data disseminated can be very diverse in nature and are generally disseminated in the form of messages intended for subscribers.

Paging is, today, a means of communication widely used by a category of users called to move often, using various means of locomotion, in very varied geographical environments.

In general, the receiver, or even the transceiver, is intended to be worn by its user, either inside a jacket pocket or, for example, hung on his belt.
The user is unaware and has no concern whatsoever of whether the receiver, or the transceiver, is correctly oriented towards the transmitter which is broadcasting the messages. Indeed, receivers or transceivers are very compact and normally equipped with an integrated antenna which determines their dimensional characteristics. This antenna, generally sensitive to the magnetic component of the carrier electromagnetic wave, component H, is most often formed by a very selective and gain-optimized metal frame, which gives the antenna thus formed a radiation pattern of unidirectional type, with good directivity.

In order that the reception, and, if applicable, the emission, is effective, it is necessary that the orientation of this type of conventional antenna is carried out as a function of the polarization of the carrier wave. The polarization of the waves emitted by the installations of the diffusers, or radiotelephony, is in general either horizontal, or vertical, very rarely circular or oblique.

In the case where such a conventional antenna is not oriented accordingly, it cannot make it possible to receive the polarized carrier wave as mentioned previously, which leads to a significant loss of detected signal, of the order of 20dB at 35dB when the orientation of the antenna is quadrature with respect to the privileged axis of polarization of the field.

In addition, this type of antenna does not have, due to its one-way radiation pattern, a capacity to receive, or transmit, radio signals in all azimuthal directions, which normally further imposes on the user. an orientation of its receiver, or of its transceiver, in the horizontal plane. At best, does this type of antenna, as shown in FIG. 1 for a metal frame antenna, with or without a ferrite core, present a unidirectional radiation pattern in two orthogonal planes, the antennas then being placed so that one of the planes is the horizontal plane, the other plane, vertical, having to correspond to the plane of polarization of the electromagnetic wave scattered, which of course implies two orientations for optimal reception.

The object of the present invention is to remedy the aforementioned drawbacks, by implementing an omnidirectional transmitting-receiving antenna system with angular diversity and polarization for which the contingencies relating to the orientation of the antenna system for optimal reception or transmission-reception are substantially eliminated.

Another object of the present invention is, in in particular, the implementation of a system of transmit-receive antennas having a substantially omnidirectional radiation pattern in one plane, the horizontal plane.

Another object of the present invention is, moreover, the implementation of a system of transmit-receive antennas having a unidirectional radiation pattern in two other planes, the three planes being orthogonal to each.

The omnidirectional transmitting and receiving antenna system with angular diversity and polarization, object of the present invention, is remarkable in that it comprises a first unidirectional radioelectric antenna in a first direction defined by two orthogonal planes, forming main planes. of this antenna, one of the planes defining a first plane, and a second radio antenna unidirectional with respect to a second direction defined by two orthogonal planes, forming main planes of this antenna, one of the planes defining a second plane. The first and second antennas are placed so that the first and second planes are orthogonal, the first and second directions are orthogonal. The antenna system thus formed has a bidirectional radiation pattern in a third plane, orthogonal to the first and second plane and formed by a main plane of the first respectively second antenna, and by a unidirectional radiation pattern in the first respectively the second plan. A coupling circuit makes it possible, on reception, to switch the output of the antenna system to one or other of the first or second antenna, as a function of the relative level of radio signal received at the output of each antenna.

The antenna system, object of the present invention, finds application in paging and, more generally, in radiocommunication or radiotelephony. mobile.

• les figures 2a, 2b, 2c, 2d, 2e et 2f représentent différents diagrammes de rayonnement d'antennes constitutives du système d'antennes et le système d'antennes, objet de la présente invention,
• les figures 3a et 3b représentent un mode de réalisation pratique du système d'antennes, objet de la présente invention,
• les figures 4a, 4b et 4c représentent les diagrammes de rayonnement dans trois plans orthogonaux du système d'antennes, objet de l'invention, tel que représenté en figures 3a, 3b,
• la figure 5 représente un schéma synoptique du circuit de couplage du système d'antennes, objet de la présente invention,
• la figure 6 représente un chronogramme du commandement séquentiel de la commutation en réception entre la première et la deuxième antenne.

It will be better understood on reading the description and on observing the drawings in which, in addition to FIG. 1 relating to the prior art,

• FIGS. 2a, 2b, 2c, 2d, 2e and 2f represent different radiation patterns of antennas constituting the antenna system and the antenna system, object of the present invention,
• FIGS. 3a and 3b represent a practical embodiment of the antenna system, object of the present invention,
• FIGS. 4a, 4b and 4c represent the radiation diagrams in three orthogonal planes of the antenna system, object of the invention, as shown in FIGS. 3a, 3b,
• FIG. 5 represents a block diagram of the coupling circuit of the antenna system, object of the present invention,
• FIG. 6 represents a chronogram of the sequential command of the switching in reception between the first and the second antenna.

A more detailed description of an omnidirectional transmitting-receiving antenna system with angular diversity and polarization, in accordance with the object of the present invention, will now be given in conjunction with FIGS. 2a to 2e and 2f.

In accordance with the aforementioned figures, it is indicated that the antenna system, object of the present invention, has a first radio antenna, denoted 1, unidirectional in a first direction, this direction, denoted OX in FIG. 2a, being defined by two planes orthogonal, the planes OX, OZ respectively OX, OY. The above-mentioned planes form the main planes of this antenna 1, one of the planes, the plane OX, OZ defining a first plane, denoted C in FIG. 2a.

The antenna system, object of the present invention, also includes a second unidirectional radio antenna, denoted 2, in a second direction, the direction OY in FIG. 2b, this direction being defined by two orthogonal planes, OX, OY, respectively OY, OZ. These two planes form main planes of the antenna 2, one of the planes, the plane OY, OZ defining a second plane, denoted B in FIG. 2b. The first 1 and the second antenna 2 are placed in the vicinity of one another so that the first C and the second plane B are orthogonal, the first and the second direction OX, respectively OY are also orthogonal. This makes it possible to obtain, for the antenna system 1,2, a substantially omnidirectional radiation pattern, formed by a bidirectional radiation pattern in a third plane A, as shown in FIG. 2c. The plane A is orthogonal to the first and to the second plane and is formed by a main plane of the first respectively of the second antenna 1,2. The substantially omnidirectional radiation pattern of the antenna system thus formed also includes a unidirectional radiation pattern in the first C respectively in the second B plane, as shown in Figures 2e and 2d.

Finally, as shown in FIG. 2f, a coupling circuit 3 makes it possible to ensure at reception an output switching of the antenna system on either of the first or second antenna 1,2, depending on the level relative radio signal received at the output of each antenna.

It will of course be understood that the antenna system which is the subject of the present invention can be used both for reception and for transmission, owing to the dual nature of the radiation pattern in reception, respectively in emission, these radiation patterns. radiation being, in accordance with the classical theory of antennas, identical to transmission and reception.

Of course, as part of a receiving device the paging function is not necessary, it can then be canceled.

A more detailed description of an omnidirectional antenna system with angular diversity and polarization, object of the present invention, will now be given in conjunction with FIGS. 3a and 3b within the non-limiting framework of an application to paging for example .

As shown in FIG. 3a above, the first antenna 1 is a metal frame antenna surrounding the actual body of the receiver R and the second antenna 2 is a ferrite core frame antenna. The metal frame antenna 1 surrounds, for example, the circuits of the receiver R, as shown in FIG. 3a, and is housed in the housing, not shown, of the receiving device, which of course includes a supply battery P in electrical energy.

The second antenna 2 also comprises a metal frame 20 with which is also associated a ferrite core 21. The second antenna with ferrite core is placed in the vicinity of one of the sides of the metal frame constituting the first antenna 1 for example.

The configuration thus produced naturally allows, for a given position of the receiver in space, to receive in all azimuth positions, that is to say for any orientation of the receiver in the plane A, a suitable signal level thanks unlike the orthogonal polar radiation diagrams relating to each of the antennas, as shown in Figure 2c.

In FIG. 3b, for the embodiment of FIG. 3a, the orthogonal induction flows received by the first 1 and the second antenna 2 are shown in the directions OX and OY. It is thus understood that, in the representation of FIG. 3b, the plane B is the plane of the sheet containing the figure 3b, the plane A is a horizontal plane orthogonal to the plane of the sheet containing the Figure 3b and the plane C is a vertical plane orthogonal to the plane of the sheet containing Figure 3b. The OXYZ coordinate system, respectively O'X'Y'Z 'corresponds to the oxyz coordinate system of Figures 2a to 2e. In FIGS. 4a, 4b and 4c, the polar diagrams of respective radiation received by the first and the second antenna are shown in the directions OX and OY.

It is thus understood that the antenna system, object of the present invention, offers the possibility of a quasi-omnidirectional reception in the horizontal plane A thanks to the coupling circuit 3, which allows, thanks to an electronic control system which will described below in conjunction with FIG. 5, to switch over the choice of one or the other constituent antenna of the antenna system according to the invention.

In general, as shown in FIG. 5, it is indicated that the coupling circuit 3 may advantageously include a switch 35 formed by at least one double-channel switch, denoted 351, this double-channel switch comprising a first input connected to the first antenna 1 and a second input channel connected to the second antenna 2. It is indicated that the first and the second antenna 1,2 are connected to the aforementioned input channels and each have tuning capacities, noted Ca₁, Ca₂. The output of the dual-channel switch 351 in fact comprises a first and a second output channel, the first output channel, in the case where the antenna system, object of the present invention is produced for a receiver of paging type, being directly connected to a reception chain, designated by RECEIVER, of the conventional type. The reception chain, or receiver, usually comprises a radio frequency stage, a radio frequency filter, a mixer circuit supplied by a local oscillator and an intermediate frequency filter, itself followed by an intermediate frequency amplifier and a frequency demodulator device intermediate. The second output channel of the dual-channel switch 351 can then be directly connected to the reference voltage or ground voltage of the device.

In addition, the coupling circuit 3 comprises a control chain for the dual-channel switch 351 as a function of the signal level delivered by the output of the antenna system.

In a nonlimiting embodiment, as shown in FIG. 5, the control chain advantageously comprises a field level detector 31 whose input is directly connected to the intermediate frequency amplifier of the receiver, this detector delivering a signal of level denoted U₀, and a threshold comparator circuit 32 receiving the signal of level U₀ and a determined threshold value, denoted U₁.

A circuit 33 of the flip-flop type is also provided in the aforementioned control chain, this flip-flop receiving the signal delivered by the comparator 32 on comparison of the level signal with the threshold signal U1. An output Q of the circuit 33 of the bistable flip-flop type makes it possible to directly control the double-track switch 351 of the switch 35 as a function of an error criterion, which will be explained later in the description.

et sortie complémentée $\overline{\text{Q}}$

du circuit bascule 33 et dont une sortie est connectée à un microprocesseur 36, lequel permet une remise à zéro sur l'entrée RESET du circuit bascule 33. Le circuit logique 34 comporte par exemple deux voies en parallèle comportant chacune un circuit de temporisation 341,342 et un circuit logique de type ET 343,344. Une entrée de chaque circuit logique de type ET est reliée à la sortie complémentée $\overline{\text{Q}}$

et à la sortie Q par l'intermédiaire du circuit de temporisation 341, respectivement à la sortie Q et à la sortie complémentée $\overline{\text{Q}}$

par l'intermédiaire du circuit de temporisation 342 de la bascule bistable 33. La sortie des circuits logiques ET 343 et 344 est reliée à un circuit logique de type OU 345, lequel délivre un signal de présence champ faible Uf au microprocesseur 36.Finally, it is indicated that the aforementioned control chain also includes a logic circuit 34 whose inputs are connected to the outputs $\overline{\text{Q}}$

and supplemented output $\overline{\text{Q}}$

of the flip-flop circuit 33 and one output of which is connected to a microprocessor 36, which allows resetting to zero on the RESET input of the flip-flop circuit 33. The logic circuit 34 comprises for example two parallel channels each comprising a timing circuit 341,342 and an ET 343,344 type logic circuit. One input of each AND type logic circuit is connected to the complemented output $\overline{\text{Q}}$

and at output Q via the timing circuit 341, respectively at output Q and at the complemented output $\overline{\text{Q}}$

through the timing circuit 342 of the flip-flop 33. The output of the AND logic circuits 343 and 344 is connected to an OR type logic circuit 345, which delivers a weak field presence signal Uf to the microprocessor 36.

• Une détection du niveau de champ radioélectrique instantané reçu à l'instant T₀ sur l'antenne 2 commutée par défaut, l'antenne à cadre métallique à noyau de ferrite, est tout d'abord effectuée, cette détection étant effectuée par le détecteur de niveau de champ 31 en sortie de l'amplificateur à fréquence intermédiaire.
• Une comparaison de ce niveau reçu à l'instant T₀ est effectuée avec le niveau de seuil U1 par le comparateur 32, ce niveau de seuil U₁ définissant le seuil de commutation.
• Si U₀ < U₁, alors, le circuit comparateur 32 déclenche la bascule 33, laquelle commande l'activation de l'antenne à cadre métallique 1 par commande de commutation du commutateur à double voie 351.
• Une activation de la constante de temps r introduite par le circuit de retard 341 est en même temps effectuée.
• Si U₀ < U₁ pendant la durée définie par la constante de temps τ précitée, alors, le dispositif engendre une information d'erreur par l'intermédiaire de la porte OU 345, confirmant la présence d'un champ faible, signal Uf, sur la première et sur la deuxième antenne.

The operating mode of the control chain previously described in connection with FIG. 5, will be described in conjunction with FIG. 6, which represents a timing diagram showing the sequential sequence of control of the antenna system, object of the present invention, such as as described in connection with FIG. 5.

• A detection of the instantaneous radio field level received at time T₀ on the antenna 2 switched by default, the antenna with a metal frame with a ferrite core, is first carried out, this detection being carried out by the level detector field 31 at the output of the intermediate frequency amplifier.
• A comparison of this level received at time T₀ is carried out with the threshold level U1 by the comparator 32, this threshold level U₁ defining the switching threshold.
• If U₀ <U₁, then, the comparator circuit 32 triggers the flip-flop 33, which controls the activation of the metal frame antenna 1 by switching command of the two-way switch 351.
• An activation of the time constant r introduced by the delay circuit 341 is carried out at the same time.
• If U₀ <U₁ during the duration defined by the above-mentioned time constant τ, then the device generates error information via the OR gate 345, confirming the presence of a weak field, signal Uf, on the first and on the second antenna.

It is of course understood that from the point of view of the operating mode of the control chain shown in FIG. 5, that the field level detector 31 provides an instantaneous voltage U₀ proportional to the field level electromagnetic HF received by the second antenna 2 activated by default.

The comparator circuit 32 receives the level signal U₀ corresponding to the electromagnetic field received at time T₀, and the reference voltage U₁ corresponding to the switching threshold. The value of the switching threshold is determined as a function of the minimum signal-to-noise ratio for which the bit error rate on the R.D.S. for example is still acceptable.

Comparator 32 outputs a logic state, which controls flip-flop circuit 33 according to the following relationships:
U₀ (T₀) <U₁ ---> comparator output = 1
U0 (T₀)> U₁ ---> comparator output = 0.

The flip-flop circuit 33 therefore receives the control information from the comparator 32 and in turn activates the first metal frame antenna 1 while the second antenna with ferrite core 2 is inhibited.

In logic circuit 34, it is in fact understood that this makes it possible to generate, from the switching information, the above-mentioned time constant τ making it possible to define the error criterion previously mentioned in the description. If in the aforementioned time interval τ the second antenna 2 with ferrite core is activated again, then the output OR logic circuit 345 generates for the microprocessor 36 so-called weak field information Uf, indicating in fact that the level of the received field is less than the minimum threshold defined by the threshold value U₁. The microprocessor 36 makes it possible to reset the flip-flop 33 to zero by the RESET command.

The previous description of the omnidirectional antenna system with angular diversity and polarization, object of the present invention, concerned the case of a paging receiver of the R.D.S. type. for example.

Of course, the antenna system, object of the present invention, can, if necessary, be used as omnidirectional transmission-reception antenna system for example in the field of application of the radiotelephone. In this case, as also shown in FIG. 5, the dual-channel switch 351 can be associated with another dual-channel switch, denoted 352. The switch 352 in fact comprises a first and a second switch. A channel of the first and second switch is connected for example to a transmitter circuit, denoted TRANSMITTER, while the other channel of the first switch is connected to the input terminal of the receiver and in particular to the radio frequency stage of it. this. The other channel of the second switch is connected for example to the ground or reference voltage of the device. The switched channels of the first and second switches are connected respectively to the first output channel and to the second output channel of the first switch 351. Thus, the second double-channel switch 352 has two switching positions, denoted I respectively II. The switching of the two switches of the second double-channel switch 352 is carried out by means of the microprocessor 36 for example, which conventionally makes it possible to switch over to the reception position according to position I, the connection of the first double switch channel 351 then being reduced to that previously described in the description in the case of the RDS type receiver or on the contrary in position II, position in which the first 1 and the second antenna 2 are supplied in parallel by the transmitter circuit. Of course, it is indicated that the switching from the receiving position I to the transmitting position II and vice versa, is controlled by means of the microprocessor 36 in a conventional manner, in accordance with the process for controlling known transceiver devices. As such, this switching will not be described in more detail. It is also understood that in order, if necessary, to take into account the disparities in efficiency or radiation pattern of the first and second antenna on transmission, devices, not shown in FIG. 5, can be provided in order to balance the emission levels of the first respectively of the second antenna.

A particularly efficient omnidirectional angular diversity and polarization transmit-receive antenna system has thus been described. In particular, in the case of use in a radio paging device for example, this permanently makes it possible to obtain an omnidirectional reception of the messages transmitted by systems such as the R.D.S. for example.

Claims (5)

Omnidirectional transmitting and receiving antenna system with angular diversity and polarization, characterized in that it comprises: a first unidirectional radio antenna in a first direction defined by two orthogonal planes, forming main planes of this antenna and one of the planes defining a first plane (C), - a second unidirectional radio antenna in a second direction, defined by two orthogonal planes, forming main planes of this antenna and one of the planes defining a second plane (B), the first and the second antenna being placed so that the first and the second plane being orthogonal, the first and second directions are orthogonal, which makes it possible to obtain for said antenna system a substantially omnidirectional radiation pattern formed by a bidirectional radiation pattern in a third plane (A), orthogonal to the first and second plane and formed by a main plane of the first respectively second antenna, and by a unidirectional radiation pattern in the first (C) respectively the second (B) plane, coupling means making it possible to ensure, on reception, an output switching of the antenna system on one or the other of the first or second antenna as a function of the relative level of radio signal received at the output of each antenna. Antenna system according to claim 1, characterized in that the first antenna is a metal frame antenna and the second antenna a ferrite core antenna, the ferrite core antenna being placed in the vicinity of one of the sides of the frame forming the metal frame antenna. Antenna system according to one of the preceding claims, characterized in that said coupling means comprise a double-channel switch, a first input channel being connected to the first antenna and a second input channel being connected to the second antenna, the output of said double-channel switch, constituting output of said antenna system, being intended to be connected, in reception, at the radio frequency input of a receiver. Antenna system according to claim 3, characterized in that it further comprises means for controlling said coupling means as a function of the level of the signal delivered by the output of said antenna system. Antenna system according to claim 4, characterized in that said coupling means comprise at least: - a radio field level detector circuit, delivering a level signal, a threshold comparator circuit receiving said level signal and delivering a comparison signal, a circuit of flip-flop type receiving said comparison signal, an output of said circuit of flip-flop type directly controlling coupling means according to an error criterion.

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