EP0260766A1 - Primary receiving unit for polarized microwaves, parabolic antenna and receiving station comprising such a unit - Google Patents

Abstract

The receiving head has only one moving part, a front depolarizer (POM), to make the selection between microwaves with conjugated polarizations. The addition, or not, of a fixed type change depolarizer (POF) provides two antenna versions, one for circular polarizations, the other for rectilinear polarizations. The assembly is designed to form a 'general public' antenna, simple to automate, and whose shadow cast on the parabolic reflector is minimal.

Description

The subject of the present invention is a reception head for microwaves which, for various channels, have simultaneously two conjugate polarizations, comprising, along the axis of propagation of the microwaves, a front depolarizer, a collector guide wave, a mode selector, a converter, and selection control means for alternately selecting one or the other of said conjugate polarizations.

The present invention also relates to a parabolic antenna and a reception station provided with such a reception head.

This type of antenna is used in particular to receive radio signals from a geostationary satellite, for example television signals whose carrier frequency is between 10 and 13 GHz.

The current trivialization of satellite television leads to seek bandwidth savings which is notably achieved by simultaneously operating for the same channel and the same satellite two polarizations of orthogonal or conjugate waves.

An antenna of the "general public" type must be able, at the best price, to alternately select any wave polarization among two in order to access, as desired, all the television programs transmitted by a satellite.

In the French patent ^No. 2377711, a receiving head is described; the selection of a television program implements two mobile devices there, namely on the one hand the converter and on the other hand the front depolarizer.

The mobility of the converter requires that the output cable is subjected to a twist; therefore the cable is subject to wear; moreover the cable not being very flexible - it is a coaxial cable - it must include a free loop which is bulky, and again the motor for controlling the movement of the converter must be powerful enough to twist the cable; all of these constraints have the result that the reception head is expensive and that it is bulky in volume which constitutes, with respect to incident waves, a mask whose shadow cast on the parabola is detrimental to the quality of the reception.

The present invention aims to eliminate these drawbacks.

To this end, a reception head according to the invention is particularly remarkable in that the said selection control means are produced by the only rorotation of an angle equal to Π / 2 of the said front depolarizer which is rotatably mounted around of said propagation axis, all the other elements of the reception head being fixed.

With the single rotation of the frontal depolarizer the selection of two conjugate waves is carried out at the lowest cost and with excellent quality.

Indeed the front depolarizer is a light piece and therefore easy to rotate and guide in rotation; thus the drop shadow is reduced to a minimum.

Such a reception head is designed to receive waves of a single type of polarization among two types, namely a first type called rectilinear X, Y, or a second type called circular D, G; the rotation of the only frontal depolarizer makes it possible to select X or Y in one case, D or G in the other case, but not both.

To be usable in both cases, a reception head according to the invention is particularly remarkable in that the said waveguide collector comprises a housing for accommodating therein, or not, a depolarizer for changing the type, the presence, or the non-presence, in said housing of said type change depolarizer having the effect of respectively allowing the reception of the waves of one or the other type among the two types of polarization.

So a receiving head is capable at the slightest cost of receiving and selecting all wave types regardless of polarization; whether or not the addition of the type change depolarizer is not a disadvantage for domestic use by the general public; indeed an antenna can, at a given moment, be pointed only towards a single satellite, or group of satellites, always transmitting either in X, Y or in D, G, whatever the channel, in other words there is There is no mixed situation X, Y and D, G and it is easy during the installation of the antenna in the user to add or not the depolarizer of change of type according to the direction which is aimed.

A reception head according to the invention therefore comprises two embodiments depending on whether the type change depolarizer is present or not.

Such a reception head is generally used at the hearth of a satellite dish which is installed outside, on the roof or on the balcony for example; a complete reception station furthermore includes internal channel selection equipment, it is then particularly advantageous if the reception head comprises a motor for controlling the rotational movement of said front depolarizer, and that said channel selection equipment comprises control means for controlling said motor.

• La figure 1 représente schématiquement une station de réception.
• La figure 2 représente les 2 modes opératoires de chacune des deux versions de tête de réception selon l'invention.
• La figure 3 représente les positions des éléments de la tête de réception.
• La figure 4 représente une tête de réception selon l'invention.

The present invention will be better understood with the aid of the nonlimiting description of an exemplary embodiment below described with the aid of the attached figures.

• Figure 1 schematically shows a receiving station.
• FIG. 2 represents the 2 operating modes of each of the two versions of reception head according to the invention.
• FIG. 3 represents the positions of the elements of the reception head.
• FIG. 4 represents a reception head according to the invention.

In FIG. 1, a reception station is schematically represented in an example of a domes installation. tick at a user's home; the station includes channel selection equipment (ESC) generally installed inside, and a reception head (TR) placed at the focal point and in the axis of the satellite dish (P) which is represented situated on a balcony (B); the axis of the parabolic reflector points to a satellite (SAT) in the direction of the arrow; the incident microwaves (MOI) are reflected towards the focal point of the dish; the reception head (TR) constitutes the main part of the antenna since this is where the microwaves are collected to generate a usable electrical signal; the electrical signal is transmitted to the interior equipment (ESC) by a coaxial cable (COAX); the element (TR) is fixed to the parabolic reflector by fixing feet (PF) generally three in number.

The elements shown in FIG. 1 are well known, but it should be emphasized that certain elements involuntarily harm the proper functioning of the assembly because of the screen effect, or of the drop shadow, which they exercise between the microwave and the dish; these are the feet (PF), the cable (COAX) and the receiving head (TR). It is clear that to reduce the price of the assembly, and improve the quality of the reception of the waves, it is necessary to reduce the weight, the bulk, the complexity of these elements while retaining their functional qualities; for example, by reducing the weight of the receiving head (TR), we can save on its volume and the size of the feet (PF) and therefore reduce the shade cast.

In known antennas, such as that described in the cited patent, there are multiple moving parts including the converter, hence the drawbacks already mentioned: need for a powerful motor, twisting of the cable, ...; we also know, to avoid rotation of the converter, the technology of the rotary joint which is applied to the waveguide but this technology is delicate, because it is necessary to maintain electrical continuity during rotation; it is an expensive solution and, therefore, does not constitute a satisfactory solution to the technical problem mentioned above.

The object of the invention is to simplify the reception head to produce an inexpensive consumer antenna with efficient and long-lasting operation.

This object is notably achieved by minimizing the number of moving parts of the receiving head and the shade cast on the parabolic reflector.

According to the invention, a satisfactory reception head comprises only one movable part, the front depolarizer; it is a light piece, the case of the conventional dielectric blade depolarizer, which is easy to rotate with a small, space-saving motor.

The operating principle of such an antenna is detailed in Figure 2 with its two versions according to the characteristics of the satellite to which the antenna is pointed.

The reception head (TR) consists of a mobile front depolarizer (POM), a waveguide collector (COG), a mode selector (SM), and a converter (CO); the selected signal is transmitted electrically in the cable (COAX).

sont à Π/2 l'une de l'autre- une onde incidente Di devient respectivement Y ou X, une onde incidente Gi devient respectivement X ou Y, et...

In the table below the transformation of the waves in a depolarizer is briefly recalled: the incident microwaves (MOI) leave the depolarizer transformed into output microwaves (MOS); circular waves with two conjugate polarizations (D for right, G for left) become rectilinear waves with two conjugate polarizations (X for horizontal, Y for vertical) and vice versa; depending on the position of the polarizer / depolarizer -the two positions P and

are at Π / 2 from each other - an incident wave Di becomes Y or X respectively, an incident wave Gi becomes X or Y respectively, and ...

The two types of polarization, circular and rectilinear, are mutually exclusive.

The first version, FIG. 2a and FIG. 2b, is suitable for a satellite which emits microwaves (MOI) of a circular type with two possible right and left conjugate incident polarizations (Di and Gi); at a given moment the user is only interested in a single program, that is to say a single polarization, either Di or Gi; the invention takes advantage of this observation.

FIG. 2a shows how, in a first position (P) of the mobile depolarizer (POM), the incident circular waves (Di, Gi) become rectilinear waves (X, Y); after passing through the waveguide (COG), the mode selector (SM) stores in a single X wave which is converted by the converter (CO) into an electrical signal which, in the case of FIG. 2a, is representative of the right incident incident circular wave Di.

) du dépolariseur frontal (POM), le signal électrique est maintenant représentatif de l'onde circulaire incidente gauche Gi.In the case of Figure 2b, similarly to the case of Figure 2a, but with a second position (

) of the frontal depolarizer (POM), the electrical signal is now representative of the left incident circular wave Gi.

FIGS. 2c and 2d correspond to the version of the reception head suitable for a satellite which transmits microwaves of a rectilinear type with two possible conjugate incident polarizations horizontal and vertical (Xi and Yi); the constitution of the reception head is identical to that of FIGS. 2a and 2b except that in the waveguide collector (COG) a fixed depolarizer (POF) has been added to effect the version change. The incident waves Xi, Yi become circular waves (D and G) through the mobile depolarizer (POM); the fixed depolarizer (POF) transforms these waves into (X and Y) so that the electrical signal present on the cable (COAX) is now representative either of the incident wave Xi in the case of FIG. 2c, or of l incident wave Yi in the case of FIG. 2d.

The material realization of such a reception head with its two versions poses no particular problem since each constituent taken in isolation is simple and well known to those skilled in the art; the technical progress achieved by the invention lies precisely in this simplicity of implementation which only a simple front depolarizer (POM) rotates by an angle Π / 2 around an axis with two operating positions, to which or not, another optional fixed depolarizer (POM); this simplicity is to be compared to the complexity of the previously known embodiments for solving the problem of reception of the various polarizations of the microwaves.

A notable advantage results from the fact that the cable (COAX) is no longer twisted: on the one hand it does not damage itself mechanically, on the other hand it can be fixed so that its drop shadow is zero.

Preferably a conventional dielectric plate depolarizer is used rather than a meander depolarizer like that indicated in the cited patent.

Preferably a radome can be directly in incorporated in the mobile depolarizer, thus the interior of the receiving head is protected from the weather.

In Figure 3 the positions in space of the various components of the receiving head are shown.

Ave Figures 3a and 3b we see the two operating positions of the receiving head for circular waves, that is to say with a single depolarizer.

With FIGS. 3c and 3d we see the two operating positions of the reception head for rectilinear waves, that is to say with two depolarizers.

The plane of the fixed depolarizer (POF) is inclined at an angle of 45 ° relative to the main axis of the converter input waveguide (CO).

The plane of the mobile depolarizer (POM) is either in the same plane as the fixed depolarizer (POF) case of Figures 3a and 3c, or in a plane perpendicular to the fixed depolarizer (POF) case of Figures 3b and 3d.

The depolarizers are here represented as thin dielectric plates having the shape of a rectangle provided with a point; this representation is obviously not limiting since there are already multiple forms of depolarizer, each form being chosen, more or less empirically, as a function of multiple parameters: dimensions of the waveguide, expected operating frequencies, etc.

It is advantageous to motorize the movement of the mobile depolarizer, this motorization does not present any particular technical difficulty in itself, especially since only a small motor is sufficient since the movement is only thwarted by friction.

A nonlimiting example of such an embodiment is drawn in perspective in FIG. 4 in which only the reception head (TR) of FIG. 1 is represented.

The references are the same as those in FIG. 2, namely: mobile depolarizer (POM), waveguide collector (COG), optional fixed depolarizer (POF), converter (CO). The wings (AI) correspond to the fixing points on the fixing feet (PF in Figure 1).

The control motor (COM) is clamped directly to the body of the waveguide and a pinion (P) fixed on the motor axis engages a toothed sector (SD) integral with the mobile depolarizer (POM). The motor is controlled from the interior selection equipment (reference ESC in FIG. 1) in a known manner. The toothed sector (SD) is a preferred embodiment with a motor which rotates alternately in each of the two directions and which stops automatically when the pinion (P) arrives at the end of the toothed sector (SD) by detecting, for example , an over-consumption of electric current.

It would be possible that the toothed sector is in fact a toothed crown with a motor rotating in one direction and an adequate device for stopping the motor when the mobile depolarize reaches the desired position.

It should be noted that a receiving head according to the invention is very compact, even with a motor, so that its shadow cast on the parabolic reflector is extremely reduced.

Claims (6)

1. Reception head for microwaves which, for various channels, have simultaneously two conjugate polarizations, comprising, along the axis of propagation of the microwaves, a front depolarizer, a waveguide collector, a selector mode, a converter, and selection control means for alternately selecting one or the other of said conjugate polarizations characterized in that said selection control means are produced by the only rotation of an angle equal to Π / 2 of said front depolarizer which is rotatably mounted around said axis of propagation, all the other said elements of the reception head being fixed. 2. Receiving head according to claim 1, characterized in that said rotation of an angle equal to Π / 2 of said front depolarizer is carried out alternately in one direction then in the other to pass from a selection position to the other. 3. Reception head according to claim 1 or 2 characterized in that said rotary front depolarizer is provided with a radome. 4. Reception head according to claim 1, 2 or 3, said microwaves being able to include either one type of polarization among two types of polarization, namely a first type known as rectilinear X, Y, or a second type known as circular D, G, characterized in that said waveguide collector comprises a housing for accommodating therein, or not, a type change depolarizer, the presence or non-presence, in said housing of said type change depolarizer having the effect of respectively allowing the reception of the waves of one or the other type among the two types of polarization. 5. Parabolic antenna characterized in that it comprises a reception head according to any one of claims 1, 2, 3 or 4. 6. Reception station comprising a parabolic antenna according to claim 5 and a channel selection equipment, characterized in that the reception head further comprises a motor for controlling the rotational movement of said front depolarizer, and in that the said channel selection equipment comprises control means for controlling said motor.

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