Mode generator device for a satellite antenna system and method for producing the same

Abstract

The present invention is related to a device for generating waveguide modes for use in a feed horn of a satellite antenna system, said waveguide modes comprising at least one excitation mode of higher order than the fundamental mode, said device comprising a waveguide containing a first waveguide section with at least three longitudinal slots extending in the inner side of said waveguide, characterized in that said waveguide contains a second waveguide section with at least three longitudinal slots extending in said inner side of said waveguide.

Claims

1. A device for generating waveguide modes for use with a feed horn of a satellite antenna system, said device comprising: a waveguide containing a first waveguide section with at least three longitudinal slots extending in the inner side of said waveguide, wherein said waveguide contains a second waveguide section with at least three longitudinal slots extending in said inner side of said waveguide, wherein said waveguide is configured to generate waveguide modes including at least one excitation mode of higher order than a fundamental mode.

2. The device for generating waveguide modes as in claim 1, wherein said first waveguide section and said second waveguide section are separated by a section without slots.

3. The device for generating waveguide modes in claim 1, wherein said at least three longitudinal slots of said second waveguide section are oriented at positions rotated around an axis of said waveguide with respect to said at least three longitudinal slots of said first waveguide section.

4. The device for generating waveguide modes as in claim 3, wherein said positions of said at least three longitudinal slots of said second waveguide sections are rotated around said axis over an angle of substantially 180 with respect to said at least three longitudinal slots of said first waveguide section.

5. The device for generating waveguide modes as in claim 1, wherein the at least three longitudinal slots of said first and second waveguide sections each have one end reaching an extremity of said waveguide.

6. The device for generating waveguide modes as in claim 1, wherein said at least three longitudinal slots of said first waveguide section have exactly three longitudinal slots and said at least three longitudinal slots of said second waveguide section have exactly three longitudinal slots.

7. The device for generating waveguide modes as in claim 6, wherein two longitudinal slots of said at least three longitudinal slots of each of said first and second waveguide sections are correspondingly mounted at angles in the range of +35 to +55 and 35 to 55 with respect to the third longitudinal slot around an axis of said waveguide, said third longitudinal slot forming a centre slot.

8. The device for generating waveguide modes as in claim 1, wherein said at least three longitudinal slots of at least one of said first waveguide section and said second waveguide section each have exactly five longitudinal slots.

9. The device for generating waveguide modes as in claim 8, wherein four longitudinal slots of said five longitudinal slots of the at least one of said first waveguide section or said second waveguide section are correspondingly mounted at angles in the range of +35 to +55 and 35 to 55 and angles of substantially +90 and 90 with respect to a fifth longitudinal slot of said five longitudinal slots around an axis of said waveguide, said fifth longitudinal slot forming a central slot.

10. The device for generating waveguide modes as in claim 1, wherein said at least three longitudinal slots of said first waveguide section and second waveguide section each have a length shorter than the distance between extremities of said device.

11. A feed antenna system comprising the device for generating waveguide modes as in claim 1.

12. A satellite antenna system comprising an offset reflector dish and the feed antenna system as in claim 1 being arranged for conveying radio waves to or from said offset reflector dish.

13. A method for generating waveguide modes using the device according to claim 1 for overcompensating squint in a satellite communication system wherein circular polarization is applied or for compensating cross-polar components in a satellite communication system wherein linear polarisation is applied.

14. A method for producing a device for generating waveguide modes for use with a feed horn of a satellite antenna system, the method comprising: die casting a waveguide, said waveguide containing a first waveguide section with at least three longitudinal slots extending in the inner side of said waveguide, wherein said waveguide contains a second waveguide section with at least three longitudinal slots extending in said inner side of said waveguide, wherein said waveguide is configured to generate waveguide modes including at least one excitation mode of higher order than a fundamental mode; and removing cores defining said at least three longitudinal slots of said first and second waveguide sections.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 represents a front view and side view of a feed horn device illuminating a parabolic offset reflector dish.

(3) FIG. 2 illustrates the effect of squint.

(4) FIGS. 3a and 3b represent the aperture fields of a parabolic reflector illuminated with a feed without cross-polarization.

(5) FIGS. 4a and 4b represent the relevant modes for squint compensation.

(6) FIG. 5 represents a low diameter waveguide section as known in the prior art.

(7) FIG. 6 represents an embodiment of the mode generator according to the invention.

(8) FIG. 7 represents another embodiment of the mode generator according to the invention.

(9) FIG. 8 illustrates the integration of a mode generator according to the present invention with a feed horn antenna.

(10) The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not necessarily correspond to actual reductions to practice of the invention. Any reference signs in the claims shall not be construed as limiting the scope. In the different drawings, the same reference signs refer to the same or analogous elements.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(11) The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims.

(12) Furthermore, the terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. Moreover, the terms top, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

(13) It is to be noticed that the term comprising, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression a device comprising means A and B should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

(14) Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases in one embodiment or in an embodiment in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

(15) Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

(16) Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

(17) It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being redefined herein to be restricted to include any specific characteristics of the features or aspects of the invention with which that terminology is associated.

(18) In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

(19) As explained in the background section, TE.sub.21 modes, i.e. higher order modes, must be generated for compensating squint or for cancelling cross-polar radiation. The required relative level and phase of the TE.sub.21 mode can be found from evaluating the secondary TE.sub.21 and TE.sub.11 radiation patterns, i.e. from the secondary radiation patterns resulting from the TE.sub.21 and TE.sub.11 excitation.

(20) From such an analysis, one finds that in the case of linear polarization, with a relative TE.sub.21 level of approximately 15 dB combined with the correct relative TE.sub.21 phase, cross-polar components caused by offset illumination are cancelled. In the case of circular polarization, this same level and phase of the TE.sub.21 modes results in the compensation of squint, i.e. the alignment of the main lobe of the transmit secondary radiation pattern with the boresight axis of the parabolic antenna. By generating progressively higher levels of the TE.sub.21 mode, one can reorient the main lobe even further than the boresight axis. This can be considered squint overcompensation and is particularly useful when the receive channel has opposite circular polarization with respect to the transmit channel. In this case, the receive main lobe is on the opposite side of the boresight axis with respect to the uncompensated transmit main lobe. Generating higher amounts of TE.sub.21 modes progressively brings the transmit main lobe closer to the receive main lobe, decreasing the transmit pointing error. Hence, it is very advantageous that the proposed device is capable of generating the required high TE.sub.21 levels.

(21) The mode generator device according to the present invention comprises a first and a second waveguide section each provided with at least three grooves on the inner side of a substantially circular waveguide. The grooves of the individual waveguide sections do not extend from one extremity of the device to the opposite extremity. Due to the cascade of two sections with their respective sets of grooves there is no need any more to have a part of the waveguide of smaller diameter in order to block TE.sub.21 modes that propagate in the unwanted backward direction. By optimisation of the configuration, it is possible to substantially suppress the backward propagating TE.sub.21 modes. Further, because of the presence of two sections, higher levels of a higher order mode can be generated. Moreover, the high levels as specified above, as well as their optimum phase relationships, together with substantial suppression of backward propagating TE.sub.21 modes can be achieved by optimizing parameters as the number of grooves, position of the grooves and the dimensions of the grooves.

(22) The optimal number of grooves also depends on the kind of polarization applied. Below, an embodiment is illustrated for circular polarization achieving squint overcompensation for a configuration with opposite transmit and receive polarizations.

(23) FIG. 6 illustrates an embodiment of the mode generator for squint overcompensation according to the present invention. Its integration with a horn antenna is shown in FIG. 8. The mode generator shown in FIG. 6 contains a total of 10 (i.e. two times 5) grooves. The basis is a section with five grooves. A similar section is added behind but rotated by 180 around the axis, with a short spacing section in between without grooves. It is possible to obtain similar performance without the 180 rotation. Such a mode generator device is shown in FIG. 7. However, the sections with grooves would have to be spaced further from each other which results in a longer structure. An arrangement with two sections, either mutually axially rotated or not, is advantageous in that it allows higher levels of TE.sub.21 modes to be generated. Within each five-groove section, the groove at 0 (groove 3 in FIG. 6) converts part of the horizontally polarized TE.sub.11 wave into the horizontally polarized TE.sub.21 wave. The grooves at approximately 45 and 45 (grooves 2 and 4 in FIG. 6) convert part of the vertically polarized TE.sub.11 wave into the vertically polarized TE.sub.21 wave. The grooves at 90 and 90 (grooves 1 and 5 in FIG. 6) have no influence on the mode generation but compensate the differential phase shift between the vertically and horizontally polarized TE.sub.11 modes, as required for circular polarization. If only cross-polar optimization for linear polarization is required then the latter grooves at 90 and 90 can be omitted.

(24) With the two section mode generator device of the invention TE.sub.21 modes with a level of 10 dB are generated while obtaining good return loss in both transmit and receive bands and ensuring a low level of backward propagating TE.sub.21 modes. Differential phase shift between vertical and horizontal TE.sub.11 modes is kept sufficiently low in both bands. As compared to a typical cross-polarized Ka-band antenna configuration, a same TE.sub.21 level (of e.g. 10 dB) for transmit now yields a considerably smaller transmit beam misalignment with reference to the receive beam. The worst case transmit pointing error is thereby also reduced.

(25) The proposed two section mode generator can be mass-manufactured as a single mechanical part by die-casting with cores (sometimes also called sliders) coming in from two sides. During the die casting the cores, which define the grooves, can be removed from the extremities of the mode generating device. As typical for die-cast parts, a small draft angle (approx. 1.5) needs to be taken into account during design so that the cores can be removed.

(26) In case there is an odd number of sections one grooved waveguide section can be integrated either in the horn antenna or in an antecedent waveguide component.

(27) While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention may be practiced in many ways. The invention is not limited to the disclosed embodiments.

(28) Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. Any reference signs in the claims should not be construed as limiting the scope.