Patent Application
20250174911
This application relates to a waveguide feed array for use in combination with a reflector antenna and a communication satellite comprising such an antenna system. In particular, the application relates to a waveguide feed array comprising overlapping clusters operating simultaneously in the transmit and receive frequency bands, enabling full-duplex communication, and producing a coverage of multiple contiguous beams, congruent in transmit and receive, using a single reflector antenna system, for example, a single offset paraboloid reflector.
Modern day communication satellites, referred to as high throughput satellites (HTS), implement multiple beam coverage with spectrum reuse to increase the overall system capacity.
Like in terrestrial cellular networks, the concept is to use a different part of the spectrum in adjacent beams to minimize interference while reusing the same part of the spectrum in non-adjacent beams to increase the number of communication channels available at any given time without extending the spectrum required, generally restricted through regulations. The reuse factor k, corresponding to the minimum number of cells or beams with different subsets of available spectrum, takes the values k=i2+ij+j2, where i and j are positive integers, to fill the complete multiple beam coverage with a repetition of the elementary cells without ever encountering two adjacent cells or beams with the same spectrum subset, sometimes referred to as a “color.” Typical values for k are 3, 4, 7, 9, 12. HTS systems typically implement a reuse factor of 4, conveniently achieved combining polarization diversity and frequency diversity. In this particular case, the available spectrum in a given frequency band B1 is divided into two frequency sub-bands, F1, F2, and two orthogonal polarizations, P1, P2,typically left hand circular polarization (LHCP) and right hand circular polarization (RHCP), which are paired (combined) to generate four types of cells with non-interfering signals, (F1, P1), (F1, P2), (F2, P1) and (F2, P2), generally referred to as a four-color scheme. The resulting multiple beam coverage is characterized by two main directions, one along which the cells have alternating frequency sub-bands and another one along which the cells have alternating polarizations. This four-color scheme is generally applied in two distinct frequency bands, B1, B2, corresponding to the transmit and the receive frequency bands, as communication satellites typically implement frequency division duplex (FDD) techniques to enable full-duplex links. The beams are often distributed on a triangular lattice, as this configuration provides enhanced cross-over levels between adjacent beams resulting in higher aggregate performance at antenna level, specifically aggregate gain and aggregate carrier upon interferer ratio (C/I).
Next generation communication satellites, referred to as very high throughput satellites (VHTS) and ultra-high throughput satellites (UHTS), are expected to increase the total system capacity by at least an order of magnitude when compared to current generation HTS systems. This requires significantly more beams and more advanced antenna systems. Historically, antenna systems onboard communication satellites have relied on reflector technology. This solution provides higher gain and angular resolution, or smaller beamwidth, with moderate complexity when compared to direct radiating arrays, particularly when very high gain is required corresponding to electrically large antenna apertures.
To address the requirements of VHTS and UHTS systems, there is a need to develop new feed array solutions compatible with larger reflector sizes and providing a complete transmit/receive multiple beam coverage for full-duplex communication with a reduced number of apertures. Typical single-feed-per-beam reflector antenna configurations generate one beam from each feed of the array located in the focal plane of the reflector geometry. To achieve a reasonably high aperture efficiency, and avoid unnecessarily oversizing the reflector diameter, three or four reflector apertures are typically required to provide a multiple beam coverage with contiguous beams, assuming dual-band (transmit/receive) feeds are used.
Multiple-feed-per-beam reflector antenna configurations generate each beam from a cluster of feeds of the array located in the focal plane of the reflector geometry. Overlapping between the clusters (feed clusters) is required to produce contiguous beams with acceptable aggregate performance. This is generally achieved sharing feeds between adjacent clusters through adequate beamforming network design. Most feed array solutions reported are limited in frequency bandwidth, thus requiring two reflector antennas to produce a complete transmit/receive coverage, with one reflector antenna generally operating in each frequency band, B1, B2.
Furthermore, feeds shared in frequency between adjacent clusters operating in a same polarization impose constraints on the electromagnetic signal distribution achievable with the beamforming networks, requiring either a lossy design or a sub-optimal phase distribution. To avoid this issue, it is generally preferred to share feeds in polarization between adjacent clusters operating in a same frequency band, which enables independent control of the distribution coefficients, thus leading to optimal design of each cluster. However, this constrains the achievable cluster layouts, resulting in configurations either requiring two separate reflectors or with reduced aggregate performance at antenna level.
Furthermore, there is an interest to reduce the number of feeds per beam, enabling higher beam density, translating into higher throughput density over the coverage for a given reflector geometry, or to provide more flexibility in cluster overlapping layouts for enhanced aggregate performance at antenna level. There is also an interest in making such multiple-feed-per-beam antenna systems compatible with smaller platforms or as a secondary payload, where solutions based on a single reflector would be preferred to facilitate accommodation and fit in smaller launchers.
It is advantageous to obtain a more versatile dual-band multiple-feed-per-beam antenna system which addresses one or more of the problems of existing antenna systems in communication satellites.
In accordance with a first aspect of the present disclosure, a waveguide feed array is provided comprising overlapping clusters (feed clusters) of elementary feeds, each feed operating in at least two distinct frequency bands, B1, B2, with dual-polarization, P1, P2, in each band, corresponding to feeds with at least 4 waveguide ports each, two per said frequency band. That is, each feed may have one port for each pairing (combination) of frequency band and polarization (B1, P1), (B1, P2), (B2, P1) and (B2, P2). Further, the feeds of a given cluster may be connected through beamforming networks, one per frequency band. For each cluster of feeds, there may be (at least) two beamforming networks (BFNs), and each cluster may have (at least) two common ports serving as electrical interface to the structure at cluster level. The waveguide feed array may have a main longitudinal direction Z, substantially orthogonal to the plane of the aperture of the feed array defined by two main directions (main transverse directions) X, Y not necessarily orthogonal. The feeds may be arranged with their longitudinal directions substantially extending in parallel to the main longitudinal direction Z of the waveguide feed array.
Further, clusters may be offset with respect to each other, the offset comprising a translation (within the plane X, Y), a rotation (around the main longitudinal direction Z), and/or a symmetry (e.g., a symmetry operation or a mirror operation with respect to a plane including the main longitudinal direction Z). The offset may be such that, along a first direction X (first main direction), adjacent clusters may share at least one feed, said adjacent clusters using at a given frequency band different polarization ports of said shared feed. Further, the offset may be such that along a second direction Y (second main direction), adjacent clusters have no feeds in common.
Further, at least one feed of each cluster may be rotated around the main longitudinal direction Z with reference to the other feeds of said cluster.
It is understood that each feed comprises a plurality of interconnected microwave devices such as a radiating element, an orthomode junction, an orthomode transducer and/or duplexing filters configured to operate as a transition between guided waves and free space.
It is further understood that the feeds may have identical design, for example, with regard to the arrangement of ports, etc. Preferably, the ports of the feeds may be arranged according to the same pattern (port arrangement) for all feeds of the waveguide feed array. This pattern may have a discrete symmetry (e.g., mirror symmetry, central symmetry, or discrete rotational symmetry, such as rotation by 180°). Further, the discrete symmetry may be such that ports corresponding to different polarizations for a given frequency band map to each other under the discrete symmetry.
The above measures provide a multiple-feed-per-beam waveguide feed array which comprises at least three clusters of dual-band dual-polarization feeds with two clusters sharing at least one feed and other two clusters having no feeds in common, each cluster producing congruent transmit and receive beams, part of a multiple contiguous beam coverage enabling full-duplex communication, when combined with an adequate reflector antenna geometry. Preferably, the waveguide feed array is designed to produce hundreds of beams with a four-color reuse scheme. For example, the waveguide feed array may be a transmit/receive K/Ka-band feed array and may be used in a reflector antenna system on board a communication satellite providing broadband access.
It is known that multiple-feed-per-beam feed arrays producing a set of contiguous beams require a level of overlapping, or feed sharing, between adjacent clusters of feeds, as this overlapping determines the cross-over level between adjacent beams over the coverage or service area for a given reflector antenna geometry. This is a major design aspect to ensure homogeneous performance across the service area. Solutions have been reported using clusters of 7 feeds or more, up to 25 feeds per beam for example. These solutions typically require sharing feeds both in polarization and in frequency. Feed sharing in polarization is implemented taking advantage of the two distinct polarization ports per frequency band of each elementary feed. The respective beamforming networks of each cluster are thus connected to different feed ports and the feed sharing does not affect the design of said beamforming networks. On the contrary, feed sharing in frequency does require the beamforming networks of adjacent clusters to use the same feed port. Ideally, a diplexer would be required to separate a given feed port into two sub-band ports, e.g., (B1, P1) into (F1, P1) and (F2, P1). However, this would result in excessive design complexity, as diplexers are generally bulky. The preferred option is instead to use passive multi-mode components such as hybrid couplers to produce the overlapping. This comes at the expense of constraints in the achievable distribution coefficients produced by the beamforming networks, and in particular on the phase distribution. This leads to a sub-optimal design resulting in degraded antenna performance.
Furthermore, feed array solutions with a large number of feeds per cluster require compact feeds, typically in the order of a wavelength, not compatible with typical transmit/receive feed designs, as the distance between adjacent clusters has a direct impact on the focal length of the reflector geometry. For these reasons, solutions reported with clusters of seven feeds or more are single-band designs and two reflector antennas are required, one for the transmit and one for the receive frequency bands.
To reduce drastically the complexity of the clusters, solutions with only three or four feeds per beam have been proposed. These solutions only share feeds in polarization, as sharing feeds in frequency would degrade substantially the aggregate antenna performance due to the larger ratio of shared feeds in frequency over the limited number of feeds per cluster. Typical solutions still make use of two reflector antennas, producing the beams in the two different frequency sub-bands from different apertures. One solution has been proposed using a single reflector to produce the contiguous beams with congruent coverage in transmit and receive. However, this comes at the expense of degraded antenna performance as the resulting rectangular beam lattice is sub-optimal.
Other solutions using a single large aperture have been reported. One solution consists in combining two single-band feed arrays through a frequency-selective sub-reflector, leading to a rather complex overall focal system. An alternative solution is the use of a single-feed-per-beam configuration with sub-optimal reflector illumination to achieve an acceptable overlap between adjacent beams. This comes at the expense of high spillover losses, typically in the order of 5 to 10 dB.
In accordance with the present disclosure as claimed, at least one feed of each cluster may be rotated around the main longitudinal direction Z with reference to the other feeds of said cluster. Arrays with elements rotated around the longitudinal direction may be known for specific applications. This technique is usually referred to as sequential rotation and applied to direct radiating arrays. Its main purpose is to reduce the cross-polarized component of the radiated electric field, e.g., the RHCP component for an electric field with its main component in LHCP, at array level taking advantage of the symmetries introduced by sequentially rotating the array elements. This technique is generally considered when the array element has poor cross-polarization performance. For example, in a group of four patch antennas, the rotation angle around the longitudinal direction is incremented 90° when turning clock-wise. This also works with increments of −90° or applying the increment anti-clock-wise, as long as the beamforming network compensates for the phase progression such that all elementary signals add up coherently in the boresight direction. Elementary feeds for broadband satellite payloads generally have very low cross-polarization, and further reduction is not required. For this reason, this technique has never been applied to multiple-feed-per-beam feed array design.
As will be also elucidated elsewhere in this specification, the waveguide feed array according to the present disclosure is found to produce unexpected benefits, which include and are not limited to reducing beamforming network complexity, advantageous both for the electrical and the mechanical designs, as well as added flexibility in defining cluster layouts with enhanced performance at antenna level. The present disclosure further benefits from the use of compact dual-band dual-polarization feeds with a footprint that may fit in a lattice between two and three wavelengths at the highest operating frequency. For example, a waveguide feed array according to the present disclosure may be designed with a lattice between 20 and 30 mm for operation in K/Ka-band.
In an embodiment, at least one feed of each cluster may be rotated by 180° around the main longitudinal direction Z with reference to the other feeds of said cluster. This at least one feed may correspond to a feed that is shared between adjacent clusters of feeds. Preferably, the feed used as array element has the at least two ports pertaining to a given cluster operating in at least two distinct frequency bands, B1, B2, on a same side, and the remaining at least two ports pertaining to an adjacent cluster operating in the same at least two distinct frequency bands, B1, B2, located on an opposite side, the arrangement of the ports being characterized by a symmetry, such as a central symmetry or an axial symmetry, that further facilitates the design of the waveguide feed array and specifically of the beamforming networks. Communication satellite payloads generally implement orthogonal polarizations in transmit and receive frequency bands, as this provides further isolation for enhanced signal duplexing at terminal level. Thus, the pairs of ports on each side of the feed will preferably have orthogonal polarizations, e.g., (B1, P1) with (B2, P2) and (B1, P2) with (B2, P1). Combining this property with a rotation of at least one feed of each cluster may lead to beamforming networks that do not overlap between adjacent clusters, thus facilitating both the electrical and the mechanical designs. In particular, the beamforming networks of each cluster may be designed and manufactured as separate units, or as groups of adjacent units, facilitating the manufacturing and assembly of a complete waveguide feed array. Each cluster has at least two beamforming networks, one per operating frequency band, B1, B2, which may be interleaved to be manufactured as a single unit that does not overlap with that of adjacent clusters. Further, all beamforming networks of all feed clusters are identical and related to each other by at least one of translation, rotation, and/or symmetry along or around at least one of the directions X, Y, Z, thus reducing significantly the design effort. The beamforming networks feeding each clusters may comprise a combination of E-plane and H-plane power dividers or reactive T-junctions in combination with adequate waveguide routing to introduce a phase difference of 180° between feeds having different angular orientations around the main longitudinal direction Z with path lengths substantially equal from a common port to all distributed ports in order to achieve wide band operation. These properties may be used to define new cluster layouts improving performance at antenna level when compared to known solutions.
In an embodiment, an angular orientation around the main longitudinal direction Z of consecutive feeds along the first main direction X may alternate by 180°, whereas the angular orientation around the main longitudinal direction Z of consecutive feeds along the second main direction Y is invariant. In specific implementations thereof, the feeds may be arranged along parallel rows of feeds in the plane of the aperture of the waveguide feed array defined by the two main directions X, Y. The rows of feeds may extend, for example, in the second main direction Y. Then, an angular orientation of the feeds around the main longitudinal direction Z may be the same for all feeds within a given row of feeds. On the other hand, the angular orientation of the feeds along the main longitudinal direction Z may differ by a predefined angle between feeds in adjacent rows of feeds. In specific implementations, the orientation around the main longitudinal direction Z may vary by 180° between feeds in adjacent rows of feeds.
In an embodiment, each cluster may comprise three feeds, with one feed rotated 180° around the main longitudinal direction Z with reference to the other two feeds of said cluster. For example, the waveguide feed array may be designed with an equilateral triangular lattice well suited for circular feeds, the array spacing being essentially the feed diameter. Furthermore, the waveguide feed array aperture plane may be defined by two main directions X, Y, not necessarily orthogonal and here at an angle of 60°, substantially orthogonal to the main longitudinal direction Z. Adjacent clusters along a first direction X share one feed in polarization, corresponding to adjacent clusters along the first direction X operating in orthogonal polarizations, and are offset with respect to each other along the first direction X, the offset corresponding to a translation by one feed diameter along the first direction X with reference to the arrangement of the radiating elements of the feeds. The shared feed along the first direction X is advantageously rotated 180° around the main longitudinal direction Z, facilitating the design of the beamforming networks connected to said shared feed. Adjacent clusters along a second direction Y have no feeds in common, corresponding to adjacent clusters along the second direction Y operating in different frequency sub-bands, and are offset with respect to each other along the second direction Y, the offset corresponding to a translation by one and a half feed diameters along the second direction Y and a rotation of 180° around the main longitudinal direction Z of the cluster. Advantageously, the angular orientation around the main longitudinal direction Z of the feeds along the second direction Y is invariant (i.e., does not change when going along the second direction Y). Thus, with reference to a first cluster having one feed rotated 180° around the main longitudinal direction Z along the first direction X, a second cluster along the second direction Y, having no feeds in common with the first cluster, has two feeds rotated 180° around the main longitudinal direction Z. With reference to the second cluster, it may be considered that one feed is rotated 180° around the main longitudinal direction Z with reference to the other two feeds of said cluster. Further, the angular orientation around the main longitudinal direction Z of each cluster, with reference to the arrangement of the radiating elements of the feeds, is invariant along a first direction X, while the angular orientation around the main longitudinal direction Z of each feed cluster alternates 180° along a second direction Y, resulting in a waveguide feed array with regularly spaced feeds and regularly spaced feed clusters. Alternatively, the angular orientation around the main longitudinal direction Z of each cluster as well as the offset distance may vary along the first direction X, providing an irregular two-dimensional lattice of clusters with advantageous properties at antenna level.
In an embodiment, each cluster may comprise four feeds, with two feeds rotated 180° around the main longitudinal direction Z with reference to the other two feeds of said cluster. For example, the waveguide feed array may be designed with an equilateral triangular lattice well suited for circular feeds, the array spacing being essentially the feed diameter. Furthermore, the waveguide feed array aperture plane may be defined by two main directions X, Y, not necessarily orthogonal and here at an angle of 60°, substantially orthogonal to the main longitudinal direction Z. Adjacent clusters along a first direction X share one feed in polarization, corresponding to adjacent clusters along the first direction X operating in orthogonal polarizations, and are offset with respect to each other along the first direction X, the offset corresponding to a translation by one feed diameter along the first direction X with reference to the arrangement of the radiating elements of the feeds. The shared feed along the first direction X is advantageously rotated 180° around the main longitudinal direction Z, facilitating the design of the beamforming networks connected to said shared feed. Adjacent clusters along a second direction Y have no feeds in common, corresponding to adjacent clusters along the second direction Y operating in different frequency sub-bands, and are offset with respect to each other along the second direction Y, the offset corresponding to a translation by two times the feed diameter along the second direction Y. Advantageously, the angular orientation around the main longitudinal direction Z of the feeds along the second direction Y is invariant. This cluster layout may correspond to previously reported designs, with a lattice of clusters essentially rectangular having an aspect ratio of √{square root over (3)}, where the distance along the second direction Y corresponds to a diagonal of said rectangular lattice. The feed arrangement with some feeds rotated around the main longitudinal direction Z facilitates greatly the design and implementation of the beamforming networks, which may be manufactured as separated units or as groups of adjacent units, simplifying the manufacturing and assembly of the complete waveguide feed array.
In an embodiment, each cluster may comprise four feeds, with two feeds rotated 180° around the main longitudinal direction Z with reference to the other two feeds of said cluster. For example, the waveguide feed array may be designed with an equilateral triangular lattice well suited for circular feeds, the array spacing being essentially the feed diameter. Furthermore, the waveguide feed array aperture plane may be defined by two main directions X, Y, not necessarily orthogonal and here at an angle of approximately 41°, substantially orthogonal to the main longitudinal direction Z. More precisely the cosine of the angle between the two main directions X, Y is equal to 2/√{square root over (7)}. Adjacent clusters along a first direction X share one feed in polarization, corresponding to adjacent clusters along the first direction X operating in orthogonal polarizations, and are offset with respect to each other along the first direction X, the offset corresponding to a translation by √{square root over (7)}/2, or approximately 1.3, times the feed diameter along the first direction X and a rotation of 120° around the main longitudinal direction Z of the cluster with reference to the arrangement of the radiating elements of the feeds. The shared feed along the first direction X is advantageously rotated 180° around the main longitudinal direction Z, facilitating the design of the beamforming networks connected to said shared feed. Adjacent clusters along a second direction Y have no feeds in common, corresponding to adjacent clusters along the second direction Y operating in different frequency sub-bands, and are offset with respect to each other along the second direction Y, the offset corresponding to a translation by two times the feed diameter along the second direction Y.
Advantageously, the angular orientation around the longitudinal direction Z of the feeds along the second direction Y is invariant. Further, the angular orientation around the longitudinal direction Z of each cluster, with reference to the arrangement of the radiating elements of the feeds, is alternating between 0° and 120° along a first direction X, while the angular orientation around the main longitudinal direction Z of each cluster remains invariant along a second direction Y, resulting in a waveguide feed array with regularly spaced feeds and regularly spaced feed clusters. The corresponding cluster layout is approximately a square lattice, providing a more regular arrangement when compared to previously reported layouts. As it will be elucidated elsewhere in this specification, this particular arrangement provides higher performance at antenna level, both in aggregate gain and C/I. Alternatively, the angular orientation around the main longitudinal direction Z of each cluster, with reference to the arrangement of the radiating elements of the feeds, may vary differently along the first direction X, providing an irregular two-dimensional lattice of clusters with different properties at antenna level.
In an embodiment, each cluster may comprise two feeds, with one feed rotated 180° around the main longitudinal direction Z with reference to the other feed of said cluster. For example, the waveguide feed array may be designed with an equilateral triangular lattice well suited for circular feeds, the array spacing being essentially the feed diameter. Furthermore, the waveguide feed array aperture plane may be defined by two main directions X, Y, not necessarily orthogonal and here at an angle of 60°, substantially orthogonal to the main longitudinal direction Z. Adjacent clusters along a first direction X share one feed in polarization, corresponding to adjacent clusters along the first direction X operating in orthogonal polarizations, and are offset with respect to each other along the first direction X, the offset corresponding to a translation by one feed diameter along the first direction X with reference to the arrangement of the radiating elements of the feeds. The shared feed along the first direction X is advantageously rotated 180° around the main longitudinal direction Z, facilitating the design of the beamforming networks connected to said shared feed. Adjacent clusters along a second direction Y have no feeds in common, corresponding to adjacent clusters along the second direction Y operating in different frequency sub-bands, and are offset with respect to each other along the second direction Y, the offset corresponding to a translation by one feed diameter along the second direction Y. Advantageously, the angular orientation around the main longitudinal direction Z of the feeds along the second direction Y is invariant. This particular arrangement provides more overlap between the clusters along the first direction X when compared to a single-feed-per-beam configuration using the same feeds and having the same lattice. As it will be elucidated elsewhere in this specification, this particular arrangement provides worse performance at antenna level when compared to alternative multiple-feed-per-beam configurations, but does provide higher beam density, which may be desirable for some applications with less demanding requirements on C/I.
It will be appreciated by those skilled in the art that two or more of the aforementioned embodiments may be combined to produce alternative cluster layouts with advantageous properties, at the expense of some added design complexity. For example, a waveguide feed array may combine clusters comprising two and three feeds in an irregular lattice of clusters as a compromise solution between two regular cluster arrangements. Alternatively, a waveguide feed array may combine clusters comprising three and four feeds in an irregular lattice of clusters as another compromise solution between two regular cluster arrangements. It is anticipated that as long as the feeds maintain an adequate arrangement, essentially with alternating angular orientation around the main longitudinal direction Z along a first direction X and invariant angular orientation around the main longitudinal direction Z along a second direction Y, it may be possible to design beamforming networks that do not overlap between adjacent clusters, thus facilitating the mechanical design and assembly of the complete waveguide feed array, as each beamforming network may be manufactured as separate units or as groups of adjacent units. Furthermore, all beamforming networks of all clusters of same size are identical and related to each other by at least one of translation, rotation, and/or symmetry along or around at least one of the main directions X, Y, Z, keeping the design effort moderate.
In a further aspect of the present disclosure, an antenna system is provided comprising at least one waveguide feed array as presently disclosed and a reflector antenna producing a coverage of multiple contiguous beams, congruent in the at least two frequency bands, B1, B2, typically a transmit and a receive frequency band, with polarization reuse along a first direction X′, corresponding to the first direction X of the feed system along which at least one pair of adjacent clusters share at least one feed in polarization, and with frequency reuse along a second direction Y′, corresponding to the second direction Y of the feed system along which adjacent clusters have no feeds in common. Furthermore, the reflector geometry may be an offset paraboloid and the waveguide feed array may be advantageously arranged to have its aperture, corresponding to the plane with directions X, Y, coinciding with the focal plane of the offset paraboloid, and the main longitudinal direction Z pointing approximately towards the center of the reflector. The spacing between feeds may be set between two and three wavelengths at the higher operating frequency, corresponding to a spacing between 20 and 30 mm in K/Ka band.
Modifications and variations of any one of the embodiments may be carried out by a person skilled in the art on the basis of the present description. In particular, the use of well-known size reduction techniques of common hollow waveguide cross-sections, such a ridged waveguide cross-section, may be considered to further reduce the footprint of the waveguide feed array, thus increasing the beam density or reducing the focal length of the antenna geometry. This may be advantageous on small platforms or for use as secondary payloads. Other transmission line technologies, such as stripline, may also be considered to further reduce the volume of the feed array while preserving the main characteristics and benefits of the present disclosure.
Further details, aspects, and embodiments will be described, by way of example, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. In the Figures, elements which correspond to elements already described may have the same reference numerals. In the drawings,
The following list of references and abbreviations is provided for facilitating the interpretation of the drawings and shall not be construed as limiting the claims.
While the presently disclosed subject matter is susceptible of embodiment in many different forms, there are shown in the drawings and will herein be described in detail one or more specific embodiments, with the understanding that the present disclosure is to be considered as exemplary of the principles of the presently disclosed subject matter and not intended to limit it to the specific embodiments shown and described.
In the following, for the sake of understanding, elements of embodiments are described in operation. However, it will be apparent that the respective elements are arranged to perform the functions being described as performed by them. In addition, to facilitate visualization of the operating waveguides, drawings illustrate the inner waveguide cavities, rather than the surrounding electrically conductive material or electrical conductor, unless otherwise stated. For example, waveguide ports may refer to electrical interfaces with corresponding flanges although not explicitly shown when inner waveguide cavities are illustrated.
Further, the presently disclosed subject matter is not limited to the embodiments, as features described herein or recited in mutually different dependent claims may be combined.
Preferably, the ports on a same side of the axis of symmetry have orthogonal polarizations, as typical communication satellite payloads implement orthogonal polarizations in transmit and receive frequency bands, providing further isolation for enhanced signal duplexing at terminal level. For example, the waveguide port 110 and the waveguide port 140 may correspond to the pairing (B1,P1) and (B2, P2), respectively, while the waveguide port 120 and the waveguide port 130 correspond to (B1, P2) and (B2, P1), respectively. This waveguide port arrangement may further facilitate the design of the beamforming networks, and in particular avoid overlapping between beamforming networks of adjacent clusters. Other waveguide port arrangements 100 may be suitable in combination with the present disclosure, while arrangements having central and/or axial symmetry are preferred to simplify further the design of the waveguide feed array and beamforming networks.
In each frequency band, B1, B2, the spectrum is further divided into two sub-bands, F1, F2, combined with two orthogonal polarizations, P1, P2, to produce a four-color scheme. Adjacent clusters 300 along a first direction X share one feed 10 and are offset with respect to each other along the first direction X, the offset corresponding to a translation by one feed diameter along the first direction X with reference to the arrangement of the radiating elements of the feeds. The shared feed 10 is advantageously rotated 180° around the main longitudinal direction Z. Adjacent clusters 300 along the direction X with a shared feed 10 operate in orthogonal polarizations.
For example, in the lower frequency band B1, the first cluster 300, marked with a thick solid line, may correspond to the pairing (F1, P1), while the adjacent cluster 300, marked with a dotted line, may correspond to the pairing (F1, P2). In the upper frequency band B2, the polarizations may be inverted as usually implemented in communication satellite systems. The cluster layout alternates these two types of clusters 300 along the first direction X. With the rotated feeds 10, the offset between adjacent clusters 300 along the first direction X may be better described as a combination of a translation by one feed diameter along the first direction X and a reflection with reference to a symmetry plane orthogonal to the second direction Y.
The benefits of rotating feeds 10 around the main longitudinal direction Z is particularly evident along the first direction X. This is illustrated with particular focus on the waveguide ports 110 of each feeds 10 of a cluster 300 marked with a thick solid line, which all operate in the same frequency band B1 and the same polarization P1. All three waveguide ports 110 of a cluster 300 are next to each other, facilitating the design of the corresponding beamforming network. Clusters 300 along a second direction Y have no feeds 10 in common and are offset with respect to each other along the second direction Y, the offset in this case corresponding to a translation by one and a half feed diameters along the second direction Y and a rotation of 180° around the main longitudinal direction Z of the clusters 300. The rotated feed 10 in this case is such that the angular orientation of the feeds around the main longitudinal direction Z is invariant along the second direction Y. Adjacent clusters 300 along the second direction Y with no feeds in common advantageously operate in the same polarization but in different frequency sub-bands. For example, in the lower frequency band B1, the first cluster 300, marked with a thick solid line, may correspond to the pairing (F1, P1), while the adjacent cluster 300, marked with a dashed line, may correspond to the pairing (F2, P1).
The four-color scheme is completed by a fourth type of cluster 300, marked with a dash-dotted line, which may correspond to the pairing (F2, P2). With this cluster layout, polarization reuse is implemented along the first direction X, while frequency reuse is implemented along the second direction Y. As can be seen, the resulting lattice of clusters 300 is approximately square with a side along the first direction X, while the second direction Y corresponds to a diagonal. Identical clusters 300, operating in a same frequency band and a same polarization, are distributed in a rectangular lattice with a much shorter distance between identical clusters 300 along the first direction X, which is sub-optimal for aggregate performance at antenna level. This may be improved introducing some irregularity in the cluster layout.
In general, a shape (or angular orientation around the main longitudinal direction Z) in terms of the arrangement of the radiating elements of the feeds of clusters may alternate by 180° from one cluster to the next when going along the second main direction Y. On the other hand, the shape of clusters may be invariant when going along the first main direction X.
Adjacent clusters 300 along the second direction Y with no feeds in common advantageously operate in the same polarization but in different frequency sub-bands. For example, in the lower frequency band B1, the first cluster 300, marked with a thick solid line, may correspond to the pairing (F1, P1), while the adjacent cluster 300, marked with a dashed line, may correspond to the pairing (F2, P1). The four-color scheme is completed by a fourth type of cluster 300, marked with a dash-dotted line, which may correspond to the pairing (F2, P2). With this irregular cluster layout, polarization reuse is implemented along the first direction X, while frequency reuse is implemented along the second direction Y. As can be seen, the resulting lattice of clusters 300 remains approximately square although slightly irregular, with a side along the first direction X, while the second direction Y corresponds to a diagonal. However, the arrangement of clusters 300 in the same color, for example, the clusters 300 marked with thick solid lines, are now in a slightly irregular triangular lattice. As it will be also elucidated elsewhere in this specification, this irregular lattice of clusters benefits performance at antenna level and in particular aggregate gain and C/I.
In each frequency band, B1, B2, the spectrum is further divided into two sub-bands, F1, F2, combined with two orthogonal polarizations, P1, P2, to produce a four-color scheme. Adjacent clusters 400 along a first direction X share one feed 10 and are offset with respect to each other along the first direction X, the offset corresponding to a translation by one feed diameter along the first direction X with reference to the arrangement of the radiating elements of the feeds. The shared feed 10 is advantageously rotated 180° around the main longitudinal direction Z, as well as the adjacent feed 10 of the same cluster 400 along the second direction Y, advantageously shared with a further adjacent cluster 400 along a third direction in the plane defined by the main directions X, Y.
Adjacent clusters 400 along the direction X with a shared feed 10 advantageously operate in orthogonal polarizations.
For example, in the lower frequency band B1, the first cluster 400, marked with a thick solid line, may correspond to the pairing (F1, P1), while the adjacent cluster 400, marked with a dotted line, may correspond to the pairing (F1, P2). In the upper frequency band B2, the polarizations may be inverted as usually implemented in communication satellite systems. The cluster layout alternates these two types of clusters 400 along the first direction X. With the rotated feeds 10, the offset between adjacent clusters 300 along the first direction X may be better described as a combination of a translation by one feed diameter along the first direction X, a reflection with reference to a symmetry plane orthogonal to the second direction Y and a further reflection with reference to a symmetry plane defined by the directions Y, Z.
The benefits of rotating feeds 10 around the main longitudinal direction Z is particularly evident along the first direction X. This is illustrated with particular focus on the waveguide ports 110 of each feeds of a cluster 400 marked with a thick solid line, which all operate in the same frequency band B1 and the same polarization P1. All four waveguide ports 110 of a cluster 400 are next to each other, facilitating the design of the corresponding beamforming network. Clusters 400 along a second direction Y have no feeds in common and are offset with respect to each other along the second direction Y, the offset in this case corresponding to a translation by two times the feed diameter along the second direction Y. The angular orientation of the feeds 10 around the longitudinal direction Z is invariant along the second direction Y. Adjacent clusters 400 along the second direction Y with no feeds in common advantageously operate in the same polarization but in different frequency sub-bands.
For example, in the lower frequency band B1, the first cluster 400, marked with a thick solid line, may correspond to the pairing (F1, P1), while the adjacent cluster 400, marked with a dashed line, may correspond to the pairing (F2, P1). The four-color scheme is completed by a fourth type of cluster 400, marked with a dash-dotted line, which may correspond to the pairing (F2, P2). With this cluster layout, polarization reuse is implemented along the first direction X, while frequency reuse is implemented along the second direction Y. As can be seen, the resulting lattice of clusters 400 is essentially rectangular with a side along the first direction X, while the second direction Y corresponds to a diagonal. This rectangular lattice has an aspect ratio of √{square root over (3)}, which also applies to the lattice of identical clusters 400, the shorter distance being along the first direction X. This cluster layout corresponds to a previously disclosed layout. However, the angular orientation of the feeds 10 around the main longitudinal direction Z according to an embodiment of the present disclosure may facilitate the design of the beamforming networks. In particular, beamforming networks may be manufactured as separate units or group of adjacent units as their design may be such that beamforming networks of adjacent clusters 400 do not overlap.
In each frequency band, B1, B2, the spectrum is further divided into two sub-bands, F1, F2, combined with two orthogonal polarizations, P1, P2, to produce a four-color scheme. Adjacent clusters 400 along a first direction X share one feed 10 and are offset with respect to each other along the first direction X, the offset corresponding to a translation by √{square root over (7)}/2, or approximately 1.3, times the feed diameter along the first direction X and a rotation of 120° around the main longitudinal direction Z of the cluster 400 with reference to the arrangement of the radiating elements of the feeds. The shared feed 10 is advantageously rotated 180° around the main longitudinal direction Z, as well as the adjacent feed 10 of the same cluster 400 along the second direction Y, advantageously shared with a further adjacent cluster 400 along a third direction in the plane defined by the main directions X, Y. Adjacent clusters 400 along the direction X with a shared feed 10 advantageously operate in orthogonal polarizations.
For example, in the lower frequency band B1, the first cluster 400, marked with a thick solid line, may correspond to the pairing (F1, P1), while the adjacent cluster 400, marked with a dotted line, may correspond to the pairing (F1, P2). In the upper frequency band B2, the polarizations may be inverted as usually implemented in communication satellite systems. The cluster layout alternates these two types of clusters 400 along the first direction X. With the rotated feeds 10, the offset between adjacent clusters 400 may be better described as a combination of a translation by √{square root over (7)}/2 times the feed diameter along the first direction X and a reflection with reference to a symmetry plane orthogonal to the second direction Y. The benefit of rotating feeds 10 around the longitudinal direction Z is particularly evident along the first direction X. This is illustrated with particular focus on the waveguide ports 110 of each feeds of a cluster 400 marked with a thick solid line, which all operate in the same frequency band B1 and the same polarization P1.
All four waveguide ports 110 of a cluster 400 are next to each other, facilitating the design of the corresponding beamforming network. Clusters 400 along a second direction Y have no feeds in common and are offset with respect to each other along the second direction Y, the offset in this case corresponding to a translation by two times the feed diameter along the second direction Y. The rotated feeds 10 in this case are such that the angular orientation of the feeds 10 around the main longitudinal direction Z is invariant along the second direction Y. Adjacent clusters 400 along the second direction Y with no feeds in common advantageously operate in the same polarization but in different frequency sub-bands.
For example, in the lower frequency band B1, the first cluster 400, marked with a thick solid line, may correspond to the pairing (F1, P1), while the adjacent cluster 400, marked with a dashed line, may correspond to the pairing (F2, P1). The four-color scheme is completed by a fourth type of cluster 400, marked with a dash-dotted line, which may correspond to the pairing (F2, P2). With this cluster layout, polarization reuse is implemented along the first direction X, while frequency reuse is implemented along the second direction Y. The resulting lattice of clusters is approximately square, with a side along the first direction X, providing enhanced aggregate performance at antenna level compared to the layout of
In each frequency band, B1, B2, the spectrum is further divided into two sub-bands, F1, F2, combined with two orthogonal polarizations, P1, P2, to produce a four-color scheme. Clusters 300, 400 along a first direction X share at least one feed 10 and are offset with respect to each other along the first direction X, the offset varying from one cluster 300, 400 to another as also the size and orientation (at least as far as the shape of the cluster in terms of radiating elements of the feeds is concerned) of clusters 300, 400 vary along the first direction X. The shared feed 10 is advantageously rotated 180° around the main longitudinal direction Z, as well as the adjacent feed 10 of the same cluster 400 along the second direction Y in the case of a four-feed cluster 400, advantageously shared with a further adjacent cluster 300, 400 along a third direction in the plane defined by the main directions X, Y. Other rotation angles may provide similar benefits. Adjacent clusters 300, 400 along the first direction X with a shared feed 10 advantageously operate in orthogonal polarizations.
For example, in the lower frequency band B1, the first cluster 300, 400, marked with a thick solid line, may correspond to the pairing (F1, P1), while the adjacent cluster 300, 400, marked with a dotted line, may correspond to the pairing (F1, P2). In the upper frequency band B2, the polarizations may be inverted as usually implemented in communication satellite systems. The cluster layout alternates these two types of clusters 300, 400 along the first direction X, while also alternating the size and angular orientation around the main longitudinal direction Z (at least as far as the shape of the cluster in terms of radiating elements of the feeds is concerned) of the clusters 300, 400. The benefit of rotating feeds 10 around the longitudinal direction Z is particularly evident along the first direction X. This is illustrated with particular focus on the waveguide ports 110 of each feeds 10 of a cluster 400 marked with a thick solid line, which all operate in the same frequency band B1 and the same polarization P1.
All four waveguide ports 110 of a cluster 400 are next to each other, facilitating the design of the corresponding beamforming network. Clusters 300, 400 along a second direction Y have no feeds in common and are offset with respect to each other along the second direction Y, the offset varying from one cluster 300, 400 to another as also the size and angular orientation around the main longitudinal direction Z (at least as far as the shape of the cluster in terms of radiating elements of the feeds is concerned) of the clusters 300, 400 vary along the second direction Y. The angular orientation of the feeds 10 around the main longitudinal direction Z is invariant along the second direction Y. Adjacent clusters 300, 400 along the second direction Y with no feeds in common advantageously operate in the same polarization but in different frequency sub-bands.
For example, in the lower frequency band B1, the first cluster 300, 400, marked with a thick solid line, may correspond to the pairing (F1, P1), while the adjacent cluster 300, 400, marked with a dashed line, may correspond to the pairing (F2, P1). The four-color scheme is completed by a fourth type of cluster 300, 400, marked with a dash-dotted line, which may correspond to the pairing (F2,P2). With this cluster layout, polarization reuse is implemented along the first direction X, while frequency reuse is implemented along the second direction Y. The combination of clusters 300, 400 of different sizes may enable alternative cluster lattices with enhanced aggregate performance at antenna level compared to regular layouts with a moderate impact on design complexity.
For example, the specific layout in
It can be seen that the feed 10 and beamforming networks 311, 312 have a broadband response as separate units. The broadband response is preserved when the separate units are combined and the reflection coefficients of the cluster 300 remain better than −18 dB both in the down-link (17.7-20.2 GHZ) and the up-link (27.5-30 GHz) frequency bands typically allocated to broadband communication satellites. The transmission coefficients demonstrate a stable response over frequency. The design presented here makes use of E-plane and H-plane T-junctions with balanced output power. Thus, one port has theoretically a transmission coefficient of −3.01 dB, while the other two have a transmission coefficient of −6.02 dB. The values obtained with the full-wave model are in line with expectations.
For example, the coefficients S12 and S13 are approximately equal to −6 dB over the complete analyzed frequency band in
Similarly, the beamforming network 412 operating in the higher frequency band B2, with rectangular waveguides having a smaller cross-section, may connect a common waveguide port 160 to four output waveguide ports 140, which may be further connected to corresponding waveguide ports 140 of the four feeds 10 of the cluster 400. The waveguide routing is such that the ports that are rotated with respect to the others around the main longitudinal direction Z are fed with a phase difference corresponding to the angle of rotation, for example, 180°. Further, the waveguide routing is such that all path lengths are substantially equal, resulting in broadband frequency response. The two beamforming networks 411, 412 are interleaved, producing a compact beamforming network unit 410.
The waveguide routing is such that all path lengths are substantially equal, resulting in broadband frequency response. The beamforming network 412 of
Specifically,
The first direction X′ corresponds to the first direction X of the waveguide feed array 200 along which adjacent clusters 400 share one feed 10. Along a second direction Y′, approximately at 60° with respect to the u-axis, the contour plots do not overlap, as this corresponds to the second direction Y of the feed array 200 along which adjacent clusters 400 have no feeds in common. Finally,
It is noted that the contour plots of each beam differ from those in
For the results reported in
Specifically,
Another important remark is that the design using three feeds per beam provides competitive antenna system performance. While the aggregate gain is slightly better than the reference cluster layout, the C/I is slightly worse, indicating that with adequate optimization of the overall geometry, comparable performance could be achieved while increasing the number of beams by approximately 50%. This is an important result as UHTS systems in particular aim at higher throughput density over the service area for national or regional broadband services. This configuration with three feeds per beam seems to be an optimum between antenna performance and beam density, as evidenced by the numerical results obtained with the design having two feeds per beam. The C/I is found to suffer particularly in that case, as well as aggregate gain in the lower frequency band due to higher spillover losses. However, it is clear that the antenna geometry is sub-optimal in that case and better results may be obtained adjusting the reflector parameters accordingly. In particular, with these clusters having a high aspect ratio of 2, an elliptical reflector may be preferable. Further improvement may also be achieved combining clusters of different sizes, as illustrated in
It should be noted that the above-mentioned embodiments illustrate rather than limit the present disclosure, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.
In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or stages other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. Expressions such as “at least one of” when preceding a list or group of elements represent a selection of all or of any subset of elements from the list or group. For example, the expression, “at least one of A, B, and C” should be understood as including only A, only B, only C, both A and B, both A and C, both B and C, or all of A, B, and C. The present disclosure may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/052186 | 1/31/2022 | WO |
