A prism for redirecting the main beam of a reflector antenna

Abstract

A microwave prism is used to redirect a reflector antenna that is part of an operational Direct-to-Home (DTH) or Very Small Aperture Terminal (VSAT) ground terminal, allowing it to receive (or transmit) signals from another satellite or orbital location without physically moving the reflector or feed horn antenna. The microwave prism works by shifting the radiation field from a horn antenna that is approximately perpendicular to the focal axis of the parabolic reflector, causing the reflector's main beam to scan accordingly. For existing reflector antennas receiving signals from currently used satellites, the prism is designed to snap into place over the feed horn and shift the field laterally a calibrated distance. The prism structure is designed to be precisely positioned and oriented without requiring skilled personnel. This system allows satellite service providers to redirect their subscribers to new satellites by shipping self-installation kits of pre-configured prisms with the correct orientation and position on the feed antenna to precisely redirect the beam to another satellite when the prism is applied. One advantage of this system is that it allows unskilled personnel, i.e., the subscribers themselves, to redirect multiple subscriber antennas in a satellite network without the expense of truck rolls and technician visits to every site. Microwave prisms to perform this function can be constructed in a variety of ways, using homogeneous slabs or blocks, gradient index (GRIN) multilayer dielectrics, geometric or gradient Fresnel zones, metasurfaces, or metamaterial prisms. The geometric and electrical constraints of the design are determined by the currently used satellites and target satellites, as well as the location of the ground terminal.

Description

[Technical Field]

[0001] <Related Applications> This application claims the benefit of priority to U.S. Provisional Application No. 62 / 981,367, filed February 25, 2020, on the contents of which provisional application is incorporated herein by reference in its entirety. [Background technology]

[0002] U.S. Patent No. 6,075,497 to Chen et al., entitled "Multiple-feed Electromagnetic Signal Receiving Apparatus," filed June 30, 1997, and granted June 13, 2000; U.S. Patent No. 9,722,316 to Haziza, Dedi David, entitled "Horn lens antenna," filed July 7, 2014, and granted August 1, 2017; and U.S. Patent No. 10,158,177 to Cook, Scott, entitled "Antenna horn with suspended dielectric tuning vane," filed March 11, 2016, and granted December 18, 2018, are incorporated herein by reference.

[0003] Satellite communications in the microwave frequency band, whether unidirectional or bidirectional, require large antennas that must be precisely pointed toward the desired satellite to maintain high signal strength while allowing large amounts of data to be distributed over a wide geographic area. The most common satellite antenna for microwave (C-, X-, Ku-, Ka-, and higher bands) applications is the horn-fired reflector, which is a center-fed or offset-fed parabolic (or nearly parabolic) reflector available in a wide variety of shapes, sizes, and operating frequencies.

[0004] Mobile platforms and ground terminals used to communicate with non-geostationary orbit (NGSO) satellites typically have motorized tracking systems and electronics to maintain connection while either the ground terminal or the satellite moves relative to the other. However, this hardware is very expensive. For stationary terrestrial locations communicating with GEO (geostationary Earth Orbit) satellites, fixed antennas that are pointed at the satellite once and then locked in place are cost-effective and simple. However, a drawback of fixed reflectors is that changing the satellite to which the antenna is connected requires skilled personnel and tools. This makes it difficult for subscribers to change their service provider or broadcast station, and for service providers or broadcast stations to change satellites or operators for capacity, commercial, or other reasons. It would be desirable to enable subscribers to easily change their antennas from their current satellite to a new satellite without the need for tools, adjustments, or significant effort, while keeping terminal and antenna costs low for the mass market.

[0005] The present disclosure introduces a system and method that allows those unskilled in reflector antennas to use microwave prisms or lenses by fastening or otherwise connecting them to a horn in a controlled orientation to direct the reflector's main beam so that it can be connected to another satellite.

[0006] As shown in FIG. 1, a parabolic reflector antenna 101 for SATCOM includes at least a parabolic reflector 103 made of a shaped piece of metal or conductive material, a horn antenna 109 that serves to feed or illuminate the reflector 103, and support structures 105, 107 that secure these components in precise relative positions and firmly point the entire assembly toward the satellite. A radome or cover 111 over the horn's mouth protects the horn from water or debris ingress. Some antennas include an additional shaped or parabolic subreflector in the beam path to better control the illumination of the main reflector and / or change its shape. Very low-cost antennas for Ku and Ka DTH most typically use offset-feed reflectors to reduce interference caused by the feed horn. The feed horn is generally highly integrated with a low-noise block (LNB) downconverter circuit 113 and a mounting arm that supports the LNB and feed. A post or wall mounting fixture is included at the rear of the reflector that allows the reflector and power assembly to be oriented and then locked in place with a bolt or other fastener.

[0007] New subscribers to broadcast or interactive satellite services either purchase an antenna 101 or are provided with one as part of their service. Although it is sometimes advertised as being self-installable and oriented, it is almost always installed by the service provider.

[0008] Although the reflector 103 is likely mounted to a solid structure and securely locked in place, it can still be dislodged by wind, snow, or other events. Correcting this problem requires a truck roll, which means sending a trained technician and tools to precisely reorient the antenna. A service visit can represent significant expense to the service provider, even if the problem only takes a few minutes to resolve.

[0009] Changing which satellite is connected when the antenna is not pre-oriented and configured for multiple receivers requires knowledge, tools, and skill. Currently, there are smartphone apps and websites that provide instructions on how to orient a satellite antenna, but the majority of subscribers are not interested in doing it themselves. For this reason, service providers are locked into specific orbital slots by their subscriber base, and the more successful a broadcast provider becomes, the less flexibility the service provider has when it wants to offer or change the satellites from which their service is provided.

[0010] Microwave lenses and prisms constructed from dielectrics, metamaterials, or metasurfaces are commonly used to control the radiation pattern or direction of antennas. Microwave lenses use the same principles as optical lenses but use materials with desirable properties at radio frequencies (high frequencies) rather than optical wavelengths. Benefits vary depending on the feature and method. Anti-reflective coatings, typically implemented as quarter-wave plates or coatings on the lens, are commonly used in microwave lenses but are not universal. Anti-reflective coatings improve the impedance match of signals traveling from free space into the lens material and, again, improve the impedance match of signals exiting the lens. Due to the difficulty of achieving the low dielectric constant required for good anti-reflective coatings, many methods exist for constructing such lenses, including the use of foams, textured surfaces, and 3D printing.

[0011] Beam shifters are common devices in optics, consisting of a polished parallel-plate prism, which can also be described as a slab of glass. When rotated to various angles relative to an incident light beam, the exit point of the light from the prism shifts laterally by a distance related to the light's angle of incidence and the thickness of the prism. Such devices contain optical anti-reflective coatings and are used as optical alignment points for aligning multiple components in a system and as laser workbenches. A typical example is the Thorlabs XYT / MA Post-Mountable Tweaker Plate, 2.5mm thick (Optical Beam Shifter), thorlabs.com. Summary of the Invention

[0012] A reflector antenna redirection device for use with a reflector antenna includes a microwave prism that receives an input field and provides an output field. The device also includes a mounting structure configured to connect the prism to the reflector antenna. The device also includes an adjustable alignment mechanism on the mounting structure for setting an adjustable position and an adjustable orientation of the microwave prism relative to the reflector antenna, the alignment mechanism defining a lateral shift of the output field relative to the input field. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing a conventional parabolic reflector antenna. [Figure 2] FIG. 1 illustrates the principle of using a prism to redirect the beam from a reflector from a currently serving satellite to a new target satellite. [Figure 3] FIG. 1 shows a parabolic reflector antenna with a redirecting prism snapped into place over the receiver. [Figure 4] FIG. 1 illustrates components of a system. [Figure 5] 1A-1C illustrate several example prism embodiments. [Figure 6]FIG. 1 illustrates geometric considerations regarding prism size and structure. [Figure 7] FIG. 1 illustrates the orientation and angle that a terminal must point relative to the originating satellite for a representative pair of satellites serving a geographic region. [Figure 8] Figure 8(a) shows how the same prism is enabled to support multiple scan angle adjustments by mounting the prism with the alignment and prism in a first position E. Figure 8(b) is a side view of Figure 8(a). Figure 8(c) is similar to Figure 8(a) but with the alignment and prism in a second position A. DETAILED DESCRIPTION OF THE INVENTION

[0014] In describing the exemplary, non-limiting embodiments shown in the drawings, specific terminology will be used for the sake of clarity. However, it is to be understood that the disclosure is not intended to be limited to the specific terminology so selected, and that each specific term includes all technical equivalents that similarly operate to accomplish a similar purpose. While several embodiments have been described for illustrative purposes, it is to be understood that the specification and claims are not limited to the illustrated embodiments, and that other embodiments not specifically shown in the drawings may also be within the scope of the disclosure.

[0015] 3 shows a reflector antenna 200 having a reflector redirection device 201. The reflector redirection device 201 allows the main beam of the reflector antenna 200 to be steered by a fixed, determined angle relative to the original angle of the antenna 200 without the redirection device 201 installed. The reflector redirection device 201 is installed on the reflector feed horn 109 with the position and orientation controlled by the device itself.

[0016] The position and orientation are configured such that for a reflector antenna 200 in a given geographic location already pointing at a particular satellite 213 (FIG. 2(a)), a reflector redirection device is provided to point the antenna instead at a specific other satellite 215 without physically moving the reflector 103 or feed horn 109. Multiple devices 201, or multiple orientations of the same device 201, can enable scanning within a ±10 degree range from the nominal angle. While this is not a hard limit, further scanning results in significantly worse performance than the nominal case without the reflector redirection device installed. As a specific example, an antenna 200 located within (say) 50 miles of Washington, DC and configured to receive signals from a satellite located at 50° W can be redirected to instead receive signals from a satellite located at 45° W, without requiring skilled installation or pointing calibration, by installing a device 201 specially designed for a 5-degree shift on the feed 109.

[0017] For convenience, the following sections describe signals and fields as being transmitted from the antenna and reflector towards one or another satellite. The round trip behavior of transmission from the satellite and reception by the antenna is not described, but is exactly similar to the case described.

[0018] As shown in Figure 2(a), the horn antenna 109 is positioned so that, in normal operation, the aperture of the horn is located at the focal point 203 of the parabolic reflector 103. In the typical operation shown in Figure 2(a), the system 101 is oriented so that the signal or antenna field 205 from the horn interacts with the reflector 103 to form a beam 207 directed toward a desired target satellite 213. As shown in Figure 2(b), steering the system 101 to form a beam 211 directed toward another satellite 215 can be accomplished by changing the orientation of the entire antenna 101, or by shifting the feed horn 109 from the focal point 203 of the reflector 103. The antenna field 209 from the offset horn then interacts with the reflector 103 to form the beam 211 directed toward the other satellite 215. However, changing the orientation of the entire antenna 101 or physically moving the horn 109 both require skilled personnel to perform and support the movements in the reflector design, and neither can be easily performed without tools as built-in operations in most cases.

[0019] As shown in Figures 2(c) and 3, a reflector redirection device 201 is added to the horn 109 at the focal point 203 of the reflector 103 to laterally shift the field 205 that originally directed the beam 207 toward the original satellite 213, generating the beam 211 at another satellite 215 instead. Here, the lateral shift refers to the direction perpendicular to the parabolic reflector's axis of symmetry, which is also the direction of the feed support arm. The lateral shift may be horizontal, vertical, or a combination of both, but should remain in a plane aligned with the original feed aperture perpendicular to the reflector axis to ensure that the well-defined phase center remains approximately on the focal plane of the reflector 103. The location of the feed aperture defines the starting point for all shift comparisons. The lateral shift and possible correction of the field angle effectively causes the reflector 103 to behave as if the horn 109 were in a different location, thus generating the beam 211 in the new desired direction.

[0020] 4, reflector redirection device 201 includes a microwave prism or prism 401 having an anti-reflective coating arrangement 403 optionally on one or both surfaces (top and bottom surfaces in the embodiment of FIG. 4), a mounting system or arrangement 407 configured to connect and secure the prism to host horn 109, and a radome or other cover 405 to protect these elements. The terms microwave prism, prism, microwave lens, and lens are all intended to apply to device 401, and the term prism is used in this disclosure to include microwave prisms.

[0021] Microwave prism configurations share many similarities in practice and principle with microwave lens configurations, including GRIN lenses. A prism refers to a refractive element whose primary purpose is to bend or shift a beam, or cone, beam, or other distribution of electromagnetic energy. A lens, on the other hand, refers to a refractive element whose primary purpose is to expand or contract a cone, beam, or other distribution of electromagnetic energy. There is no strict distinction between these two concepts, as prisms can be designed to concentrate energy and lenses can be designed to bend energy. For the present disclosure, a prism is considered more meaningful because the primary purpose of device 401 is to bend and shift energy, not expand or contract, although some expansion and contraction may also be included.

[0022] The prism 401 and attachment mechanism 407 are specific to a particular make or model of reflector antenna 101 and associated horn 109, and are also specific to a particular satellite 213, 215. The attachment mechanism 407 may be, for example, a fastener (such as a bolt, nut, screw, etc.) or an adhesive.

[0023] As shown in FIG. 4 , in one embodiment, microwave prism 401 includes a body 402 having a first prism surface 402a and a second prism surface 402b opposite the first surface 402a. Prism body 402 has a top surface, a bottom surface, and at least one side surface, and may have a cross-section of any suitable shape, such as circular, square, or rectangular. First prism surface 402a is on the top surface of body 402, and second prism surface 402b is on the bottom surface of body 402. First prism surface 402a and second prism surface 402b are flat. Anti-reflective coating arrangement 403 may be a coating applied to first prism surface 402a and second prism surface 402b. In one embodiment, the anti-reflective coating mechanism has a top coating surface and a bottom coating surface, with the first coating mechanism 403a having a bottom coating surface in contact with the top prism surface 402a of the prism body 402 and the second coating mechanism 403b having a top coating surface in contact with the bottom prism surface 402b of the prism body 402.

[0024] In the embodiment of Figure 4, the prism is a parallel-plate prism. First prism surface 402a is parallel to second prism surface 402b. In addition, the flared side of horn 109 forms a front opening, and the front edge of the flared side forms a planar front periphery. Horn 109 also has a central longitudinal axis extending from the rear of the horn to the front of the horn. First prism surface 402a and second prism surface 402b are approximately parallel to the planar mouth of horn 109 and perpendicular to the longitudinal axis of horn 109.

[0025] In one embodiment, the horn 109 and the reflector redirection device 201 can instead be connected to a common support, such as a frame or housing, and the mounting system or mechanism 407 can connect the reflector redirection device 201 to the support rather than the horn 109.

[0026] Prism 401 functions by being positioned near or at the aperture of horn antenna 109 in a particular orientation, constrained by mounting mechanism 407. In Figure 5, prism 401, when properly positioned, creates a lateral offset 507 in the corresponding locations of input and output fields 505 entering and exiting the device relative to the original or unperturbed field location 506 of the antenna field from horn 109 in the absence of prism 401.

[0027] The antenna field emanating from the feed horn is not highly collimated like that coming from a laser (due to the much longer wavelength of microwaves compared to the short wavelength of laser light); instead, the field is spherically or conically diverged between the feed horn 109 and the reflector 103. Therefore, due to this difference between lasers and microwaves, the reflector redirection device 201, unlike a simple planar beam shifter for optics, can include corrections to allow for the cone-shaped divergence of the energy coming from the horn. For example, the reflector redirection device 201 can have non-flat surfaces (particularly the prism bottom surface 402b and / or the prism top surface 402a) to correct for the field curvature and effective phase center axial position of the output field exiting the redirection device 201 for non-zero optical power.

[0028] The core action of prism 401 is to shift the field laterally relative to the location of horn 109. This can be done in any suitable way, some examples of which are shown and described in the embodiments of Figures 5(a) to 5(f) for various configurations of reflector redirection device 201.

[0029] As shown in FIG. 5(a), the simplest option is to configure microwave prism 401 as an optical beam shifter or parallel-plate prism 401a formed with a uniformly high dielectric constant. Prism 401 is held at a defined angle relative to horn antenna 109, more specifically, first surface 402a and / or second surface 402b are at an angle relative to the plane of the aperture of horn 109 and an angle relative to the central longitudinal axis of horn 109. It may optionally include an anti-reflection layer 403 to support higher performance. However, to generate a large lateral shift or offset 507, this embodiment may require the prism to be very thick, have a high field incidence angle (limiting transmission efficiency), and a large dielectric constant ε. These factors combine to make prism option 401a bulky and heavy.

[0030] As shown in FIG. 5(b), another prism 401b includes bonding and anti-reflection layers to more smoothly redirect signals throughout the structure via a series of one or more wedges 508. Like prism 401a, prism 401b has a central body or plate 502 with a parallel profile, and one or more wedges 508 extend outward from the top and / or bottom of central plate 502 and are connected to the central body (e.g., by adhesive) or integrally formed therewith. A first set 508a of one or more wedges is disposed on a first side (top) of body 502, and a second set 508b of one or more wedges is disposed on a second side (bottom) of body 502.

[0031] The wedges 508 may have any suitable shape. However, in the illustrated embodiment, each wedge 508 is generally triangular in shape, having a first major planar surface facing the body 502, a second major planar surface facing away from the body 502, and a minor minor surface. The bottom surface of the lowest wedge in the first set 508a of wedges abuts the top surface 502a of the body 502, and the top surface of each wedge abuts the bottom surface of an adjacent wedge. The top surface of the highest wedge in the second set 508b of wedges abuts the bottom surface 502b of the body 502, and the bottom surface of each wedge abuts the top surface of an adjacent wedge.

[0032] Each wedge has an acute angle formed between its first and second major surfaces. In one embodiment, the first set 508a of wedges has a compound angle that can be the same as the offset angle θ of the bottom surface 402b of the body 502 relative to the plane of the mouth of the horn 109. The second set 508b of wedges also has a compound angle that can be the same as the offset angle θ of the top surface 402a of the body 502 relative to the plane of the mouth of the horn 109. Thus, the bottom wedge surface of the bottom wedge 508b of the lower wedge set is generally parallel to the plane of the horn mouth and to the top wedge surface of the top wedge 508a of the upper wedge set. Thus, the acute angle of the upper wedge set 508a is aligned with one side of the body 502 (i.e., the left side in the embodiment of FIG. 5(b)), and the acute angle of the bottom wedge set 508b is aligned with the opposite side of the body 502 (i.e., the right side). In this configuration, the signal travels offset and generally parallel to the original signal axis 506, which may also be parallel to the central horn longitudinal axis.

[0033] In one embodiment, the multiple dielectric layers ε1, ε2, ε3, ε4, and ε5 of each wedge 508 have successively increasing dielectric constants moving away from the center plate 502, with ε1 being the smallest and ε5 being the largest. That is, the center plate 502 has the highest dielectric constant, and each adjacent wedge 508 from the center plate 502 has a successively smaller dielectric constant. This design allows for increased transmission efficiency by increasing the number of layers and resulting in a much smaller angle of field incidence at each layer, but does little to minimize the size and mass of the design. Thus, each wedge 508 refracts the signal. Each wedge 508 in the bottom wedge set 508b incrementally increases the angle of the signal relative to the original axis 506. Each wedge 508 in the top wedge set 508a decreases the angle of the signal relative to the original axis 506 until the signal is approximately parallel to the original axis 506 or is otherwise at a desired angle relative to the original axis 506. An anti-reflective coating 403 may be disposed on the top surface of the top wedge 506a and the bottom surface of the bottom wedge 506b.

[0034] FIG. 5(c) shows a metamaterial and metasurface prism 401c, which may also incorporate the concept of a transmit array. This embodiment reduces the mass of the prism 401c by reducing the amount of material required, but at the expense of a corresponding reduction in operating bandwidth and increased insertion loss. Rather than using a bulky dielectric whose properties are defined by its dielectric constant and shape, the metasurface prism has one or more layers of metamaterial or metasurface suspended in air by a support structure. For this embodiment, the prism 401c can be composed of two layers 531, 535 of spatially varying metamaterial or metasurface that change the field direction from the horn 109 at two points by introducing a phase gradient into the transmitted field. The metamaterial or metasurface prism does not rely on refraction within the dielectric regions as a conventional prism does, and does not include the dielectric regions included in 401a and 401b. Thus, the bottom metamaterial or metasurface 531 refracts the signal away from the original signal axis 506, causing the signal to travel at an angle to the original signal axis 506. The top metamaterial or metasurface 535 also refracts the signal back parallel to the original signal axis 506. The double refraction causes the signal to be offset both from and parallel to the original signal axis 506.

[0035] The gap or separation between the two layers 531, 535 is required to allow the distance for the field to propagate and create a lateral offset. The greater the separation, the greater the lateral offset. The separation is maintained by a mechanical structure 533 inside the prism structure, which maintains the space between the layers 531, 535 as an air gap. For example, the mechanical structure 533 can be a support or beam, and one or both of the layers 531, 535 can be connected to the support at different locations that maintain the desired air gap distance between them. This support structure inside the prism is separate in purpose and implementation from the structure 407 that holds the prism 401 relative to the feed 109 and can be implemented using supports, bolts, clips, or other physical mechanisms to maintain a fixed spacing between the two layers 531, 535. The artificial dielectric or metasurface structures that form the layers 531 and 535 require their structure to be periodically varied across the surface of each layer 531, 535 to set a phase gradient across the surface and therefore steer the beam, thereby limiting the usable bandwidth of the design. Metamaterial or metasurface designs are often narrowband and lossy, but may be sufficient for some applications. The transmission efficiency through both layers is an important metric for this style of implementation.

[0036] Figure 5(d) shows a corrugated prism 401d, which reduces the thickness of the structure. This in turn allows the support structure 407 and radome 405 to be smaller, thereby reducing weight. The large height of the prisms shown in 401a and 401b is also reduced by introducing molded corrugations on the top and bottom surfaces of prism 401d. The corrugations have a sawtooth shape. From the left, each tooth on the top surface has a straight, leading edge that is generally parallel to the longitudinal axis of the horn, followed by an angled, trailing edge.

[0037] Prism 401d shows a folded version of prism 401a, but the same approach can be applied to multilayer 401b. By using Fresnel-type corrugations on the top and bottom surfaces 401d, the size and shape of the prism can be collapsed to maintain roughly the same beam steering characteristics, but the height of the prism is reduced. This creates a dispersive effect that limits the operating bandwidth but is likely to be less dispersive than metasurface / metamaterial approaches. The top and bottom corrugated surfaces of 401d may be anti-reflective coated to match the shape of the corrugations themselves. The bottom surface refracts the signal at an angle relative to the original signal axis 506, while the top surface refracts the signal back parallel to (and offset from) the original signal axis 506.

[0038] In Figure 5(e), a graded-index (graded index) or non-uniform prism 401e with full control over the internal dielectric constant ε(x,y,z) offers the enormous advantage of packing functionality into the smallest possible continuous package. The challenge with both smoothly varying (continuous) and stepped gradient designs is creating the often complex shapes and structures necessary to achieve the required performance.

[0039] Figure 5(f) shows two half prisms 401f. Because the mass of the prism 401 is a major factor in the design of the redirection device 201, other measures can be taken to reduce the mass of the prism, including removing regions of dielectric material inside the prism when unnecessary, effectively forming two half prisms 401f separated from each other by a distance or air gap. In some embodiments, this gap may be implemented as a hollow region that can be built into an otherwise solid prism, reducing weight but eliminating the need for a separate mounting or support structure similar to the support 533. The half prisms 401f can be triangular-shaped with flat or curved surfaces. As shown, the upper half prism can have an inward-facing surface that is curved to be slightly concave, and the lower half prism can have an inward-facing surface that is curved to be slightly convex. The inward-facing surface of the upper half prism faces and has a shape that mates with the inward-facing surface of the lower half prism. The profile of the inner surface of the prism matches the field propagation direction at each angle, allowing the field to remain straight without refracting at the interface, as if the removed material were still there. This mass reduction technique is also useful when the loss tangent of the available dielectric is high compared to air. The bottom surface of the lower half prism 401f forms an angle θ with the plane of the horn mouth, refracting the signal so that it is at an angle relative to the original signal axis 506. The top surface of the lower half prism 401f further refracts the signal. The bottom surface of the upper half prism 401f refracts the signal back parallel to the original signal axis 506, and the top surface of the upper half prism 401f further refracts the signal so that it is parallel to, but offset from, the original signal axis 506. The greater the distance between the upper and lower half prisms 401f, the greater the achievable lateral offset of the signal from the original signal axis 506.

[0040] Because fields propagating through a dielectric region do not expand as much as they would if they propagated through air alone, the effective phase center of the fields arriving from device 201 may no longer coincide with the reflector. Even if the lateral position can be accurate, the distance of the phase center of the feed distribution to the reflector still needs to match the focal length of the reflector to maintain aperture efficiency. The inclusion of non-zero optical gain (through surface curvature or internal dielectric gradient) can be used to correct both the angular distribution of the field and the effective phase center.

[0041] The required size of prism 401 is determined jointly by the amount of lateral shift required for the field and the geometry of the reflector. A good prism should be small, lightweight, and compact to minimize cost and simplify installation. However, prism 401 must be sized so that it can intercept all of the output from the feed horn and redirect all of that energy to the reflector.

[0042] 6, for a reflector with a small f / D (focal length 603 to diameter 605) ratio, or equivalently a wide illumination cone angle 609, a particular prism 611 embodiment of a particular thickness must be large enough laterally at the base of the prism to cover the original radiation pattern cone 631 from the horn, large enough at the exit of the prism 611 to emit energy across the entire surface of the re-centered cone 633, and allow for sufficient internal thickness 615 and width 613 to reshape the energy sufficiently to follow the desired path 607. If a thicker (625) prism 621 embodiment is needed to provide the necessary lateral shift (generally, more shift requires a thicker prism to provide more room to propagate), then the prism must also be wider (623) (at least at the output), so that the volume and mass of the prism are (generally roughly) proportional to the cube of the prism thickness. This creates an essential requirement to minimize prism thickness while achieving other performance parameters, such as also controlling mass.

[0043] The f / D ratio also affects the amount of lateral shift required to steer the reflector to a given angle. A reflector with a low f / D ratio allows for a smaller change in the effective feed position 109 to produce a larger shift in the beam scan angle, as in many common consumer DTH antennas. A reflector with a high f / D has a smaller cone angle, so a smaller prism is required to shift the aperture field by a given distance, but a larger physical shift is required to achieve the same scan angle of the main beam in degrees.

[0044] In one embodiment, the reflector redirection device 201 is integrated into (and connected using a fastener mechanism, adhesive, etc.) an existing horn antenna. Thus, it is configured to work with the existing horn antenna and parabolic reflector. The characteristics of the prism 401 are designed to accommodate the antenna system 101. However, in other embodiments, the horn antenna and parabolic reflector can be designed to work with the device 201, including a mounting mechanism 407 ready for easy and precise installation of the device 201, strong mounting arms 107 (FIG. 1) to support the additional weight of the device 201 without bias, and a sufficiently large f / D ratio to optimize the overall mass of the system 201.

[0045] For a given pair of satellites, i.e., currently used satellite 213 and new target satellite 215 (FIG. 2), the correction angle that must be applied by reflector steering device 201 and the direction relative to the current antenna pointing direction that the offset should be applied is based on the angular distance between the two satellites and the location on Earth from which the satellites are observed.

[0046] Figure 7 shows the terrestrial differential angle that must be applied. The relatively small diameter reflector 103 used for DTH (typically between 40 and 80 cm) has a fairly wide beam, so the correction resolution is very coarse. Based on the target installation location of the reflector redirection device 201, a map similar to that of Figure 7 is referenced to select the required correction angle and direction. The correction angle and direction are then applied by implementing a separate prism and mounting design for each combination, with an adjustable fixture or mounting configuration setting the scan angle and direction appropriately using a single prism and fixture design for a larger geographic area. The prism is effectively rotated by the correction angle around the central axis of the horn antenna 109 to point the resulting beam at the target satellite based on the location of the system 200. Prism or setting selection can be performed before shipping the device to the end user, or the end user can be provided with instructions for using a specific numbered or labeled setting depending on the user's location. That is, the instructions may be, "For your zip code ABC, rotate the mounting clip so that the arrow is in position D before installing it on your antenna."

[0047] These instructions apply to the embodiment shown in Figures 8(a) and 8(b). Horn antenna 109 is shown mounted centered at point 811. Prism 401 (shown for illustrative purposes only and contained within radome 405 of device 201) shifts the horn field so that it is re-centered exiting the prism to point 813. A set of detents and alignment markings are provided on the outer housing or radome material for adjustable alignment by the end user or prior to shipment. The alignment markings allow the user to adjust the mounting structure to set an adjustable position and orientation of the microwave prism relative to the reflector antenna, and in particular, relative to horn feed 109. That is, mounting structure 407 mounts device 201 to antenna 101 in a fixed manner, but at a position and orientation defined by the adjustable alignment markings. The alignment mechanism defines multiple positions and orientations of the microwave prism relative to the mounting structure and can be set at the factory based on geographic location. Thus, the end user can determine the appropriate settings based on the geographic location of the installation location (such as by using the map of FIG. 7).

[0048] Changing the orientation of the prism 401 relative to the central axis of the feed horn 109 changes the angle of the re-steered beam relative to the original mounted antenna. For example, the prism can be rotated about the central axis of the feed horn 109, thereby directing the resulting beam east or west of the original beam direction and adjusting the elevation angle at which the beam is pointed above the horizon to precisely point at the desired satellite 215. One or more support or fastening members can be provided to move the prism 401. For example, fastening members can movably connect the prism 401 to the radome 405 or mounting structure 407, such that the prism 401 can change its orientation relative to the feed horn 109.

[0049] FIG. 8(c) shows device 401 aligned at position A, while FIG. 8(a) shows device 401 aligned at position E. Note that the signal emanating from the horn is offset from the prism, as shown in FIGS. 5(a)-5(f). An alignment 817 can be connected to prism 401, so that rotating alignment 817 between various positions rotates the entire prism 401. When prism and alignment 817 are in position E (FIG. 8(a)), the phase center 813 of the prism is offset from the phase center 811 of the horn. More specifically, the phase center 813 of the prism is approximately at 2 o'clock relative to the phase center 811 of the horn. When prism and alignment 817 are in position A (FIG. 8(c)), the phase center 813 of the prism is approximately at 4 o'clock relative to the phase center 811 of the horn. Thus, as the alignment rotates, the phase center 813 of the prism rotates, which in turn moves the signal output by the prism. In another embodiment, different positions of alignment may produce different angles of the prism.

[0050] The prism 401 can be any shape or any of a variety of orientations relative to the feed horn, as described above in Figures 4-6, and the shape and boundaries of the radome are then selected to adequately cover the prism.

[0051] After aligning the adjustable alignment 817, the device is fixedly connected to the horn in any suitable manner. For example, the mounting system 407 may include a snap connector 819 that snaps onto the antenna's mounting bar and is stabilized and oriented by the horn shroud 815. Once installed, the device now directs the reflector to point its main beam toward the new desired satellite 215. The mounting mechanism 407 holds the device fixedly in the proper position to intercept all of the field from the horn 109 that would otherwise reach the reflector 103, shifting the field laterally to effect a change in the scan angle of the reflector antenna 101. At this time, no further movement or activity is required during proper operation of the antenna 101 and the device 201. When it is desired that the antenna be redirected back to the original currently serving satellite 213, the device 201 can be removed by detaching the mounting mechanism 819.

[0052] It should be noted that the drawings may be illustrative, and the specification and claims may use geometric or relational terminology such as right, left, upper, lower, top, bottom, lateral, top, bottom, elongated, parallel, lateral, orthogonal, angled, rectangular, square, circular, rounded, axial, etc. These terms are not intended to limit the disclosure and are generally used for convenience to facilitate explanation based on the examples shown in the drawings. Additionally, the geometric or relational terminology may not be precise. For example, signals and planes may not be exactly perpendicular or parallel to each other, but may still be considered perpendicular or parallel.

[0053] The above description and drawings should be considered merely illustrative of the principles of the present disclosure. The system may be configured in various shapes and sizes and is not intended to be limited by the embodiments. Numerous applications of the system will readily occur to those skilled in the art. Therefore, it is not desired to limit the disclosure to the disclosed examples or to the exact construction and operation shown and described. Rather, all suitable modifications and equivalents may be resorted to that fall within the scope of the present disclosure.

Claims

1. A reflector antenna direction changing device (201) for use with a reflector antenna comprising a reflector (103) having a reflection axis and a feed horn (109), a microwave prism (401) that receives an input field and provides an output field; a mounting structure (407) connecting the microwave prism to the reflector antenna (200) and mounting the microwave prism on the feed horn (109); an alignment mechanism provided on the mounting structure for positioning and orienting the microwave prism (401) relative to the reflector antenna (200) and for determining a lateral shift of the output field relative to the input field orthogonal to the reflection axis; Equipped with the reflector antenna redirection device redirects the input field from the original satellite (213) to a new target satellite (215) without manual fine-tuning; Reflector antenna redirection device.

2. A device as described in claim 1, wherein the mounting structure connects the microwave prism (401) to a mounting arm (107) of a reflector antenna.

3. The device of claim 1 or 2, wherein the microwave prism (401) comprises a parallel plate prism (401a).

4. 4. The device of claim 3, wherein the parallel plate prism (401a) has a plurality of wedges (508) added to the input and output faces of the microwave prism to reduce the angle of incidence and improve transmission through the device.

5. 3. The device of claim 1, wherein the microwave prism (401) comprises two or more layers (531, 535) of a spatially gradient metasurface or metamaterial.

6. 6. The device of claim 1, wherein the microwave prism comprises a Fresnel grating.

7. 6. The device of claim 1, wherein the microwave prism (401e) has a continuous or step gradient refractive index structure.

8. 6. A device according to any one of claims 1, 2 and 5, wherein the microwave prism (401) has two dielectric sub-prisms (401f), the inner boundaries of which are cut to ensure nominal incidence of the input and output fields at all points on the inner surface.

9. The device of any one of claims 1 to 8, further comprising a radome (405) covering the microwave prism.

10. The device of any one of claims 1 to 9, wherein the mounting structure is clipped or snapped onto the reflector antenna (200).

11. 11. The device of claim 1, wherein the mounting structure (407) and prism (401) are customized for a particular reflector antenna variant and combination of original and new satellites.

12. the alignment mechanism is adjustable to define multiple positions and orientations of the microwave prism (401) relative to the mounting structure; the plurality of locations are set at the factory based on geographic location; A device according to any one of claims 1 to 11.

13. The device of claim 1 , wherein the orientation is set by an end user based on a geographic location.

14. a horn antenna (109) providing an antenna field; A reflector antenna redirection device (201) according to any one of claims 1 to 13; Equipped with the mounting structure (407) positions the microwave prism (401) relative to the horn antenna (109); the reflector antenna redirection device (201) comprises an adjustable alignment mechanism that defines a plurality of adjustable positions of the microwave prism (401) relative to the horn antenna (109), each of the plurality of adjustable positions defining a respective shift of the output field relative to the antenna field; A reflector antenna (200).

15. 15. The device of claim 14, wherein the microwave prism (401) redirects the antenna field from an original satellite (213) to a new target satellite (215) without manual fine-tuning.

16. 16. The device of claim 14 or 15, further comprising a radome (405) covering the microwave prism (401).

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