Patent Application
20230178895
The present disclosure relates to antenna designs and more particularly to antennae that are useful for deployment from space-constrained platforms such as satellites.
Modern sensor platforms are continuously shrinking in size to promote cost effectiveness for higher quantity deployments, especially for volume-constrained platforms. One such example is so-called “small satellites,” or “Small-Sats,” which are a cheaper alternative to traditional satellites that allow for more rapid development cycles at lower cost, thereby providing more available assets to the end-user. These “Small-Sats” can serve a number of communications, ISR (Intelligence, Surveillance, and Reconnaissance), ES (Electronic Surveillance) and EW (Electronic Warfare) functions in the optical, microwave (frequency greater than 1 GHz), and/or Radio-frequency (RF) domains. Each of the microwave and RF functions requires an antenna.
However, volume is always critical in a satellite, and an effective antenna must be comparable to or larger than its operating frequency's wavelength, which in the RF domain (i.e. frequencies below 1 GHz) can range from 30 centimeters to 3 meters and more. Accordingly, it can be useful for a satellite's antenna to be initially stored on or in the satellite in a “stowed” configuration that minimizes the required volume for transit, and to “deploy” the antenna to its full size after the satellite has reached orbit. For this reason, currently implemented antenna solutions for satellite RF communication rely mainly on aperture (dish) antennae, such as parabolic reflectors having a deployable perimeter truss, which can be stowed in transit and then opened up (deployed) in orbit.
However, dish antennae are often plagued by surface roughness and tension issues. Also, dish antenna extend significantly away from the satellite due to the reflector and/or feed, which creates a moment arm that can be a drain on the attitude control of the satellite. Furthermore, the stowed volume of a dish antenna, while less than its deployed volume, can still be significant, thereby limiting the space available for other apparatus within the satellite. This problem is especially critical for Small-Sats.
With reference to
The length of the patch 100 is typically comparable to one half of the center wavelength of the antenna, while the thickness of a simple microstrip patch antenna can typically be very small, thereby allowing such an antenna to be implemented on the surface of a satellite without consuming a significant volume within the satellite.
However, simple patch antennae, such as the design illustrated in
One approach to increasing the bandwidth of a patch antenna is to implement a “stacked” patch antenna design. With reference to
Each of the patches 100a, 100b in a stacked patch antenna functions more or less as a separate antenna. As such, the spacing between the patches must be adjusted such that they are in phase coherence, so that their signals will add coherently at the center frequency of the antenna bandwidth. A stacked patch antenna thereby provides higher gain than a single patch antenna, because signals are coherently received and transmitted by more than one patch.
Furthermore, a stacked patch antenna can provide a wider bandwidth than a single patch antenna by stagger-tuning the resonant frequency of each individual patch element. This is accomplished by slightly varying the dimensions of each of the two or more stacked patches 100a, 100b, so that their center frequencies are offset from each other, resulting in a cumulative bandwidth that is “stagger-tuned,” thereby providing a broader bandwidth.
The total gain of a RF sensor can be further increased by implementing an array of stacked patch antennae. For example,
Similarly,
The bandwidth ratio (ratio of highest impedance matched frequency to lowest impedance matched frequency) of a stacked patch antenna can be as large as about 2:1, which compares favorably with conventional dish antennae or microstrip patch antennae. In addition, a stacked patch antenna can provide a significant (7-8 dBi, i.e. dB above “isotropic”) unit gain, and the polarization of the antenna can be easily controlled by the patch geometry.
However, because it is necessary to provide significant gaps between the patches so that they will be in additive phase with each other, the thickness of a stacked patch antenna will be relatively large compared to a microstrip patch antenna. For example, the thickness of a two-patch stacked antenna can be as large as one half of the wavelength of its center frequency, and the total thickness for designs that include more than two stacked patches will be proportionally even larger.
With reference to
Ultimately, volume and envelope constraints dictate the maximum thickness of a stacked patch antenna. Even if high dielectric spacer layers 202 are included, the large wavelengths at frequencies below 1 GHz require excessive thicknesses that can limit a stacked patch antenna's application to satellites, and especially to Small-Sats.
What is needed, therefore, is a high gain, broadband antenna design that is suitable for satellite applications, including Small-Sats.
The present disclosure is a high gain, broadband antenna design that can be implemented on a communication platform. Embodiments are suitable for space-constrained communication platforms, including Small-Sats. The disclosed antenna is an expandable stacked patch antenna having a significantly reduced weight and stowed thickness, while being expanded to its required operating thickness upon deployment.
The disclosed antenna design takes advantage of the fact that much of the thickness of a stacked patch antenna arises from gaps between the patches. In a conventional stacked patch antenna, these gaps are established and maintained by layers of high dielectric PCB materials having high mass densities and typical dielectric constants between 2.0 and 10.0. For weight savings, the disclosed antenna design, when expanded, provides unfilled gaps and/or gaps filled with low and/or high dielectric foams rather than PCB materials. It is notable that when gaps filled with low dielectric foam are included, it is largely as a mechanical convenience, in that the antenna characteristics would not be greatly affected if these layers of low dielectric material were replaced by air-filled or vacuum-filled gaps.
The disclosed antenna design is a stacked patch antenna that can be transitioned by an expansion mechanism from a relatively thinner stowed configuration, in which the gaps between the conductor layers are reduced or eliminated, to a relatively thicker deployed configuration in which the required gaps are provided between the conductor layers. Known approaches to determining the panel and dielectric materials and the gaps between patches can be used when designing embodiments of the present disclosure, such as the approaches and formulae that appear in IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 46, NO. 9, SEPTEMBER 1998, which is incorporated herein in its entirety for all purposes.
In various embodiments, the expansion mechanism includes rotation of threaded rods, pneumatic expansion of telescoping rods, injection of a gas such as air, CO2 or nitrogen gas into the gaps, injection of a chemical sublimate (e.g. benzoic acid) into the gaps, and/or injection of expandable foams into the gaps.
In some embodiments, layers of foam are not included in the antenna design, such that the thickness of the antenna in its stowed configuration is approximately equal to the sum of the thicknesses of the panels upon which the conductors are deposited. In other embodiments, conventional layers of low and/or high dielectric foam are included in gaps that are not collapsed when the antenna is in the stowed configuration. In still other embodiments where it is desirable to include layers of low and/or high dielectric constant materials within one or more of the gaps, the gaps are nevertheless collapsed in the stowed configuration, and are inflated with low and/or high dielectric foam during deployment of the antenna, such that the thickness of the antenna in its stowed configuration is approximately equal to the sum of the thicknesses of the panels upon which the conductors are deposited.
In various embodiments, the antenna is an antenna assembly that includes a phased array of stacked patch sub-antennae, for example arranged in a cross configuration or in a linear configuration. In some of these embodiments where the communication platform is a satellite, the antenna assembly is folded about the outer surface of the satellite when in the stowed configuration, and is transitioned to a planar configuration in the deployed configuration.
Depending on the embodiment, the antenna can be excited by any mechanism known in the art, such as aperture coupling to the stacked patch antenna, probe feeding the stacked patch antenna, or feeding the stacked patch antenna through a microstrip line.
One general aspect of the present disclosure is an expandable stacked patch antenna that can be implemented on a communication platform for RF communication. The stacked patch antenna includes a ground plane applied to a ground plane panel, a plurality of conducting patches substantially aligned with each other above the ground plane, each of the conducting patches being applied to a patch supporting panel, an RF feed suitable for communication with the stacked patch antenna, and an expansion mechanism configured to transition the plurality of conducting patches from a stowed configuration in which gaps between the ground plane and patch supporting panels are minimized, to a deployed configuration in which the gaps between the ground plane and patch supporting panels are enlarged as needed such that the antenna is optimized for communication over a specified range of RF frequencies.
In embodiments, the RF feed is an aperture coupled to the stacked patch antenna. And in some of these embodiments the expansion mechanism includes at least one rotatable threaded rod configured to adjust at least one of the gaps between the ground plane and patch supporting panels.
In any of the above embodiments, the expansion mechanism can include at least one telescoping, pneumatically extendable rod configured to adjust at least one of the gaps between the ground plane and patch supporting panels when the telescoping rod is extended. In some of these embodiments, the telescoping rod includes at least one locking pin or nub configured to fix and secure a length of the telescoping rod when the telescoping rod is extended.
In any of the above embodiments, the expansion mechanism can include a fluid reservoir containing a fill material, the fluid reservoir being in fluid communication with a thin-walled inflatable container that is inserted within one of the gaps between the ground plane and patch supporting panels, the fluid reservoir and thin-walled inflatable container being configured to expand the gap in which the thin-walled container is inserted when the thin-walled inflatable container is inflated with the fill material. In some of these embodiments, the fill material is one of a gas, a chemical sublimate, an expandable foam, a low dielectric fill material having a dielectric constant of less than 1.2, and a high dielectric fill material having a dielectric constant of greater than 2.
In any of the above embodiments, at least one of the gaps between the ground plane and patch supporting panels can be determined by at least one limiting cable extending between the layers that bound the gap.
In any of the above embodiments, the stacked patch antenna can be an antenna array comprising a plurality of stacked patch sub-antennae. In some of these embodiments, when the stacked patch antenna is in its deployed configuration, the stacked patch sub-antennae are arranged in a planar cross pattern comprising four stacked patch sub-antennae extending in four perpendicular directions from a common center area. And some of these embodiments further include a fifth stacked patch sub-antenna located in the common center area.
In other embodiments where the stacked patch antenna is an antenna array comprising a plurality of stacked patch sub-antennae, when the stacked patch antenna is in its deployed configuration, the stacked patch sub-antennae can be arranged as a single, linear row of stacked patch sub-antennae.
In still other embodiments where the stacked patch antenna is an antenna array comprising a plurality of stacked patch sub-antennae, when the stacked patch antenna is in its deployed configuration, the stacked patch sub-antennae can be arranged as a grid of stacked patch sub-antennae.
In any of the embodiments where the stacked patch antenna is an antenna array comprising a plurality of stacked patch sub-antennae, when the stacked patch antenna is in its stowed configuration, the antenna array can be folded about the communication platform.
A second general aspect of the present invention is method of implementing a high gain broadband antenna on a communication platform. The method includes providing a stacked patch antenna according to claim 1, the stacked patch antenna being in its stowed configuration, incorporating the stacked patch antenna onto and/or into the communication platform, and activating the expansion mechanism of the stacked patch antenna, thereby causing the stacked patch antenna to transition to its deployed configuration.
In some of these embodiments, the communication platform is a satellite, and the expansion mechanism is activated after launch of the satellite into space.
In any of the above embodiments, the expansion mechanism can include a fluid reservoir containing a fill material, the fluid reservoir being in fluid communication with an inflatable thin-walled container that is inserted within one of the gaps between the ground plane and patch supporting panels, the fluid reservoir and thin-walled inflatable container being configured to expand the gap in which the thin-walled container is inserted when the thin-walled inflatable container is inflated with the fill material. In some of these embodiments, the thin-walled container is shaped as a cuboid when inflated with the fill material.
In any of the above embodiments, the expansion mechanism can include at least one of a threaded rod configured to adjust at least one of the gaps between the ground plane and patch supporting panels, and a telescoping, pneumatically extendable rod configured to adjust at least one of the gaps between the ground plane and patch supporting panels when the telescoping rod is extended. And in some of these embodiments, the stacked patch antenna is an antenna array comprising a plurality of stacked patch sub-antennae, and wherein when the stacked patch antenna is in its stowed configuration, the antenna array is folded about the communication platform.
The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventive subject matter.
The present disclosure is a high gain, broadband antenna design that can be implemented on a communication platform. Embodiments are, suitable for space constrained platforms, including Small-Sats. The disclosed antenna is an expandable stacked patch antenna having a significantly reduced weight and stowed thickness in which the gaps between the conductor layers are reduced or eliminated, while being expanded upon deployment by an expansion mechanism so as to provide the required gaps between the conductor layers.
In some embodiments, spacer layers 200a, 200b, 202 are not included in the design, such that the total thickness of the antenna in its stowed configuration is approximately equal to the sum of the thicknesses of the panels 102a, 102b, 106 upon which the conductors are deposited. In the embodiment of
In the embodiment of
During deployment of the antenna of
In some embodiments, extension of the rods 300 continues until the limiting cables 310 are fully extended or until the rods 300 are fully extended or a stop pin is reached when the optimal spacing is achieved.
In similar embodiments, a separate set of threaded rods is associated with and fixed to each of the layers 102a, 102b, 202, while clearance holes are provided in the other layers as needed, such that all of the layers 102a, 102b, 202 are lifted by their associated threaded rods 300. This approach not only provides for deployment of the antenna, but also enables the gaps to be adjusted after deployment so as to optimize the antenna for different transmit frequencies and bandwidths.
In various embodiments, low dielectric gaps can be filled with are air, a gas such as nitrogen, or a vacuum, since vacuum and virtually all gases and have very similar low dielectric constants.
The optimal spacings between the patches 102a, 102b, 202 and the ground plane 108 are selected so as to provide optimal performance for the desired frequency range. For example, the spacing can be selected such that the radio waves generated by all of the patches add together coherently in the desired transmit direction at the center frequency of the antenna bandwidth or at the highest frequency of the antenna bandwidth. Another approach is to adjust the spacing between patches such that each pair is optimized for a slightly different frequency, thereby “stagger tuning” the antenna and further increasing its bandwidth. Known approaches to determining the panel and dielectric materials and the gaps between patches can be used when designing embodiments of the present disclosure, such as the approaches and formulae that appear in IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 46, NO. 9, SEPTEMBER 1998, which is incorporated herein in its entirety for all purposes.
In other embodiments, the expansion mechanism employs pneumatically expandable telescoping rods. In the example of
With reference to
With reference to
In various embodiments, the fill material is a gas, such as air, carbon dioxide, or nitrogen gas, a low dielectric constant chemical sublimate having a dielectric constant less than 1.2 (e.g. benzoic acid), and/or a low dielectric expandable foam having a dielectric constant that is less than 1.2. Limiting cables (not shown) can also be included between the panels 102a, 102b, 106 to precisely define the maximum size of each of the gaps upon inflation of the thin-walled containers 500a, 500b.
In the embodiment of
It will be noted that the embodiment of
Depending on the embodiment, the satellite 114 can communicate with the antenna by any mechanism known in the art, such as by extending a microstrip feed line to the primary, bottom-most patch element 108. While not visible in the drawings, the antennae of
In various embodiments, the disclosed antenna is an antenna assembly that includes a plurality of expandable stacked patch antennae, for example in a manner similar to
The foregoing description of the embodiments of the disclosure has been presented for the purposes of illustration and description. Each and every page of this submission, and all contents thereon, however characterized, identified, or numbered, is considered a substantive part of this application for all purposes, irrespective of form or placement within the application. This specification is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. Many modifications and variations are possible in light of this disclosure.
Although the present application is shown in a limited number of forms, the scope of the disclosure is not limited to just these forms, but is amenable to various changes and modifications. The disclosure presented herein does not explicitly disclose all possible combinations of features that fall within the scope of the disclosure. The features disclosed herein for the various embodiments can generally be interchanged and combined into any combinations that are not self-contradictory without departing from the scope of the disclosure. In particular, the limitations presented in dependent claims below can be combined with their corresponding independent claims in any number and in any order without departing from the scope of this disclosure, unless the dependent claims are logically incompatible with each other.
