LENS ANTENNA SYSTEM
1. An antenna system comprising:
- a plurality of lens sets, each lens set including;
at least one feed element aligned with the lens and configured to direct a signal through the lens at a desired direction.
An antenna system that includes a plurality of lens sets. Each lens set includes a lens and at least one feed element. At least one feed element is aligned with the lens and configured to direct a signal through the lens at a desired direction.
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|Intelligent antenna metamaterial method and apparatus|
Patent #US 10,446,927 B2
Current AssigneeMetawave Corporation
Sponsoring EntityMetawave Corporation
- 1. An antenna system comprising:
a plurality of lens sets, each lens set including; a lens; at least one feed element aligned with the lens and configured to direct a signal through the lens at a desired direction.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
- 21-31. -31. (canceled)
This application claims the benefit of U.S. Provisional Application No. 62/472,991, filed Mar. 17, 2017, the entire contents of which are incorporated herein by reference.
The present invention relates to a multiple beam phased array antenna system. More particularly, the present invention relates to a broadband wide-angle multiple beam phased array antenna system with reduced number of components using wide-angle gradient index lenses each with multiple scannable beams.
Phased arrays are a form of aperture antenna for electromagnetic waves that can be constructed to be low-profile, relatively lightweight, and can steer the resulting high-directivity beam of radio energy to point in a desired direction with electrical controls and no moving parts. A conventional phased array is a collection of closely-spaced (half-wavelength) individual radiating antennas or elements, where the same input signal is provided to each independent radiating element subject to a specified amplitude and a time or phase offset. The energy emitted from each of the radiating elements will then add constructively in a direction (or directions) determined by the time/phase offset configuration for each element. The individual antennas or radiating elements for such a phased array are designed such that the radiated energy angular distribution or pattern from each feed in the array mutual coupling environment, sometimes called the embedded element or scan element gain pattern, is distributed as uniformly as possible, subject to the physical limitations of the projected array aperture over a wide range of spatial angles, to enable the maximum antenna gain over the beam scanning angles. Examples of conventional phased arrays are described in U.S. Pat. Nos. 4,845,507, 5,283,587, and 5,457,465.
In comparison to other common methods of achieving high directivity radio beams, such as reflector antennas (parabolic or otherwise) and waveguide-based horn antennas, phased arrays offer many benefits. However, the cost and power consumption of an active phased array, namely one incorporating amplifiers at the elements for the reception and/or transmission functions, are proportional to the number of active feeds in the array. Accordingly, large, high-directivity phased arrays consume relatively large amounts of power and are very expensive to manufacture.
Phased arrays typically require that the entire aperture is filled with closely-spaced feeds to preserve performance over the beam steering range when using conventional approaches. Densely packing feeds (spaced approximately half of a wavelength at highest frequency of operation) is required to preserve aperture efficiency and eliminate grating lobes. Broadband phased arrays are constrained by the element spacing, aperture filling fraction requirements, and the types of circuits used for phase or time offset control, in addition to the bandwidth limitations of the radiating elements and the circuitry.
For example, an approximately square 65 cm 14.5 GHz Ku-band phased array that is required to steer its beam to about 70 degrees from the array normal or boresight would require more than 4000 elements, each with independent transmit (Tx)-and/or receive (Rx) modules, phase shifters or time delay circuits, and additional circuitry. All the elements must be powered whenever the terminal is operating, which introduces a substantial steady-state DC current requirement.
Every element or feed in an active phased array must be enabled for the array to operate, resulting in high power drain, e.g., 800 W or more for a 4000-element array, depending on the efficiency of the active modules. There is no ability to disable certain elements to reduce power consumption without dramatically impacting the array performance.
Various techniques have been developed in support of sparse arrays, where the element spacings can be as large as several wavelengths. Periodic arrays with large element spacings yield grating lobes, but appropriately choosing randomized locations for the elements breaks up the periodicity and can reduce the grating lobes. These arrays have found limited use, however, as the sparse nature of the elements leads to a reduced aperture efficiency, requiring a larger array footprint than is often desired. See Gregory, M. D., Namin, F. A. and Werner, D. H., 2013. “Exploiting rotational symmetry for the design of ultra-wideband planar phased array layouts.” IEEE Transactions on Antennas and Propagation, 61(1), pp. 176-184, which is hereby incorporated by reference.
Another way to limit the effect of grating lobes is by using highly-directivity array elements, because the total array pattern is the product of the array factor, i.e. the pattern of an array of isotropic elements, and the element gain pattern. If the element pattern is very directive, this product suppresses most of the grating lobes outside the main beam region. An example is the Very Large Array (VLA). The VLA consists of many large, gimballed reflector antennas forming a very sparse array of highly directive elements (the reflectors), each with a narrow element pencil beam which dramatically reduces the magnitude of the sidelobes in the total radiation pattern from the array. See P. J. Napier, A. R. Thompson and R. D. Ekers, “The very large array: Design and performance of a modern synthesis radio telescope.” Proceedings of the IEEE, vol. 71, no. 11, pp. 1295-1320, November 1983; and www.vla.nrao.edu/, which is hereby incorporated by reference.
The invention provides a family of phased array antennas constructed from a relatively small number of elements and components compared with a conventional phased array. The array uses a relatively small number of radiating elements, each of which is a relatively electrically large, e.g., 5 wavelengths, GRadient INdex (GRIN) lens, specially optimized, with at least one or multiple feed elements in its focal region. Each array element comprises the GRIN lens and one or more feed elements in the focal region of each lens. The lens-feeds set may have one or more beams whose element pattern directions may be varied or controlled to span the desired beam steering range or field of regard. In the case of one feed or cluster of feeds excited to operate as a single effective feed, the position of the feed or cluster may be physically moved relative to the focal point of the lens to effect beam steering. In the case of beam steering with no moving parts, a set of multiple feeds may be placed in the focal region of each lens and the selection (e.g. by switching) of the active feed or feed cluster produces an element beam that is directed to a specific beam direction. The specific structure of the GRIN lens can be optimized in a suitable manner, such as in accordance with the invention disclosed in Applicant'"'"'s co-pending U.S. Provisional Application No. 62/438,181, filed Dec. 22, 2016, the entire contents of which are hereby incorporated by reference.
In one embodiment, the array would steer one or more beams over a specified angular range or field of regard with no moving parts by having multiple feeds in the focal region of each lens and selecting the active feed to steer the element beam. In another highly-simplified embodiment an array with minimal parts count could also be implemented by physically moving each feed element in the corresponding lens'"'"'s focal region. In this simplified embodiment, the set of feed elements across the entire array could be moved together, such that only two actuators ganged across all the lenses are required, or with independent actuators for each lens for improved control. The overall array pattern is obtained by an antenna circuit and/or antenna processing device, which may combine the corresponding active feed elements at each lens with phase/time delay circuits and an active or passive corporate feed network.
The beam scanning performance of the array is controlled at two levels: coarse beam pointing and fine beam pointing. The coarse beam pointing of each lens is obtained by selecting a specific feed or small cluster of feeds excited to act as a single feed (or feed location) in the focal region of each lens. The lens and feed combination produces a directive but relatively broad beam consistent with the lens size in wavelengths and in a direction dependent on the displacement of the feed from the lens nominal focal point. By combining the corresponding feed elements in each lens of the array with appropriate phase shifts or time delays, fine control of beam pointing and high directivity due to the overall array aperture size is obtained. The set of feeds in the focal region of each lens for full electronic beam steering occupies only a fraction of the area associated with each lens so that the number of feeds and components is much lower compared with a conventional phased array. Furthermore, it is evident that, since power need be applied only to the active feeds, the power consumption of this array is substantially less than for a conventional phased array, which must have all its elements supplied with power. This specialized phased array design substantially reduces the total component count, cost, and power consumption compared with a conventional phased array with equivalent aperture size while maintaining comparable technical performance.
Furthermore, each lens and its multiple feed elements can form multiple beams simply by enabling and exciting separate feed elements in each lens with independent RF signals. Thus, the technology can be used with associated electronics for beam pointing control, and hardware and software interfaces with receive and transmit subsystems, allowing simultaneous one-way or two-way communications with one or more satellites or other remote communication nodes. The multiple beam capability along with reduced parts count and lower power consumption compared with a conventional phased array is particularly valuable in applications where it is desired to communicate with more than one satellite or, for example, to enable a “make-before-break” connection to non-geostationary satellites as they pass over the terminal.
The relatively small number of components and the flexibility afforded by having the element patterns be directive and capable of being steered over a wide range of angles offers substantial cost savings. The individually scanning antenna elements (e.g., lenses) allow for wide field of regard and, even though grating lobes exist due to the large element spacing, the degrees of freedom afforded by optimizing the element positions and orientations and the beam directions and directivity of the elements allows minimizing magnitudes of the grating lobes in the radiation pattern(s) of the array.
The array of lenses is not a sparse array, as the lenses fill the aperture area of the array. The phase center of each lens may be offset slightly, which thus breaks up the periodicity of the entire array and reduces grating lobes while having relatively low impact on efficiency, in addition to the reductions afforded by the steerable element patterns.
The new phased array antenna system has an array of electrically-large, high-gain antenna elements, each element comprising a microwave lens which may be a gradient index (GRIN) lens with one or more feeds in its focal region. Each lens and feed subsystem can form multiple independent element patterns whose beams are steered according to the displacement of the feeds from the nominal lens focal point. Further, by combining and phasing the corresponding ports of a multiplicity of such lens and feed subsystems a high gain beam is formed with finely controlled beam direction. In this way, the antenna beam is scanned by first steering the element patterns for coarse pointing (via the lens set circuitry), and then fine-pointing the array beam using the relative phase or time delays to each feed (via the antenna circuitry). The antenna circuitry may use digital beam forming techniques where the signals to and from each feed are processed using a digital signal processor, analog-to-digital conversion, and digital-to-analog conversion. The electrically large element apertures are shaped and tiled to fill the overall array aperture for high aperture efficiency and gain. Furthermore, the array need not be planar but the lens/feed subsystems may be arranged on curved surfaces to be conformal to a desired shape such as for aircraft. The scanning, high-directivity elements require fewer active components compared with a conventional phased array, thereby yielding substantial cost and power savings. Furthermore, the array of lenses may be placed to form arrays of arbitrary form factors such as symmetrical or elongated arrays.
Furthermore, each lens can form simultaneous multiple beams by activating the appropriate feed elements. These feed elements may be combined with their own phasing or time delay networks or even with digital beam forming circuitry to form multiple high gain beams from the overall array. Design flexibility inherent in the extra degrees of freedom afforded by the lens and feed combinations along with the lens orientations and positions allows for grating lobe suppression as well as a broad field of view. The antenna system may be part of a communications terminal that includes acquisition and tracking subsystems that produce single or multiple beams covering a broad field of regard for such applications as satellite communications (Satcom) on-the-move (SOTM), 5G, broadband point-point or point-multipoint and other terrestrial or satellite communications systems. The antenna design with such lens naturally supports multiple simultaneous independently steerable beams. These simultaneous beams may be used for many applications such as: sensors for surveillance; reception of multiple transmission sources; multiple transmission beams; “make-before-break” links with non-geostationary, e.g., low earth orbit (LEO) or medium earth orbit (MEO) satellite constellations; and null placement for interference reduction without incurring the high cost of a conventional multi-beam phased array. Furthermore, the phased array antenna system can be used on spacecraft for single or multiple beam or shaped beam satellite applications.
These and other objects of the invention, as well as many of the intended advantages thereof, will become more readily apparent when reference is made to the following description, taken in conjunction with the accompanying drawings.
In addition to Phased Array incarnations, MIMO (multi-input multi-output) communication systems could also make use of the capability provided by a collection lenses and associated circuitry. Although the signal processing is different for a MIMO compared to a conventional phased array, both can make use of steered beams to enhance signal strength and improve communications in a noisy or interferer-filled environment.
In describing the illustrative, non-limiting preferred embodiments of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents that operate in similar manner to accomplish a similar purpose. Several preferred embodiments of the invention are described for illustrative purposes, it being understood that the invention may be embodied in other forms not specifically shown in the drawings.
Turning to the drawings,
The PCB forming the base of the feed set 150 within each lens set further includes signal processing and control circuitry (“lens set circuit”). The feed elements 152 may be identical throughout the feed set 150, or individual feeds 152 within the feed set 150 may be independently designed to optimize their performance based on their location beneath the lens 112. The physical arrangement of the feed elements 152 within the feed set 150 may be uniform on a hexagonal or rectilinear grid, or may be nonuniform, such as on a circular or other grid to optimize the cost and radiation efficiency of the lens array 100 as a whole. The feed elements 152 themselves may be any suitable type of feed element. For example, the feed elements 152 may correspond to printed circuit “patch-type” elements, air-filled or dielectric loaded horn or open-ended waveguides, dipoles, tightly-coupled dipole array (TCDA) (see Vo, Henry “DEVELOPMENT OF AN ULTRA-WIDEBAND LOW-PROFILE WIDE SCAN ANGLE PHASED ARRAY ANTENNA.” Dissertation. Ohio State University, 2015), holographic aperture antennas (see M. ElSherbiny, A. E. Fathy, A. Rosen, G. Ayers, S. M. Perlow, “Holographic antenna concept, analysis, and parameters”, IEEE Transactions on Antennas and Propagation, Volume 52 issue 3, pp. 830-839, 2004), other wavelength scale antennas, or a combination thereof. In some implementations, the feed elements 152 each have a directed non-hemispherical embedded radiation pattern.
Signals received by the lens array 100 enter each lens set 110 through the respective lens 112, which focuses the signal on one or more of the feed elements 152 of the feed set 150 for that lens set 110. The signal incident to a feed element is then passed to signal processing circuitry (lens set circuitry, followed by the antenna circuitry), which is described below. Likewise, signals transmitted by the lens array 100 are transmitted from a specific feed set 150 out through the respective lens 112.
The number of electrical and radio-frequency components (e.g., amplifiers, transistors, filters, switches, etc.) used in the lens array 100 is proportional to the total number of feed elements 152 in the feed sets 150. For example, there can be one component for each feed element 152 in each feed set 150. However, there can be more than one component for each feed element 152 or there can be several feed elements 152 for each component.
As shown, each lens set 110 has a hexagonal shape, and is immediately adjacent to a neighboring lens set 110 at each side to form a hexagonal tiling. Immediately adjacent lenses 112 may be in contact along their edges. The feed sets 150 are smaller in area than the lenses 112 due to the lens-feed optics, and can be substantially the same shape or a different shape than the lenses 112. While described herein as hexagonal, the lens may have other shapes, such as square or rectangular that allow tiling of the full array aperture. The feed sets 150 may not be in contact with one another and thus may avoid shorting or otherwise electronically interfering with one another. Because of the optical nature of the element beams formed at each lens, the feed displacement to produce scanned element beams is always substantially less than the distance in the focal plane from the lens center to its edge. Therefore, the number of feeds necessary to “fill” the required scan range or field of regard is less than for an array which must have the total aperture area fully populated by feed elements.
In some implementations of the lens array 100, the feed sets 150 fill approximately 25% of the area of each lens 112. The lens array 100 maintains similar aperture efficiency and has a total area similar to a conventional phased array of half-wavelength elements but with substantially fewer elements. In such implementations, the lens array 100 may include approximately only 25% of the number of feed elements as the conventional phased array in which the feed sets 150 fill 100% of the area of the lens array 100. Because the number of electrical and radio-frequency components used in the lens array 100 is proportional to the total number of feed elements 152 in the feed sets 150, the reduction of the number of feed elements 152 also reduces the number and complexity of the corresponding signal processing circuit components (amplifiers, transistors, filters, switches, etc.) by the same fraction. Furthermore, since only the selected feeds in each lens need be supplied with power, the total power consumption is substantially reduced compared with a conventional phased array.
As shown, the lens array 100 may be situated in a housing 200 having a base 202 and a cover or radome 204 that completely enclose the lens sets 110, feed sets 150, and other electronic components. In some implementations, the cover 204 includes an access opening for signal wires or feeds. The housing 200 is relatively thin and can form a top surface 206 for the lens array 100. The top surface 206 can be substantially planar or slightly curved. The lens sets 110 can also be situated on a substrate or base layer, such as a printed circuit board (PCB), that has electrical feeds or contacts that communicate signals with the feed elements 152 of the feed sets 150. The lens sets 110 may be arranged on the same plane, offset at different heights, or be tiled conformally across a nonplanar surface.
The circuitry within the sensing device 304 included in each feed element 152 may contain amplifiers, polarization control circuits, diplexers or time division duplex switches, and other components. Further, the sensing device 304 may be implemented as discrete components or integrated circuits. Further yet, the sensing device 304 may contain up- and down-converters so that the signal processing may take place at an intermediate frequency or even at baseband. While only a single phasing network is shown here for each beam to keep the drawing from being too cluttered, it is understood that, for each beam, a transmit phasing network and a receive phasing network may be employed. For some bands, such as Ku-band, it may be possible to employ a single time delay network that will serve to phase both the transmit and receive beam, keeping them coincident in angle space over the entire transmit and receive bands. Such broadband operation could also be possible over other Satcom bands. The figure shows how two simultaneous beams may be formed by having two such phasing networks. Extensions to more than two simultaneous beams should be evident from the description.
In operation, a signal received by the first lens 112a passes to the respective feed set 150a. The signal is received by the antennas 302 and circuits 304 of the first feed set 150a and passed to the shifters 306. Thus, the first feed element 152a1 receives the signal and passes it to the first summer/divider 308a via its respective shifter 306, and the second feed element 152a2 receives the signal and passes it to the second summer/divider 308b via its respective shifter 306. The second lens 112b passes the signal to its respective feed set 150b. The first feed element 152b1 receives the signal and passes it to the first summer/divider 308a via its respective shifter 306, and the second feed element 152b2 receives the signal and passes it to the second summer 308b via its respective shifter 306.
Signals are also transmitted in reverse, with the signal being divided by the summer/divider 308 and transmitted out from the lenses 112 via the shifters 306 and feed sets 150a. More specifically, the first divider 308a passes a signal to be transmitted to the first feed elements 152a1, 152b1 of the first and second feed sets 150a, 150b via respective shifters 306. And the second divider 308b passes the signal to the second feed elements 152a2, 152b2 of the first and second feed sets 150a, 150b via respective shifters 306. The feed elements 152a1, 152a2 of the first feed set 150a transmit the signal via the first lens 112a and the feed elements 152b1, 152b2 of the second feed set 150b transmit the signal via the second lens 112b.
Accordingly, the first summer/divider 308a processes all the signals received/transmitted over the first feed element 152 of each respective feed set 150, and the second summer/divider 308b processes all the signals received/transmitted over the second feed element 152 of each respective feed set 150. Accordingly, the first summer/divider 308a may be used to form beams that scan an angle associated with the first feed elements 152a, and the second summer/divider 308b may be used to form beams that scan an angle associated with the second feed elements 152b.
In the examples of
Accordingly, a phase center 24 of each lens 112 is perturbed by optimized distances ri and rotation angles αi of the lens axis of symmetry from a geometric center 20 (i.e., the unperturbed phase center) which would typically have been tiled on a uniform hexagonal or rectangular grid. The specific optimized placement of the lens axis of symmetry can be determined by any suitable technique, such as described in the Gregory reference noted above. The position of the lens axis of symmetry determines the phase center. According to the methods in the Gregory reference, for example, disturbing the periodicity of the array by small amounts in this manner suppresses the grating lobes. This process functions because grating lobes are formed by the formation of a periodic structure, which is known as a grating. By eliminating the periodicity between elements, there is no longer a regular grating structure, and grating lobes are not formed. The number of lenses, the shape or boundary of the array, the number of feeds, or the location of the feeds beneath the lens do not change the principles of this mitigation strategy.
A controller can further be provided to control the actuators 172, 174 and move the feed elements 152 to a desired position with respect to the lenses 112. Though the support 170 is shown as a single board, it can be multiple boards that are all connected to common actuators to be moved simultaneously or to separate actuators so that the individual boards and lens sets 110 can be separately controlled. Accordingly,
A corresponding process is provided to transmit a signal over the array. A Transmit Digital Processor 1112 sends the signal to be transmitted to a Digital-to-Analog Converter (DAC) 1108. The DAC 1108 converts low frequency (or possibly baseband) bits to an analog intermediate frequency (IF) and is connected to a mixer 1104. The mixer 1104 up-converts the signal from the DAC 1108 to RF, amplifies the signal for transmit, and sends the signals to the feed elements with the appropriate phase (e.g., selected by the transmit digital processor 1112) to form a beam in the desired direction. Many variations evident to those skilled in the art may be employed while maintaining the unique features of the invention.
Advantages of the Invention
An embedded element radiation pattern is the radiation pattern produced by an individual element in a phased array while in the presence of the other elements of the phased array. Due to interactions between the elements (e.g., mutual coupling), this embedded radiation pattern differs from the pattern the element would have if the element were isolated or independent of the other elements. Given the embedded radiation element pattern(s) of one or more elements of the phased array, the radiation pattern of the array as a whole may be computed (e.g., using pattern multiplication). In typical phased arrays, the element pattern has a fixed beam direction. The phased array according to the present disclosure includes elements (e.g., lenses, aperture antennas) that may have steerable radiation patterns.
The lens array 100 includes elements that are electrically large compared to the half-wave elements used in conventional phased arrays, and implemented in such a way that the radiation pattern of each element may be steered to point broadly in the direction of desired beam scanning. An embedded element radiation pattern and beam direction of each lens 112 (e.g., an array element) of the lens array 100 is determined by the location of the corresponding active feed element 152 relative to the focal point of the lens 112. Accordingly, the array 100 has a flexible radiation pattern.
Any kind of lens may be used in the array 100, such as a homogeneous dielectric lens, inhomogeneous gradient-index dielectric lens, a lens composed of metamaterial or artificial dielectric structures, a substantially flat lens constructed using one or more layers of a metasurface or diffraction grating, flattened lenses such as Fresnel lenses, hybrid lenses constructed from combinations of metamaterial and conventional dielectrics, or any other transmissive device that acts as a lens to collimate or focus RF energy to a focal point or locus. In some embodiments, movement of the location of the active feed element 152 is achieved without moving parts using a cluster of multiple independently-excited feeds 152 that is scanned by changing which of the feeds 152 is excited, as explained above with reference to
Therefore, using relatively electrically large lenses as elements of a phased array enables the phased array to have a tunable or scannable element pattern. Further, using lenses as elements of the phased array enables an entire array aperture may to be covered by radiating sub-apertures (e.g., the lenses). This may increase aperture efficiency and gain of the array antenna.
Another benefit of using lenses with steerable beams as elements of a phased array is that a phased array that includes lenses as elements may include fewer electrical and RF components as compared to a conventional phased array. In an illustrative example, the phased array 100 includes 19 lens sets 110 (i.e., elements) having a diameter of 13 cm each and arranged in a hexagonal tiling pattern to efficiently fill an overall aperture that is roughly equivalent in performance to a 65 cm diameter phased array. The area behind each lens 112 may be only partially covered or filled by the feed elements 152, whereas in a conventional phased array, the entire surface of the aperture of the phased array may be covered with feed elements. Further the feed elements 152 may be no more densely packed than in the conventional phased array (e.g., half-wave). Accordingly, the phased array 110 may include fewer feed elements as compared to the conventional phased array. Since each feed element in either the conventional or lens-based phased array includes associated circuitry (e.g., the detector 304), reducing the number of feed elements may reduce the number of circuits included in the phased array 100. In addition, because only one feed element 152 may be active at a time per lens 112 to generate a beam, some embodiments of the lens array 100 allows circuits, such as the shifter 306, to be shared by multiple feed elements 152, as described with reference to
Further, the lens array 100 may consume less power as compared to a conventional phased array. In an illustrative example, the lens array 100 operates at a transmit RF power of 40 W (46 dBm). The total transmit power is distributed over the lens modules 110 of the lens array 100 (i.e., the elements of the phased array), where in each of the lens modules 110 a single feed element 152 is activated to create a single beam. As described above, one embodiment of the lens array 100 includes 19 lens modules 110. For this reason, it is necessary for each feed element 152 to handle about 1/19 of the total 40 W power (i.e., slightly more than 2 W or 33 dBm). The unused feed elements 152 in each of the lens sets 110 may be turned off and need not dissipate any quiescent DC power for either the receive or transmit circuitry. Accordingly, the lens array 100 may consume less power as compared to a conventional phased array in which each feed element is activated. In an example of the lens array 100, each of the lens sets 110 includes between 20 and 60 independent feed elements 152 behind the lens 112. A receive-only implementation of the lens array 100 may be expected to consume less than 10% of the DC power of the equivalent conventional receive-only phased array aperture.
The beamforming system for the lens array 100 may include the feed element 152 switches 1002 and 716, the shifters 306, the summation/dividers 308, the processing device 1202, or a combination thereof. To generate a beam in a desired direction, the processing device 1202 selects positions of an active feed element for each lens set 110 and computes the appropriate phase or time delay for each lens set 110. The time/phase delay and power combination/division may be performed before or after the upconversion/downconversion step at the RF, IF, or Baseband. The processing device 1202 sets the positions of the active feed elements by sending control signals to activate one of the feed elements 152 for each of the lens sets 110 or by sending control signals to adjust positions of the feed elements 152 using one or more of the actuators 172, 174. The processing device 1202 further sends one or more control signals to one or more of the switches 1002, 716, the shifters 306, the summation/dividers 308, or a combination thereof to set the time/phase delay and power combination/division for each lens set 110.
While GRIN lenses are the preferred embodiment for many applications, the lenses 112 need not be GRIN. For example, in applications that deal with a limited field of regard or limited bandwidth, smaller homogeneous lenses may suffice. Also, in some circumstances, metamaterial lenses or flat lenses composed of metasurfaces or artificial dielectrics may be optimal. Generally, inhomogeneous lenses designed according to the optimization method of application Ser. No. 62/438,181 will provide better radiation patterns over any given beam steering or scanning range (particularly as the scanning angle increases past 45 deg), and shorter focal lengths than homogeneous lenses, and will provide better broadband frequency responses than metamaterial or metasurface-based lenses.
Satellite communications antennas must limit their sidelobe power spectral density (PSD) envelopes to meet Federal Communications Commission (FCC) and International Telecommunication Union (ITU) standards. This requires careful control of sidelobes. However, for the lens array with electrically large lens sets 110 as described herein, grating lobes are created when sidelobe energy from all the lens sets 110 constructively interferes in an undesired direction. However, the high-directivity of the radiation patterns of the lens sets 110 may reduce many of the effects of the grating lobes, since the directivity of the lens radiation patterns, which is multiplied by the array factor, drops off quickly, unlike the response of a conventional array.
Ordinarily, the use of a high-directivity array element (e.g., lens) to mitigate the effect of grating lobes would result in a very narrow scanning range within the angular width of the array radiation pattern. However, allowing the lens sets 110 themselves to scan their embedded element patterns across the desired field of view preserves both the scanning performance and radiation pattern profile of the original antenna. Additional mitigation of the grating lobes may be obtained by perturbing the locations of the phase centers to break the symmetry of the regular grid of lens sets 110, as described with reference to
Breaking the symmetry (periodicity) of the lens sets 110 positions in two or three dimensions reduces the degree to which the energy will constructively interfere in any direction. Furthermore, the location of the phase centers of the lens sets 110 may be arranged on a nonuniform, aperiodic grid to minimize the effect of grating lobes. The physical locations of the phase centers in one, two, or three dimensions are randomized and/or optimized to minimize the grating lobes and improve the radiation pattern. The phase centers may be selected by a stochastic optimizer in either an arbitrary or pseudo-ordered fashion as a part of the terminal design process. The lens sets 110 are constructed such that their physical center and phase center (generally coincident with the axis of symmetric within the lens) are spatially separated, where each lens in the lens set 100 may have a different offset between the phase and physical center, as described with reference to
Many variants of optimization methods may be applied to the reduction of grating lobes. As an example, the (x, y) location of the axis of symmetry of each lens 112 with respect to the geometric center of the lens set 110 when in its proper location of the periodically-tiled phased array 100 is encoded as a constant in a hexagonal or rectangular lattice with a variable offset. The offset may be encoded in two variables for Cartesian, cylindrical, or some other convenient coordinate system. A stochastic optimization algorithm (such as Genetic Algorithm, Particle Swarm, or Covariance Matrix Adaptation Evolutionary Strategy, among others) coupled with a software routine for predicting the array factor and resulting array pattern from a combination of embedded lens radiation patterns and lens set 110 locations is then used to select the specific parameterized offsets for the phase center of each lens 112 element, as controlled by the axis of symmetry of each lens 112 element. The axis of symmetry location, and thus the phase center locations, are fixed when the array is manufactured, and does not vary during operation. The small offset of the axis of symmetry from the geometric center of the lens introduces only a small difference in coarse beam-pointing angle between adjacent lens sets 112 (which can be corrected for by corresponding small changes in the location of the feed array 150 beneath the lens set 112), and the same feeds 152 can be selected between adjacent lens sets 112 to point the coarse beam in the desired direction for the entire array. In all of these cases, the space occupied by the lens sets 112 do not change, but the location of their axis of symmetry does change to control the phase center. As described herein, the lens array 100 may offset the phase center of the lens 112 without changing the geometric center (centroid) of the lens set 110 or introducing gaps in an aperture of the lens array 100 (e.g., using the actuator(s) 172, 174.
The optimizer can minimize the grating lobes via the array factor alone, or can apply the embedded element (e.g., lens set) radiation patterns to the array factor and optimize the radiation pattern sidelobes directly. Considering the array pattern directly requires more sophisticated multi-objective optimization strategies A hybrid approach involves constructing a worst-case mask that the array factor must satisfy to guarantee that the sidelobes will satisfy the regulatory masks at all angles and frequencies.
The size of the lens 112 is a trade of cost vs. performance and complexity. Increasing the size of the individual lens 112 reduces the number of elements in the phased array, thus simplifying the circuitry, but also increases the lens set 110-lens set 110 separation distance, the magnitude of the grating lobe problem, and the cost and complexity of each individual feed element 152. Reducing the size of the individual elements increases the number of lens sets 110, but reduces the grating lobes, and the cost and complexity of each feed element 152 and lens set 110.
The use of electrically-large phased array elements (e.g., lens sets) with individually electrically-scanned patterns may be worthwhile if the element has much lower cost for a given aperture size compared to the cost of the conventional phased array elements that would otherwise fill that area and produce similar antenna terminal performance. For a switched-feed scanning lens antenna, the cost of the lens itself is relatively small and the cost of the array antenna may be proportional to the number of feed elements and their circuitry.
In some examples of the phased array 100, only a fraction of the area (25-50%) behind the lens 112 in each lens set 110 is populated with feed elements 152, and the feed elements 152 may be separated by more than half of a wavelength. For this reason, when considering a given aperture area that can be covered by a lens set 110, the cost for the lens set 110 can be much smaller when compared to the equivalent phased array that includes relatively more feed elements.
Each feed element 152 behind a given lens 112 is associated with a particular set of circuits depending on the application of the array as a whole. The simplest case is either a receive-only or transmit-only single-polarization circuit. A controllable polarization circuit for operation in Ku-band tilted Horizontal/Vertical polarized SATCOM, or a circular polarizer for K/Ka SATCOM, together with a dual-polarized feed antenna 152, can be used to support either mobile operation or polarization-independent operation.
Combined receive/transmit operation in a single terminal can be performed with an active transmit/receive switch for time-division duplexing, or by using a diplexer circuit element for frequency-division duplex operation, as described with reference to
The lens array 100 may include a single shifter 306 in each lens set 110 for each supported simultaneous beam, rather than one for each feed element 152 as would be required in a conventional phased array, as described with reference to
Due to the relatively large element separation of the lens sets 110 and the relatively small number of lens sets 110 in the lens array 100, the shifters 306 may have relatively higher discretization as compared to those of a standard phased array. For example, the shifters 306 may correspond to 8-bit or higher number of bits time delay units, rather than the 4 or 6-bit time delay units of a typical conventional phased array. However, due to the relatively small number of lens sets 110 and associated shifters/time delay units 306 in the phased array 100, the additional resolution of the shifters 306 may not represent a significant cost.
In contrast with other large-element phased arrays, such as the Very Large Array of Napier (27 gimbaled reflector antennas, each 25 m in diameter), the lens array 100 of lens sets 110 proposed herein can support multiple simultaneous beams in nearly arbitrary directions within a field of regard. This is implemented by exciting two or more separate feed elements 152 behind each lens 112 with a separate input signal and time offset unique to each lens set 110. Since each feed element 152 of a single lens 112 will radiate an independent beam, an array of lens sets 110 can generate independent high-directivity beams.
In contrast with conventional phased arrays, the array 100 of lenses 112 herein can support multiple beams with a minimum of added circuitry, while a conventional (analog) phased array would replicate the entire feed network for each beam. Since only one feed element 152 and one phase shifter 306 is activated to produce a single, beam, two independent beams may be included by adding one layer of additional switches, and one additional phase shifter 306 to each lens set 110.
The lens array 100 is described as a ground terminal for satellite communications, and could be used for both stationary and mobile ground terminals. In this communication mode, potential mounting and applications may include schools, homes, businesses, or NGOs, private or public drones, unmanned aerial systems (UAS), military, civilian, passenger, or freight aircraft, passenger, friend, leisure, or other maritime vehicles, and ground vehicles such as buses, trains, and cars. The lens array 100 as described can also be applied for the space segment of a satellite communication system as an antenna on a satellite for multiple spot beams and/or shaped beams, for dynamically-reconfigurable point-point terrestrial microwave links, cellular base stations (such as 5G), and any other application that requires or is benefited by dynamic multiple beamforming.
The lens array antenna terminals may be used for stationary or mobile applications where the angular field of regard requires the beam or multiple beams to be formed over relatively wide spatial angles. For example, for a Satcom terminal atop an aircraft it is desirable that the range of angles beat least 60 degrees and even 70 degrees or more to ensure that the antenna can communicate with geostationary satellites at various orbital locations relative to the aircraft. For non-geostationary satellite systems, the beam or beams must be able to track the satellites as they pass overhead, whether the terminal is stationary, e.g. atop a building or on a tower, or mobile such as on a vehicle. In both cases the range of angles depends on the number and locations of the satellites and the minimum acceptable elevation angle from the terminal to the satellite. Therefore, antenna systems must generally have a broad field of regard or the range of beam steering angles.
It is further noted that the description uses several geometric or relational terms, such as thin, hexagonal, hemispherical and orthogonal. In addition, the description uses several directional or positioning terms and the like, such as below. Those terms are merely for convenience to facilitate the description based on the embodiments shown in the figures. Those terms are not intended to limit the invention. Thus, it should be recognized that the invention can be described in other ways without those geometric, relational, directional or positioning terms. In addition, the geometric or relational terms may not be exact because of, for example, tolerances allowed in manufacturing, etc. And, other suitable geometries and relationships can be provided without departing from the spirit and scope of the invention.
As described and shown, the system and method of the present invention include operation by one or more circuits and/or processing devices, including the CPU 1202 and processors 1110, 1112. For instance, the system can include a lens set circuit and/or processing device 150 to adjust embedded radiation patterns of the lens sets, for instance including the components of 304 and associated control circuitry; and an antenna circuit and/or processing device to adjust the antenna radiation pattern, which may take the form of a beamforming circuit and/or processing device such as 306 and 308, or their digital alternatives as in 1102, 1104, 1106, 1108, 1110, and 1112, and the antenna circuitry may include additional components such as 1202, 1206, and 1208. It is noted that the processing device can be any suitable device, such as a chip, computer, server, mainframe, processor, microprocessor, PC, tablet, smartphone, or the like. The processing devices can be used in combination with other suitable components, such as a display device (monitor, LED screen, digital screen, etc.), memory or storage device, input device (touchscreen, keyboard, pointing device such as a mouse), wireless module (for RF, Bluetooth, infrared, Wi-Fi, etc.). The information may be stored on a computer hard drive, on a CD ROM disk or on any other appropriate data storage device, which can be located at or in communication with the processing device. The entire process is conducted automatically by the processing device, and without any manual interaction. Accordingly, unless indicated otherwise the process can occur substantially in real-time without any delays or manual action.
The system and method of the present invention is implemented by computer software that permits the accessing of data from an electronic information source. The software and the information in accordance with the invention may be within a single, free-standing processing device or it may be in a central processing device networked to a group of other processing devices. The information may be stored on a chip, computer hard drive, on a CD ROM disk or on any other appropriate data storage device.
Within this specification, the terms “substantially” and “relatively” mean plus or minus 20%, more preferably plus or minus 10%, even more preferably plus or minus 5%, most preferably plus or minus 2%. In addition, while specific dimensions, sizes and shapes may be provided in certain embodiments of the invention, those are simply to illustrate the scope of the invention and are not limiting. Thus, other dimensions, sizes and/or shapes can be utilized without departing from the spirit and scope of the invention. Each of the exemplary embodiments described above may be realized separately or in combination with other exemplary embodiments.
The foregoing description and drawings should be considered as illustrative only of the principles of the invention. The invention may be configured in a variety of shapes and sizes and is not intended to be limited by the preferred embodiment. Numerous applications of the invention will readily occur to those skilled in the art. Therefore, it is not desired to limit the invention to the specific examples disclosed or the exact construction and operation shown and described. Rather, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.