Patent Grant
11990685
This U.S. patent application claims priority under 35 U.S.C. § 119 to: India Application No. 202121023515, filed on 27 May 2021. The entire contents of the aforementioned application are incorporated herein by reference.
The disclosure herein generally relates to antenna scanning systems, and, more particularly, computer controlled electromechanical Millimeter Wave (MMW) frequency antenna scanning system and beam steering for the same.
Millimeter Wave (MMW) frequency band of 24 GHz to 28 GHz is being considered quite important for emerging areas of Radio Frequency (RF) sensing (radars in civilian applications) and 5th Generation (5G) deployments in wireless communications. Radar applications range from machine inspection (by measuring vibration), counting people and tracking, and the like. On the other hand, it is envisaged that future 5G deployments will utilize this frequency band for very high data rate. For both the application scenarios, a need exists for scanning an antenna beam over a large angular swath where the antenna beam itself displays high directivity, i.e. narrow beam width rather than using a single antenna with omnidirectional coverage. Omnidirectional antenna has the property of low gain thereby requiring more transmit power; this is critical at MMW frequency bands due to high propagation loss. Moreover, an omnidirectional antenna will pick up radio waves from both the desired object (or user) as well as interfering sources; thereby making detection more difficult.
A standard alternative is to implement electronic scanning of antenna beam using phased-array concept. However, the phased-array concept works well with a narrow band system. An array factor that defines the directivity and beam scanning angle is frequency sensitive. Both values change as the operating frequency changes and therefore the array needs to be reconfigured when the system is wideband. Typically, bandwidth >10% of center frequency. On the other hand, the emerging areas of 5G or ultra-wideband radar expect a frequency bandwidth of greater than 20% or 500 MHz. To introduce frequency independence, conventional concepts like multiband array, a frequency tapered array and an array with varying element sizes and element distances may be employed. Cost and size of the antenna scanning system is a concern with these conventional concepts.
Embodiments of the present disclosure present technological improvements as solutions to one or more of the above-mentioned technical problems recognized by the inventors in conventional systems.
In an aspect, there is provided a Millimeter Wave (MMW) frequency antenna scanning system comprising: a microstrip antenna positioned horizontally in an XY plane of a Cartesian coordinate system and cooperating with a Radio Frequency (RF) chain to receive and transmit radio waves; a first conducting plate positioned at a first predetermined distance from the microstrip antenna, wherein the first conducting plate is connected to a ground terminal and configured to reflect the radio waves; a metasurface disposed such that a center point thereof is at a second predetermined distance, along a Z-axis in the Cartesian coordinate system, from a radiating face of the microstrip antenna; two or more posts having a first end and a second end, positioned on opposite sides of the first conducting plate, wherein the first end is coupled to the metasurface, and configured to have vertical movement along the Z-axis; and a controller unit in communication with the two or more posts via the second end thereof, wherein the controller unit comprises: two or more motors wherein each of the two or more motors are configured to independently control the vertical movement of an associated post from the two or more posts along the Z-axis, such that the vertical movement results in a tilt of the connected metasurface with reference to an orientation of the microstrip antenna; and one or more data storage devices configured to store instructions; one or more communication interfaces; and one or more hardware processors operatively coupled to the one or more data storage devices via the one or more communication interfaces, wherein the one or more hardware processors are configured by the instructions to: generate a driving voltage for synchronously controlling the two or more motors such that the coupled metasurface tilts with reference to the orientation of the microstrip antenna by an inclination angle for beam steering that provides a predetermined directivity to the microstrip antenna, wherein the beam steering involves steering of beams of the radio waves.
In another aspect, there is provided a processor implemented method comprising the steps of: positioning a microstrip antenna horizontally, in an XY plane of a Cartesian coordinate system, and cooperating with a Radio Frequency (RF) chain (104) to receive and transmit radio waves; positioning a first conducting plate at a first predetermined distance from the microstrip antenna, wherein the first conducting plate is connected to a ground terminal and configured to reflect the radio waves; disposing a metasurface such that a center point thereof is at a second predetermined distance, along a Z-axis in the Cartesian coordinate system, from a radiating face of the microstrip antenna; positioning two or more posts, having a first end and a second end, on opposite sides of the first conducting plate, wherein the first end is coupled to the metasurface, and configured to have vertical movement along the Z-axis; generating a driving voltage, by a controller unit for synchronously controlling two or more motors, wherein each of the two or more motors are configured to independently control the vertical movement of an associated post from the two or more posts along the Z-axis; and performing beam steering by the vertical movement that results in a tilt of the coupled metasurface with reference to an orientation of the microstrip antenna by an inclination angle, to achieve a predetermined directivity associated with the microstrip antenna, wherein the beam steering involves steering of beams of the radio waves.
In accordance with an embodiment of the present disclosure, the first predetermined distance and the second predetermined distance are optimized based on impedance matching, radiation gain and accuracy of the beam steering.
In accordance with an embodiment of the present disclosure, the first predetermined distance is based on a wavelength (λ) corresponding to a frequency of interest and the second predetermined distance is 8 millimeter (mm).
In accordance with an embodiment of the present disclosure, the first predetermined distance is an odd multiple of λ/4.
In accordance with an embodiment of the present disclosure, the inclination angle is identical to an angle of tilt θ of a main lobe of a transmitted or received radio waves from the microstrip antenna.
In accordance with an embodiment of the present disclosure, the metasurface is square shaped.
In accordance with an embodiment of the present disclosure, the microstrip antenna is characterized by: a substrate that accommodates a radiating patch on a first surface and a second conducting plate on an opposite surface; sides of the radiating patch and sides of the substrate are separated by a predefined region; a portion of a side of the radiating patch proximate a corner of the radiating patch and extends into the predefined region along two adjacent sides of the substrate, proximate the corner; a feed point disposed at an empirically determined position in the radiating patch; and a shorting pin disposed at an empirically determined position in a portion of the radiating patch that extends into the predefined region.
In accordance with an embodiment of the present disclosure, the substrate is square shaped, and the radiating patch is rectangular shaped.
In accordance with an embodiment of the present disclosure, the two or more motors are stepper motors.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, serve to explain the disclosed principles.
Exemplary embodiments are described with reference to the accompanying drawings. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. Wherever convenient, the same reference numbers are used throughout the drawings to refer to the same or like parts. While examples and features of disclosed principles are described herein, modifications, adaptations, and other implementations are possible without departing from the scope of the disclosed embodiments.
The Millimeter Wave (MMW) frequency band of 24 GHz to 28 GHz is gaining importance in Radio Frequency (RF) applications and 5th Generation (5G) deployments in wireless communications. Detection by an omnidirectional antenna is less efficient considering it picks up radio waves from interfering sources. To meet the need for scanning the antenna beam over a large angular swath with high directivity, a phased array implementation may be considered. However, the phased array implementation works better with a narrow band system. Alternatives like multiband array, frequency tapered array and arrays with varying element sizes and element distances are cost intensive and size of the antenna scanning system is also a concern.
In a classical consideration for 5G deployment at MMW frequency bands, “small cells” i.e. cells that cover a region of 250 m to 300 m each are required, due to the high propagation losses associated with MMW. Moreover, there are issues involved with obstruction due to buildings, infrastructure where MMW radio waves cannot penetrate the structures. This consideration leads to a practical deployment scenario where thousands of 5G base stations are needed to be installed to cover an urban area. Thus, size and cost of an antenna scanning system is a very important consideration. The technical problem of providing an MMW frequency antenna scanning system using a single small size antenna capable of scanning as desired at a desired precision is addressed in the present disclosure. The antenna scanning system provided is an electromechanical system that makes the system cost effective. Computer control provides the precision control in beam steering from remote. Use of a metasurface and configuration of a microstrip antenna (described later in the description) addresses the concern on the size of the antenna scanning system.
In the context of the subject disclosure, definitions of certain expressions and their usage are as explained herein below.
Referring now to the drawings, and more particularly to
Reference numerals of one or more components of the MMW frequency antenna scanning system as depicted in the
The MMW frequency antenna scanning system 100 further comprises a first conducting plate 106, positioned at a first predetermined distance from the microstrip antenna, wherein the first conducting plate 106 is connected to a ground terminal and configured to reflect the radio waves. In an embodiment, the first conducting plate 106 is a metallic plate. The ground terminal may or may not be same as the ground terminal of the RF chain 104.
The MMW frequency antenna scanning system 100 further comprises a metasurface 108, disposed such that a center point of the metasurface 108 is at a second predetermined distance, along a Z-axis in the Cartesian coordinate system, from a radiating face of the microstrip antenna 102.
The metasurface 108 rests on two or more posts 110 positioned on opposite sides of the first conducting plate 106. Accordingly, in an embodiment, the MMW frequency antenna scanning system 100 comprises the two or more posts 110 having a first end and a second end, positioned on opposite sides of the first conducting plate 106, wherein the first end is coupled to the metasurface 108, and configured to have vertical movement along the Z-axis. In an embodiment, the two or more posts 110 are made of an insulating material such as Polytetrafluoroethylene (PTFE), Bakelite, and the like. In an embodiment employing two posts, the first end of each post is coupled to a midpoint of opposite sides of the metasurface. Alternatively, in an embodiment employing four posts, the first end of each post is coupled to a midpoint of each side of the metasurface.
The MMW frequency antenna scanning system 100 further comprises a controller unit 112 that is in communication with the two or more posts 110 via the second end of the two or more posts. In an embodiment, the controller unit 112 comprises two or more motors 112A, wherein each of the two or more motors 112A are configured to independently control the vertical movement of an associated post from the two or more posts 110 along the Z-axis, such that the vertical movement results in a tilt of the connected metasurface 108 with reference to an orientation of the microstrip antenna 102. In an embodiment, the two or more motors 112A are Direct Current (DC) motors such as stepper motors.
The controller unit 112 further comprises one or more data storage devices or memory 112B configured to store instructions; one or more communication interfaces 112C; and one or more hardware processors 112D operatively coupled to the one or more data storage devices via the one or more communication interfaces 112C, wherein the one or more hardware processors 112D are configured by the instructions to perform beam steering.
The one or more hardware processors 112D can be implemented as one or more microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, graphics controllers, logic circuitries, and/or any devices that manipulate signals based on operational instructions. Among other capabilities, the processor(s) are configured to fetch and execute computer-readable instructions stored in the memory. In the context of the present disclosure, the expressions ‘processors’ and ‘hardware processors’ may be used interchangeably. In an embodiment, the one or more hardware processors 112D can be implemented in a variety of computing systems, such as laptop computers, notebooks, hand-held devices, workstations, mainframe computers, servers, a network cloud and the like.
In an embodiment, the communication interface(s) or input/output (I/O) interface(s) 112C may include a variety of software and hardware interfaces, for example, a web interface, a graphical user interface, and the like and can facilitate multiple communications within a wide variety of networks N/W and protocol types, including wired networks, for example, LAN, cable, etc., and wireless networks, such as WLAN, cellular, or satellite. In an embodiment, the I/O interface(s) can include one or more ports for connecting a number of devices to one another or to another server.
The one or more data storage devices or memory 1128 may include any computer-readable medium known in the art including, for example, volatile memory, such as static random access memory (SRAM) and dynamic random access memory (DRAM), and/or non-volatile memory, such as read only memory (ROM), erasable programmable ROM, flash memories, hard disks, optical disks, and magnetic tapes.
In an embodiment, the one or more hardware processors 112D are configured to generate a driving voltage for synchronously controlling the two or more motors 112A such that the coupled metasurface 108 tilts with reference to the orientation of the microstrip antenna 102 by an inclination angle for beam steering that provides a predetermined directivity to the microstrip antenna, wherein the beam steering involves steering of beams of the radio waves. In an embodiment, the predetermined directivity (degree to which the radio wave is transmitted/received is concentrated in a single direction) is empirically determined. In accordance with the present disclosure, the inclination angle is identical to an angle of tilt θ of a main lobe of a transmitted or received radio waves from the microstrip antenna 102.
In an embodiment, the first predetermined distance and the second predetermined distance are optimized based on impedance matching, radiation gain and accuracy of the beam steering. The antenna's input impedance matching with corresponding RF circuitry's output impedance is critical to minimize reflection of the radio waves or maximize power transfer. Best performance may be assessed empirically and accordingly the first predetermined distance and the second predetermined distance may be determined.
In an embodiment, the first predetermined distance is based on domain knowledge pertaining to cavity antenna. Accordingly, the first predetermined distance is based on a wavelength (λ) corresponding to a frequency of interest. In an embodiment, for the frequency of interest 28 GHz, λ is 10.7 mm. In an embodiment, the first predetermined distance is an odd multiple of λ/4, for instance, 3 λ/4 or 5 λ/4, and the like.
In an embodiment of the present disclosure, the second predetermined distance is empirically determined as 8 millimeter (mm). This is further explained under Experimental evaluation with reference to Table 2 later in the description.
In accordance with an embodiment of the present disclosure, the method 200 comprises, positioning the microstrip antenna 102 horizontally, in an XY plane of a Cartesian coordinate system, at step 202, such that the microstrip antenna 102 cooperates with a Radio Frequency (RF) chain 104 of the system 100 to receive and transmit the radio waves. The first conducting plate 106 is positioned at the first predetermined distance from the microstrip antenna 102, at step 204, wherein the first conducting plate 106 is connected to the ground terminal and configured to reflect the radio waves. The metasurface 108 is disposed, at step 206, such that the center point of the metasurface 108 is at the second predetermined distance, along the Z-axis in the Cartesian coordinate system, from the radiating face of the microstrip antenna 102. The two or more posts 110, having the first end and the second end, on opposite sides of the first conducting plate 106, are positioned at step 208, wherein the first end is coupled to the metasurface 108, and configured to have vertical movement along the Z-axis. The driving voltage is then generated, at step 210, by the controller unit 112 for synchronously controlling the two or more motors 112A, wherein each of the two or more motors are configured to independently control the vertical movement of an associated post from the two or more posts 110 along the Z-axis. Beam steering is performed, at step 212, by the vertical movement that results in a tilt of the coupled metasurface 108 with reference to an orientation of the microstrip antenna 102 by an inclination angle, to achieve a predetermined directivity associated with the microstrip antenna 102, wherein the beam steering involves steering of beams of the radio waves.
Table 2 below shows beam steering characteristics of the MMW frequency antenna scanning system 100 for various values of separation between the metasurface 108 and the microstrip antenna 102 represented by the second predetermined distance I. The angle rotate represents the inclination angle of the metasurface 108 with respect to the horizontally placed microstrip antenna 102.
From Table 2, it may be noted that the second predetermined distance of 8 mm is optimum for which the beam is steered by the exact same angle as the metasurface inclination angle (rotate) while maintaining the same offset angle which appears due to the fact that when the metasurface 108 is horizontally placed (rotate=0°), the peak beam is directed towards −5° angle. Also, S11 is below −15 dB for the entire angle rotate (up to 40°). For the other values of the second predetermined distance, there is some error noted, thereby concluding that 8 mm is an optimum separation for which beam is steered (up to +/−40°) with no error as well as maintaining a good impedance matching (below −15 dB).
The MMW frequency antenna scanning system 100 of the present disclosure was simulated using Ansys HFSS for its reflection coefficient (S11) curve to study impedance matching characteristics.
In the radiation plot, the numerical values distributed over the outermost circle represents the angle θ and the numerical values (vertically arranged) mentioned at the circumference of each inner circle represent the radiation gain value in dB. It may be noted from
To clearly understand the beam steering behavior, different marker points have been placed at the peak point of the main beam corresponding to every inclination angle of the metasurface 108 so that the marker value can clearly notate the angle θ by which the beam has steered. Markers m1, m2, m3, m4 and m5 correspond to mark the peak of main beam for the inclination angle 0°, 10°, 20°, 30° and 40° respectively. The second predetermined distance between the microstrip antenna 102 and the metasurface 108 is fixed at 8 mm irrespective of the inclination angle.
For rotate=0°, it means the metasurface 108 is placed horizontally above the microstrip antenna 102 at 8 mm distance, the peak beam is lying at θ=−5 deg. The beam corresponding to this setup is considered as the reference beam.
For rotate=10°, it means that the metasurface 108 is inclined (towards the Y-axis) by an angle 10° w.r.t the vertical Z-axis, the peak beam lying at θ=5°. Here, it is observed that the peak beam (corresponding to 10° rotate) got steered with the same angle (10°) as that of the metasurface inclination angle.
For rotate=20°, it means that the metasurface 108 is inclined (towards the Y-axis) by an angle 20° w.r.t the vertical Z-axis, the peak beam lying at θ=15°. Here, it is observed that the peak beam got steered w.r.t the reference beam with the same angle) (20°) as that of metasurface inclination angle.
For rotate=30°, it means that metasurface 108 is inclined (towards the Y-axis) by an angle 30° w.r.t the vertical Z-axis, the peak beam lying at θ=25°. Here, it is observed that the peak beam got steered w.r.t the reference beam with the same angle) (30°) as that of the metasurface inclination angle.
For rotate=40°, it means that metasurface 108 is inclined (towards the Y-axis) by an angle 40° w.r.t the vertical Z-axis, the peak beam lying at θ=35°. Here, it is observed that the peak beam got steered w.r.t the reference beam with the same angle) (40°) as that of the metasurface inclination angle.
Therefore, concluding the above facts, the main beam is getting steered with the same angle as that of metasurface inclination angle.
It may be noted that the beam steering is happening only in φ=90° plane because the metasurface 108 is allowed to incline towards the Y-axis. Similarly, if the metasurface 108 is allowed to incline towards the X-axis, then the beam steering behavior will be observed for φ=0° plane.
When the metasurface 108 was placed on top of the microstrip antenna 102 at a distance of 4 mm then S11 lies between −10 dB and −15 dB at frequency of interest 28 GHz for various inclination angles of the metasurface 108, which does not match the requirement (S11≤−15 dB as desired in MMW applications). Considering this requirement, the S11 dip illustrates not a good matching except for inclination angle of 20°.
Hence, in accordance with the present disclosure, the separation between antenna and metasurface (the second predetermined distance) was optimized to get the S11 dip (@28 GHz) below −15 dB for every inclination angle of the metasurface 108. Also, the beam needs to get steered with the same angle as that of angle rotate. The optimized second predetermined distance which fulfills both these criteria is 8 mm. Hence, only the intrinsic property of the metasurface 108 is not sufficient enough to achieve beam steering as desired for MMW applications. It also depends upon the design of the microstrip antenna 102 provided in the present disclosure along with the optimization of the distance between the microstrip antenna 102 and the metasurface 108 in the MMW frequency antenna scanning system 100. The computer controlled electromechanical system 100 thus provides a cost effective and compact MMW frequency antenna scanning system with desired beam steering.
The illustrated steps are set out to explain the exemplary embodiments shown, and it should be anticipated that ongoing technological development will change the manner in which particular functions are performed. These examples are presented herein for purposes of illustration, and not limitation. Further, the boundaries of the functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternative boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. Alternatives (including equivalents, extensions, variations, deviations, etc., of those described herein) will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Such alternatives fall within the scope of the disclosed embodiments. Also, the words “comprising,” “having,” “containing,” and “including,” and other similar forms are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. It must also be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise.
Furthermore, one or more computer-readable storage media may be utilized in implementing embodiments consistent with the present disclosure. A computer-readable storage medium refers to any type of physical memory on which information or data readable by a processor may be stored. Thus, a computer-readable storage medium may store instructions for execution by one or more processors, including instructions for causing the processor(s) to perform steps or stages consistent with the embodiments described herein. The term “computer-readable medium” should be understood to include tangible items and exclude carrier waves and transient signals, i.e., be non-transitory. Examples include random access memory (RAM), read-only memory (ROM), volatile memory, nonvolatile memory, hard drives, CD ROMs, DVDs, flash drives, disks, and any other known physical storage media.
It is intended that the disclosure and examples be considered as exemplary only, with a true scope of disclosed embodiments being indicated by the following claims.
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| Number | Date | Country | |
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| 20230006346 A1 | Jan 2023 | US |
