Patent Publication Number: US-2023137593-A1

Title: Frustum-designed radar reflector for elevator positioning

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority pursuant to 35 U.S.C. 119(a) to Chinese Application No. 202111272942.1, filed Oct. 29, 2021, which application is incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     Various embodiments described herein relate generally to measurement systems used in conjunction with an elevator system. More particularly, various embodiments of the present disclosure relate to radar-based elevator positioning systems involving radar signal measurements for precise determination of a position of an elevator car within an elevator shaft. 
     BACKGROUND 
     Industrial and commercial applications may use elevator systems to facilitate the transport of people, cargo, and/or the like throughout various levels of a multi-story building. In particular, an elevator positioning system may be used to monitor the real-time position (e.g., the height) of an elevator car within an elevator shaft, such that the elevator car may move between one or more desired positions along the elevator shaft. Real-time positioning is vital for further control of the elevator car, including stop positing, unexpected car movement protection, overspeed detection, and brake permeance monitoring. 
     BRIEF SUMMARY 
     Various embodiments described herein provide a radar reflector including three or more triangular panels defining a pyramidal frustum volume having a base plane and an upper plane that are parallel. The pyramidal frustum volume is configured to directly reflect radar signals originating from a radar transceiver back to the radar transceiver based at least in part on the triangular panels being approximately mutually perpendicular at a projected apex above the upper plane. Base plane geometry of the pyramidal frustum volume is based at least in part on the number of triangular panels included by the radar reflector (e.g., triangular base plane for three-panel radar reflector, rectangular base plane for four-panel radar reflector). 
     In various embodiments, the three or more triangular panels each include an upper vertex portion that interfaces with other upper vertex portions of the other triangular panels to form the upper plane of the pyramidal frustum volume. In various embodiments, each triangular side panel includes lateral edges having protruding joint features, and the three or more triangular panels are connected to each other via the protruding joint features. In various embodiments, each triangular panel is configured with an upper vertex angle determined based at least in part on a total number of triangular side panels for the radar reflector. In various embodiments, the base plane of the pyramidal frustum volume is defined in a particular geometric shape configured to cause the radar signals reflected by the pyramidal frustum volume to have a particular signature associated with the particular geometric shape. For example, the particular geometric shape is radially asymmetrical. In various embodiments, each pair of the triangular panels forms an angle at the projected apex of between approximately 80 degrees and approximately 100 degrees. 
     In various embodiments, the three or more triangular panels are manufactured from a common material panel. In various embodiments, the radar reflector and the radar transceiver are configured for determining radar-based distance measurements for an elevator positioning system configured to determine a position of an elevator car within an elevator shaft. In various embodiments, the radar reflector is configured to interface with an attachment feature of the elevator shaft or an attachment feature of the elevator car via the upper plane of the pyramidal frustum volume. 
     Various embodiments of the present disclosure provide a radar reflector array including a plurality of radar reflectors connected in a planar arrangement. Each radar reflector includes three or more triangular panels defining a pyramidal frustum volume having a base plane and an upper plane that are parallel. The pyramidal frustum volume of each radar reflector is configured to directly reflect radar signals originating from a radar transceiver back to the radar transceiver based at least in part on the triangular panels being approximately mutually perpendicular at a projected apex above the upper plane. A first ratio between a total area spanned by the base planes of the plurality of radar reflectors and a height of the radar reflector array is significantly greater than a second ratio between an area spanned by one base plane of one radar reflector and a height of the one radar reflector. 
     In various embodiments, the three or more triangular panels of a radar reflector each include an upper vertex portion that interfaces with other upper vertex portions to form the upper plane of the pyramidal frustum volume of the radar reflector. In various embodiments, each triangular side panel of a radar reflector of the radar reflector array includes lateral edges having protruding joint features, and the three or more triangular panels are connected to each other via the protruding joint features. In various embodiments, each triangular panel of a radar reflector of the radar reflector array is configured with an upper vertex angle determined based at least in part on a total number of triangular side panels for the radar reflector of the radar reflector array. In various embodiments, the base plane of the pyramidal frustum volume of a particular radar reflector of the radar reflector array is defined in a particular geometric shape configured to cause the radar signals reflected by at least the particular radar reflector of the radar reflector array to have a particular signature associated with the particular geometric shape. For example, the particular geometric shape is radially asymmetrical. In various embodiments, each pair of the triangular panels of a radar reflector of the radar reflector array forms an angle at the projected apex of between approximately 80 degrees and approximately 100 degrees. 
     In various embodiments, the three or more triangular panels of at least one radar reflector are manufactured from a common material panel. In various embodiments, the radar reflector array and the radar transceiver are configured for determining radar-based measurements for an elevator positioning system configured to determine a position of an elevator car within an elevator shaft. In various embodiments, the radar reflector array is configured to interface with an attachment feature of the elevator shaft or an attachment feature of the elevator car via each upper plane of the plurality of radar reflectors. 
     Various embodiments of the present disclosure provide a radar reflector for determining a position of an elevator car within an elevator shaft using radar-based distance measurements. The radar reflector includes three or more triangular panels defining a pyramidal volume having a base plane and an apex. The triangular panels being approximately mutually perpendicular at the apex of the pyramidal volume. With the triangular panels being approximately mutually perpendicular at the apex, the pyramidal volume is configured to directly reflect radar signals originating from a radar transceiver back to the radar transceiver. 
     In various embodiments, each triangular side panel includes lateral edges having protruding joint features, and the three or more triangular panels are connected to each other via the protruding joint features. In various embodiments, each triangular panel is configured with an upper vertex angle determined based at least in part on a total number of triangular side panels for the radar reflector. In various embodiments, the base plane of the pyramidal frustum volume is defined in a particular geometric shape configured to cause the radar signals reflected by the pyramidal frustum volume to have a particular signature associated with the particular geometric shape. For example, the particular geometric shape is radially asymmetrical. In various embodiments, each pair of the triangular panels forms an angle at the projected apex of between approximately 80 degrees and approximately 100 degrees. 
     In various embodiments, the three or more triangular panels are manufactured from a common material panel. In various embodiments, the radar reflector and the radar transceiver are configured for determining radar-based distance measurements for an elevator positioning system configured to determine a position of an elevator car within an elevator shaft. In various embodiments, the radar reflector is configured to interface with an attachment feature of the elevator shaft or an attachment feature of the elevator car via an exterior-facing surface of at least one of the three or more triangular panels. 
     Various embodiments of the present disclosure provide a radar reflector array for determining a position of an elevator car within an elevator shaft using radar-based distance measurements. The radar reflector array includes a plurality of radar reflectors connected in a planar arrangement. Each radar reflector includes three or more triangular panels defining a pyramidal volume having a base plane and an apex. The pyramidal volume is configured to directly reflect radar signals originating from a radar transceiver back to the radar transceiver based at least in part on the triangular panels being approximately mutually perpendicular at the apex of the pyramidal volume. A first ratio between a total area spanned by the base planes of the plurality of radar reflectors and a height of the radar reflector array is significantly greater than a second ratio between an area spanned by one base plane of one radar reflector and a height of the one radar reflector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
         FIG.  1    schematically illustrates an exemplary system for determining a position of an elevator car within an elevator shaft, in accordance with various embodiments; 
         FIG.  2    illustrates a perspective view of an exemplary radar reflector, in accordance with various embodiments; 
         FIG.  3    illustrates a perspective view of an internal volume of an exemplary radar reflector in accordance with various embodiments; 
         FIG.  4    illustrates an example schematic for manufacturing an exemplary radar reflector in accordance with various embodiments; 
         FIGS.  5 A-C  illustrate various exemplary radar reflectors in accordance with various embodiments of the present disclosure; 
         FIG.  6    illustrates a side view of an exemplary radar reflector, in accordance with various embodiments; 
         FIGS.  7 A-B  illustrate configuration of an exemplary radar reflector such that radar signals reflected by the exemplary radar reflector comprise a signature unique to the exemplary radar reflector in accordance with various embodiments described herein; 
         FIG.  8    illustrates an exemplary radar reflector array comprising a plurality of individual radar reflectors, in accordance with various embodiments; and 
         FIG.  9    illustrates a perspective view of an exemplary radar reflector in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure more fully describes various embodiments with reference to the accompanying drawings. It should be understood that some, but not all embodiments are shown and described herein. Indeed, the embodiments may take many different forms, and accordingly this disclosure should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. 
     It should be understood at the outset that although illustrative implementations of one or more aspects are illustrated below, the disclosed assemblies, systems, and methods may be implemented using any number of techniques, whether currently known or not yet in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, but may be modified within the scope of the appended claims along with their full scope of equivalents. While values for dimensions of various elements are disclosed, the drawings may not be to scale. 
     The words “example,” or “exemplary,” when used herein, are intended to mean “serving as an example, instance, or illustration.” Any implementation described herein as an “example” or “exemplary embodiment” is not necessarily preferred or advantageous over other implementations. 
     Elevator positioning systems may use radar-based distance measurements for accurate and precise determinations of a position of an elevator car within an elevator shaft. As understood by those of skill in the field to which the present disclosure pertains, radar-based distance measurement may rely on emitting radar signals, and detecting and measuring reflections of the radar signals from a radar reflecting surface. However, imperfections in the positioning and installation of radar reflecting surfaces (e.g., reflector plates, reflector slabs) may cause the reflections of the radar signals, or reflected radar signals, to be mis-directed away from a radar transceiver configured to detect the radar signal reflections, or at least cause the reflections of radar signals to be detected with low and inadequate signal strength due to non-normal or non-perpendicular incidence angle of the reflected radar signals at the radar transceiver. In particular, horizontal tilt of radar reflecting surfaces even to the extent of one degree may cause attenuation of detected signal strength of reflected radar signals of between approximately -60 dBm (decibel relative to one milliwatt) to -180 dBm. This attenuating effect is exacerbated as elevator shafts may extend for long distances and elevations. As such, existing reflecting plates and reflecting slabs are required to be installed with minimal horizontal tilt angles, which is difficult at installation even with laser leveling tools and devices. Further, material deformation over time, due to heat and stress for example, may cause a horizontal tilt angle of such existing reflecting plates and reflecting slabs to reach unacceptable values, therefore requiring routine horizontal calibration. 
     Various embodiments described herein relate to a radar reflector configured for use in an elevator positioning system, the radar reflector configured to directly reflect radar signals to a radar transceiver for reliable radar-based measurement with improved signal strength. Direct reflection of radar signals by the radar reflector may be understood by reflected radar signals having approximately parallel trajectories with original, pre-reflection radar signals, such that the reflected radar signals are approximately directed towards the radar transceiver for detection with an approximately normal or perpendicular incidence angle. For instance, in various embodiments, the reflected radar signals have a trajectory different from the trajectory of the original (e.g., pre-reflected) radar signals by less than 5 degrees. In some embodiments, the difference in trajectories of the reflected radar signals and the original radar signals is less than 3 degrees. In some embodiments, the difference in trajectories of the reflected radar signals and the original radar signals is less than 1 degree. In some embodiments, the difference in trajectories of the reflected radar signals and the original radar signals is preferably less than 0.3 degrees. Thus, various embodiments provide a radar reflector configured for direct or parallel reflection of radar signals to enable improved detection of reflected radar signals through improving detected signal strength of the reflected radar signals at the radar transceiver. Use of radar reflectors in accordance with various embodiments described herein therefore improve upon the use of radar-based elevator positioning systems through improvement of the reflection of radar signals for distance determinations. 
     That is, such direct reflection of radar signals back to the radar reflector improves upon radar-based distance measurements in elevator positioning systems, in some examples. Various embodiments provide a radar reflector that that is configured to directly reflect radar signals back to the radar transceiver, even when being tilted or angled to a certain extent, such that radar-based measurements can be used in elevator car positioning. 
     In various embodiments, the radar reflector includes three or more triangular panels to form a pyramidal frustum volume, and direct reflection of radar signals is enabled by the triangular panels being approximately mutually perpendicular. As the volume of the radar reflector is a frustum, the triangular panels do not physically meet at a pyramidal apex, in various embodiments; however, the triangular panels are approximately perpendicular (e.g., forming an angle preferably between 85 degrees and 95 degrees) at a projected (e.g., extended, hypothetical, extrapolated) apex. With the triangular panels being at least approximately mutually perpendicular, a radar signal impacting one panels is reflected towards at least one other panel, at which the radar signal is again reflected at a trajectory substantially parallel with its original trajectory. Thus, the reflected radar signals are directly oriented and travel towards the radar transceiver from which the original radar signals originate. 
     Due to the multi-panel reflection against approximately perpendicular panels, the radar reflector may have horizontal tilt angles to an extent (e.g., at least greater than 0.1 degrees) without causing reflected radar signals to have significantly attenuated signal strength at the radar transceiver. In some embodiments, a radar reflector in accordance with various embodiments described herein may have a horizontal tilt angle (e.g., due to imperfections and misalignment during installation, due to material expansion or deformation over time) of greater than approximately 0.5 degrees without significant signal strength loss of the reflected radar signals at the radar transceiver. In some example embodiments, the radar reflector may have a horizontal tilt angle of greater than approximately 1 degree and less than approximately 5 degrees without significant signal strength loss of the reflected radar signals at the radar transceiver. In some examples, the radar reflector is preferably maintained with a horizontal tilt angle of less than 2 degrees for optimal radar signal reflection. Thus, the radar reflector may have some horizontal tilt without causing the radar signals to be indirectly or mis-directly reflected to a significant extent. 
     As described, the triangular panels are approximately mutually perpendicular at a projected apex, and the projected apex is positioned above an upper plane of the radar reflector. That is, the pyramidal frustum volume of the radar reflector includes a base plane and an upper plane, and the triangular panels of the radar reflector converge towards the upper plane. In various embodiments, the upper plane of the radar reflector is formed by upper vertex portions of each of the triangular panels being folded, bent, and/or the like, and the upper plane is substantially parallel with the base plane. With the radar reflector having a pyramidal frustum volume with a base plane and an upper plane, an overall height of the radar reflector is optimized and minimized. Further, the radar reflector having an upper plane instead of a pyramidal apex enables improved interfacing and attachment of the radar reflector to the elevator shaft or the elevator car, for example. 
       FIG.  1    schematically illustrates an exemplary elevator positioning system  100  according to various embodiments described herein. The elevator positioning system  100  is configured for determining a position (e.g., a height) of an elevator car  105  within the elevator shaft  101 . For example, an elevator positioning system  100  may be configured to determine the relative position (e.g., the relative height) of an elevator car within an elevator shaft as measured in a vertical direction (e.g., a direction extending parallel to a central axis of the elevator shaft along a height of the elevator shaft). In various embodiments, the elevator positioning system  100  is configured to determine the position of the elevator car  105  based at least in part on radar-based distance measurements, specifically measurements of a distance between a radar transceiver  106  and a radar reflector  110 . Thus, in various embodiments, the radar transceiver  106  and the radar reflector  110  are arranged within the elevator shaft  101  such that the elevator positioning system  100  may determine a position of the elevator car  105  within the elevator shaft  101  at a particular instance. 
     Generally, the elevator shaft  101  may comprise an internal shaft portion configured to house an elevator car  105  such that a full range of motion of the elevator car  105  exists within the internal shaft portion of the elevator shaft. As illustrated, the internal shaft portion of the elevator shaft  101  may be defined within a plurality of outer walls of the elevator shaft  101 , such as, for example, a top shaft surface, a bottom shaft surface, and one or more sidewalls extending in a substantially vertical direction between the top shaft surface and the bottom shaft surface. In various embodiments, the elevator shaft  101  comprises one or more rail fixtures  102  attached to one or more sidewalls, and the elevator car  105  is configured to travel in a guided movement along the rail fixtures  102 . For example, the elevator car  105  comprises wheels configured to interface with the rail fixtures  102  for smooth and guided movement of the elevator car  105 . 
     In various embodiments, a shaft height of the elevator shaft  101  may be defined by a distance between the top shaft surface and the bottom shaft surface, as measured in the vertical direction. For example, in various embodiments, one or more of the top shaft surface and the bottom shaft surface may be centered about the central axis of the elevator shaft  101  such that a perpendicular axis extending from a center of the respective surface may be coaxial with the central axis of the elevator shaft  101 . Further, in various embodiments, one or more of the top shaft surface and the bottom shaft surface may comprise at least substantially planar surfaces extending along a horizontal plane. As a non-limiting example, each of the top shaft surface and the bottom shaft surface may extend along a respective horizontal plane such that the top shaft surface and the bottom shaft surface are parallel to one another. In such an exemplary configuration, the height of the elevator shaft may be defined by the distance along the central axis of the elevator shaft  101  between the top shaft surface and the bottom shaft surface. As previously discussed, the elevator positioning system  100  is configured to determine a relative height of the elevator car  105  within the elevator shaft  101 ; for example, the relative height of the elevator car  105  may reference and/or be a fraction of the height of the elevator shaft  101 . 
     In various embodiments, an elevator car  105  disposed within an elevator shaft  101  may be configured in a substantially level configuration wherein a top car surface and a bottom car surface each comprise an at least substantially planar surface extending along respective horizontal planes, each plane being perpendicular to the vertical direction, as described herein. For example, the top car surface and the bottom car surface may be parallel to one another. Further, in various embodiments, the top car surface and the bottom car surface may be parallel to one or more of the top shaft surface and the bottom shaft surface. In various embodiments, the elevator car  105  is substantially level based at least in part on configuration and control of the wheels of the elevator car interfacing with the rail fixtures  102 . 
     As illustrated, in various embodiments, the elevator car  105  may be configured such that the top car surface is arranged in an upward-facing configuration so as to face toward the top shaft surface of the elevator shaft  101  positioned vertically above the elevator car  105 . Further, in various embodiments, the elevator car  105  may be configured such that bottom car surface is arranged in a downward-facing configuration so as to face toward the bottom shaft surface of the elevator shaft  101  positioned vertically beneath the elevator car  105 . In various embodiments, an elevator car  105  may be installed within an elevator shaft  101  in an at least partially suspended configuration such that one or more gravitational forces acting on the elevator car  105  may stabilize the bottom car surface in an at least substantially horizontal configuration perpendicular to the vertical direction. 
     In various embodiments, the elevator car  105  may have a range of motion within the internal shaft portion of the elevator shaft  101  that may be defined in an at least substantially vertical direction by the rail fixtures  102 . With controlled motion of the elevator car  105  (e.g., for delivery of people, cargo, and/or the like between different levels of a building), the position or height of the elevator car  105  within the elevator shaft may be variable over time, and the elevator positioning system  100  is configured to determine a position of the elevator car  105  at different timepoints and to record a time-dependent or time-variable profile of elevator car position. 
     As described herein, in various embodiments, the elevator positioning system  100  may comprise a radar transceiver  106  configured to emit a signal (e.g., a RF wave, a radar wave, and/or the like) and receive a reflection comprising at least a portion of the emitted signal reflected back from a radar reflector  110  of the elevator positioning system  100 . That is, generally, the radar transceiver  106  is configured to transmit original radar signals  112  (e.g., pre-reflection, non-reflected, outbound) and to receive reflected radar signals  114 . As a non-limiting example, in various embodiments, the radar transceiver  106  may comprise a single chip, Frequency Modulation Continuous Wave (FMCW) element be configured to emit a signal comprising a 60 GHz radar wave. In various embodiments, a radar transceiver  106  may be configured to receive reflected radar signals  114  and subsequently transmit transceiver signal data indicative of the detected reflection to a controller. As a non-limiting example, in various embodiments, the radar transceiver  106  may be configured to detect one or more signals present within an elevator shaft (e.g., reflected radar signals  114 ) using a dielectric lens antenna. 
     In various embodiments, a radar transceiver  106  is attached to a surface such that the radar transceiver  106  is disposed within the internal shaft portion of the elevator shaft  101  and arranged in an at least substantially vertical configuration (e.g., facing a vertically upward direction, facing a vertically downward direction). As discussed, the elevator positioning system  100  includes a radar reflector  110  configured to directly reflect radar signals back to the radar transceiver  106 , and the radar reflector  110  is also disposed within the internal shaft portion of the elevator shaft. In particular, the radar reflector  110  and the radar transceiver  106  may be at least substantially vertically aligned. In some embodiments, the radar reflector  110  and the radar transceiver  106  are centered or aligned with respect to a vertical axis (e.g., a central axis of the elevator shaft  101 , a sidewall of the elevator shaft  101 , a rail fixture  102  parallel to a sidewall). As a result, radar signals travelling vertically within the internal shaft portion of the elevator shaft  101  and originating from the radar transceiver  106  may reach and impact at least a portion of the radar reflector  110 . 
     Generally, one of the radar transceiver  106  or the radar reflector  110  is attached to a static surface, such as a surface of the elevator shaft  101 , and the other one of the radar transceiver  106  or the radar reflector  110  is attached to the elevator car  105 . As such, a distance between the radar transceiver  106  and the radar reflector  110  varies based at least in part on the position of the elevator car  105  within the elevator shaft  101 .  FIG.  1    illustrates a non-limiting example in which the radar transceiver  106  is fixedly secured to the top car surface of the elevator car  105  in a vertically upwards orientation, while the radar reflector is fixedly secured near the top shaft surface of the elevator shaft  101  in a vertically downwards orientation. In other non-limiting examples, the radar reflector  110  may be attached to the top car surface of the elevator car  105 , while the radar transceiver  106  may be fixedly attached at or near the top shaft surface of the elevator shaft  101 . In further non-limiting examples, the radar reflector  110  may be attached at a bottom shaft surface of the elevator shaft  101  in an upward-facing configuration, while the radar transceiver  106  may be fixedly attached to the bottom car surface of the elevator car  105  in a downward-facing configuration. In further yet non-limiting examples, the radar reflector  110  may be fixedly attached to a bottom car surface of the elevator car  105  in a downward-facing configuration, while the radar transceiver  106  may be fixedly attached to the bottom shaft surface of the elevator shaft  101  in an upward-facing configuration. Thus,  FIG.  1    illustrates one of many configurations of an elevator positioning system  100   in which one of the radar transceiver  106  and the radar reflector  110  has a fixed relative position within the elevator shaft  101  and the other one of the radar transceiver  106  and the radar reflector  110  is attached to the elevator car  105 , such that a distance between the radar transceiver  106  and the radar reflector  110  corresponds with the position of the elevator car  105 . 
     As illustrated in  FIG.  1   , the radar reflector  110  may have a fixed relative position within the elevator shaft  101  in some configurations of the elevator positioning system  100 , and the radar reflector  110  may be accordingly attached to the elevator shaft via a rail fixture  102 . In various embodiments, the rail fixture  102  comprises an attachment feature  103  that interfaces with an upper plane of the radar reflector  110 . As discussed, the radar reflector  110  is defined with a pyramidal frustum volume having a base plane and an upper plane, and the upper plane advantageously minimizes an overall height of the radar reflector  110  and provides an interfacing platform for attachment to the elevator shaft  101  (e.g., via the attachment feature  103 ) in some configurations, or the elevator car  105  (e.g., via a top car surface, via a bottom car surface) in other configurations. 
       FIG.  2    illustrates a perspective view of an example radar reflector  110  and an attachment feature  103 . In the illustrated embodiment, the attachment feature  103  is configured to be fixedly attached at one end to a rail fixture  102  of the elevator shaft  101 , while interfacing at another end to an upper plane  210  of the radar reflector  110 , such that the radar reflector  110  is fixed at a static position within the elevator shaft  101 . As discussed, in other configurations, the upper plane  210  of the radar reflector  110  may directly interface with a top shaft surface of the elevator shaft  101  or a bottom shaft surface of the elevator shaft  101 , such that the radar reflector  110  is fixed at a static position within the elevator shaft  101 . In other non-limiting example configurations, the upper plane  210  of the radar reflector  110  directly interfaces with a top car surface of the elevator car  105  or a bottom car surface of the elevator car  105 , such that a relative position of the radar reflector  110  within the elevator shaft  101  corresponds to the relative position of the elevator car  105  within the elevator shaft  101 . 
     As illustrated in  FIG.  2   , the radar reflector  110  has a pyramidal frustum geometry and is comprised of three or more triangular panels  205 . In various embodiments, each of the three or more triangular panels  205  are similarly dimensioned. For example, the triangular panels  205  are configured with the same height or length and the same base or width. In the illustrated embodiment, the radar reflector  110  is comprised of three triangular panels  205  such that the pyramidal frustum volume of the radar reflector  110  is based on a triangular pyramid. In other non-limiting examples, the radar reflector  110  is comprised of four triangular panels, thus having a rectangular pyramidal frustum volume. In some embodiments, the radar reflector  110  has an even number of triangular panels  205  greater than three such that each triangular panel  205  has a corresponding opposite panel. 
     Due to the frustum-based geometry of the radar reflector  110 , the radar reflector  110  includes a base plane  215  that is at least substantially parallel with the upper plane  210 . As the triangular panels  205  are angled and converge towards the upper plane  210  in a pyramidal fashion, the base plane  215  of the radar reflector  110  may span a greater area than the upper plane  210 , and the geometry of the base plane  215  of the radar reflector  110  depends at least in part on the number of triangular panels  205 . In the illustrated embodiment, for example, the base plane  215  is triangular due at least in part on the radar reflector  110  comprising three triangular panels  205 . 
     In various embodiments, the radar reflector  110  is configured and oriented such that original radar signals  112  enter an interior volume of the radar reflector  110  through the base plane  215  of the radar reflector  110  and are reflected by interior-facing surfaces of the triangular panels  205 .  FIG.  3    illustrates a perspective view into the interior volume  305  of a radar reflector  110 . As shown, the base plane  215  of the radar reflector  110  is defined by bottom edges  310  of each triangular panel  205 , and in the illustrated embodiment, the base plane  215  is triangular. In various embodiments, the base plane  215  is only circumferentially defined such that the interior volume  305  of the radar reflector  110  is openly accessible. That is, the base plane  215  is not spanned by a panel or some material that would obstruct radar signals from traversing into the interior volume  305  of the radar reflector  110 . As referred to within the context of the present disclosure, orientation of the radar reflector  110  may refer to accessibility of the interior volume of the radar reflector  110  through the base plane  215 . In the illustrated embodiment of  FIG.  2    for example, the radar reflector  110  may be in a downward-facing orientation as the base plane  215  is positioned below the upper plane  210  and the interior volume of the radar reflector  110  is accessible through the base plane  215  from below the radar reflector  110 . 
       FIG.  3    further illustrates configuration of the triangular panels  205  to form the pyramidal frustum volume of the radar reflector  110 . In various embodiments, each of the triangular panels  205  comprise joint features  315  for connection to other triangular panels  205 . Specifically, the joint features  315  are positioned on at least one lateral edge  320  of each triangular panel  205 , and the triangular panels  205  are connected at their lateral edges  320  via the joint features  315  to form the pyramidal frustum volume. In various embodiments, the joint features  315  may comprise a bent or folded tab that planarly interfaces with a surface or a joint feature  315  of another triangular panel  205 . In various other embodiments, the joint features  315  may comprise hinges having channels that align with channels present in another triangular panel  205  and a dowel, rod, screw, nail, and/or the like for securing the alignment of said channels. 
     In various embodiments, the joint features  315  are configured to enable configuration of an angle between two triangular panels  205  along their lateral edges  320  that are connected via the joint features  315 . That is, the joint features  315  may have a rotation mechanism (e.g., via hinging) enabling precise configuration of an angle between two triangular panels  205  along their lateral edges  320 , such as during construction and installation of the radar reflector  110 . Similarly, the joint features  315  may be configured to maintain an established or configured angle between two triangular panels  205  along their lateral edges after construction and installation and during use of the radar reflector  110 . In the illustrated embodiment of  FIG.  3   , the three triangular panels  205  are approximately mutually perpendicular (e.g., preferably forming an angle between 80 degrees and 100 degrees) along their lateral edges  320 , such that the pyramidal frustum volume is similar to a perpendicular corner of three surfaces. Thus, each joint feature  315  between two of the three triangular panels  205  may be configured to enable configuration of a 90 degree angle between the two triangular panels  205  (e.g., during construction, during installation, during calibration) and to maintain the 90 degree angle within a certain degree of freedom or tolerance. 
     Referring now to  FIG.  4   , a schematic outline of triangular panels  205  is provided. As illustrated, each triangular panel  205  includes two lateral edges  320  that are configured to connect with lateral edges  320  of other triangular panels  205  to form a pyramidal frustum volume of the radar reflector  110 . As discussed, one or both of the lateral edges  320  of a triangular panel  205  may include joint features  315  (e.g., tabs to be bent or folded to planarly interface with a surface or a joint feature  315  of another triangular panel  205 ) to enable or aid connection between triangular panels  205 . 
     Each triangular panel  205  additionally includes a bottom edge  310 . When the three or more triangular panels  205  are connected via their lateral edges  320 , the bottom edges  310  of the three or more triangular panels  205  define and outline the base plane  215  of the radar reflector  110 . As such, the geometry of the base plane  215 , or the number of edges defining the base plane  215 , depends upon the total number of triangular panels  205  of the radar reflector  110 . 
     Each triangular panel  205  may be at least substantially isosceles; that is, each lateral edge  320  of a triangular panel  205  may be approximately the same length. In various embodiments, the length of the lateral edges  320  of the triangular panels  205  is approximately 1 meter. In some example embodiments, the length of the lateral edges  320  is between approximately 0.1 meters and approximately 1 meter. In some example embodiments, the length of the lateral edges  320  is between approximately 0.5 meters and approximately 1 meter. In some example embodiments, the length of the lateral edges  320  is between approximately 0.25 meters and approximately 0.75 meters. In some example embodiments, the length of the lateral edges  320  is one of approximately 0.1 meters, approximately 0.2 meters, approximately 0.3 meters, approximately 0.4 meters, approximately 0.5 meters, approximately 0.6 meters, approximately 0.7 meters, approximately 0.8 meters, approximately 0.9 meters, or approximately 1 meter. 
     Each triangular panel  205  then may be at least substantially vertically symmetric. A triangular panel  205  comprises an upper vertex portion  405  located at and including the upper vertex of the triangular panel, the upper vertex formed by the intersection of the two lateral edges  320  of the triangular panel  205 . In various embodiments, the vertex angle  410  spanned by the upper vertex of each triangular panel  205  (e.g., between the lateral edges  320  of the triangular panel  205 ) is based at least in part on the number of triangular panels  205  of the radar reflector  110 . For example, a radar reflector  110  having a large number of triangular panels  205  may require the upper vertex of each triangular panel  205  to span a smaller upper vertex angle  410 . 
     In various embodiments, the upper vertex portions  405  for the three or more triangular panels  205  are configured to form the upper plane  210  of the radar reflector  110 . An upper vertex portion  405  of a triangular panel  205  may be defined as a portion of the triangular panel  205  including the upper vertex and spanning across the triangular panel  205  to a line that is at least substantially parallel with the bottom edge  310  (e.g., the dotted line in  FIG.  4   ). The line to which the upper vertex portion  405  spans may be configured at a height within the triangular panel  205  in order to configure the overall height of the radar reflector  110 . For example, the line being near the upper vertex of a triangular panel  205  and thereby causing the upper vertex portion  405  to span a small area may result in the radar reflector  110  having a larger overall height. 
     In various embodiments, the line defining the upper vertex portion  405  may be between points that are approximately 0.05 meters to approximately 0.1 meters along the lateral edges  320  from the upper vertex. That is, the upper vertex portion  405  may be an approximately 0.05 meter to an approximately 0.1 meter corner of a triangular panel  205 . In some example embodiments, the upper vertex portion  405  spans approximately one-tenth of the lateral edges of one triangular panel  205  (e.g., an approximately 0.1 meter corner of a triangular panel  205  with 1 meter lateral edges). In some example embodiments, the upper vertex portion  405  spans approximately one-fourth of the lateral edges of one triangular panel  205 . In some example embodiments, the upper vertex portion  405  spans between approximately one-twentieth to approximately one-fourth of the lateral edges of one triangular panel  205 . For example, for a triangular panel  205  having approximately one meter lateral edges  320 , the upper vertex portion  405  is defined by a line spanning between points on the lateral edges  320  that are between approximately 0.05 meters to 0.25 meters along the lateral edges  320 . 
     Configuration of the upper vertex portions  405  to form the upper plane  210  of the radar reflector  110  may involve causing an upper vertex portion  405  to be at an angle relative to the remainder of the triangular panel  205  (e.g., along the line bounding the upper vertex portion  405 ). For example, the upper vertex portions  405  of the triangular panels  205  may be bent down, folded down, hinged at an angle, and/or the like. As a result of the upper vertex portions  405  being bent at an angle with their respective triangular panel  205 , the upper vertex portions  405  are planarly parallel when the three triangular panels  205  are connected at their lateral edges  320 . Further, the upper vertex portions  405  may at least substantially overlap when the three triangular panels  205  are connected approximately perpendicularly at their lateral edges  320  such that the upper vertex portions  405  may planarly interface and may be secured. Returning briefly to  FIG.  2   , for example, the illustrated upper plane  210  is formed based at least in part on upper vertex portions  405  of each of the triangular panels  205  being at least substantially planarly parallel and interfacing. In various embodiments, the area spanned by the upper plane  210  is between approximately 0.05 meters squared and approximately 0.15 meters squared. In some example embodiments, the area spanned by the upper plane  210  is approximately 0.1 meters squared. In some example embodiments, the area spanned by the upper plane is approximately 0.1 meters squared to approximately 0.2 meters squared. 
     In various embodiments, the upper plane  210  formed by the upper vertex portions  405  includes a hole for interfacing with the attachment feature  103  of the elevator shaft  101  or with a surface of the elevator car  105 . For example, the upper plane  210  includes a screw hole configured to align with a screw hole of the attachment feature  103  or a screw hold of a surface of the elevator car  105 . As such, the radar reflector  110  is configured to be attached and secured to the elevator shaft  101  or the elevator car  105  via the upper plane  210 . 
     In some embodiments, one or more of the upper vertex portions  405  may instead be removed from the triangular panels  205 , thus forming one or more trapezoidal panels from the triangular panels  205 . The trapezoidal panels are again connected via their lateral edges  320  to form the pyramidal frustum volume of the radar reflector  110 . Due to the removal of the upper vertex portions  405  then, the upper plane  210  may only be circumferentially defined, similar to the base plane  215 . In some embodiments, an upper panel may be laid across the upper edges of the trapezoidal panels to substantively form the upper plane  210 . 
       FIG.  4    further illustrates triangular panels  205  of a radar reflector  110  being efficiently and compactly manufactured. As illustrated, the design and dimensions of the triangular panels  205  can be compactly arranged within a minimized rectangular plane. In various embodiments, the minimized rectangular plane may represent a common material panel  400  from which the triangular panels  205  are formed. A total area required of the common material panel  400  to manufacture multiple triangular panels  205  is then optimized and reduced due to compact arrangement of the multiple triangular panels  205 . Each triangular panel  205  can then be cut or forged from the common material panel  400  without substantial waste of are of the common material panel  400  (e.g., using a metal cutting laser). 
     In various embodiments, the triangular panels  205  are formed from a metal material configured to reflect radar signals and/or any other radar-reflective material, and as such, the common material panel  400  may be comprised uniformly of metal material on at least one surface. In various embodiments, at least one surface of the common material panel  400  may be coated in radar-reflective material, such as radar-reflective paint, to increase reflectiveness of radar signals. 
     As previously discussed, a radar reflector  110  may include more than three triangular panels  205 . Generally, a radar reflector  110  including more than three triangular panels  205  has an even number of triangular panels  205  such that each triangular panel  205  has an opposite and corresponding triangular panel  205 . Thus, a radar reflector  110  may have a number of triangular panel pairs, in various embodiments. 
       FIGS.  5 A-C  illustrate example radar reflectors  110  having more than three triangular panels  205 . In various embodiments, the total number of triangular panels  205  affects the geometry of the base plane  215 . Referring first to  FIG.  5 A , a radar reflector  110  have four triangular panels  205  is illustrated, and the base panel  215  is substantially square-shaped.  FIG.  5 B  illustrates a radar reflector  110  having six triangular panels  205 , and the base panel of the illustrated radar reflector  110  is substantially hexagonal. In  FIG.  5 C , a radar reflector  110  comprising eight triangular panels  205  is illustrated, thereby forming an octagonal pyramidal frustum volume with a base plane  215  that is substantially octagonal. 
     Each pair of triangular panels  205  of a radar reflector  110  having more than three triangular panels  205  (e.g., radar reflectors  110  illustrated in  FIGS.  5 A-C ) is approximately perpendicular at a projected apex.  FIG.  6    illustrates a side view of a pair of two triangular panels  205  of a radar reflector  110  having more than three triangular panels  205 . As illustrated, the pair of two triangular panels  205  of the radar reflector  110  comprises a first triangular panel  205 A and a second triangular panel  205 B. Each triangular panel  205  comprises a respective upper vertex portion  405 , and the upper vertex portions  405  are configured (e.g., bent) at an angle to form the upper plane  210  of the radar reflector. For example, as illustrated, the first upper vertex portion  405 A of the first triangular panel  205 A is planarly parallel and interfacing with the second upper vertex portion  405 B of the second triangular panel  205 B. 
     As discussed, a pair of triangular panels  205  is approximately perpendicular at a projected apex  605  or an extrapolated intersection. As illustrated, the projected apex  505  is a point at which the triangular panels  205  would pyramidally converge if not for the configuration of the upper vertex portions  405  to form a frustum volume with an upper plane  210 . The projected apex  605  is then a point positioned above the upper plane  210  and is hypothetical, extended, extrapolated, and/or the like. 
     Due to the perpendicularity of the first triangular panel  205 A and the second triangular panel  205 B, the radar reflector  110  is configured to directly reflect radar signals. As illustrated in  FIG.  6   , original radar signals  112  may have a trajectory towards the radar reflector  110 , and the original radar signals  112  may impact one of the first triangular panel  205 A or the second triangular panel  205 B. From this impact, the original radar signals  112  become reflected and are directed to impact with the other one of the first triangular panel  205 A or the second triangular panel  205 B. From impact with the other one of the first triangular panel  205 A or the second triangular panel  205 B, reflected radar signals  114  may have a trajectory away from the radar reflector  110  and at least substantially parallel (and opposite) with the trajectory of the original radar signals  112 . 
     Thus, perpendicularity of the triangular panel pair enables direct reflection of radar signals in substantially parallel and opposite trajectories. Advantageously, in some examples, the radar reflector may be horizontally tilted to a certain extent (e.g., inadvertently due to imperfections or misalignments during installation) without significantly mis-directing the reflected radar signals  114  away from the radar transceiver  106 . For example, in contrast with the illustrated embodiment, the original radar signals  112  may have a trajectory that is not exactly normal or perpendicular with the base plane  215  and the upper plane  210  of the radar reflector  110 ; however, the reflected radar signals  114  may have a trajectory with minimal deviation away from the radar transceiver  106 . As such, approximately perpendicularity of the triangular panel pair in the radar reflector  110   enables improved detection of reflected radar signals  114  (e.g., increased signal strength) at the radar transceiver  106 . In various embodiments, the angle between the triangular panel pair at the projected apex  605  is approximately 90 degrees, or approximately perpendicular. In some example embodiments, the angle between the triangular panel pair at the projected apex  605  is between approximately 65 degrees and approximately 115 degrees. In some example embodiments, the angle between the triangular panel pair at the projected apex  605  is between approximately 78 degrees and approximately 102 degrees. In some example embodiments, the angle between the triangular panel pair at the projected apex  605  is preferably between approximately 85 degrees and approximately 95 degrees. 
     In various embodiments, a subset of the triangular panels  205  of a radar reflector  110  may be uniquely configured to cause the radar reflector  110  to reflect radio signals with a unique signature or pattern. Unique configuration of some triangular panels  205  causes unique geometry of the base plane  215 .  FIGS.  7 A-B  illustrate unique configuration of a triangular panel  205  of a radar reflector  110 . In various embodiments, a triangular panel  205  is parallel shifted. Referring first to  FIG.  7 A , a radar reflector  110  having four triangular panels  205  and a square base plane geometry is illustrated. That is, as illustrated, the base plane  215  of the radar reflector  110  is approximately square. Reflected radar signals  114  reflected by the radar reflector  110  may have a particular signal strength, signal pattern, frequency spectrum pattern, frequency peak width, resonant frequencies, and/or the like. 
     The radar reflector  110  illustrated in  FIG.  7 A  may be modified by parallel shifting a particular triangular panel  205 A, as illustrated in  FIG.  7 B . Through parallel shift of the particular triangular panel  205 A, the particular triangular panel  205 A remains approximately perpendicular with an opposite paired triangular panel at a projected apex. Neighboring triangular panels  205  may be configured to have larger widths, wider upper vertex angles, and/or the like. As a result of the parallel shift of the particular triangular panel  205 A, the base plane  215  is approximately rectangular, therefore having less rotational or radial symmetry. Thus, the base plane  215  may be considered to be asymmetric as a result of the unique configuration of a subset of the triangular panels  205  of the radar reflector. The parallel shift of the particular triangular panel  205 A results in greater distance between the particular triangular panel  205 A and its corresponding, opposite, or paired triangular panel  205 . Thus, reflected radar signals  114  that are reflected by the modified radar reflector  110  (e.g., specifically reflected by the particular triangular panel  205 A or its paired triangular panel  205 ) may have a different signal strength, signal pattern, frequency spectrum pattern, frequency peak width, resonant frequencies, and/or the like from reflected radar signals reflected by an unmodified radar reflector  110  (e.g., the radar reflector illustrated in  FIG.  7 A ). 
     Thus, in various embodiments, the radar reflector  110  may be configured with a unique or asymmetric base plane geometry and arrangement of triangular panels  205  in order to provide reflected radar signals  114  with unique characteristics or a unique signature. As such, such a radar reflector  110  may uniquely improve detection of reflected radar signals  114  from the radar reflector  110  by aiding differentiation and distinguishment of the reflected radar signals  114  from other signal noise. 
       FIG.  8    illustrates a radar reflector array  800  comprising multiple radar reflectors  110 . In various embodiments, a radar reflector array  800  spans a wider horizontal area than one radar reflector  110 , and the radar reflector array  800  may be installed within the internal shaft portion of the elevator shaft  101  to maximize reflection of radar signals emitted by the radar transceiver  106 , or to maximize the amount of reflecting surface available to reflect radar signals emitted by the radar transceiver  106 . In particular, the radar reflector array  800  advantageously increases the horizontal area for radar signal reflection while minimizing an overall height of the radar reflector array  800 . Due to the confined space of the internal shaft portion of the elevator shaft  101 , the advantageously minimized height of the radar reflector array  800  minimizes restrictions on the range of motion of the elevator car  105 . Generally then, a first ratio of the horizontal area spanned by the radar reflector array  800  to the height of the radar reflector array  800  is significantly greater than a second ratio of the horizontal area spanned by one radar reflector  110  to the height of one radar reflector  110 . 
     In various embodiments, the height of the radar reflector array  800  is substantially similar to the height of one radar reflector  110 . For example, the radar reflectors  110  of the radar reflector array  800  are positioned in a planar arrangement, or positioned to be horizontally adjacent. In various embodiments, the radar reflectors  110  of the radar reflector array  800  are connected in the arrangement via the bottom edges  310  of the triangular panels  205 . In the illustrated embodiment, six radar reflectors  110  each having three triangular panels  205  (e.g., therefore having triangular base plane geometry) are connected and arranged to form a hexagonal radar reflector array  800 . 
       FIG.  9    illustrates another non-limiting example radar reflector  110 . Similar to previously described radar reflectors in accordance with various embodiments of the present disclosure, the illustrated radar reflector  110  of  FIG.  9    comprises three triangular panels  205 . In particular, the illustrated radar reflector  110  has a pyramidal volume formed from the three triangular panels  205  and having a base plane and an apex  605 . That is, the illustrated radar reflector  110  of  FIG.  9    may be an alternative embodiment to the previously described radar reflectors  110  having pyramidal frustum volumes with a base plane and an upper plane, and in the illustrated embodiment, the radar reflector  110  includes an apex  605  in lieu of an upper plane. Thus, in the illustrated embodiment, the triangular panels  205  of the radar reflector  110  are approximately mutually perpendicular at the apex  605  of the pyramidal volume (e.g., instead of at a projected or extrapolated apex of a pyramidal frustum volume). 
     Due to an absence of an upper plane in the radar reflector  110  of the illustrated embodiment, the radar reflector  110  may be fixedly attached to an attachment feature  103  of the elevator shaft  101  or the elevator car  105  through different or alternative means. In particular, the attachment feature  103  of the elevator shaft  101  may be attached at one end to a rail fixture  102  and may be attached at the other end to an exterior surface of at least one of the triangular panels  205 , as illustrated in  FIG.  9   . 
     In some embodiments, multiple radar reflectors  110  having a pyramidal volume with a base plane and an apex, similar to the radar reflector  110  illustrated in  FIG.  9   , may be arranged horizontally to form a radar reflector array. For example, a radar reflector array such as the example radar reflector array  800  described in the context of  FIG.  8    may be comprised of radar reflectors  110  of pyramidal volumes. In some embodiments, a radar reflector array may comprise one or more radar reflectors  110  having pyramidal frustum volumes and one or more radar reflectors  110  having pyramidal volumes. As aforementioned, a radar reflector array may be particular advantageous in minimizing height while maximizing a horizontal area at which radar signals may be reflected. In an example embodiment, a radar reflector array includes radar reflectors  110  having pyramidal volumes, and the radar reflector array is configured for attachment to an attachment feature of the elevator shaft  101  and/or the elevator car  105  via an exterior-facing surface of at least one of the radar reflectors  110  of the radar reflector array. 
     Generally, various embodiments of the present disclosure provide radar reflectors and arrays or arrangements thereof for improved direction of reflected radar signals, which then improves detection of reflected radar signals for more accurate radar-based distance measurements for an elevator positioning system. Radar reflectors described herein have pyramidal frustum volumes formed by triangular panels, an upper plane, and a base plane. Other example radar reflectors described herein may have pyramidal volumes formed by triangular panels and having a base plane and an apex. The triangular panels are configured to be approximately mutually perpendicular at an apex (e.g., a projected apex above an upper plane of a pyramidal frustum volume, an apex of a pyramidal volume) and/or along lateral edges, which cause reflected radar signals to advantageously have at least substantially parallel trajectories with their original (e.g., pre-reflectional) radar signals. With parallelism between the reflected radar signals and the original radar signals, the reflected radar signals are more precisely directed back to a radar transceiver. As a result, the reflected radar signals are detected with improved signal strength at the radar transceiver. Meanwhile, the pyramidal frustum volume of a radar reflector generally minimizes a height of the radar reflector, enabling compact positioning and installation within an elevator shaft. 
     Many modifications and other embodiments will come to mind to one skilled in the art to which this disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the disclosure is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.