Patent Publication Number: US-2023141288-A1

Title: Communication network base station with rotman lens

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 17/026,253, filed Sep. 20, 2020, which claims priority to U.S. Provisional Patent Application No. 63/032,999, filed Jun. 1, 2020; U.S. Provisional Patent Application No. 63/033,023, filed Jun. 1, 2020; U.S. Provisional Patent Application No. 63/034,675, filed Jun. 4, 2020; U.S. Provisional Patent Application No. 63/034,729, filed Jun. 4, 2020; U.S. Provisional Patent Application No. 63/034,751, filed Jun. 4, 2020; U.S. Provisional Patent Application No. 63/034,769, filed Jun. 4, 2020; and U.S. Provisional Patent Application No. 63/034,937, filed Jun. 4, 2020. The entire contents and disclosure of these applications are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to apparatus and methods of operating a communication network and, more particularly, apparatus and methods of operating a base station in communication network. 
     BACKGROUND 
     The dramatic growth in the number of smartphones, tablets, wearables, and other data-consuming devices, coupled with the advent of enhanced multimedia applications, has resulted in a tremendous increase in the volume of mobile data traffic. According to industry estimates, this increase in data traffic is expected to continue in the coming years and cellular networks might need to deliver as much as 100-1000 times the capacity of current commercial cellular systems. While 4G technologies address some of capacity demands of future mobile broadband users, a mobile broadband user expects to be seamlessly connected all the time, at any location, to any device. This poses stringent requirements on the fifth generation (5G) network, which must provide users with a uniform and seamless connectivity experience regardless of where they are and what device/network they connect to. 
     Existing 5G system architecture, and specifically 5G base stations, suffer from low energy efficiency and thus consume large amounts of power, when parameters such a spectral efficiency, number of users, number of radio frequency chains, are set to be equal. 
     SUMMARY 
     In one example, a base station for a communication network is provided. The base station comprises at least one transmit planar component and at least one receive planar component. Each of the planar components includes a first end, a second end located opposite the first end, a cavity space and M number of antennas. The cavity space is bounded by B number of beam ports along a first side of the cavity space and by M number of array ports along a second side of the cavity space. The cavity space is in operative communication with the beam ports and with the array ports to form a Rotman lens. The M number of antennas are arranged in an array and are located along the second end of the planar component. Each of the antennas is in operative communication with a corresponding one of the array ports. 
     In general, in some aspects, the subject matter of the present disclosure encompasses a base station for a communication network, in which the base station includes at least one transmit component, and at least one receive component, each of the transmit components of the at least one transmit component and each of the receive components of the at least one receive components including a corresponding: a first end; a second end located opposite the first end; a cavity space bounded by a plurality of beam ports along a first side of the cavity space and by a plurality of array ports along a second side of the cavity space, the cavity space being in operative communication with the beam ports and with the array ports to form a Rotman lens; and multiple antennas that are arranged in an array and are located along the second end, in which each antenna of the multiple antennas is in operative communication with a different corresponding array port of the plurality of array ports. 
     Implementations of the base station can include one or more of the following features. For example, in some implementations, the base station includes: multiple radio frequency (RF) chains; a signal processor coupled to the plurality of RF chains; a transmit matrix switch operatively coupled to the signal processor and to the at least one transmit component; and a receive matrix switch operatively coupled to the signal processor and to the at least one receive component, in which the signal processor is in operative communication with the transmit matrix and the receive matrix through the plurality of RF chains. 
     The at least one RF chain of the multiple RF chains can include both a digital-to-analog converter and an up converter or both an analog-to-digital converter and a down converter. 
     In some implementations, a number of antennas is selected such that a half power beamwidth of each antenna of the multiple antennas is 1.5 degree or less. The half power beamwidth of each antenna of the multiple antennas can be about 1 degree. 
     In some implementations, the number of antennas is 88. 
     In some implementations, a number of beam ports for the at least one transmitting component is 88 and a number of beam ports for the at least one receiving component is 32. 
     In some implementations, each of the at least one transmit component and the at least one receive component further includes: a first set of waveguides extending between the first end and the beam ports; and a second set of waveguides extending between the array ports and the second end. 
     In some implementations, the at least one transmit component, and the at least one receive component are planar components. 
     In general, in another aspect, the subject matter of the present disclosure encompasses a base station for a communication network. The base station includes an analog beamforming section that includes at least one transmit component, and at least one receive component, each transmit component of the at least one transmit component and each receive component of the at least one receive component including a corresponding: a first end; a second end located opposite the first end; a cavity space bounded by multiple beam ports along a first side of the cavity space and by multiple array ports along a second side of the cavity space, the cavity space being in operative communication with the beam ports and with the array ports to form a Rotman lens; and multiple antennas that are arranged in an array and are located along the second end, in which each antenna of the multiple antennas is in operative communication with a different corresponding array port of the multiple array ports. 
     Implementations of the foregoing base station can include one or more of the following features. For example, in some implementations, the base station includes a digital beamforming section that includes: multiple radio frequency (RF) chains; and a signal processor coupled to the multiple RF chains. The analog beamforming section further can include: a transmit matrix switch operatively coupled to the signal processor and to the at least one transmit component, and a receive matrix switch operatively coupled to the signal processor and to the at least one receive component, in which the signal processor is in operative communication with the transmit matrix and the receive matrix through the multiple RF chains. In some implementations, the at least one RF chain of the multiple RF chains includes both a digital-to-analog converter and an up converter or both an analog-to-digital converter and a down converter. 
     In some implementations, a number of antennas is selected such that a half power beamwidth of each antenna of the multiple antennas is 1.5 degree or less. The half power beamwidth of each antenna of the multiple antennas can be about 1 degree. 
     In some implementations, the number of antennas is 88. 
     In some implementations, a number of beam ports for the at least one transmit component is 88 and a number of beam ports for the at least one receive component is 32. 
     In some implementations, each of the at least one transmit component and the at least one receive component further includes: a first set of waveguides extending between the first end and the beam ports; and a second set of waveguides extending between the array ports and the second end. 
     In some implementations, the at least one transmit component, and the at least one receive component are planar components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. 
         FIG.  1    is a schematic representation of an example embodiment of a radar system in accordance with the present disclosure. 
         FIG.  2    is a schematic illustration of an example embodiment of a front end including a transmit module and a receive module. 
         FIG.  3    is a schematic illustration of an example embodiment of a transmit planar component and a receive planar component. 
         FIG.  4    is a schematic illustration of an example embodiment of a half block of a transmit planar component and a half block of a receive planar component where waveguides and a Rotman lens are formed thereon. 
         FIG.  5    is a schematic illustration of a close-up view of an example embodiment of a polarization rotator on the half block of the transmit planar component. 
         FIG.  6    is a schematic illustration of an example polarization rotator including a first section, an iris section and a second section. 
         FIG.  7 A  is a schematic illustration of a cross-sectional view across an example first section of a polarization rotator of a planar component. 
         FIG.  7 B  is a schematic illustration of an example polarization of waves in a first section of a polarization rotator. 
         FIG.  8 A  is a schematic illustration of a cross-sectional view across an example iris section of the polarization rotator of the planar component; 
         FIG.  8 B  is a schematic representation of an example of polarization of waves in the iris section of the polarization rotator; 
         FIG.  9 A  is a cross-sectional view across the second section of the polarization rotator of a planar component; 
         FIG.  9 B  is a schematic representation of an example of polarization of waves in the second section of the polarization rotator; 
         FIG.  10    is a schematic illustration of an example embodiment of a front end where a Rotman lens and a transmission lines are formed with microstrips; 
         FIG.  11    is a schematic illustration of an example embodiment of a half block of a planar component for a front end device including a Rotman lens with sidewall absorbers; 
         FIG.  12    shows a computer graphic illustration of an example embodiment of a fixture to test performance of a sidewall absorber; 
         FIG.  13    is a graph showing the minimum reflection (S 11 ) and the maximal transmission (S 12 ) for the iris section for given dimensions of the iris section; 
         FIG.  14    is an illustration of reflections around example triangular teeth of sidewall absorbers of the Rotman lens; 
         FIG.  15    is a schematic illustration of an example base station implementing the Rotman lens; 
         FIG.  16    is a graph plotting energy efficiency versus spectral efficiency for base stations supporting 200 beams and implemented with various types of technology; and 
         FIG.  17    is a graph plotting energy efficiency versus spectral efficiency for base stations support 8 beams and implemented with various types of technology. 
     
    
    
     DETAILED DESCRIPTION 
     Range-finding systems use reflected waves to discern, for example, the presence, distance and/or velocity of objects. Radio Detection And Ranging (radar) and other rangefinding systems have been widely employed in applications, by way of non-limiting example, in autonomous vehicles such as self-driving cars, as well as in wireless communications modems of the type employed, such as in Massive-MIMO (multiple-in-multiple-out) networks, 5G wireless telecommunications, all by way of non-limiting example. 
     The radar system may include optimized RF front-end device(s) aiding in achieving higher resolution by improving azimuth resolution, elevation resolution, or any combination thereof. Azimuth resolution is the ability of a radar system to distinguish between objects at similar range but different bearings. Elevation resolution is the ability of a radar system to distinguish between objects at similar range but different elevation. Angular resolution characteristics of a radar are determined by the antenna beam-width represented by the −3 dB angle which is defined by the half-power (−3 dB) points. In some embodiments, radar system or phased array system disclosed herein may have a −3 dB beam-width of 1.5 degree or less in both azimuth resolution and elevation resolution. In particular, the radar system can be configured to achieve finer azimuth resolution and elevation resolution by employing an RF front-end device having two linear antennas arrays arranged perpendicularly and a Rotman lens as a phase shifting network, as will be described below. 
       FIG.  1    shows a schematic illustration of an example radar system  100  having the abovementioned functionalities. The radar system  100  may include a millimeter wave radar that emits a low power millimeter wave operating at 76-81 GHz (with a corresponding wavelength of about 4 mm). The radar system can also operate at other frequency ranges that are below 76 GHz or above 81 GHz. The radar system may comprise any one or more elements of a conventional radar system, a phased array radar system, an AESA (Active Electronically Scanned Array) radar system, a synthetic aperture radar (SAR) system, a MIMO (Multiple-Input Multiple-Output) radar system, and/or a phased-MIMO radar system. 
     A conventional radar system may be a radar system that uses radio waves transmitted by a transmitting antenna and received by a receiving antenna to detect objects. A phased array radar system may be a radar system that manipulates the phase of one or more radio waves transmitted by a transmitting and receiving module and uses a pattern of constructive and destructive interference created by the radio waves transmitted with different phases to steer a beam of radio waves in a desired direction. 
     The radar system  100  may be provided on a movable object to sense an environment surrounding the movable object. Alternatively, the radar system may be installed on a stationary object. 
     A movable object can be configured to move within any suitable environment, such as in air (e.g., a fixed-wing aircraft, a rotary-wing aircraft, or an aircraft having neither fixed wings nor rotary wings), in water (e.g., a ship or a submarine), on ground (e.g., a motor vehicle, such as a car, truck, bus, van, motorcycle, bicycle; a movable structure or frame such as a stick, fishing pole; or a train), under the ground (e.g., a subway), in space (e.g., a spaceplane, a satellite, or a probe), or any combination of these environments. The movable object can be a vehicle, such as a vehicle described elsewhere herein. In some embodiments, the movable object can be carried by a living subject, or taken off from a living subject, such as a human or an animal. 
     In some cases, the movable object can be an autonomous vehicle which may be referred to as an autonomous car, driverless car, self-driving car, robotic car, or unmanned vehicle. In some cases, an autonomous vehicle may refer to a vehicle configured to sense its environment and navigate or drive with little or no human input. As an example, an autonomous vehicle may be configured to drive to any suitable location and control or perform all safety-critical functions (e.g., driving, steering, braking, parking) for the entire trip, with the driver not expected to control the vehicle at any time. As another example, an autonomous vehicle may allow a driver to safely turn their attention away from driving tasks in particular environments (e.g., on freeways), or an autonomous vehicle may provide control of a vehicle in all but a few environments, requiring little or no input or attention from the driver. 
     In some instances, the radar systems may be integrated into a vehicle as part of an autonomous-vehicle driving system. For example, a radar system may provide information about the surrounding environment to a driving system of an autonomous vehicle. An autonomous-vehicle driving system may include one or more computing systems that receive information from a radar system about the surrounding environment, analyze the received information, and provide control signals to the vehicle&#39;s driving systems (e.g., steering wheel, accelerator, brake, or turn signal). 
     The radar system  100  that may be used on a vehicle to determine a spatial disposition or physical characteristic of one or more targets in a surrounding environment. The radar system may advantageously have a built-in predictive model for object recognition or high-level decision making. For example, the predictive model may determine one or more properties of a detected object (e.g., materials, volumetric composition, type, color, etc.) based on radar data. Alternatively or additionally, the predictive model may run on an external system such as the computing system of the vehicle. 
     The radar system may be mounted to any side of the vehicle, or to one or more sides of the vehicle, e.g. a front side, rear side, lateral side, top side, or bottom side of the vehicle. In some cases, the radar system may be mounted between two adjacent sides of the vehicle. In some cases, the radar system may be mounted to the top of the vehicle. The system may be oriented to detect one or more targets in front of the vehicle, behind the vehicle, or to the lateral sides of the vehicle. 
     A target may be any object external to the vehicle. A target may be a living being or an inanimate object. A target may be a pedestrian, an animal, a vehicle, a building, a sign post, a sidewalk, a sidewalk curb, a fence, a tree, or any object that may obstruct a vehicle travelling in any given direction. A target may be stationary, moving, or capable of movement. 
     A target object may be located in the front, rear, or lateral side of the vehicle. A target object may be positioned at a range of about 1, 2, 3, 4, 5, 10, 15, 20, 25, 50, 75, or 100 meters from the vehicle. A target may be located on the ground, in the water, or in the air. A target object may be oriented in any direction relative to the vehicle. A target object may be orientated to face the vehicle or oriented to face away from the vehicle at an angle ranging from 0 to 360 degrees. 
     A target may have a spatial disposition or characteristic that may be measured or detected. Spatial disposition information may include information about the position, velocity, acceleration, and other kinematic properties of the target relative to the terrestrial vehicle. A characteristic of a target may include information on the size, shape, orientation, volumetric composition, and material properties, such as reflectivity, material composition, of the target or at least a part of the target. 
     A surrounding environment may be a location and/or setting in which the vehicle may operate. A surrounding environment may be an indoor or outdoor space. A surrounding environment may be an urban, suburban, or rural setting. A surrounding environment may be a high altitude or low altitude setting. A surrounding environment may include settings that provide poor visibility (night time, heavy precipitation, fog, particulates in the air). A surrounding environment may include targets that are on a travel path of a vehicle. A surrounding environment may include targets that are outside of a travel path of a vehicle. A surrounding environment may be an environment external to a vehicle. 
     Referring to  FIG.  1   , in some embodiments, the radar system  100  may comprise a front end in which at least two phased array modules are arranged perpendicularly with each other and the received signals are processed by the correlator of the phased array module. The processed data (e.g., post correlated data) may further be processed by a signal analysis module  101  for object recognition, constructing point cloud image data and other analysis. In some embodiments, a phased array module of the front end  10  may comprise a transmit logic  12 , receive logic  14  and correlation logic  16  illustrated in  FIG.  1   . The phased array module and SERDES may include those described in U.S. Pub. No. 2018/0059215 entitled “Beam-Forming Reconfigurable Correlator (Pulse Compression Receiver) Based on Multi-Gigabit Serial Transceivers (SERDES)”, which is incorporated by reference herein in its entirety. 
     For example, the transmit logic  12  may comprise componentry of the type known in the art for use with radar systems (and particularly, for example, in pulse compression radar systems) to transmit into the environment or otherwise a pulse based on an applied analog signal. In the illustrated embodiment, this is shown as including a power amplifier  18 , band pass filter  20  and transmit antenna  22 , connected as shown or as otherwise known in the art. 
     The receive logic  14  comprises componentry of the type known in the art for use with RADAR systems (and particularly, for example, in pulse compression RADAR systems) to receive from the environment (or otherwise) incoming analog signals that represent possible reflections of a transmitted pulse. In point of fact, those signals may often include (or solely constitute) noise. In the illustrated embodiment, the receive logic includes receive antenna  24 , band pass filter  26 , low noise amplifier  28 , and limiting amplifier  30 , connected as shown or as otherwise known in the art. 
     The correlation logic  16  correlates the incoming signals, as received and conditioned by the receive logic  14 , with the pulse transmitted by the transmit logic  12  (or, more aptly, in the illustrated embodiment, with the patterns on which that pulse is based) in order to find when, if at all, there is a high correlation between them. Illustrated correlation logic comprises serializer/deserializer (SERDES)  32 , correlator  34  and waveform generator  36 , coupled as shown (e.g., by logic gates of an FPGA or otherwise) or as otherwise evident in view of the teachings hereof. 
       FIG.  2    illustrates an example embodiment of a front-end apparatus for a millimeter wave radar. A millimeter wave radar may emit a low power millimeter wave operating at 76-81 GHz (with a corresponding wavelength of about 4 mm). The radar system can also operate at other frequency range that is below 76 GHz or above 81 GHz. The radar system may comprise any one or more elements of a conventional radar system, a phased array radar system, an AESA (Active Electronically Scanned Array) radar system, a synthetic aperture radar (SAR) system, a MIMO (Multiple-Input Multiple-Output) radar system, and/or a phased-MIMO radar system. A conventional radar system may be a radar system that uses radio waves transmitted by a transmitting antenna and received by a receiving antenna to detect objects. 
     As shown in  FIG.  2   , the front-end apparatus may include phased array modules, i.e., a transmit module  40  and a receive module  42 . Each phased array module may include a front end device and a phased array logic. Specifically, the transmit module may include a transmit front end device  40   a  and a transmit logic  12  while the receive module may include a receive front end device  42   a  and a receive logic  14 . Each of the transmit front end device  40   a  and the receive front end device  42   a  may be embodied as a planar component such that the transmit front end device  40   a  and the receive front end device  42   a  include a transmit planar component and a receive planar component respectively.  FIG.  3    shows the transmit planar component  41  and the receive planar component  43  in isolation. Moreover, each of the planar components  41 ,  43  may be operatively connected with the corresponding phased array logic  12  or  14  by including, for example, a slot  44  ( FIG.  3   ) to accommodate the corresponding phased array logic. 
     The planar component  41 / 43  may be embodied in the form of a rectangular substrate or plate, as shown in  FIG.  3   , and may include a first end  41   a / 43   a  and a second end  41   b / 43   b  that are located on opposite longitudinal ends of the rectangular substrate. The first end  41   a / 43   a  of the planar component  41 / 43  may be operatively connected to the phased array logic  12 / 14  at the slot  44 , and the second end  41   b / 43   b  of the planar component  41 / 43  may include an array of antennas  22 / 24 . The phased array logic  12 / 14  may connect to the planar component  41 / 43  at the slot  44  forming a right angle near the first end  41   a / 43   a . The array of transmit antennas  22  and the array of receive antennas  24  may be perpendicular to one another if the transmit planar component  41  and the receive planar component  43  are arranged to be perpendicular to one another ( FIGS.  2 - 4   ). 
     The planar component  41 / 43  may formed from a split block assembly in that the planar component  41 / 43  is formed by assembling a plurality of blocks. For example, the planar component  41 / 43  may be formed from half blocks  48 / 49  that substantially mirror one another along a plane that divides the planar component  41 / 43  in half thereby forming two symmetrical halves.  FIG.  4    only shows one of the two half blocks  48 / 49 . 
     The inner surfaces of the blocks of the planar components  41 / 43  are formed with recesses or cavities that form the inner structure of the planar components  41 / 43  as will be described below. The recesses or cavities on the blocks  41   a / 43   a  may be formed by a variety of manufacturing methods known in the art (e.g., computer numerical control (CNC) machining, injection molding, or the like) capable to achieving desired fabrication tolerances. As shown in  FIGS.  5 - 6   , some curved surfaces (i.e., chamfers) may remain on the planar components  41 / 43  due to the non-zero diameter of the end bit of the CNC milling machine which may be 20 mils, for example. 
     The planar component  41 / 43  may be made of metals (e.g., aluminum), metallic alloys, thermoplastics, other materials known in the art, or a combination thereof. For example, the planar component  41 / 43  may be made of thermoplastics primarily, and be plated or coated with metals (e.g., gold) or metallic alloys to reduce weight. 
     In some embodiments, a phased array module  40 / 42  may include a phase shifting network in the RF front-end device. In some embodiments, the phase shifting network may be implemented using a Rotman lens (e.g., see Rotman lens  23  in  FIG.  1   ), which may be interposed between the phased array logic (e.g., the transmit logic  12  or the receive logic  14  in  FIG.  1   ) and the array of multiple transmit antennas (e.g., antennas  22 / 24  in  FIG.  1   ). In some cases, the RF front-end device may comprise a phase shifting network, such as the Rotman lens  23 , and a linear antennas array. 
     The transmit antennas  22  and/or the receive antennas  24  can be any suitable type of antennas. For example, the antennas  22 / 24  may be a microstrip patch array, Vivaldi antennas, slot coupled patches, horns and others. In some embodiments, the antennas  22 / 24  may be microstrip bipodal vivaldi antennas that are fed by the Rotman lens  23 . For example, the antennas array may be coupled to the array ports of the Rotman lens  23  on a one-to-one basis. 
       FIG.  4    is a schematic illustration of an example embodiment of a half block of a transmit planar component and a half block of a receive planar component where waveguides and a Rotman lens are formed thereon. The Rotman lens shown in  FIG.  4    is an example of the Rotman lens  23  shown in  FIG.  1    and may include a cavity space  50 , and a perimeter of the cavity space  50  may include a first side, a second side that is opposite the first side, a third side, and a fourth side that is opposite the third side. Input ports or beam ports  50   a  may be located on the first side while output ports or array ports  50   b  may be located on the second side of the cavity space  50 . The Rotman lens may be configured such that the beam ports  50   a  are near the first end  41   a / 43   a  of the planar component  41 / 43  while the array ports  50   b  are near the second end  41   b / 43   b  thereof. 
     If one of the beam ports  50   a  is excited, the electromagnetic waves will be emitted into the cavity space  50  and will reach a corresponding one of array ports  50   b . The shape of contour with the array ports  50   b  and the length of waveguides  52 , which connect the ends  41   a / 41   b / 43   a / 43   b  of the planar component  41 / 43  and the ports  50   a / 50   b , are determined so that, a progressive phase taper is created on the array antennas  22 / 24  and thus a beam is formed at a particular direction in the space. 
     In the present embodiment, the Rotman lens for the transmit front end device  40   a  has 63 beam ports and 72 array ports, while the Rotman lens for the receive front end device  42   a  has 30 beam ports and 72 array ports. Moreover, the front end  10  has an azimuth scanning angle of 50 degrees and an elevation scanning angle of 40 degrees. These values may vary depending on how the Rotman lens is embodied. Moreover, the front end  10  may include 72 transmit antennas and 72 receive antennas where the antennas  22 ,  24  are equidistantly spaced apart from one another. 
     The Rotman lens may serve as a robust and low-cost broadband phase shifting network for the disclosed RF front-end devices  40   a / 42   a  and structures. In these cases, active circuitry may be integrated with the beam ports of the Rotman lens, and the lens itself may then be optimized to provide accurate phasing. In accordance with another aspect of the disclosure, some embodiments may include a Rotman lens with enhanced focusing functionality to provide the phasing with low power loss. 
     The third side and the fourth side of the Rotman lens may include dummy ports or sidewall absorbers  50   c ,  50   d , such as radio frequency absorbers, are formed to suppress reflections from the sides of the Rotman lens. The radio frequency absorbers may be made of wave absorbing materials such as Eccosorb® MCS, LS26 or BSR. 
       FIGS.  4  and  11    illustrate embodiments of the Rotman lens with jagged sidewall absorbers  50   c ,  50   d . Sidewall absorbers  50   c ,  50   d  having shapes shown in  FIG.  11    may be effective at attenuating the wavefront of the incident pulses. The shape of the sidewall absorbers  50   c ,  50   d  may include a plurality of sharp triangular “teeth.” As shown in  FIG.  14   , these triangular teeth  64  may be formed such that the imaginary lines  62  extending between adjacent vertices of the triangular teeth  64  pointing into the cavity space  50  of the Rotman lens, may be oriented to be substantially normal to the curvature of the wavefront. Under such a configuration, a substantial amount of energy may be captured in-between the teeth  64  thereby allowing for an effective dissipation by the sidewall absorbers  50   c ,  50   d , as observable in  FIG.  14   . 
     The properties of a sidewall absorber  50   c / 50   d  may be tested on a fixture  66  a simulated embodiment of which is illustrated in  FIG.  12   . The properties of a sidewall absorber  50   c / 50   d  may be tested on the fixture  66  by feeding a signal into the fixture through its input waveguide port and measuring the reflection coefficient S 11  on a Network Analyzer with waveguide millimeter-wave test heads, a simulated embodiment of which is illustrated in  FIG.  12   . Specifically, by emitting waves through the slot  68  towards the triangular teeth  64  of a sidewall absorber  50   c / 50   d  secured in a depression of the fixture  66  and measuring the amount of reflection from the triangular teeth  64 , it is possible to test the effectiveness of the sidewall absorber  50   c / 50   d.    
     As shown in  FIG.  10   , the Rotman lens  23  can be implemented using waveguides, microstrip, stripline technologies or any combination of the above. In some embodiments, the Rotman lens may be microstrip-based Rotman lens. In some embodiments, the Rotman lens  23  may be a waveguide-based Rotman lens. In some cases, waveguides may be used in place of transmission lines. 
     In the embodiments of  FIGS.  4 - 9 B , the planar component  41 / 43  further includes waveguides  52  between the first end  41   a / 43   a  and the beam ports  50   a  and between the array ports  50   b  and the second end  41   b / 43   b . The waveguides  52  may be embodied as rectangular waveguides integrated into the planar component  41 / 43  such that the waveguides  52  form walls that guide the propagation of electromagnetic waves through the planar component  41 / 43  during transmission or reception of antenna signals from the first end  41   a  to the second end  41   b  or vice versa. 
     Each of the waveguides  52  may provide a hollow space through which the electromagnetic waves propagate. While  FIGS.  5 - 6    show only one half of the hollow space of the waveguides  52 , the hollow space of the half blocks  48 / 49  may form an enclosed space that extends along the planar component  41 / 43  and may take on various geometries to affect the polarization of the waves at different locations of the front end device  40   a / 42   a . Specifically, the shape of the cross-section of the hollow space may be described based on a reference rectangular cross-section  54  with a given width in the width directions and a given height in the height directions. The waveguide  52  may include a section where the cross-section of the hollow space is as large as the reference rectangular cross-section  54  or smaller than the reference rectangular cross-section  54  as will be described below. 
     Each of the waveguides  52  of the Rotman lens  23  may further include a polarization rotator  56  to control the polarization of the waves out of and into the phased array logics.  FIGS.  5 - 6    show an example embodiment of the polarization rotator  56  integrated onto the waveguides  52 . The polarization rotator  56  may include a first section  56   a , an iris section  56   b , and a second section  56   c  which are continuously arranged in a longitudinal direction of the planar component  41 / 43 . 
       FIG.  5    shows an inner side of a half block  48  of the transmit planar component  41  where the polarization rotator  56  is formed near the first end  41   a . The polarization rotator  56  may be similarly formed near the first end  43   a  of the receive planar component  43 . In the first section  56   a  of the polarization rotator  56  ( FIGS.  7 A- 7 B ), the waveguide  52  may include a first set of cuboid obstructions  58   a  that protrude into the hollow space in opposite height directions such that the height of the cross-section of the first section  56   a  is less than the given height of the reference rectangular cross-section  54  while the width of the cross-section of the first section  56   a  may be the same as the given width of the reference rectangular cross-section  54 . Such height and width may be substantially constant throughout the first section  56   a  in the longitudinal directions. 
     In the iris section  56   b  of the polarization rotator  56  ( FIGS.  8 A- 8 B ), the waveguide  52  may include a diagonal set of cuboid obstructions  58   b  that protrude into the hollow space from diagonally opposite corners of the reference rectangular cross-section  54  such that an octagonal, cross-sectional area of the iris section  56   b  is obtained. This cross-sectional area of the iris section  56   b  may be substantially constant throughout the iris section  56   b  in the longitudinal directions. 
     It should be noted that  FIG.  8 A  shows a cross-section across the iris section  56   b  of the polarization rotator  56  observed from the viewpoint of the first section  56   a  such that the second section  56   c  is visible behind the iris section  56   b  while  FIG.  8 B  shows a cross section across the iris section  56   b  of the polarization rotator  56  observed from the viewpoint of the second section  56   c  such that first section  56   a  is visible behind the iris section  56   b.    
     In the second section  56   c  of the polarization rotator  56  ( FIGS.  9 A- 9 B ), the waveguide  52  may include a second set of cuboid obstructions  58   c  that protrude into the hollow space from opposite width directions such that the width of the cross-section of the second section  56   c  is less than the given width of the reference rectangular cross-section  54  while the height of the cross-section of the second section  56   c  may be the same as the given height of the reference rectangular cross-section  54  ( FIG.  9 A ). Such height and width may be substantially constant throughout the second section  56   c  in the longitudinal directions. 
     Various dimensions of the iris section  56   b  ( FIG.  6   ) can affect different parameters of the radar system. The height  60   a  of the cuboid obstructions  58   b  in the iris section  56   b  can be used to tune total effective bandwidth and can affect a balance between bandwidth and central band frequency. The length  60   b  of the cuboid obstructions  58   b  of the iris section  56   b  can be used to tune the effective band center. The gap  60   c  of the iris section  56   b , which is measured between a sidewall of the cuboid obstructions  58   b  and a sidewall of the second section  56   c , can affect both the bandwidth and insertion loss of the polarization rotation. In one example embodiment, the height  60   a  of the cuboid obstructions  58   b  of the iris section  56   b , the length  60   b  of the cuboid obstructions  58   b  of the iris section  56   b , and the gap  60   c  of the iris section  56   b  may respectively be 0.017 in., 0.094 in., and 0.035 in. Moreover, the entire length of the polarization rotator that is the combined length of the first section  56   a , the iris section  56   b , and the second section  56   c  may be less than 2λ where λ is equal to a wavelength of the waves traveling through the front end. 
     The aforementioned dimensions of the iris section  56   b  may affect the performance of the antenna which may be described in terms of S-parameters (where SNM represents the power transferred from Port M to Port N in a multi-port network), as shown in the graph of  FIG.  13   . In one embodiment of the iris section  56 , the dimensions of the iris section  56   b  may control the locations of a minima of S 11  (minimum reflection) and a maxima of S 21  (maximum transmission) as well as the beamwidth. In the example of  FIG.  13   , S 11  has a minima of about −31.019899 dB at 78.5 GHz while S 21  has a maxima of about −0.00099132481 dB. 
     Due to the complex interaction of the tuning parameters, a systematic tuning approach to getting the needed bandwidth, central frequency and insertion loss are needed when designing the polarization rotator  56 . The process for tuning should be to pick nominal values for the three aforementioned parameters. Nominal values are based on the waveguide  52  selected and are typically ¼ to 1 times the waveguide long dimension depending on the parameter. Once nominal values are chosen length for the iris section should be tuned to achieve the needed central frequency response. After central frequency response is achieved, the height of the cuboid obstruction  58   b  should be tuned to get the desired bandwidth and insertion loss. If bandwidth and insertion loss are not achieved, the gap of the iris section  56   b  can be changed to help insertion loss. The gap of the iris section should typically be 30-50% of the long dimension of the waveguide  52 . Deviations from this lead to very narrow bandwidths or high insertion loss. Once the desired insertion loss and bandwidth are achieved a re-tune of the length of the iris section will shift the central frequency back to the desired position from the shift due to adjustments to parameters such as the height of the cuboid obstructions  58   b  and the gap  60   c  of the iris section  56 . 
     As shown in  FIG.  4   , the waveguides  52  extending between the first end  41   a / 43   a  and the beam ports  50   a  of the Rotman lens  23  may form a first set of waveguides  52   a  in the transmit planar component  41  and the receive planar component  43 . Each waveguide in the first set of waveguides  52   a  may further include one or more polarization rotator(s)  56 . In the present embodiment of the front end  10 , each waveguide in the first set of waveguides  52   a  in the transmit planar component  41  and the receive planar component  43  includes a first polarization rotator  56 A where the first section  56   a  of the first polarization rotator  56  is located nearer the first end  41   a  than the second section  56   c  thereof. 
     As further shown in  FIG.  4   , the waveguides  52  extending between the second end  41   b / 43   b  and the array ports  50   b  of the Rotman lens  23  in the transmit planar component  41  and in the receive planar component  43  may form a second set of waveguides  52   b . Each waveguide  52  in the second set of waveguides  52   b  in the receive planar component  43  may further include one or more polarization rotator  56 . In the present embodiment of the front end  10 , each waveguide in the second set of waveguides  52   b  in the receive planar component  43  includes a second polarization rotator  56 B which is positioned adjacent the array of antennas  22 / 24  and in which the first section  56   a  of the polarization rotators  56  is nearer the second end  43   b  than the second section  56   c  thereof. 
     The electromagnetic waves propagating through the present apparatus may be in the Transverse Electric (TE)  10  mode. The polarization of the waves may be altered by the polarization rotators  56  located throughout the transmit front end device  40   a  and the receive front end device  42   a.    
     Waves originating from the transmit logic  12  are polarized to be perpendicular to the plane of the Rotman lens  23  ( FIG.  7 B ) but undergo a 90-degree polarization rotation or twist to become polarized parallel to the plane of the Rotman lens ( FIG.  9 B ) as the waves propagate through the first polarization rotators  56 A of the first set of waveguides  52   a  of the transmit planar component  41 . Specifically, the waves move through the first polarization rotator  56 A (i.e., the first section  56   a , the iris section  56   b  and the second section  56   c  thereof), and the E-plane of the waves is polarized to be parallel to the plane of the Rotman lens  23  of the transmit planar component  41 . Thereafter, the polarization of the waves may be unchanged by propagation through the rest of the transmit front end device  40   a , including the Rotman lens  23 , before being transmitted from the transmit antennas  22 . If the transmit planar component  41  is oriented to be horizontal about the ground, the polarization of the waves would change from vertical to horizontal in the transmit front end device  40   a.    
     As shown in  FIGS.  2 - 4   , the linear array of receive antennas  24  is arranged perpendicularly relative to the linear array of transmit antennas  22 . Despite this configuration, the receive antennas  24  of the receive front end device  42   a  may detect the waves that were horizontally polarized and were transmitted by the transmit front end device  40   a . The detection of these waves may be improved by the fact that the receive front end device  42   a  includes two set of polarization rotators  56 A,  56 B. In other words, the waves arriving at the receive antennas  24  may undergo another 90-degree polarization rotation by the second polarization rotators  56 B of the second set of waveguides  52   b  in the receive planar component  43 . Specifically, the waves move through the first section  56   a , the iris section  56   b  and the second section  56   c  (from  FIG.  7 B  to  FIG.  9 B ) of the second polarization rotator  56 B and are polarized to become parallel the plane of the Rotman lens  23  of the receive planar component  43  (or vertical if the receive planar component  43  is positioned vertically about the ground surface). After these detected waves propagate through the Rotman lens, the polarization of these waves may undergo yet another 90-degree polarization rotation at the first polarization rotators  56 A of the first set of waveguides  52   a  of the receive planar component  43 . Specifically, the waves move through the second section  56   c , the iris section  56   b , and the first section  56   a  (from  FIG.  9 B  to  FIG.  7 B ) of the first polarization rotators  56 A and are polarized to become perpendicular to the plane of the Rotman lens  23  of the receive planar component  43  (i.e., with a horizontal polarization about the ground surface if the receive front end device is perpendicular to the ground surface). The waves thus reach the receive logic  14  at the same polarization relative to the phased array logic at which the waves were transmitted from the transmit logic  12 . 
     The first set of waveguides  52   a  in the transmit planar component  41 , the second set of waveguides  52   b  in the receive planar component  43 , and the first set of waveguides  52   a  in the receive planar component  41  make up the three sets of waveguides  52  that include polarization rotators  56  in the present embodiment of the front end  10 . Thus, the waves undergo three 90-degree polarization rotations or twists during propagation through the transmit front end device  40   a  and the receive front end device  42   a.    
     However, the number of sets of waveguides  52  including polarization rotators  56  may be a different odd number such as one or seven. In an alternative embodiment of the front end  10 , there could be polarization rotators  56  in the first set of waveguides  52  on the transmit planar component  41  only and none on the receive planar component  43  such that the total number of sets of waveguides including polarization rotators  56  is one, for example. 
     Alternatively, while each waveguide in the aforementioned sets of waveguides  52  includes a single polarization rotator  56 , it is possible for one waveguide  52  to have more than one polarization rotator  56 . For example, each of the first set of waveguides  52   a  extending between the first end  41   a  and the beam ports  50   a  in the transmit planar component  41  may include two polarization rotators  56  (e.g., a first polarization rotator  56 A and a second polarization rotator  56 B in order of wave propagation), each of the second set of waveguides  52   b  extending between the array ports  50   b  and the second end  41   b  in the transmit planar component  41  may include one polarization rotator  56  (e.g., a first polarization rotator  56 A), each the second set of waveguides  52   b  extending between the second end  43   b  and the array ports  50   b  in the receive planar component  43  may include two polarization rotators  56  (e.g., a second polarization rotator  56 B and a first polarization rotator  56 A in order of wave propagation), and each the first set of waveguides  52   a  extending between the beam ports  50   a  and the first end  43   a  of the receive planar component  43  may include two polarization rotators  56  (e.g., a second polarization rotator  56 B and a first polarization rotator  56 A in order of wave propagation). In such an alternative arrangement of the polarization rotators  56 , there would be a total of seven 90-degree polarization rotations or twists during propagation through the transmit front end device  40   a  and the receive front end device  42   a.    
     The expression “90-degree polarization rotation” or other expressions relating to rotating the polarization of the waves by “90-degree” or “90 degrees” are meant to include rotation by 270 degrees, 630 degrees, or the like in the opposite rotational direction or rotation by 450 degrees or the like in the same rotational direction as long as the finally reached position can be reached through a rotation by 90 degrees. 
     In one example arrangement of the front end  10 , the transmit module  40  and the receive module  42  may be configured in a bi-static manner. The bi-static configuration may refer to the working configuration where the receiving module  42  and the transmitting module  40  are separated or not co-located. The illustrated example shows that the vertically arranged receive module  42  is configured to be in a receiving mode while the horizontally arranged transmit module  40  is configured to be in a transmission mode. The bi-static Tx/Rx configuration of the two phased array modules may be fixed or switchable. In some cases, the vertical receive module  42  and horizontal transmit module  40  can be switched such that the vertical module is the transmitter and the horizontal module is the receiver. 
     If the radar system is in the bi-static Tx/Rx configuration, one or more parameters of the antenna arrays (e.g., gain, directivity) for the receiving and transmitting may be different. Similarly, one or more configurations of the Rotman lens or RF absorbers corresponding to one (transmit/receive) front-end device may be different from those of the perpendicularly arranged (receive/transmit) front-end device. 
     In alternative embodiment ( FIG.  10   ), the front end  10  may feed an array of microstrip patch antennas using microstrip delay-line beamformer. The microstrip patch antennas may be fabricated using printed circuit board technologies. The patch antennas are resonant antennas fed by a true time delay microstrip beamformer without using a lens. An array of Vivaldi antennas may also be connected to the microstrip-based Rotman lens. This may advantageously provide a device with compact and smaller structure, improved accuracy and easy fabrication. In an example receiving module, the patch antennas may be selected (e.g., by selecting patch size and location) such that the patch array operates at the center frequency which is about 78.5 GHz. In some embodiments, the patch array may comprise 32 patches. Those skilled in the art will appreciate that other number of patches that is smaller than or greater than 32 can be utilized. 
       FIG.  15    shows a schematic illustration of an example 5th generation mobile network (5G) system  1000 , which is also referred to as a 5G base station. The example 5G base station is equipped with hybrid beamforming in which the analog beamformer in the hybrid beamforming is based on one or more Rotman lenses. The system  1000  may include two separated identical antenna arrays, one for transmitting by transmit antennas  1038  and the other for receiving by receive antennas  1040 . As shown in  FIG.  15   , each of the transmit and receive arrays may be composed of a non-zero number of antenna elements, e.g., M antenna elements, in that there are an M number of transmitting paths and an M number of receiving paths in this architecture. But the number of transmitting paths and the number of receiving paths can be different as well. All parts of the system  1000  may be designed to operate in millimeter-wave frequencies. The radio frequency (RF) head  1031  through each transmitting path may include a preamplifier  1034 , a power amplifier  1042 , and a bandpass filter  1036  and the RF head  1031  through each receiving path comprises a bandpass filter  1048 , a limiter  1046 , and a low noise amplifier  1044 . The power amplifier is used in each line to satisfy the required Effective Isotropic Radiated Power (EIRP) for 5G base stations. 
     Hybrid beamforming in this type of 5G system  1000  often includes two sections, i.e., analog beamforming  1001  and digital beamforming  1003 . In the embodiment of  FIG.  15   , the digital beamforming  1003  is applied in the signal processor  1002  to generate an N number of separated and independent signals (RF chains  1020 ). In an example embodiment, there may be 8 RF chains  1020 . Moreover, the network for analog beamforming  1001  in this embodiment is formed of two Rotman lenses  1028 ,  1030  each of which includes an M number of array ports  1032  and a B number of beam ports  1026  providing multiple orthogonal beams. The number M may be selected such that a half-power beamwidth of each antenna can be, e.g., 1.5 degree or less, such as about a 1-degree beamwidth. For example, for a total beamwidth of the transmitting antenna array or the receiving antenna array of 132 degrees, the number M can be 88, for an individual antenna beamwidth of 1.5 degrees. In some implementations, the same Rotman lens may be utilized for the transmit path and the receive path. In some implementations, the number B of beam ports can be different for the transmit portion of the system  1000  than for the receive portion of the system  1000 . For example, the number B of beam ports for the transmitting Rotman lens  1028  can be 88, whereas the number B of beam ports for the receiving Rotman lens  1030  can be 32. In order to select the intended beam ports  1026  to transmit/receive the RF chains  1020  towards/from the targets, a transmit matrix switch  1022  and a receive matrix switch  1024  are provided. 
     The matrix switches  1022 ,  1024  connect the N number of RF chains  1020  to the B number of beams provided to the Rotman lenses  1028 ,  1030 . The system  1000  can support an N number of beam(s) simultaneously. For example, in a 5G base station with 8 beams, the matrix switches  1022 ,  1024  should be able to connect each RF chain  1020  to each beam port  1026  of the Rotman lens  1028 ,  1030  such that the matrix switch can connect all RF chains  1020  to all beam ports  1026  of the Rotman lens. In the receiving arms  1020  of the digital beamforming portion  1003 , the signals in millimeter-wave frequencies received from the matrix switch  1024  are converted to signals in lower frequencies by the down converters  1019  while the signals with frequencies lower than those in the millimeter-wave range in the transmitting arms  1020  of the digital beamforming portion  1003  are converted to signals in millimeter-wave frequencies by the up converters  1018  before being passed to matrix switch  1022 . Local oscillator signals  1021  are input into the up converters  1018  and the down converters  1019  for up/down conversion of intermediate frequency (IF) signals. To convert the digital and analog signals to each other, analog-to-digital converters  1016  and digital-to-analog converters  1014  may be provided. 
     The signal processor  1002  may include a plurality of layers  1004 ,  1006 ,  1008 ,  1010  and  1012  for data transmission in accordance with conventional models such as the open system interconnections (OSI) reference model or the Internet protocol suite. Under the OSI model, the layers may include the physical layer, the data link layer including the media access control (MAC), the network layer, the transport layer, the session layer, the presentation layer, and the application layer. In the OSI model, the physical layer is the layer most closely associated with the physical connection between devices and transmits and/or receives the raw bit-stream over the physical medium. The data link layer defines the format of the data being transmitted/received and is responsible for flow control and error control in intra-network communications. A MAC sublayer within the data-link layer controls the hardware responsible for interaction with the transmission medium. The network layer facilitates data transfer between different networks. The network layer breaks data from the transport layer into packets when sending data or reassembles packets when receiving data. When transmitting, the transport layer takes data from the session layer and breaks it into segments before sending it to the network layer. When receiving, the transport layer reassembles the segments into data that the session layer can consume. The transport layer also can be configured to perform flow control for determining an optimal speed of transmission and to perform error control to ensure that the received data is complete. The session layer is configured to open and close communication between devices. The presentation layer prepares data so that it can be used by the application layer and is configured to perform encryption and compression of data. The application layer includes the protocols for manipulating data for use with user applications. Under the TCP/IP model, the layers may include the network access layer, the Internet layer, the transport layer, and the application layer. 
     The graph in  FIG.  16    illustrates energy efficiency versus spectral efficiency for base stations implemented with different types of technology and corresponding power consumption for each type of technology. The base stations for each technology support 200 beams (Nu=200) and have 200 RF chains. The first type of base stations (‘HB with IF Phase Shifter’) utilizes hybrid beamforming, which combines analog beamforming and digital beamforming, with IF phase shifters. The second type of base stations (‘HB with RF Phase Shifter’) utilizes hybrid beamforming with RF phase shifters. The third type of base stations (‘HB with Rotman Lens’) utilizes hybrid beamforming with Rotman lenses, and the fourth type of base stations (‘DB with 200 beams’) simply utilizes digital beamforming. As observable from the power consumption calculations, the base stations utilizing hybrid beamforming with Rotman lenses provide comparable spectral efficiency performance with significantly better energy efficiency. 
     The graph in  FIG.  17    also illustrates energy efficiency versus spectral efficiency for base stations implemented with the same four types of technology and having 200 RF chains but producing 8 beams. It can be observed that the base stations utilizing hybrid beamforming with Rotman lenses still provide comparable spectral efficiency performance with significantly better energy efficiency. 
     Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.