Patent Publication Number: US-2021165072-A1

Title: Dual-sided Radar Systems and Methods of Formation Thereof

Description:
This application is a divisional application of U.S. application Ser. No. 15/724,953, filed on Oct. 4, 2017, which application is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to a radar system, and, in particular embodiments, to dual-sided radar system structures, methods of formation, and methods of operation thereof. 
     BACKGROUND 
     Portable devices such as tablets, smart phones, and smart watches have become popular recently due to the rapid advancement in low-cost semiconductor technologies. Portable devices may need to acquire information about objects on opposing sides of the device to perform autofocusing of a camera or for shutting the screen off during a phone conversation, as examples. Various implementations may be used to accomplish this including laser ranging and time-of-flight (ToF) modules. However such modules may be expensive and/or require openings in the housing of the portable device. Therefore, portable devices which incorporate alternative means of acquiring information about objects on opposing sides of the device may be desirable to decrease cost, improve functionality, and increase resilience of the device housing. 
     SUMMARY 
     In accordance with an embodiment of the invention, a radar system includes a substrate. The substrate includes a first surface and a second surface. The first surface is opposite the second surface. The radar system further includes transmitter front-end circuitry attached to the substrate. The transmitter front-end circuitry is configured to transmit a transmitted radio frequency (RF) signal in a first direction away from the first surface and in a second direction away from the second surface. The radar system also includes a first receive antenna and a second receive antenna. The first receive antenna is disposed at the first surface and is configured to receive a first reflected RF signal propagating in the second direction. The first reflected RF signal is generated by the transmitted RF signal. The second receive antenna is disposed at the second surface and is configured to receive a second reflect RF signal propagating in the first direction. The second reflected RF signal is generated by the transmitted RF signal. 
     In accordance with another embodiment of the invention, a method of operating a radar system includes transmitting, by transmitter front-end circuitry attached to a substrate, a transmitted radio frequency (RF) signal in a first direction away from a first surface of the substrate and in a second direction away from a second surface of the substrate. The first direction is opposite the first direction. The method of operating the radar system further includes receiving, by a first receive antenna disposed at the first surface of the substrate, a first reflected RF signal generated by the transmitted RF signal. The first reflected RF signal is propagating in the second direction. The method of operating the radar system also includes receiving, by a second receive antenna disposed at the second surface of the substrate, a second reflected RF signal generated by the transmitted RF signal. The second reflected RF signal is propagating in the first direction. 
     In accordance with still another embodiment of the invention, a method of forming a radar system includes forming a first receive antenna and a first ground plane region by patterning a first conductive layer on a first surface of a first laminate layer of a radar package and forming a transmit antenna and a second ground plane region by patterning a second conductive layer on a second surface of the first laminate layer. The second surface is opposite the first surface. The method of forming the radar system further includes forming a second laminate layer of the radar package over the second conductive layer, forming a third conductive layer over the second laminate layer, forming a second receive antenna by patterning the third conductive layer, and attaching a radio frequency integrated circuit (RFIC) chip to the radar package. The RFIC is coupled to the transmit antenna, the first receive antenna, and the second receive antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1A  illustrates an example gesture recognition application in which a smartwatch is controlled using various hand gestures,  FIG. 1B  illustrates various example hand gestures that may be used to control a smartwatch,  FIG. 1C  illustrates a block diagram of a radar system that includes a radar front end circuit and processing circuitry, and  FIG. 1D  illustrates a plan view of a radar system circuit that includes a radar front end circuit implemented as a radio frequency integrated circuit in accordance with embodiments of the invention; 
         FIG. 2A  illustrates an example radar system including a radar package attached to a printed circuit board,  FIG. 2B  illustrates a cross-sectional view of the radar package including a transmit antenna, a front receive antenna, and a back receive antenna, and  FIG. 2C  illustrates a housing enclosing the printed circuit board and the radar package in accordance with embodiments of the invention; 
         FIG. 3  illustrates a cross-sectional view of an example radar package including a transmit antenna within a substrate, a front receive antenna at a front surface of the radar package, and a back receive antenna at a back surface of the radar package in accordance with an embodiment of the invention; 
         FIG. 4  illustrates an example laminate radar package including a transmit antenna between two laminate layers, a front receive antenna at a front surface of the radar package, and a back receive antenna at a back surface of the radar package in accordance with an embodiment of the invention; 
         FIG. 5  illustrates an example radar system including a housing enclosing a transmit antenna, a front receive antenna, and a back receive antenna attached to a multiplayer printed circuit board in accordance with an embodiment of the invention; 
         FIGS. 6A and 6B  illustrate an example radar package including a transmit antenna, a front receive antenna, and three back receive antennas in accordance with an embodiment of the invention where  FIG. 6A  illustrates a top view of the radar package and  FIG. 6B  illustrates a three-dimensional view of the relative locations of antennas and ground planes within the radar package; 
         FIGS. 7A and 7B  illustrate another example radar package including a transmit antenna, a front receive antenna, and three back receive antennas in accordance with an embodiment of the invention where  FIG. 7A  illustrates a top view of the radar package and  FIG. 7B  illustrates a three-dimensional view of the relative locations of antennas and ground planes within the radar package; 
         FIGS. 8A and 8B  illustrate an example radar package including front transmit and receive antennas, a back transmit antenna, and three back receive antennas in accordance with an embodiment of the invention where  FIG. 8A  illustrates a top view of the radar package and  FIG. 8B  illustrates a three-dimensional view of the relative locations of antennas and ground planes within the radar package; 
         FIGS. 9A and 9B  illustrate an example radar package including a transmit antenna, three front receive antennas, and three back receive antennas in accordance with an embodiment of the invention where  FIG. 9A  illustrates a top view of the radar package and  FIG. 9B  illustrates a three-dimensional view of the relative locations of antennas and ground planes within the radar package; 
         FIGS. 10A and 10B  illustrate an example radar package including a transmit antenna, a front receive antenna, and five back receive antennas in accordance with an embodiment of the invention where  FIG. 10A  illustrates a top view of the radar package and  FIG. 10B  illustrates a three-dimensional view of the relative locations of antennas and ground planes within the radar package; 
         FIGS. 11A and 11B  illustrate a method of forming a radar system in accordance with an embodiment of the invention where  FIG. 11A  illustrates steps  1102  through  1116  and  FIG. 11B  illustrates steps  1118  through  1130 ; 
         FIG. 12  illustrates a method of operating a radar system including detecting objects on opposing sides of a substrate in accordance with an embodiment of the invention; 
         FIG. 13  illustrates a method of operating a radar system including tracking movement of an object on one side of a substrate and detecting another object on an opposing side of the substrate in accordance with an embodiment of the invention; 
         FIG. 14  illustrates a method of operating a radar system including tracking movement of an object in three dimensional space on one side of a substrate and detecting another object on an opposing side of the substrate in accordance with an embodiment of the invention; and 
         FIG. 15A  illustrates an example gesture recognition application in which a mobile phone includes a radar package,  FIG. 15B  illustrates an example gesture recognition application in which a pair of headphones include a radar package, and  FIG. 15C  illustrates an example gesture recognition application in which a personal assistant device includes a radar package in accordance with embodiments of the invention. 
     
    
    
     Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale. The edges of features drawn in the figures do not necessarily indicate the termination of the extent of the feature. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The making and using of various embodiments are discussed in detail below. It should be appreciated, however, that the various embodiments described herein are applicable in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use various embodiments, and should not be construed in a limited scope. 
     Portable devices may utilize multiple antenna elements for beamforming, transmit diversity and MIMO configurations, and as radar sensors that can detect user motions (known as gesture sensors). Gesture sensors may be configured in a portable device as an interface to control functionality of the device as well as to gather information about objects in the area around the portable device. 
     In various embodiments, a radar-based gesture detection system is used to directly control a device such as a computer, a smartphone, or a tablet computer, or to control a remote device such as a vehicle, an electronic system within a building, or a home appliance. For example, when the remote device is a car, an embodiment gesture detection system allows a human actor to control various operations of the car from outside the car. 
       FIG. 1A  illustrates an example radar system application in which a smartwatch  100  is controlled using various hand gestures. As shown, smartwatch  100  includes a display element  102  physically coupled to a radar system  104 . During operation, radar system  104  transmits RF signals  110  to target  114 , which may be a human hand, and receives reflected RF signals  112  that are reflected by target  114 . These reflected RF signals  112  are processed by the radar system to determine the position and motion of target  114  and/or to determine whether target  114  is providing a particular gesture. In some embodiments, radar system  104  may include a radar system circuit  108  that is disposed within a housing  106 . At least a portion of housing  106  is transparent or partially transparent to RF signals transmitted and received by radar system circuit  108 . It should be appreciated that radar system circuit  108  may also be disposed within the body of display element  102 . 
     In alternative embodiments, radar system circuit  108  may be embedded within other devices including, but not limited to, car keys, smart phones, tablet computers, audio/visual equipment, kitchen appliances, HVAC controls, and automobiles. In some applications, such as automotive applications, radar system circuit  108  may be embedded within a mobile device such as a car key or smart phone, which in turn communicates with a remote device to be controlled, such as an automobile or kitchen appliance. The data transfer between the mobile device and remote device could include any of a wide variety of communications technologies, including, e.g., Bluetooth, V2X, etc. 
     Example hand gestures shown in  FIG. 1B  may include, for example, a “thumbs-up” gesture  122 , a “closed fist” gesture  124 , a “thumb-to-finger” gesture  126 , or a “button press” gesture  128 . Each of these example gestures could be used to control the functionality of smartwatch  100  or some other device or system. For example, “thumbs-up” gesture  122  could be used to open a smartwatch application, “closed fist” gesture  124  could be used to close the smartwatch application, “thumb-to-finger” gesture  126  in conjunction with motion between the thumb and index finger may be used to virtually rotate the hands on the clock display of smartwatch  100 , and “button press” gesture  128  could be used to start and stop a stopwatch feature of smartwatch  100 . In various embodiments, recognized gestures may be static or dynamic. Static gestures may be made by holding a hand in a fixed position such as the gestures  122 ,  124  and  128 , and dynamic gestures may be made by moving the hand or a portion of the hand, such as moving the index finger with respect to the thumb such as with gesture  126 . It should be understood that the above-mentioned gestures are just a few examples of many possible gestures that may be recognized by embodiment radar systems. 
       FIG. 1C  illustrates a block diagram of radar system  104  that includes radar front-end circuit  132  and processing circuitry  134 . During operation, positions and gestures of target  114  may be detected by the radar system  104 . For example, a gesture of two fingers tapping each other could be interpreted as a “button press,” or a gesture of a rotating thumb and finger may be interpreted as turning a dial. While target  114  is depicted in  FIG. 1C  as being a hand, radar system  104  may also be configured to determine gestures and positions of other types of targets such as a human body, machinery and other types of animate or inanimate objects. Radar system  104  may be implemented, for example, using a two-dimensional mm-wave phase-array radar that measures the position and relative speed of target  114 . The mm-wave phase-array radar transmits and receives signals in the 50 GHz to 80 GHz range. Alternatively, frequencies outside of this range may also be used. In some embodiments, radar front-end circuit  132  operates as a frequency modulated continuous wave (FMCW) radar sensor having multiple transmit and receive channels. 
     Radar front-end circuit  132  transmits and receives radio signals for detecting target  114  in three-dimensional space. For example, radar front-end circuit  132  transmits an incident RF signal and receives a RF signal that is a reflection of the incident RF signal from target  114 . The received reflected RF signal is downconverted by radar front-end circuit  132  to determine beat frequency signals. These beat frequency signals may be used to determine information such as the location, speed, angle, etc., of target  114  in three-dimensional space. 
     In various embodiments, radar front-end circuit  132  is configured to transmit incident RF signals toward target  114  via transmit antennas  142  and to receive reflected RF signals from target  114  via receive antennas  144 . Radar front-end circuit  132  includes transmitter front-end circuits  138  coupled to transmit antennas  142  and receiver front-end circuit  140  coupled to receive antennas  144 . 
     During operation, transmitter front-end circuits  138  may transmit RF signals toward target  114  one at a time or simultaneously. While two transmitter front-end circuits  138  are depicted in  FIG. 1C , it should be appreciated that radar front-end circuit  132  may include fewer or greater than two transmitter front-end circuits  138 . Each transmitter front-end circuit  138  includes circuitry configured to produce the incident RF signals. Such circuitry may include, for example, RF oscillators, upconverting mixers, RF amplifiers, variable gain amplifiers, filters, transformers, power splitters, and other types of circuits. 
     Receiver front-end circuit  140  receives and processes the reflected RF signals from target  114 . As shown in  FIG. 1C , receiver front-end circuit  140  is configured to be coupled to four receive antennas  144 , which may be configured as a 2×2 antenna array. In alternative embodiments, receiver front-end circuit  140  may be configured to be coupled to greater or fewer than four antennas, with the resulting antenna array being of various n×m dimensions depending on the specific embodiment and its specifications. Receiver front-end circuit  140  may include, for example, RF oscillators, upconverting mixers, RF amplifiers, variable gain amplifiers, filters, transformers, power combiners and other types of circuits. 
     Radar circuitry  136  provides signals to be transmitted to transmitter front-end circuits  138 , receives signals from receiver front-end circuit  140 , and may be configured to control the operation of radar front-end circuit  132 . In some embodiments, radar circuitry  136  includes, but is not limited to, frequency synthesis circuitry, upconversion and downconversion circuitry, variable gain amplifiers, analog-to-digital converters, digital-to-analog converters, digital signal processing circuitry for baseband signals, bias generation circuits, and voltage regulators. 
     Radar circuitry  136  may receive a baseband radar signal from processing circuitry  134  and control a frequency of an RF oscillator based on the received baseband signal. In some embodiments, this received baseband signal may represent a FMCW frequency chip to be transmitted. Radar circuitry  136  may adjust the frequency of the RF oscillator by applying a signal proportional to the received baseband signal to a frequency control input of a phase locked loop. Alternatively, the baseband signal received from processing circuitry  134  may be upconverted using one or more mixers. Radar circuitry  136  may transmit and digitize baseband signals via a digital bus (e.g., a USB bus), transmit and receive analog signals via an analog signal path, and/or transmit and/or receive a combination of analog and digital signals to and from processing circuitry  134 . 
     Processing circuitry  134  acquires baseband signals provided by radar circuitry  136  and performs one or more signal processing steps to evaluate them. In an embodiment, processing circuitry  134  acquires a baseband signal that represents the beat frequency signals. The signal processing steps may include performing a fast Fourier transform (FFT), a short-time Fourier transform (STFT), target classification, machine learning, and the like. Results of the signal processing steps are used to determine and perform an action on the device, such as smartwatch  100  of  FIG. 1A . In addition to processing the acquired baseband signals, processing circuitry  134  may also control aspects of radar front-end circuit  132 , such as the transmissions produced by radar front-end circuit  132 . 
     The various components of radar system  104  may be partitioned in various ways. For example, radar front-end circuit  132  may be implemented on one or more RF integrated circuits (RFICs), antennas  142  and  144  may be disposed on a circuit board, and processing circuitry  134  may be implemented using a processor, a microprocessor, a digital signal processor and/or a custom logic circuit disposed on one or more integrated circuits/semiconductor substrates. Processing circuitry  134  may include a processor that executes instructions stored in a non-transitory memory to perform the functions of processing circuitry  134 . In some embodiments, however, all or part of the functionality of processing circuitry  134  may be incorporated on the same integrated circuit/semiconductor substrate on which radar front-end circuit  132  is disposed. 
     In some embodiments, some or all portions of radar front-end circuit  132  may be implemented in a package that contains transmit antennas  142 , receive antennas  144 , transmitter front-end circuits  138 , receiver front-end circuit  140 , and/or radar circuitry  136 . In some embodiments, radar front-end circuit  132  may be implemented as one or more integrated circuits disposed on a circuit board, and transmit antennas  142  and receive antennas  144  may be implemented on the circuit board adjacent to the integrated circuits. In some embodiments, transmitter front-end circuits  138 , receiver front-end circuit  140 , and radar circuitry  136  are formed on a same radar front-end integrated circuit (IC) die. Transmit antennas  142  and receive antennas  144  may be part of the radar front-end IC die, or may be separate antennas over or adjacent to the radar front-end IC die. The radar front-end IC die may further include conductive layers, such as redistribution layers (RDLs), used for routing and/or for the implementation of various passive or active devices of radar front-end circuit  132 . In an embodiment, transmit antennas  142  and receive antennas  144  may be implemented using the RDLs of the radar front-end IC die. 
       FIG. 1D  illustrates a plan view of radar system circuit  108  that includes radar front-end circuit  132  implemented as an RFIC coupled to transmit antennas  142  and receive antennas  144  implemented as patch antennas disposed on or within substrate  152 . In some embodiments, substrate  152  may be implemented using a circuit board on which radar front-end circuit  132  is disposed and on which transmit antennas  142  and receive antennas  144  are implemented using conductive layers of the circuit board. Alternatively, substrate  152  represents a wafer substrate on which one or more RDLs are disposed and on which transmit antennas  142  and receive antennas  144  are implemented using conductive layers on the one or more RDLs. It should be appreciated that the implementation of  FIG. 1D  is just one of many ways that embodiment radar systems may be implemented. 
     In addition to gesture sensing, a radar system may also provide information about objects in the environment surrounding the portable device. For example, a radar system may sense the presence of an object, determine the physical location of an object, track movement of an object in one, two, or three dimensions, measure the size of an object, determine the material composition of an object, and/or determine the identity of an object. 
     In various applications, a portable device may benefit from radar functionality on two opposing sides of the portable device. In these applications, a dual-sided radar may be implemented that provides radar functionality to both sides. For example, a smart phone or a tablet may have cameras on both sides of the device. Autofocusing may be performed on both sides using the dual-sided radar. Additional functionality such as the ability to track movement of objects may be used to rapidly adjust focus and prevent blurred images while recording video or rapidly capturing images. 
     Additional applications of dual-sided radar systems may include material identification, blood pressure tracking, pulse rate monitoring, collision avoidance, object identification and activity identification, audio source tracking, contact tracking, and biometric identification. For example, a smartwatch may use the front-facing radar of a dual-sided radar system to gesture sensing while using the back-facing radar for blood pressure monitoring, pulse rate monitoring, and contact tracking to know if a user is wearing the watch or if it is on the charger. As another example, a portable device may utilize a dual-sided radar system to track an audio source in a room to filter out unwanted additional noise and/or to determine the identity of a speaker. 
     As still another example, an augmented reality/virtual reality (AR/VR) device may use the back-facing radar of a dual-sided radar system for biometrics and contact tracking while using the front-facing radar to accurately overlay images and/or information onto the physical environment in front of a user and also as a collision avoidance system to alert the user if a physical object is too close. Such an AR/VR device may also detected shoulder and arm movements of a user as input to increase realism in a simulation or as commands to the AR/VR device. 
     Radar systems may also be used to obtain detailed information about objects in the environment surrounding the radar system. For example, a user may direct the back-facing camera of a smart phone or a tablet at a group of people and receive an overlay on the screen that includes the distance, height, and pulse rate of individual people as well as object information such as material composition, size, and object identities. Such enhanced imaging may also be used in AR/VR devices to quickly provide information to a user. 
     In various embodiments, a dual-sided radar system includes one or more transmit antennas attached to a substrate. The one or more transmit antennas are configured to transmit a first RF signal in first direction away from a front side of the dual-sided radar system and a second RF signal in a second direction away from an opposite back side of the dual-sided radar system. The dual sided radar system also includes a first receive antenna configured to receive RF signals at the front side of the dual-sided radar system and second receive antenna configured to receive RF signals at the back side of the dual-sided radar system. The RF signals received by the first receive antenna may be generated by the first RF signal reflecting off of one or more objects located at a distance on the front side of the dual-sided radar system. The RF signals received by the second receive antenna may be generated by the second RF signal reflecting off of one or more objects located at a distance on the back side of the dual-sided radar system. 
     The dual-sided radar system may further include RF circuitry configured to detect objects located in the regions on the front side and the back side of the dual-sided radar system. For example, the RF circuitry may determine the location of a first object located some distance from the dual-sided radar system on the front side according to a reflected RF signal generated by the first RF signal and received by the first receive antenna. Likewise, the RF circuitry may determine the location of a second object located some other distance from the dual-sided radar system on the back side according to another reflected RF signal generated by the second RF signal and receive by the second receive antenna. 
     A dual-side radar system may include a front-facing radar tailored for short range detection and a back-facing radar tailored for long range detection. For example, the front-facing radar may be configured to have an optimal range of 0.1 m to 2.5 m while the back-facing radar may be configured to have an optimal range of 3 m to 5 m. An optimal range for a radar system does not indicate that the radar is inoperable outside of the optimal range, but may instead indicate an intended range of operation or a range within which information obtained is accurate to a certain tolerance. 
     Dual-sided radar systems may advantageously provide similar capabilities as other non-radar modules with lower power consumption, smaller module size, better accuracy, longer range, and increased versatility. For example, a portable device utilizing conventional ToF modules for autofocusing may require multiple ToF modules, consume more power and have lower accuracy under low-light conditions. In contrast, a dual-sided radar system may have a single radar module that is smaller than a single ToF module, consumes less power, and is unaffected by ambient light as well as providing additional functionality such as the features described above. 
     Additionally, conventional range detecting systems using lasers or ToF typically require an opening in the housing of the portable device because many common housing materials are not transparent to the visible and/or infrared spectrum. For example, most of the housing of a portable device that includes a conventional laser module of ToF module may be opaque to visible and/or infrared light while an opening including a transparent glass or plastic is included overlapping the laser module or ToF module. Dual-sided radar systems may advantageously allow for housings that do not include openings over the radar module which may in turn allow for better environmental resistance for the portable device as well as improving housing aesthetics. 
     Embodiments provided below describe various structures, methods of forming, and methods of operating a radar system, and in particular, radar systems that include a dual-sided radar module. The following description describes the embodiments. An embodiment radar system is described using  FIGS. 2A, 2B, and 2C . An embodiment radar package is described using  FIG. 3 . An embodiment laminate radar package is described using  FIG. 4 . An embodiment radar system is described using  FIG. 5 . Several embodiment radar packages are described using  FIGS. 6A-10B . An embodiment method of forming a radar system is described using  FIGS. 11A and 11B . Three embodiment methods of operating a radar system are described using  FIGS. 12-14 . Three embodiment gesture recognition applications are described using  FIGS. 15A, 15B, and 15C . 
       FIG. 2A  illustrates an example radar system including a radar package attached to a printed circuit board,  FIG. 2B  illustrates a cross-sectional view of the radar package including a transmit antenna, a front receive antenna, and a back receive antenna, and  FIG. 2C  illustrates a housing enclosing the printed circuit board and the radar package in accordance with embodiments of the invention. 
     Referring to  FIG. 2A , an example radar system includes a radar package  58  attached to a printed circuit board (PCB)  34 . The PCB  34  may include additional electronic devices, processors, memory, and the like. In various embodiments, the PCB  34  is a main board for an electronic device including the radar system. For example, the PCB  34  may be the main board for a smartwatch, cellular device, laptop computer, or IoT device, virtual reality headset, radar module in a vehicle, and the like. 
     The radar package  58  includes a transmit antenna  45  attached to a substrate  52 . In various embodiments, the transmit antenna  45  is configured to transmit an RF signal in one or more directions outwardly from substrate  52  and the radar package  58 . In one embodiment, transmit antenna  45  is an omnidirectional antenna. In other embodiments, transmit antenna  45  is a directional antenna and is implemented as a patch antenna in one embodiment. In some cases transmit antenna  45  may be implemented as an array of antenna elements. 
     The transmit antenna  45  may transmit a front side transmitted RF signal  10  directed away from a front side  18  of the radar system and a back side transmitted RF signal  20  directed away from a back side  19  of the radar system. As illustrated, the front side  18  and the back side  19  of the radar system may be opposite directions. In some implementations the front side transmitted RF signal  10  and the back side transmitted RF signal  20  may not be transmitted in exactly opposite directions and instead be in substantially opposite directions. The transmit antenna  45  may transmit in only one direction or in more directions depending on specific implementations. 
     Front side transmitted RF signal  10  and back side transmitted RF signal  20  may be identical or substantially similar. For example, both the front side transmitted RF signal  10  and the back side transmitted RF signal  20  may be fed from the same transmission line. In other implementations, front side transmitted RF signal  10  and back side transmitted RF signal  20  may by fed from different sources and be substantially different from one another. 
     The radar package  58  also includes a front side receive antenna  42  and a back side receive antenna  82  attached to the substrate  52 . Front side receive antenna  42  is configured to receive a front side reflected RF signal  12  propagating in a substantially opposite direction as front side transmitted RF signal  10  The front side reflected RF signal  12  is received at the front side receive antenna  42  on the front side  18  of substrate  52 . Front side reflected RF signal  12  may be generated by the front side transmitted RF signal  10 . For example, front side transmitted RF signal  10  may be reflected by objects in the region on the front side  18  of the radar system. 
     Back side receive antenna  82  is similarly configured to receive a back side reflected RF signal  22  propagating in substantially the opposite direction as back side transmitted RF signal  20 . The back side reflected RF signal  22  is receive at the back side receive antenna  82  on the back side  19  of substrate  52 . Back side reflected RF signal  22  may be generated by the back side transmitted RF signal  20  as a result of objects and/or the environment on the back side  19  region of the radar system. 
     A number of properties of the transmitted RF signals may be affected by objects and/or the environment which may then be measureable by the radar system from the received reflected RF signals. These properties may include signal amplitude, frequency, phase information, and the like. The properties may in turn be interpreted to obtain information about the region surrounding the radar system. A possible advantage of radar package  58  is the ability to obtain radar information in the regions on both sides of a single substrate  52 . 
     Referring now to  FIG. 2B , a cross-sectional view is shown of radar package  58  including an integrated circuit (IC) chip  32 . The IC chip  32  may include RF front end circuitry in addition to other circuitry and may be configured to process RF signals transmitted and received at antennas included in the radar system and is an RFIC in one embodiment. 
     In various embodiments, the RF front end circuitry is designed to operate in a super high frequency (SHF) or an extremely high frequency (EHF) regime. For example, the IC chip  32  may contain millimeter wave (MMW) circuitry designed to operate in the unlicensed band from 57 GHz to 64 GHz. Additionally or alternatively, the IC chip  32  may contain circuitry designed to operate in the 28 GHz regime (in 5G applications, for example). The IC chip  32  may have a receive interface connected to receiving antennas and/or a transmit interface connected to transmitting antennas. In some configurations, a receive interface and a transmit interface may be combined into a single interface. 
     In various embodiments, IC chip  32  includes a semiconductor substrate. In one embodiment, the semiconductor substrate includes silicon. In another embodiment, the semiconductor substrate includes silicon germanium (SiGe). In still another embodiment, the semiconductor substrate includes gallium arsenide (GaAs). Other suitable materials suitable for use as a substrate for IC chip  32  may be apparent to those of ordinary skill in the art. 
     The IC chip  32  may be attached to an outer surface of substrate  52  or may be included within substrate  52  as shown. Various interconnects in various layers may couple IC chip  32  to transmit antenna  45 , front side receive antenna  42 , and back side receive antenna  82 . IC chip  32  may be included in radar package  58  using any suitable attachment method including, but not limited to wire bonding, surface mounting, adhesive, ball grid array (BGA), conductive pillars, and the like. The IC chip  32  may include additional components such as active and passive devices, metal layers, dielectric layers, doped and intrinsic semiconductor regions, redistribution layers, and other components known in the art. In various embodiments, IC chip  32  has already undergone back end of line (BEOL) processing before being attached to substrate  52 . 
     Interconnects  79  may couple IC chip  32  to circuitry on PCB  34  using solder balls  70 . In addition to providing an electrical connection between the radar package  58  and the PCB  34 , solder balls  70  may also create a physical attachment of radar package  58  to PCB  34 . Other attachment methods are also possible and may be apparent to those of ordinary skill in the art. 
     An opening  17  may be included in the PCB  34  on the front side  18  of the radar package  58 . The opening  17  may allow RF signals to pass through the PCB  34 . In some cases, the opening  17  may reduce attenuation and improve the gain of RF signals transmitted and received on the front side  18  of substrate  52 . However, in other implementations, opening  17  may be omitted. For example, a low-loss material may be used to implement the PCB  34  and may overlap the entire front side  18  of substrate  52 . In some implementations the low-loss material may act as an RF lens for antennas in radar package  58 . 
     As a specific example, for an autofocus application of dual-sided radar, a camera located on the front side  18  of the radar system typically capture images of a user that is located relatively close to the radar system. Materials may be chosen that overlap the transmit antenna  45  and front side receive antenna  42  on the front side  18  that act as an RF waveguide to focus RF signals for close-up applications. In contrast, a camera located on the back side  19  of the radar system may typically capture images of objects located relatively far away from the radar system. The radar system may be configured to use a broad beam for the back side transmitted RF signal  20  by choosing materials of appropriate shape and composition to overlap the transmit antenna  45  and the back side receive antenna  82  on the back side  19  of the radar system. 
     Referring now to  FIG. 2C , the radar system includes a housing  56  which encloses PCB  34  and radar package  58 . The housing  56  may be an outer casing of a device such as a smartwatch, cellular device, laptop computer, IoT device, virtual reality headset, and the like. Alternatively, housing  56  may be an outer casing of a module including the radar package and additional functionality such as a radar module in a vehicle. As shown, the RF signals on the front side  18  and the back side  19  of the housing  56  pass through outer surfaces of the housing  56  to the radar package  58 . 
     The housing  56  may advantageously be implemented using materials that are transparent or partially transparent to RF signals allowing the PCB  34  and the radar package  58  to be fully enclosed within the housing  56  while still maintaining desired functionality. In various embodiments, the housing  56  may include a plastic material. Alternatively, housing  56  may be implemented using materials that are opaque or partially opaque to RF signals and an opening may be used to allow RF signals to pass through the housing  56 . The opening in the housing  56  may be uncovered exposing an outer surface of the radar package  58  and/or the PCB  34  or be covered by an RF transparent material. 
       FIG. 3  illustrates a cross-sectional view of an example radar package including a transmit antenna within a substrate, a front receive antenna at a front surface of the radar package, and a back receive antenna at a back surface of the radar package in accordance with an embodiment of the invention. The example radar package of  FIG. 3  may be a specific implementation of the radar package as described in reference to  FIG. 2  as well as in other embodiments. 
     Referring to  FIG. 3 , a radar package  58  includes a transmit antenna  45 , a front side receive antenna  42 , and a back side receive antenna  82  implemented using four conductive layers. Back side receive antenna  82  and a front side receiving ground plane region  62  may be implemented in a first conductive layer  71 . Front side receiving ground plane  62  may act as electromagnetic shielding for front side receive antenna  42  by blocking incident RF signals originating on the back side  19  of radar package  58 . For example, radar package  58  may be configured to determine the range of objects on the front side  18  of the radar package  58  by transmitting the front side transmitted RF signal  10  using transmit antenna  45  and receiving a front side reflected RF signal  12  at front side receive antenna  42 . Reflected RF signals originating from objects on the back side  19  of radar package  58  may be blocked by front side receiving ground plane  62  from reaching front side receive antenna  42 . 
     Transmit antenna  45  may be implemented in a second conductive layer  72 . In one embodiment, transmit antenna  45  is implemented as an omnidirectional antenna and is configured to transmit the front side transmitted RF signal  10  and the back side transmitted RF signal  20  away from a front surface of substrate  52  located on the front side  18  of the radar package  58  and away from a back surface of substrate  52  located on the back side  19  of the radar package  58  respectively. In other embodiments, separate transmit antennas may be included in radar package  58  which only transmit RF signals away from a single side of the radar package  58 . 
     Optionally, transmit antennas may transmit RF signals at an angle relative to surfaces of substrate  52 . For example, objects on a side of radar package  58  in a particular application may consistently be located at a 30° angle relative to the normal direction of a surface on that side. Various possible directional antenna arrangements may be used to transmit RF signals on that side at a requisite angle such as multiple antennas. 
     A third conductive layer  73  may include a back side receiving ground plane region  92 . Back side receiving ground plane region  92  may serve as an electromagnetic shield for back side receive antenna  82  in a similar manner as described for front side receiving ground plane  62 . That is, RF signals originating on the front side  18  of radar package  58  may be blocked from reaching back side receive antenna  82 . 
     In various embodiments, the second conductive layer  72  and the third conductive layer  73  may be implemented as a single conductive layer. Additionally, second conductive layer  72  and third conductive layer  73  may be considered a single conductive layer formed in two steps that include a lower conductive layer, an insulating layer, and an upper conductive layer. For example, the lower conductive layer may be formed and patterned to form transmit antenna  45  and the insulating layer may be formed over the lower conductive layer. The insulating layer may include a patternable resist which may then be patterned before the upper conductive layer is formed over insulating layer. The insulating layer may then be removed to pattern the upper conductive layer forming the back side receiving ground plane region  92 . 
     Front side receive antenna  42  and interconnects  79  may be implemented in a fourth conductive layer  74 . Interconnects  79  may include an interface for connecting to solder balls  70  such as solder pads. An additional metal layer may be included on a side of the radar package  58  to electrically couple the first conductive layer  71  to the fourth conductive layer  74 , especially for grounding purposes. 
     Various transmission lines, interconnects, contact pads, and redistribution lines may be included in any of the conductive layers described herein. For example, a transmit antenna  45  may be fed directly using a transmission line in the second conductive layer  72  which is coupled to IC chip  32  using interconnects. Alternatively, transmit antenna  45  may be fed indirectly from a transmission line in another layer such as third conductive layer  73 . Similar transmission lines and interconnects may exist to couple front side receive antenna  42  and back side receive antenna  82  to IC chip  32 . 
     The conductive layers described herein include a conductive material and may include a metal in various embodiments. For example, each conductive layer may include one or more of copper (Cu), silver (Ag), gold (Au), aluminum (Al), tungsten (W), platinum (Pt), and palladium (Pd), for example. In some applications, conductive layers may include other conductive materials such as graphene, conductive ceramics, polysilicon, and others. Other suitable conductive materials may also be apparent to those of ordinary skill in the art. 
       FIG. 4  illustrates an example laminate radar package including a transmit antenna between two laminate layers, a front receive antenna at a front surface of the radar package, and a back receive antenna at a back surface of the radar package in accordance with an embodiment of the invention. 
     Referring to  FIG. 4 , an example laminate radar package  458  is shown which includes a transmit antenna  45 , a front side receive antenna  42  and corresponding front side receiving ground plane region  62 , and a back side receive antenna  82  and corresponding back side receiving ground plane region  92 . The antennas and ground plane regions are implemented using a first laminate layer  77 , a second laminate layer  78 , and four conductive layers  71 ,  72 ,  73 , and  74 . The laminate radar package  458  may be a specific implementation of radar package  58  as previously described in reference to  FIGS. 2A-2C and 3 . All similarly labeled elements may share common features as described in previous and subsequent embodiments in addition to having various differences as described in reference to  FIG. 4 . 
     Laminate radar package  458  is implemented using multiple conductive layers and laminate layers. The conductive layers may be patterned to form ground planes, redistributions lines, transmission lines, planar antennas, contact pads, and the like. In some embodiments, the conductive layers may be formed from a metal foil, metal layer, or metallization that has been laminated to a laminate layer. In one embodiment, the conductive layers comprise copper (Cu). In some embodiments, the conductive layers comprise other conductive materials such as silver (Ag) and aluminum (Al). In some embodiments, the conductive layers may comprise different conductive materials. 
     The laminate layers may separate the conductive layers and provide structural support for laminate radar package  458 . In various embodiments, the laminate layers comprise a low-loss high frequency material such as a woven glass reinforced hydrocarbon ceramic and/or polytetrafluoroethylene (PTFE). In some embodiments, the laminate layers comprise a pre-impregnated composite material (PPG). One or more of the laminate layers may be commercial laminate material manufactured with copper cladding on one or both surfaces. 
     One type of laminate material that may be used to form the conductive layers and laminate layers in laminate radar package  458  is copper clad laminate. Sheets of copper clad laminate material may be fabricated as single-sided or double-sided copper clad sheets. During the fabrication process, copper sheets may be placed on one or both sides of the laminate material. Some combination of heat and pressure may then be applied to facilitate attachment of the copper sheets to the laminate material. 
     A conductive layer on a surface of a laminate layer may be an electrodeposited (ED) foil or a rolled foil, for example. A rolled foil sheet may be produced by repeatedly feeding the foil sheet through rollers to evenly reduce the thickness of the foil sheet. ED foil may be more rigid and have a different grain structure. In contrast, rolled foil may be smooth and flexible. In some cases, rolled foil may be advantageous in RF applications, due to decreased surface roughness. 
     One or more vias  75  connect the first conductive layer  71  and the third conductive layer  73 . For example, prior to attaching the second laminate layer  78  to the first laminate layer  77 , one or more vias  75  may be formed as through substrate vias (TSVs) passing through the first laminate layer  77  from the first conductive layer  71  on a back side  19  surface of the first laminate layer  77  to an opposing surface of the first laminate layer  77 . The one or more vias  75  may be exposed at the opposing surface such that electrical contact is made with third conductive layer  73  upon attachment of second laminate layer  78  to first laminate layer  77 . Alternatively, the one more vias  75  may be implemented as blind vias after second laminate layer  78  is attached to first laminate layer  77  electrically connecting first conductive layer  71  to third conductive layer  73 . 
     In various embodiments, the one or more vias  75  may provide electrical coupling between front side receiving ground plane region  62  and back side receiving ground plane region  92 . In this way front side receiving ground plane region  62  and back side receiving ground plane region  92  may be coupled to a ground or reference potential in order to provide electromagnetic shielding of respective sides of front side receive antenna  42  and back side receive antenna  82 . Additional vias may be included to electrically couple other conductive layers and components as necessary for specific functionality in various applications. 
       FIG. 5  illustrates an example radar system including a housing enclosing a transmit antenna, a front receive antenna, and a back receive antenna attached to a multiplayer printed circuit board in accordance with an embodiment of the invention. The example radar system of  FIG. 5  may be alternative implementation of the radar system as described in reference to  FIG. 2  and may be applied to the embodiment of  FIG. 2  as well as to other embodiments. 
     Referring to  FIG. 5 , a radar system  504  includes a transmit antenna  45 , a front side receive antenna  42  and corresponding front side receiving ground plane region  62 , and a back side receive antenna  82  and corresponding back side receiving ground plane region  92 . The antennas and ground plane regions are implemented using a front PCB  51  and a back PCB  53 . The combination of front PCB  51  and back PCB  53  may be a specific multilayer PCB implementation of PCB  34  as described in other embodiments. However, in contrast to other embodiments which utilize a radar package attached to a PCB, in radar system  504  the antennas, ground plane regions, and IC chip  32  may be directly attached to front PCB  51  and back PCB  53  as part of a PCB  34 . 
     In this configuration, a common ground layer  38  disposed between front PCB  51  and back PCB  53  may be used to implement both front side receiving ground plane region  62  and back side receiving ground plane region  92  as well as transmit antenna  45 . Through-hole vias  76  may then provide electrical coupling to a front side conductive layer  37  and a back side conductive layer  39 . One or more front side receive antennas  42  may be implemented in front side conductive layer  37  while one or more back side receive antennas  82  may be implemented in back side conductive layer  39 . 
     The PCB  34  may be disposed in a housing  56  which may be as previously described in reference to  FIG. 2B . RF signals may pass through outer surfaces of the housing  56  including front and back side transmitted RF signals  10  and  20 , and front and back side reflected RF signals  12  and  22 . 
       FIGS. 6A and 6B  illustrate an example radar package including a transmit antenna, a front receive antenna, and three back receive antennas in accordance with an embodiment of the invention where  FIG. 6A  illustrates a top view of the radar package and  FIG. 6B  illustrates a three-dimensional view of the relative locations of antennas and ground planes within the radar package. The example radar package illustrated in  FIGS. 6A and 6B  may be a specific implementation of other example radar packages as described in previous embodiments such as in reference to  FIGS. 2A-2C and 3-5 , for example. 
     Referring to  FIGS. 6A and 6B , a top view and a three-dimensional view of a radar package  658  is shown which includes a transmit antenna  45  disposed within a substrate  52  and configured to transmit a front side transmitted RF signal  10  and a back side transmitted RF signal  20 . In this embodiment, transmit antenna  45  is implemented as an omnidirectional antenna, but other configurations are possible. The radar package  658  further includes a front side receive antenna  42  and a corresponding front side receiving ground plane region  62  attached to substrate  52 . Front side receive antenna  42  is configured to receive front side reflected RF signal  12  which may be generated when front side transmitted RF signal  10  reflects off an object located at a distance on a front side  18  of radar package  658 . 
     Radar package  658  also includes a first back side receive antenna  81 , a second back side receive antenna  83 , and a third back side receive antenna  84 . RF signals originating from the front side  18  of radar package  658  may be blocked from reaching the back side receive antennas using a first back side receiving ground plane region  91 , a second back side receiving ground plane region  93 , and a third back side receiving ground plane region  94 . 
     The back side receive antennas are configured to receive corresponding reflected RF signals including a first back side reflected RF signal  21 , a second back side reflected RF signal  23 , and a third back side reflected RF signal  24 . These back side reflected RF signals may be generated when back side transmitted RF signal  20  reflects off an object located at a distance on a back side  19  of radar package  658 . Each back side reflected RF signal may have different properties as determined by radio frequency circuitry coupled to the back side receive antennas. For example, comparison of phase information included in the back side reflected RF signals may allow radar package  658  to track movement of an object located at a distance on the back side of radar package  658  and moving in a direction parallel to a back side surface of substrate  52 . 
     As an example, a single receive antenna configuration may be used to track movement of an object in a direction that is perpendicular to a surface of the substrate. As a second example, a configuration of two receive antennas arranged in a row may be used to track movement of an object in both the direction perpendicular to the surface of the substrate and a direction parallel to the surface of the substrate and the row of two receive antennas. Such a configuration may allow the radar package to track two dimensional movement of an object. 
     As a third example, a configuration of three receive antennas arranged in a row of two antennas and a column of two antennas may be used to track movement of an object in the direction perpendicular to the surface of the substrate, the direction parallel to both the surface of the substrate and the row of two receive antennas, and in a direction parallel to both the surface of the substrate and the column of two receive antennas. Such as configuration may allow the radar package to track three dimensional movement of an object. In this way, the first back side receive antenna  81 , the second back side receive antenna  83 , and the third back side receive antenna  84  of radar package  658  may be used to track three dimensional movement of an object located at a distance on the back side  19  of the radar package  658 . 
       FIGS. 7A and 7B  illustrate another example radar package including a transmit antenna, a front receive antenna, and three back receive antennas in accordance with an embodiment of the invention where  FIG. 7A  illustrates a top view of the radar package and  FIG. 7B  illustrates a three-dimensional view of the relative locations of antennas and ground planes within the radar package. The example radar package illustrated in  FIGS. 7A and 7B  may be a specific implementation of other example radar packages as described in previous embodiments such as in reference to  FIGS. 2A-2C and 3-5 , for example. 
     Referring to  FIGS. 7A and 7B , a top view and a three-dimensional view of a radar package  758  is shown which includes a transmit antenna  45  disposed within a substrate  52  and configured to transmit a front side transmitted RF signal  10  and a back side transmitted RF signal  20 . Similar to radar package  658 , radar package  758  includes one front side receive antenna and three back side receive antennas. Radar package  758  differs from previous embodiments, in that the first back side receive antenna  81 , the second back side receive antenna  83 , and the third back side receive antenna  84  are arranged in a single column rather than the right angle configuration of radar package  658 . 
     In some implementations, including additional receive antennas in a row or column may increase the accuracy of tracked object movement along a direction parallel to the row or column. For example, in the single column configuration of radar package  758 , three receive antennas may be used to track movement of an object in a direction perpendicular to a back side  19  surface of a substrate  52  as well as in a direction parallel to both the back side  19  surface and the column of three receive antennas. The resolution of the tracked movement may be improved by the inclusion of three receive antennas rather than two receive antennas as previously described. Additional receive antennas may be included as part of the column to further increase resolution. In various embodiments, a row of receive antennas may also be included to enable three-dimensional movement tracking. 
       FIGS. 8A and 8B  illustrate an example radar package including front transmit and receive antennas, a back transmit antenna, and three back receive antennas in accordance with an embodiment of the invention where  FIG. 8A  illustrates a top view of the radar package and  FIG. 8B  illustrates a three-dimensional view of the relative locations of antennas and ground planes within the radar package. The example radar package illustrated in  FIGS. 8A and 8B  may be a specific implementation of other example radar packages as described in previous embodiments such as in reference to  FIGS. 2A-2C and 3-5 , for example. 
     Referring to  FIGS. 8A and 8B , a top view and a three-dimensional view of a radar package  858  is shown which includes a front side transmit antenna  40  and a corresponding front side transmit ground plane region  60  and a back side transmit antenna  80  with a corresponding back side transmit ground plane region  90 . Radar package  858  is similar to previously described radar packages except for the inclusion of a separate transmit antenna for each transmit direction. For example, front side transmit ground plane region  60  may block transmitted RF signals from propagating to the back side  19  of radar package  858 . Similarly, back side transmit ground plane region  90  may block transmitted RF signals from propagation to the front side  18  of radar package  858 . 
     As illustrated, the configuration of receive antennas in radar package  858  is similar to radar package  758 . The combination of front side transmit antenna  40  and back side transmit antenna  80  may function in a similar manner to transmit antenna  45  of other embodiments. The separation of front side transmit antenna  40  and back side transmit antenna  80  may advantageously enable flexibility in the parameters of front side transmitted RF signal  10  and back side transmitted RF signal  20 . For example, frequency, intensity, and transmit timing and duration may all be adjusted independently for front side transmitted RF signal  10  and back side transmitted RF signal  20 . 
     It should be noted that although the configuration of radar package  858  for back side object detection is three receive antennas arranged in a single column as in radar package  758 , a right angle configuration as in radar package  658  is also possible with a two directional transmit antenna configuration. For example, the locations of back side transmit antenna  80  and the third back side receive antenna  84  could be switched in radar package  858 . Radar package  858  is illustrated and described as an example of a radar package using separate front side and back side transmit antennas. Other radar packages described herein as well as other configurations not described explicitly may also be implemented using a front side transmit antenna and a back side transmit antenna. Such additional configurations may be apparent to those of ordinary skill in the art. 
       FIGS. 9A and 9B  illustrate an example radar package including a transmit antenna, three front receive antennas, and three back receive antennas in accordance with an embodiment of the invention where  FIG. 9A  illustrates a top view of the radar package and  FIG. 9B  illustrates a three-dimensional view of the relative locations of antennas and ground planes within the radar package. The example radar package illustrated in  FIGS. 9A and 9B  may be a specific implementation of other example radar packages as described in previous embodiments such as in reference to  FIGS. 2A-2C and 3-5 , for example. 
     Referring to  FIGS. 9A and 9B , a top view and a three-dimensional view of a radar package  958  is shown which includes three front side receive antennas and three back side receive antennas with corresponding receive ground plane regions. Specifically, radar package  958  includes a first front side receive antenna  41  and a first front side receive ground plane region  61 , a second front side receive antenna  43  and a second front side receive ground plane region  63 , and a third front side receive antenna  44  and a third front side receive ground plane region  64  in addition to a right angle back side receive antenna configuration. The back side receive antenna configuration of radar package  958  is similar to radar package  658 . 
     In the configuration of radar package  958 , a transmit antenna  45  is configured to transmit RF signals on a front side  18  and a back side  19  of a substrate  52 . Objects located at a distance on the front side  18  and the back side  19  may generate respective reflected signals which are received by the front side receive antennas and the back side receive antennas. Specifically, first front side receive antenna  41 , second front side receive antenna  43 , and third front side receive antenna  44  may be configured to receive a first front side reflected RF signal  11 , a second front side reflected RF signal  13 , and a third front side reflected RF signal  14  respectively. In this configuration, radar package  958  may be configured to track three-dimensional movement of objects located on both the front side  18  and the back side  19  of the radar package  958 . 
       FIGS. 10A and 10B  illustrate an example radar package including a transmit antenna, a front receive antenna, and five back receive antennas in accordance with an embodiment of the invention where  FIG. 10A  illustrates a top view of the radar package and  FIG. 10B  illustrates a three-dimensional view of the relative locations of antennas and ground planes within the radar package. The example radar package illustrated in  FIGS. 10A and 10B  may be a specific implementation of other example radar packages as described in previous embodiments such as in reference to  FIGS. 2A-2C and 3-5 , for example. 
     Referring to  FIGS. 10A and 10B , a top view and a three-dimensional view of a radar package  1058  is shown which includes a front side receive antenna and five back side receive antennas with corresponding receive ground plane regions. Radar package  1058  has a similar configuration as radar package  658  except that two additional back side receive antennas are included. Specifically, radar package  1058  includes a fourth back side receive antenna  85  with a corresponding fourth back side receive ground plane region  95  and a fifth back side receive antenna  86  with a corresponding fifth back side receive ground plane region  96  which are configured to receive fourth back side reflected RF signal  25  and fifth back side reflected RF signal  26  respectively. 
     In the configuration of radar package  1058 , the resolution of both the vertical and horizontal components parallel to a back side  19  surface of substrate  52  may be improved by including fourth back side receive antenna  85  and fifth back side receive antenna  86 . Similar to previous embodiments, the configuration illustrated in Figure to may include more antennas or fewer antennas depending on desired functionality for specific applications. 
       FIGS. 11A and 11B  illustrate a method of forming a radar system in accordance with an embodiment of the invention where  FIG. 11A  illustrates steps  1102  through  1116  and  FIG. 11B  illustrates steps  1118  through  1130 . 
     Referring to  FIG. 11A , the method  1100  of forming the radar system includes a step  1102  of forming the radar system includes providing a first laminate layer of a radar package. The first laminate layer may comprise a laminate material and may be a PCB in various embodiments. The method  1100  further includes a step  1104  of forming a first conductive layer on a first surface of the first laminate layer. Alternatively, the first conductive layer may already be present on the first surface of the first laminate layer and step  1104  may be omitted. After forming the first conductive layer, method  1100  includes a step  1106  of patterning the first conductive layer to form one or more antennas and one or more ground plane regions. The one or more antennas and one or more ground lane regions may be antennas and ground plane regions on a back side of a radar package as described in previous embodiments. 
     The method  1100  further includes a step  1108  of forming a second conductive layer on a second surface of the first laminate layer. The second surface may be an opposing surface relative to the first surface. As with the first conductive layer, the second conductive layer may already be present on the second surface of the first laminate layer and step  1108  may be omitted. After forming the second conductive layer, the method  1100  also includes a step  1110  of patterning the second conductive layer to form an antenna. The antenna patterned from the second conductive layer may a transmit antenna as described in previous embodiments. In some embodiments, additional antennas may be patterned in the second conductive layer as well as other components. 
     Still referring to  FIG. 11A , the method  1100  also includes a step  1112  of forming an insulating layer over the second conductive layer. The insulating layer may prevent a subsequently formed third conductive layer from making electrical contact with the second conductive layer. After the insulating layer is formed, the method  1100  includes a step  1114  of forming a third conductive layer over the insulating layer and a step  1116  of patterning the third conductive layer to form one or more ground plane regions and first interconnects. The one or more ground plane regions may correspond to subsequently formed antennas as described in previous embodiments. 
     Now referring to  FIG. 11B , the method  1100  includes a step  1118  of forming a second laminate layer of the radar package over the third conductive layer and a step  1120  of forming a fourth conductive layer over the second laminate layer. As with previous steps, the fourth conductive layer may optionally already be present on the second laminate layer and step  1120  may be omitted. The method  1100  further includes a step  1122  of patterning the fourth conductive layer to form one or more antennas and second interconnects. 
     The method  1100  also includes a step  1124  of attaching an IC chip to the radar package. The IC chip may be an RFIC chip in various embodiments. Step  1124  may be performed at any suitable time during the process of forming the radar package. For example, in some embodiments, the RFIC chip may be coupled to the second interconnects in the fourth conductive layer and may be attached after step  1122 . In other embodiments, the IC chip may be enclosed within the second laminate layer and may be coupled to the first interconnects in the third conductive layer and may be attached prior to step  1120 . Alternatively, the IC chip may be attached at a different time or to different conductive layers and may also be attached to a separate substrate in the radar system in some embodiments. 
     Still referring to  FIG. 11B , the method  1100  includes a step  1126  of coupling the IC chip to the antennas using the first interconnects. Optionally, the IC chip may use interconnects in a different conductive layer to connect to the antennas. Additionally, step  1126  may also be performed at the same time as step  1124  where the same connections may function as both physical and electrical connections. 
     After the radar package has been formed, the method  1100  further includes a step  1126  of attaching the radar package to a PCB using the second interconnects. The radar package may be attached to the PCB as in previous embodiments, such as in reference to  FIG. 2 , for example. After the radar package has been attached to the PCB, method  1100  may include a step  1130  of enclosing the radar package and the PCB in a housing to form a radar system. The housing may also be as previously described. 
       FIG. 12  illustrates a method of operating a radar system including detecting objects on opposing sides of a substrate in accordance with an embodiment of the invention. 
     Referring to  FIG. 12 , a method  1200  of operating a radar system includes a step  1202  of transmitting a transmitted RF signal in a first direction away from a first side of a substrate and in a second direction away from an opposite second side of the substrate. Optionally, two separate RF signals may be transmitted in each of the first direction and the second direction. In this scenario, the two separate RF signals may be transmitted by the same transmit antenna or by different transmit antennas as previously described. 
     The method  1200  may further include a step  1204  of receiving a first reflected RF signal generated by the transmitted RF signal at the first side of the substrate by a first receive antenna followed by a step  1206  of detecting a first object located on the first side of the substrate according to the first reflected RF signal. The method  1200  also includes a step  1208  of receiving a second reflected RF signal generated by the transmitted RF signal at the second side of the substrate by a second receive antenna followed by a step  1210  of detecting a second object located on the second side of the substrate according to the second reflected RF signal. 
       FIG. 13  illustrates a method of operating a radar system including tracking movement of an object on one side of a substrate and detecting another object on an opposing side of the substrate in accordance with an embodiment of the invention. 
     Referring to  FIG. 13 , a method  1300  of operating a radar system includes steps  1202 ,  1204 ,  1208 , and  1210  as previously described in reference to method  1200  of  FIG. 12 . In contrast to method  1200 , method  1300  includes a step  1305  of receiving a second reflected RF signal generated by the transmitted RF signal at the first side of the substrate by a second receive antenna. 
     The method  1300  further includes a step  1306  of tracking movement of a first object located on the first side of the substrate and moving in a direction parallel to the substrate according to the first and second reflected RF signals. Receiving a second reflected RF signal at the first side may increase the functionality of the radar system and allow for two-dimensional movement tracking including a direction parallel to the first surface of the substrate as well as a direction perpendicular to the surface of the substrate. 
       FIG. 14  illustrates a method of operating a radar system including tracking movement of an object in three dimensional space on one side of a substrate and detecting another object on an opposing side of the substrate in accordance with an embodiment of the invention. 
     Referring to  FIG. 14 , a method  1400  of operating a radar system includes steps  1202 ,  1204 ,  1305 ,  1208 , and  1210  as previously described in reference to method  1300  of  FIG. 13 . In addition to these steps, method  1400  includes a step  1406  of receiving a third reflected RF signal generated by the transmitted RF signal at the first side of the substrate by a third receive antenna. 
     The method  1400  further includes a step  1407  of tracking movement of a first object located on the first side of the substrate according to the first, second, and third reflected RF signals, the object moving in a direction that has nonzero components in two orthogonal directions parallel to the substrate. Similar to the increased functionality afforded to method  1300  over method  1200  by step  1305 , step  1406  of method  1400  enables the additional functionality of step  1407 . Alternatively, the step  1406  of receiving the third reflected RF signal may enable improved resolution in a direction parallel to the substrate rather than adding a third measureable component to the movement tracking. 
       FIGS. 15A, 15B, and 15C  illustrate three example radar systems including a radar package where  FIG. 15A  illustrates a mobile phone,  FIG. 15B , illustrates a pair of headphones, and  FIG. 15C  illustrates a personal assistant device in accordance with several embodiments of the invention. The mobile phone, headphones, and personal assistant devices as well as other similar electronic devices may incorporate dual-sided radar packages as described in any of the various embodiments herein. 
     Referring to  FIGS. 15A, 15B, and 15C , radar packages  58  are included in various electronic devices such as a mobile phone  1501 , a pair of headphones  1502 , and a personal assistant device  1503 . Each radar package  58  is configured to transmit a front side transmitted RF signal  10  and a back side transmitted RF signal  20 . In addition, each radar package  58  is further configured to receive a front side reflected RF signal  12  and a back side reflected RF signal  22 . Each radar package  58  and RF signal may be as previously described in various embodiments. 
     The labels of “front side” and “back side” are merely convenient labels and may or may not have any direct meaning regarding the electronic device transmitting and receiving the RF signals. For example, in the case of mobile phone  1501  the front side and back side RF signals may correspond with what one may consider the front side and back side of the mobile phone  1501 . Alternatively, in the case of the personal assistant device, the front side and back side RF signals may only correspond to sides of radar package  58  and may not correspond to a “front side” or “back side” of personal assistant device  1503 . 
     The dual-sided radar package configuration as implemented in mobile phone  1501 , headphones  1502 , and personal assistant device  1503  may be advantageously configured to perform various control and monitoring functions congruent with desired functionality of the specific electronic device. For example, radar package  58  as implemented in mobile phone  1501  may be configured to be controlled using gesture sensing on the front side of the device as well as compensate for unwanted motion while using the front side camera. At the back side, radar package  58  of mobile phone  1501  may be configured to provide imaging functionality, object tracking and ranging, and compensation for unwanted motion while using the back side camera. 
     As another example, radar package  58  as implemented in headphones  1502  may be configured to determine whether headphones  1502  are currently being worn by a user and monitor various biometrics such as heart rate at a front side of radar package  58  while being configured to be controlled using gesture sensing at a back side of radar package  58 . As still another example, radar package  58  as implemented in personal assistant device  1503  may be may be configured to use both sides of radar package  58  to provide gesture control and object tracking and ranging in a region around personal assistant device  1503 . For example, radar package  58  may provide substantially 360° coverage around personal assistant device  1503 . Alternatively, radar functionality may be provided on two sides of personal assistant device  1503  in to regions that are each defined by an angle less than 180°. 
     Example embodiments of the present invention are summarized here. Other embodiments can also be understood from the entirety of the specification as well as the claims filed herein. 
     Example 1. A radar system including: a substrate including a first surface and a second surface, the first surface being opposite the second surface; transmitter front-end circuitry attached to the substrate, the transmitter front-end circuitry being configured to transmit a transmitted radio frequency (RF) signal in a first direction away from the first surface and in a second direction away from the second surface; a first receive antenna disposed at the first surface, the first receive antenna being configured to receive a first reflected RF signal propagating in the second direction, the first reflected RF signal being generated by the transmitted RF signal; and a second receive antenna disposed at the second surface, the second receive antenna being configured to receive a second reflect RF signal propagating in the first direction, the second reflected RF signal being generated by the transmitted RF signal. 
     Example 2. The radar system of example 1, further including: RF circuitry disposed on the substrate, the RF circuitry being configured to detect a first object located in the first direction according to the first reflected RF signal, and detect a second object located in the second direction according to the second reflected RF signal. 
     Example 3. The radar system of one of examples 1 and 2, farther including: a housing fully enclosing the substrate, the transmitter front-end circuitry, the first receive antenna, and the second receive antenna, wherein the transmitter front-end circuitry is further configured to transmit the transmitted RF signal by transmitting the transmitted RF signal through a first surface and a second surface of a housing, the first surface being opposite the second surface, the first receive antenna is further configured to receive the first reflected RF signal by receiving the first reflected RF signal through the first surface of the housing, and the second receive antenna is further configured to receive the second reflected RF signal by receiving the second reflected RF signal through the second surface of the housing. 
     Example 4. The radar system of one of examples 1 to 3, further including: a third receive antenna disposed at the first surface of the substrate, the third receive antenna being configured to receive a third reflected RF signal generated by the transmitted RF signal, the third reflected RF signal propagating in the second direction; and RF circuitry disposed on the substrate, the RF circuitry being configured to track movement of an object moving in a third direction parallel to the first surface. 
     Example 5. The radar system of example 4, further including: a fourth receive antenna disposed at the first surface of the substrate, the fourth receive antenna being configured to receive a fourth reflected RF signal generated by the transmitted RF signal, the fourth reflected RF signal propagating in the second direction, wherein the RF circuitry is further configured to track movement of the object by tracking movement of the object in the third direction, and tracking movement of the object in a fourth direction, the fourth direction being both parallel to the first surface and perpendicular to the third direction. 
     Example 6. The radar system of one of examples 1 to 5, farther including: a transmit antenna disposed within the substrate and coupled to the transmitter front-end circuitry, the transmit antenna being configured to transmit the transmitted RF signal by transmitting a first transmitted RF signal in the first direction, and transmitting a second transmitted RF signal in the second direction. 
     Example 7. The radar system of one of examples 1 to 5, further including: a first transmit antenna disposed at the first surface and coupled to the transmitter front-end circuitry, the first transmit antenna being configured to transmit a first transmitted RF signal in the first direction; and a second transmit antenna disposed at the second surface and coupled to the transmitter front-end circuitry, the second transmit antenna being configured to transmit a second transmitted RF signal in the second direction. 
     Example 8. A method of operating a radar system, the method including: transmitting, by transmitter front-end circuitry attached to a substrate, a transmitted radio frequency (RF) signal in a first direction away from a first surface of the substrate and in a second direction away from a second surface of the substrate, the first direction being opposite the first direction; receiving, by a first receive antenna disposed at the first surface of the substrate, a first reflected RF signal generated by the transmitted RF signal, the first reflected RF signal propagating in the second direction; and receiving, by a second receive antenna disposed at the second surface of the substrate, a second reflected RF signal generated by the transmitted RF signal, the second reflected RF signal propagating in the first direction. 
     Example 9. The method of example 8, further including: detecting, by RF circuitry disposed on the substrate, a first object located in the first direction according to the first reflected RF signal; and detecting, by the RF circuitry, a second object located in the second direction according to the second reflected RF signal. 
     Example 10. The method of one of examples 8 and 9, wherein transmitting the transmitted RF signal includes transmitting the transmitted RF signal through a first surface and a second surface of a housing, the first surface being opposite the second surface, receiving the first reflected RF signal includes receiving the first reflected RF signal through the first surface of the housing, receiving the second reflected RF signal includes receiving the second reflected RF signal through the second surface of the housing, and the housing fully encloses the substrate, the transmitter front-end circuitry, the first receive antenna, and the second receive antenna. 
     Example 11. The method of one of examples 8 to 10, further including: receiving, by a third receive antenna disposed at the first surface of the substrate, a third reflected RF signal generated by the transmitted RF signal, the third reflected RF signal propagating in the second direction; and tracking movement of an object by RF circuitry disposed on the substrate, wherein the object is moving in a third direction parallel to the first surface. 
     Example 12. The method of example 11, further including: receiving, by a fourth receive antenna disposed at the first surface of the substrate, a fourth reflected RF signal generated by the transmitted RF signal, the fourth reflected RF signal propagating in the second direction, wherein tracking movement of the object includes tracking movement of the object in the third direction, and tracking movement of the object in a fourth direction, the fourth direction being both parallel to the first surface and perpendicular to the third direction. 
     Example 13. The method of one of examples 8 to 12, wherein transmitting the transmitted RF signal includes transmitting, by a transmit antenna disposed within the substrate and coupled to the transmitter front-end circuitry, a first transmitted RF signal in the first direction, and transmitting, by the transmit antenna, a second transmitted RF signal in the second direction. 
     Example 14. The method of one of examples 8 to 12, where transmitting the transmitted RF signal includes transmitting, by a first transmit antenna disposed at the first surface and coupled to the transmitter front-end circuitry, a first transmitted RF signal in the first direction, and transmitting, by a second transmit antenna disposed at a the second surface and coupled to the transmitter front-end circuitry, a second transmitted RF signal in the second direction. 
     Example 15. A method of forming a radar system, the method including: forming a first receive antenna and a first ground plane region by patterning a first conductive layer on a first surface of a first laminate layer of a radar package; forming a transmit antenna and a second ground plane region by patterning a second conductive layer on a second surface of the first laminate layer, the second surface being opposite the first surface; forming a second laminate layer of the radar package over the second conductive layer; forming a third conductive layer over the second laminate layer; forming a second receive antenna by patterning the third conductive layer; and attaching a radio frequency integrated circuit (RFIC) chip to the radar package, the RFIC being coupled to the transmit antenna, the first receive antenna, and the second receive antenna. 
     Example 16. The method of example 15, further including: forming a via passing through the first laminate layer from the first conductive layer to the second conductive layer, the via coupling the first ground plane region to the second ground plane region. 
     Example 17. The method of one of examples 15 and 16, further including: forming interconnects by patterning the third conductive layer; and attaching the radar package to a printed circuit board using the interconnects. 
     Example 18. The method of example 17, further including: enclosing the radar package and the printed circuit board in a housing, wherein the housing includes a first surface and a second surface, the first surface of the housing completely overlaps a first side of the radar package, the second surface of the housing completely overlaps a second side of the radar package opposite the first side. 
     Example 19. The method of one of examples 15 to 18, wherein forming the transmit antenna and the second ground plane region includes forming the transmit antenna by patterning a lower conductive layer of the second conductive layer, the lower conductive layer being on the second surface of the first laminate layer, forming an insulating layer over the lower conductive layer, forming an upper conductive layer of the second conductive layer over the insulating layer, and forming the second ground plane region by patterning the upper conductive layer. 
     Example 20. The method of one of examples 15 to 19, further including: forming a third receive antenna by patterning the first conductive layer, the third receive antenna being coupled to the RFIC chip; and forming a third ground plane region by patterning the second conductive layer, the third ground plane region being coupled to the second ground plane region. 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.