Patent Publication Number: US-11047951-B2

Title: Surface mount assembled waveguide transition

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present patent application is a continuation of U.S. patent application Ser. No. 14/972,825, filed on Dec. 17, 2015, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
     Radio detection and ranging (RADAR) systems can be used to actively estimate distances to environmental features by emitting radio signals and detecting returning reflected signals. Distances to radio-reflective features can be determined according to the time delay between transmission and reception. The radar system can emit a signal that varies in frequency over time, such as a signal with a time-varying frequency ramp, and then relate the difference in frequency between the emitted signal and the reflected signal to a range estimate. Some systems may also estimate relative motion of reflective objects based on Doppler frequency shifts in the received reflected signals. Directional antennas can be used for the transmission and/or reception of signals to associate each range estimate with a bearing. More generally, directional antennas can also be used to focus radiated energy on a given field of view of interest. Combining the measured distances and the directional information allows for the surrounding environment features to be mapped. The radar sensor can thus be used, for instance, by an autonomous vehicle control system to avoid obstacles indicated by the sensor information. 
     Some example automotive radar systems may be configured to operate at an electromagnetic wave frequency of 77 Giga-Hertz (GHz), which corresponds to millimeter (mm) electromagnetic wavelength (e.g., 3.9 mm for 77 GHz). These radar systems may use antennas that can focus the radiated energy into tight beams in order to enable the radar system to measure an environment with high accuracy, such as an environment around an autonomous vehicle. Such antennas may be compact (typically with rectangular form factors; e.g., 1.3 inches high by 2.5 inches wide), efficient (i.e., there should be little 77 GHz energy lost to heat in the antenna, or reflected back into the transmitter electronics), and inexpensive to manufacture. 
     SUMMARY 
     The present application discloses embodiments that relate to a radar system. In one aspect, the present application describes a radar system. The radar system may include a plurality of radiating waveguides each having a waveguide input. The radiating waveguides are aligned on a plane defined by a center of a width of the radiating waveguide and a length of the radiating waveguide. Each radiating waveguide may include at least one radiating element. The radar system may also include at least one coupling component mounted to a circuit board. The radar system may further include a beamforming network. The beamforming network may include a beamforming network input and a plurality of beamforming network outputs. Each beamforming network output may be coupled to one of the waveguide inputs. The beamforming network may also include at least one coupling port. The coupling component may extend from the circuit board into a coupling port of the radar system such that the coupling port couples the beamforming network to the coupling component. 
     In another aspect, the present application describes a method. The method involves receiving electromagnetic energy by a waveguide, where the waveguide is aligned on a plane defined by a center of a width of the waveguide and a length of the waveguide. The method also includes radiating, via radiating components of the waveguide, at least a portion of the electromagnetic energy by radiating components of the waveguide. A portion of the electromagnetic energy that is not radiated is reflected as reflected electromagnetic energy. The method also includes coupling at least a portion of the reflected electromagnetic energy to an attenuation port, where the attenuation port is aligned perpendicular to the plane. The method further includes coupling at least a portion of the reflected electromagnetic energy to an attenuation component, wherein the attenuation component is disposed on a circuit board. The method additionally includes at least one of (i) receiving electromagnetic energy by a waveguide and (ii) coupling at least a portion of the reflected electromagnetic energy to an attenuation port is performed by at least one coupling component mounted to a circuit board. 
     In yet another aspect, the present application describes an apparatus. The apparatus may include a circuit board configured to propagate an electromagnetic signal. The apparatus may also include a waveguide configured to propagate an electromagnetic signal. Additionally, the apparatus may include a coupling component configured to couple a signal between the circuit board and the waveguide, where the coupling component is mounted to a surface of the circuit board. 
     In still another aspect, a system is provided that includes means for receiving electromagnetic energy by a waveguide, where the waveguide is aligned on a plane defined by a center of a width of the waveguide and a length of the waveguide. The system also includes means for radiating at least a portion of the electromagnetic energy by radiating means of the waveguide. A portion of the electromagnetic energy that is not radiated is reflected as reflected electromagnetic energy. The system also includes means for coupling at least a portion of the reflected electromagnetic energy to an attenuation port, where the attenuation port is aligned perpendicular to the plane. The system further includes means for coupling at least a portion of the reflected electromagnetic energy to a means for attenuation, wherein the means for attenuation is disposed on a circuit board. The system additionally includes at least one of (i) receiving electromagnetic energy by a waveguide and (ii) coupling at least a portion of the reflected electromagnetic energy to an attenuation port is performed by at least one means for coupling mounted to a circuit board. 
     The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the figures and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a flowchart of an example method to radiate electromagnetic energy. 
         FIG. 2A  illustrates a first layer of an example antenna, in accordance with an example embodiment. 
         FIG. 2B  illustrates a second layer of an example antenna, in accordance with an example embodiment. 
         FIG. 2C  illustrates an assembled view of an example antenna, in accordance with an example embodiment 
         FIG. 2D  illustrates an assembled view of an example antenna, in accordance with an example embodiment. 
         FIG. 2E  illustrates conceptual waveguide channels formed inside an assembled example antenna, in accordance with an example embodiment. 
         FIG. 2F  illustrates four sets of transmitting waveguide channels formed inside an assembled example antenna. 
         FIG. 3A  illustrates a network of wave-dividing channels of an example antenna, in accordance with an example embodiment. 
         FIG. 3B  illustrates an alternate view of the network of wave-dividing channels of  FIG. 3A , in accordance with an example embodiment. 
         FIG. 4A  illustrates an example surface mount assembled waveguide transition, in accordance with an example embodiment. 
         FIG. 4B  illustrates top-down view of two pairs of mounting points for coupling components surface mounted on a circuit board, in accordance with an example embodiment. 
         FIG. 4C  illustrates an example arrangement of waveguide terminations and loads on a circuit board, in accordance with an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying figures, which form a part hereof. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, figures, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     The following detailed description discloses an apparatus including an antenna for a radar system for an autonomous vehicle, for instance, and a method for operating such an antenna. In some examples, the antenna may be a “dual open-ended waveguide” (DOEWG) antenna. The term “DOEWG” can refer to a short section of a horizontal waveguide channel plus a vertical channel that splits into two parts, where each of the two parts of the vertical channel includes an output port configured to radiate at least a portion of electromagnetic waves that enter the antenna. 
     An example DOEWG antenna may comprise, for example, two metal layers (e.g., aluminum plates) that can be machined with computer numerical control (CNC), aligned properly, and joined together. The first metal layer may include a first half of an input waveguide channel, where the first half of the first waveguide channel includes an input port that may be configured to receive electromagnetic waves (e.g., 77 GHz millimeter waves) into the first waveguide channel. The first metal layer may also include a first half of a plurality of wave-dividing channels. The plurality of wave-dividing channels may comprise a network of channels that branch out from the input waveguide channel and that may be configured to receive the electromagnetic waves from the input waveguide channel, divide the electromagnetic waves into a plurality of portions of electromagnetic waves (i.e., power dividers), and propagate respective portions of electromagnetic waves to respective wave-radiating channels of a plurality of wave-radiating channels. The DOEWG may also include at least a printed circuit board (PCB) backplane configured to absorb some electromagnetic radiation. 
     Further, the first metal layer may include a first half of the plurality of wave-radiating channels, where respective wave-radiating channels may be configured to receive the respective portions of electromagnetic waves from the wave-dividing channels, and where first halves of the respective wave-radiating channels include at least one wave-directing member configured to propagate sub-portions of electromagnetic waves to another metal layer. 
     Moreover, the second metal layer may include second halves of the input waveguide channel, the plurality of wave-dividing channels, and the plurality of wave-radiating channels. The second halves of the respective wave-radiating channels may include at least one pair of output ports partially aligned with the at least one wave-directing member and configured to radiate the sub-portions of electromagnetic waves propagated from the at least one wave-directing member out of the second metal layer. More particularly, a combination of a given wave-directing member with a corresponding pair of output ports may take the form of (and may be referred to herein as) a DOEWG, as described above. 
     While in this particular example the antenna includes multiple wave-dividing channels and multiple wave-radiating channels, in other examples the antenna may include only a single channel configured to propagate all the electromagnetic waves received by the input port to one or more wave-radiating channels. For instance, all the electromagnetic waves may be radiated out of the second metal layer by a single DOEWG. Other examples are possible as well. 
     Furthermore, while in this particular example, as well as in other examples described herein, the antenna apparatus may be comprised of at least two metal layers, it should be understood that in still other examples, one or more of the channels described above may be formed into a single metal layer, or into more than two metal layers that make up the antenna. Still further, within examples herein, the concept of electromagnetic waves (or portions/sub-portions thereof) propagating from one layer of a DOEWG antenna to another layer is described for the purpose of illustrating functions of certain components of the antenna, such as the wave-directing members. In reality, electromagnetic waves may not be confined to any particular “half” of a channel during certain points of their propagation through the antenna. Rather, at these certain points, the electromagnetic waves may propagate freely through both halves of a given channel when the halves are combined to form the given channel. 
     In some embodiments discussed herein, the two metal layers may be joined directly, without the use of adhesives, dielectrics, or other materials, and without methods such as soldering, diffusion bonding, etc. that can be used to join two metal layers. For example, the two metal layers may be joined by making the two layers in physical contact without any further means of coupling the layers. 
     In some examples, the present disclosure is directed toward a printed circuit board (PCB) backplane configured to absorb some electromagnetic radiation. The previously-discussed radiating waveguides may be configured to receive an electromagnetic signal at the radiating waveguide input, propagate the electromagnetic signal down a length of the radiating waveguide, and coupled to at least a portion of the electromagnetic signal to at least one radiating element configured to radiate the coupled electromagnetic signal. However, a portion of the electromagnetic signal may not be radiated and may be either reflected or contained within the waveguide. This electromagnetic energy may produce undesired effects in the radar system. Therefore, to reduce the effects from electromagnetic energy that was not radiated, it may be desirable to absorb the non-radiated electromagnetic energy into a load. The waveguides may each be coupled to an attenuation port (or termination port) configured to absorb non-radiated electromagnetic energy that is present in the waveguide. 
     In one example, each of the beamforming network outputs may have a corresponding waveguide shunt, that is the end of the waveguide, located on the opposite end of the waveguide from the respective beamforming network output. Of the shunts, one may be coupled to the beamforming network input. The remaining shunts may each be coupled to a respective attenuation port (or termination port). In some examples, each shunt, including the shunt with the feed, may be coupled to an attenuation port. The attenuation port may be aligned perpendicular to the main length of the waveguide. Additionally, the attenuation port may include a geometry to impedance match the waveguide to the attenuation component. For example, the attenuation port may be a hole in a waveguide block coupling a circuit board layer to a waveguide layer. 
     The attenuation port may couple a waveguide of the beamforming network to an attenuation component located on the PCB via a coupling component located in the attenuation port. The attenuation component may include metallic traces on the PCB. The metallic traces may function to couple the non-radiated electromagnetic energy out of the waveguide into the PCB. Once the non-radiated electromagnetic energy has coupled to the traces, various different means may be used to absorb the non-radiated electromagnetic energy. In one example, the traces may be coupled to other components that may dissipate the non-radiated electromagnetic energy. In one example, the traces may be coated with an electrically lossy material that will absorb electrical current present on the surface of the traces when it couples to the non-radiated electromagnetic energy. In another example, the PCB may have microstrip lines configured to absorb the non-radiated electromagnetic energy. The microstrip lines may absorb the non-radiated electromagnetic energy based on the lines being made from an electromagnetically lossy material, such as Nickel Chrome. In another example, the PCB may be constructed from an electromagnetically lossy material. 
     In one example, each attenuation port may function to absorb non-radiated electromagnetic energy itself. In a different example, each attenuation port may function to route the non-radiated electromagnetic energy to an attenuation component configured to absorb energy from more than one attenuation port. 
     The antenna apparatus may include a waveguide feed. The waveguide feed may be a port in the metallic structure that enables an electromagnetic wave to enter the antenna apparatus. When the electromagnetic wave enters the antenna apparatus, it may be divided and radiated as previously discussed. The coupling component may function as a bidirectional component. It may both provide a feed signal to the waveguide and remove non-radiated electromagnetic energy from the waveguide. 
     Both the attenuation port and a waveguide feed of the antenna apparatus may have an associated port impedance. The port impedance may affect the percentage of the electromagnetic energy that the port can couple into or out of the antenna apparatus. Therefore, it may be desirable to optimize the port impedance so energy can efficiently enter or leave the antenna apparatus. There may be several methods by which the port impedance may be optimized. In some examples, a port geometry may be altered in order to adjust the port impedance. In other examples, a coupling component may form a portion of the port. The coupling component may have a designed impedance so that energy can efficiently enter or leave the antenna apparatus. In some examples, the coupling component may be a metallic component that is surface mounted to a PCB using surface-mount technology (SMT). The coupling component may extend from the PCB into the waveguide. The coupling component may operate in a differential mode to excite or capture electromagnetic energy. 
     Referring now to the figures,  FIG. 1  is a flowchart of an example method  100  for the operation of a radar system. It should be understood that other methods of operation not described herein are possible as well. 
     It should also be understood that a given application of such an antenna may determine appropriate dimensions and sizes for various machined portions of the two metal layers described above (e.g., channel size, metal layer thickness, etc.) and/or for other machined (or non-machined) portions/components of the antenna described herein. For instance, as discussed above, some example radar systems may be configured to operate at an electromagnetic wave frequency of 77 GHz, which corresponds to millimeter electromagnetic wave length. At this frequency, the channels, ports, etc. of an apparatus fabricated by way of method  100  may be of given dimensions appropriated for the 77 GHz frequency. Other example antennas and antenna applications are possible as well. 
     Although the blocks are illustrated in a sequential order, these blocks may also be performed in parallel, and/or in a different order than those described herein. Also, the various blocks may be combined into fewer blocks, divided into additional blocks, and/or removed based upon the desired implementation. 
     Moreover, the method  100  of  FIG. 1  may be implemented by the devices described in conjunction with  FIGS. 2A-2F, 3A, 3B, and 4A-4C . 
     At block  102 , the method  100  includes receiving electromagnetic energy (e.g., 77 GHz millimeter electromagnetic waves) by a waveguide. The electromagnetic energy may be received from a waveguide feed coupled to the waveguide. In one example, receiving electromagnetic energy by a beamforming network input of the waveguide may be performed via a port in a bottom layer and coupling the electromagnetic energy from the port into the waveguide. 
     Additionally, the waveguide may be aligned on a plane defined by a center of a width of the waveguide and a length of the waveguide. For example, and as discussed with respect to the following figures, the waveguide may be constructed in a block. The waveguide and associated beamforming network may be created on a plane of the block. Further, the feed of the waveguide may be located perpendicular to the plane and couple energy from outside the waveguide into the waveguide. 
     At block  104 , the method  100  includes radiating at least a portion of the electromagnetic energy by radiating components of the waveguide. The waveguide may have one or more radiating components. The radiating components may take the form of antennas, slots, or other radiating structures. During the transmission of signals, the radiating components are configured to convert guided electromagnetic energy from inside the waveguide to unguided electromagnetic energy radiated into free space, such that the electromagnetic energy is transmitted by the radiating components. Notably, a radiating component may not transmit all the electromagnetic energy that is exposed to the respective radiating component. Based on both an impedance and polarization match, the radiating component may only transmit a portion of the electromagnetic energy to which it is exposed. A portion of the electromagnetic energy that is not radiated is reflected back into the waveguide as reflected electromagnetic energy. The reflected electromagnetic energy is generally undesired; therefore, it may be desirable to remove it from the radar system by attenuation. 
     At block  106 , the method  100  includes coupling at least a portion of the reflected electromagnetic energy to an attenuation port. The attenuation port is aligned perpendicular to the plane. Due to the perpendicular alignment of the attenuation port, the attenuation port removes at least a portion of the reflected electromagnetic energy from the plane of the waveguide. 
     In some examples, the radar system may include a plurality of attenuation ports. Each attenuation port may be coupled to an elongated segment of the waveguide. Further, each attenuation port may be shaped so as to match (or approximately match) an impedance of the waveguide. By impedance matching, the amount of the reflected electromagnetic energy that is coupled from the waveguide to the attenuation port may be maximized. 
     At block  108 , the method  100  includes coupling at least a portion of the reflected electromagnetic energy to an attenuation component. The attenuation component may essentially act as a receiving antenna. 
     In example embodiments, the attenuation component is disposed on a circuit board located outside of, or on an external surface of, the waveguide block structure. By having the attenuation component on a circuit board: (i) the attenuation component may be easy to manufacture, (ii) the at least a portion of the reflected electromagnetic energy may be removed from the waveguide block structure, and (iii) the circuit board may be used to attenuate the at least a portion of the reflected electromagnetic energy. 
     In some examples, the attenuation component may include traces on the surface of the circuit board. The traces may receive the at least a portion of the reflected electromagnetic energy from the coupling component of the attenuation port. In some examples, a surface of the traces may be configured to absorb the portion of the reflected electromagnetic energy. In some further examples, the attenuation component may include at least one microstrip line on the circuit board. Yet further, the attenuation component may include conductive and/or resistive ink printed on the circuit board. The conductive and/or resistive ink may be applied to the PCB through a photo mask, photo imaging, or by other means. The conductive and/or resistive ink may be applied to gaps between the tips of differential pairs or to other gaps in lines on the PCB. Further, conductive and/or resistive ink may be applied to between a PCB line and a grounding element. 
     At block  110 , the method  100  includes dissipating the portion of the reflected electromagnetic energy coupled to the attenuation component by the attenuation component. The attenuation component may be configured to act as a load or termination. When acting as a load or termination, the attenuation component may dissipate, that is reduce and/or get rid of, the reflected electromagnetic energy. The attenuation component may use various different ways to dissipate (or absorb) the reflected electromagnetic energy. In some examples, the attenuation component may be mounted on a lossy PCB. The lossy PCB will dissipate the reflected electromagnetic energy. In another example, a resistive surface of a traces (or other component) may cause dissipation of the reflected electromagnetic energy. In yet another example, the attenuation component may include a differential pair of lines configured to dissipate the reflected electromagnetic energy. The attenuation component may also be a single line, rather than a differential pair. In another example, the attenuation component may be made from Nickel Chrome (NiCr) as NiCr dissipates electromagnetic energy. In yet further examples, the attenuation component may be a resistive ink dot that dissipates electromagnetic energy. In other examples, the attenuation component may include microstrip and/or transmission lines on the PCB. 
     In some examples, the PCB may also be coupled to at least one heat sink. Because of the energy contained in the reflected electromagnetic energy, absorbing the energy may increase the temperature of the PCB. A heat sink may be able to dissipate heat from the PCB. 
     At block  112 , the method  100  includes performing by at least one coupling component mounted to a circuit board at least one of (i) receiving electromagnetic energy by a waveguide and (ii) coupling at least a portion of the reflected electromagnetic energy to an attenuation port. In some examples, the coupling component may be configured to efficiently allow the waveguide to receive electromagnetic energy at an input. In other examples, the coupling component may be configured to efficiently couple at least a portion of the reflected electromagnetic energy to an attenuation port. In some examples, the method may include both the receiving and coupling being performed by coupling components. 
     As previously discussed, both the attenuation port and a waveguide feed of the antenna apparatus may have an associated port impedance. The port impedance may affect the percentage of the electromagnetic energy that the port can couple into or out of the antenna apparatus. Therefore, it may be desirable to optimize the port impedance so energy can efficiently enter or leave the antenna apparatus. The presently-disclosed coupling component may form a portion of the port and function to optimize the port impedance. The coupling component may be designed impedance so energy can efficiently enter or leave the antenna apparatus. 
       FIG. 2A  illustrates an example first metal layer  200  including a first half of a plurality of waveguide channels  202 . These waveguide channels  202  may comprise multiple elongated segments  204 . At a first end  206  of each elongated segment  204  may be a plurality of collinear wave-directing members  208 , each with sizes similar or different from other wave-directing members. In line with the description above, the first ends  206  of the elongated segments  204  may be referred to herein as a first half of wave-radiating channels. 
     At a second end  210  of the channels  202  opposite the first end  206 , one of the elongated segments  204  may include a through-hole  212  (i.e., input port). A given amount of power may be used to feed a corresponding amount of electromagnetic waves (i.e., energy) into the apparatus, and the through-hole  212  may be the location where these waves are fed into the apparatus. In line with the description above, the single channel/segment of the waveguide channels  202  that includes the input port may be referred to herein as an input waveguide channel. Further, the second end  210  of the channels  202  may be coupled to attenuation components (not shown here), as discussed throughout this disclosure. 
     Upon entering the apparatus, the electromagnetic waves may generally travel in the +x direction, as shown, towards an array of power dividers  214  (i.e., a “beam-forming network”). The array  214  may function to divide up the electromagnetic waves and propagate respective portions of the waves to respective first ends  206  of each elongated segment  204 . More specifically, the waves may continue to propagate in the +x direction after leaving the array  214  toward the wave-directing members  208 . In line with the description above, the array  214  section of the waveguide channels may be referred to herein as wave-dividing channels. 
     As the portions of the electromagnetic waves reach the wave-directing members  208  at the first end  206  of each elongated segment  204  of the waveguide channels  202 , the wave-directing members  208  may propagate through respective sub-portions of the electromagnetic energy to a second half of the waveguide channels (i.e., in the +z direction, as shown). For instance, the electromagnetic energy may first reach a wave-directing member that is recessed, or machined further into the first metal layer  200  (i.e., a pocket). That recessed member may be configured to propagate a smaller fraction of the electromagnetic energy than each of the subsequent members further down the first end  206 , which may be protruding members rather than recessed members. 
     Further, each subsequent member may be configured to propagate a greater fraction of the electromagnetic waves travelling down that particular elongated segment  204  at the first end  206  than the member that came before it. As such, the member at the far end of the first end  206  may be configured to propagate the highest fraction of electromagnetic waves. Each wave-directing member  208  may take various shapes with various dimensions. In other examples, more than one member (or no members) may be recessed. Still other examples are possible as well. In addition, varying quantities of elongated segments are possible. 
     A second metal layer may contain a second half of the one or more waveguide channels, where respective portions of the second half of the one or more waveguide channels include an elongated segment substantially aligned with the elongated segment of the first half of the one or more waveguide channels and, at an end of the elongated segment, at least one pair of through-holes partially aligned with the at least one wave-directing member and configured to radiate electromagnetic waves propagated from the at least one wave-directing member out of the second metal layer. 
     Within examples, the elongated segment of the second half may be considered to substantially align with the elongated segment of the first half when the two segments are within a threshold distance, or when centers of the segments are within a threshold distance. For instance, if the centers of the two segments are within about ±0.051 mm of each other, the segment may be considered to be substantially aligned. 
     In another example, when the two halves are combined (i.e., when the two metal layers are joined together), edges of the segments may be considered to be substantially aligned if an edge of the first half of a segment and a corresponding edge of the second half of the segment are within about ±0.051 mm of each other. 
     In still other examples, when joining the two metal layers, one layer may be angled with respect to the other layer such that their sides are not flush with one another. In such other examples, the two metal layers, and thus the two halves of the segments, may be considered to be substantially aligned when this angle offset is less than about 0.5 degrees. 
     In some embodiments, the at least one pair of through-holes may be perpendicular to the elongated segments of the second half of the one or more waveguide channels. Further, respective pairs of the at least one pair of through-holes may include a first portion and a second portion. As such, a given pair of through-holes may meet at the first portion to form a single channel. That single channel may be configured to receive at least the portion of electromagnetic waves that was propagated by a corresponding wave-directing member and propagate at least a portion of electromagnetic waves to the second portion. Still further, the second portion may include two output ports configured as a doublet and may be configured to receive at least the portion of electromagnetic waves from the first portion of the pair of through-holes and propagate at least that portion of electromagnetic waves out of the two output ports. 
       FIG. 2B  illustrates the second metal layer  220  described above. The second metal layer  220  may include a second half of the plurality of waveguide channels  202  of the first metal layer  200  shown in  FIG. 2A  (i.e., a second half of the input waveguide channel, the wave-dividing channels, and the wave-radiating channels). As shown, the second half of the waveguide channels  202  may take on the general form of the first half of the channels, so as to facilitate proper alignment of the two halves of the channels. The elongated segments of the second half  222  may include second halves of the array of power dividers  224 . As described above, electromagnetic waves may travel through the array  224 , where they are divided into portions, and the portions then travel (i.e., in the +x direction, as shown) to respective ends  226  of the second halves of the elongated segments  222 . 
     Further, an end  226  of a given elongated segment may include multiple pairs of through-holes  228 , which may be at least partially aligned with the wave-directing members  208  of the first metal layer  200 . More specifically, each pair of through-holes may be at least partially aligned with a corresponding wave-directing member, also referred to as a reflecting element, such that when a given sub-portion of electromagnetic waves are propagated from the first metal layer  200  to the second metal layer  220 , as described above, those sub-portions are then radiated out of the pair of through-holes (i.e., a pair of output ports) in the −z direction, as shown. Again, the combination of a given wave-directing member and a corresponding pair of output ports may form a DOEWG, as described above. 
     Moreover, a combination of all the DOEWGs may be referred to herein as a DOEWG array. In antenna theory, when an antenna has a larger radiating aperture (i.e., how much surface area of the antenna radiates, where the surface area includes the DOEWG array) that antenna may have higher gain (dB) and a narrower beam width. As such, in some embodiments, a higher-gain antenna may include more channels (i.e., elongated segments), with more DOEWGs per channel. While the example antenna illustrated in  FIGS. 2A and 2B  may be suitable for autonomous-vehicle purposes (e.g., six elongated segments, with five DOEWGs per segment), other embodiments may be possible as well, and such other embodiments may be designed/machined for various applications, including, but not limited to, automotive radar. 
     For instance, in such other embodiments, an antenna may include a minimum of a single DOEWG. With this arrangement, the output ports may radiate energy in all directions (i.e. low gain, wide beam width). Generally, an upper limit of segments/DOEWGs may be determined by a type of metal used for the first and second metal layers. For example, metal that has a high resistance may attenuate an electromagnetic wave as that wave travels down a waveguide channel. As such, when a larger, highly-resistive antenna is designed (e.g., more channels, more segments, more DOEWGs, etc.), energy that is injected into the antenna via the input port may be attenuated to an extent where not much energy is radiated out of the antenna. Therefore, in order to design a larger antenna, less resistive (and more conductive) metals may be used for the first and second metal layers. For instance, in embodiments described herein, at least one of the first and second metal layers may be aluminum. Further, in other embodiments, at least one of the first and second metal layers may be copper, silver, or another conductive material. Further, aluminum metal layers may be plated with copper, silver, or other low-resistance/high-conductivity materials to increase antenna performance. Other examples are possible as well. 
     The antenna may include at least one fastener configured to join the first metal layer to the second metal layer so as to align the first half of the one or more waveguide channels with the second half of the one or more waveguide channels to form the one or more waveguide channels (i.e., align the first half of the plurality of wave-dividing channels with the second half of the plurality of wave-dividing channels, and align the first half of the plurality of wave-radiating channels with the second half of the plurality of wave-radiating channels). To facilitate this in some embodiments, the first metal layer, a first plurality of through-holes (not shown in  FIG. 2A ) may be configured to house the at least one fastener. Additionally, in the second metal layer, a second plurality of through-holes (not shown in  FIG. 2B ) may be substantially aligned with the first plurality of through-holes and configured to house the at least one fastener for joining the second metal layer to the first metal layer. In such embodiments, the at least one fastener may be provided into the aligned first and second pluralities of through-holes and secured in a manner such that the two metal layers are joined together. 
     In some examples, the at least one fastener may be multiple fasteners. Mechanical fasteners (and technology used to facilitate fastening) such as screws and alignment pins may be used to join the two metal layers together. Further, in some examples, the two metal layers may be joined directly to each other, with no adhesive layer in between. Still further, the two metal layers may be joined together using methods different than adhesion, diffusion bonding, soldering, brazing, and the like. However, it is possible that, in other examples, such methods may be used in addition to or alternative to any methods for joining metal layers that are known or not yet known. 
     In some embodiments, one or more blind-holes may be formed into the first metal layer and/or into the second metal layer in addition to or alternative to the plurality of through-holes of the first and/or the second metal layer. In such embodiments, the one or more blind-holes may be used for fastening (e.g., housing screws or alignment pins) or may be used for other purposes. 
       FIG. 2C  illustrates an assembled view of an example antenna  240 . The example antenna  240  may include the first metal layer  200  and the second metal layer  220 . The second metal layer  220  may include a plurality of holes  242  (through-holes and/or blind-holes) configured to house alignment pins, screws, and the like. The first metal layer  200  may include a plurality of holes as well (not shown) that are aligned with the holes  242  of the second metal layer  220 . 
     Further,  FIG. 2C  illustrates a DOEWG array  244  of a given width  246  and a given length  248 , which may vary based on the number of DOEWGs and channels of the antenna  240 . For instance, in an example embodiment, the DOEWG array may have a width of about 11.43 mm and a length of about 28.24 mm. Further, in such an example embodiment, these dimensions, in addition to or alternative to other dimensions of the example antenna  240 , may be machined with no less than about a 0.51 mm error, though in other embodiments, more or less of an error may be required. Other dimensions of the DOEWG array are possible as well. Further, in some examples, other shaped outputs may be used for the radiating elements. Although shown as ovals in  FIG. 2C , the radiating elements can take any shape and the shape is not critical to the present disclosure. In some examples, the radiating elements may be square, circular, linear, z-shaped, etc. 
     In some embodiments, the first and second metal layers  200 ,  220  may be machined from aluminum plates (e.g., about 6.35 mm stock). In such embodiments, the first metal layer  200  may be at least 3 mm in thickness (e.g., about 5.84 mm to 6.86 mm). Further, the second metal layer  220  may be machined from a 6.35 mm stock to a thickness of about 3.886 mm. Other thicknesses are possible as well. 
     In some embodiments, the joining of the two metal layers  200 ,  220  may result in an air gap or other discontinuity between mating surfaces of the two layers. In such embodiments, this gap or continuity can be proximate to (or perhaps as close as possible to) a center of the length of the antenna apparatus and may have a size of about 0.05 mm or smaller. 
       FIG. 2D  illustrates another assembled view of the example antenna  240 . As shown, the first metal layer  200  may include a plurality of holes  250  (through-holes and/or blind-holes) configured to house alignment pins, screws, and the like. One or more of the plurality of holes  250  may be aligned with the holes  242  of the second metal layer  220 . Further,  FIG. 2D  shows the input port  212 , where the antenna  240  may receive electromagnetic waves into the one or more waveguide channels  202 . In addition,  FIG. 2D  features multiple attenuation ports  252 . The attenuation ports  252  may couple from waveguides within the first metal layer  200  to attenuation components on a PCB (not shown in  FIG. 2D ). The attenuation ports  252  may take the form of attenuation port  404  of  FIG. 4A . 
       FIG. 2E  illustrates conceptual waveguide channels  260  formed inside an assembled example antenna. More particularly, the waveguide channels  260  take the form of the waveguide channels  202  of  FIGS. 2A and 2B . For instance, the channels  260  include an input port  262  to the input waveguide channel  264 . The channels  260  also include wave-dividing channels  266  and a plurality of radiating doublets  268  (i.e., a DOEWG array). As described above, when electromagnetic waves enter the channels  260  at the input port  262 , they may travel in the +x direction through the input waveguide channel  264  and be divided into portions by the wave-dividing channels  266  (e.g., by the power dividers). Those portions of electromagnetic waves may then travel in the +x direction to respective radiating doublets  268 , where sub-portions of those portions are radiated out each DOEWG through pairs of output ports, such as pair  270 , for instance. 
     In a particular wave-radiating channel, a portion of electromagnetic waves may first be propagated through a first DOEWG with a recessed wave-directing member  272  (i.e., an inverse step, or “well”), as discussed above. This recessed wave-directing member  272  may be configured to radiate the smallest fraction of energy of all the members of the DOEWGs of the particular wave-radiating channel. In some examples, subsequent wave-directing members  274  may be formed (e.g., protruded, rather than recessed) such that each subsequent DOEWG can radiate a higher fraction of the remaining energy than the DOEWG that came before it. Phrased another way, each wave-directing member  272 ,  274  may generally be formed as a “step cut” into a horizontal (+x direction) channel (i.e., a wave-radiating channel, or the “first end” of an “elongated segment” as noted above) and used by the antenna to tune the amount of energy that is radiated vs. the amount of energy that is transmitted further down the antenna. 
     In some embodiments, a given DOEWG may not be able to radiate more than a threshold level of energy and may not be able to radiate less than a threshold level of energy. These thresholds may vary based on the dimensions of the DOEWG components (e.g., the wave-directing member, a horizontal channel, a vertical channel, a bridge between the two output ports, etc.), or may vary based on other factors associated with the antenna. 
     In some embodiments, the first and second metal layers may be machined such that various sides of the waveguide channels  260  have rounded edges, such as edge  276 ,  278 , and  280 , for example. 
     Further shown in  FIG. 2E  are both attenuation ports  282  and attenuation components  284 . The attenuation components  284  may be coupled to the attenuation ports  282 . And the attenuation ports  282  may be coupled to the elongated segments  222  of the wave-dividing channels  266 . The design of the attenuation components  284  and attenuation ports  282  are discussed further with respect to  FIG. 4B . 
       FIG. 2F  illustrates four sets of transmitting waveguide channels formed inside an assembled example antenna.  FIG. 2F  presents one example layout for a plurality of waveguides for use in an automotive radar system. The layout shown in  FIG. 2F  shows one example layout of the plurality of waveguides in a layer. As shown in  FIG. 2F , there are four sets of waveguides configured to transmit electromagnetic radiation. Two sets on the left are labeled as L 1 - 1  through L 1 - 5  and L 2 - 1  through L 2 - 5  and the two sets on the right are labeled as R 1 - 1  through R 1 - 5  and R 2 - 1  through R 2 - 5 . Each set of waveguides has a radiating region shown as  290 L and  290 R. Each set of waveguides has a beam forming section shown as  292 L and  292 R. The beamforming sections  292 L and  292 R may include sections of waveguides that are not in straight lines. The waveguides shown in  FIG. 2F  may be similar to those described with respect to the other figures of the present disclosure. 
     Yet further, also shown in  FIG. 2F  are eight receiving waveguides located in region  294 . Although the present disclosure is generally related to coupling attenuation components and attenuation ports to radiating waveguides, each may also be coupled to receiving waveguides, such as those located in region  294 . 
       FIG. 3A  illustrates a network of wave-dividing channels  300  of an example antenna, in accordance with an example embodiment.  FIG. 3B  illustrates an alternate view of the network of wave-dividing channels  300 , in accordance with an example embodiment. 
     In some embodiments, the network (e.g., beam-forming network, as noted above) of wave-dividing channels  300  may take the form of a tree of power dividers, as shown in FIG.  3 A. Energy may enter the antenna through the input waveguide channel and is divided (i.e., split) into smaller portions of energy at each power divider, such as power divider  302 , and may be divided multiple times via subsequent power dividers so that a respective amount of energy is fed into each of the wave-radiating channels (energy A-F, as shown). The amount of energy that is divided at a given power divider may be controlled by a power division ratio (i.e., how much energy goes into one channel  304  versus how much energy goes into another channel  306  after the division). A given power division ratio may be adjusted based on the dimensions of the corresponding power divider. Further, each power divider and associated power division ratio may be designed/calculated in order to achieve a desired “power taper” at the wave-radiating channels. In such a case, the antenna may be designed with a “Taylor window” (e.g., radiation ripples drop off at edges) or other window such that sidelobes of the antenna&#39;s far-field radiation pattern may be low. As an example, the power division ratios of the power dividers may be set such that energy portions A, B, C, D, E, and F are approximately 3.2%, 15.1%, 31.7%, 31.7%, 15.1%, 3.2% of the energy, respectively. Other example power divisions are possible as well. 
     Within examples, a technique for dividing energy between two channels  304 ,  306  may be to use a structure of channels (e.g., a “four-port branchline coupler”) such as that shown at the bottom of  FIG. 3A . Such a technique and structure design may include attenuation components  310  and attenuation ports  308  at the end of a channel, as shown in  FIGS. 3A and 3B , where each of the attenuation ports  308  is configured to couple energy that returns backwards through the channel to one of the attenuation components  310 . The attenuation components  310  may be configured to absorb the returned energy. The design of the attenuation components  310  and attenuation ports  308  are discussed further with respect to  FIG. 4B . 
       FIG. 4A  illustrates an example waveguide  402  termination comprising attenuation port  404 , attenuation components  410 , and the coupling component  408 . The attenuation components  410  may be mounted on a PCB  406  (e.g. the attenuation components  410  may be metallic traces on a PCB). Additionally, the coupling component  408  may be mounted on the PCB via SMT technology. The PCB may be mounted to a bottom surface of an antenna like that shown in  FIG. 2D . Furthermore,  FIG. 4A  illustrates one example use of a coupling component  408 . The coupling component  408  may also be used in instances other than the presently disclosed antenna apparatus. For example, the coupling component  408  may be used in any instance where an electromagnetic signal is being coupled into and/or out of a waveguide. 
     Although  FIG. 4A  is shown with the coupling component  408  surface mounted to attenuation components  410 , in other examples, the coupling component  408  may be surface mounted to a component that feed an electromagnetic signal for transmission by the antenna unit. In such examples, the coupling component  408  may be surface mounted to a pair of traces than provide a differential electromagnetic signal for transmission by the antenna unit. Additionally, the coupling component  408  may be a bidirectional component that may be able to both feed an electromagnetic signal for transmission by the antenna unit and couple an electromagnetic signal from the waveguide to an attenuation component. 
     The waveguide  402  of  FIG. 4A  may be a portion of a waveguide elongated segments, such as elongated segments  204  of  FIG. 2A . More specifically, the waveguide  402  of  FIG. 4A  may be one of the elongated segments that does not include the feed. As previously discussed, during the operation of the antenna some electromagnetic energy that is not radiated by the radiation components may be reflected back into the waveguide. In order to remove the reflected electromagnetic energy, the waveguide  402  may be coupled to an attenuation port  404 . The attenuation port  404  may be aligned perpendicularly, and out of the plane of the waveguide  402 . The attenuation port  404  may be configured to couple the reflected electromagnetic energy to an attenuation component (shown here as lines  410 ) located on a PCB  406  by way of a coupling component  408 . 
     In some examples, such as shown in  FIG. 4A , each attenuation port  404  may be shaped in a way to match (or approximately match) an impedance of the waveguide. By impedance matching, the amount of the reflected electromagnetic energy that is coupled from the waveguide  402  to the attenuation port  404  may be maximized. For example, the attenuation port  404  may have portions that are of different dimensions to achieve the correct impedance matching. 
     However, in other examples, the attenuation port  404  may not be shaped in a way to impedance match. The attenuation port  404  may be a through-hole in a portion of the radar block. Thus, there may be little or no impedance matching performed when the attenuation port  404  is designed. Therefore, the coupling component  408  may facilitate performing impedance matching in a non-impedance matched port. 
     Additionally, the attenuation port  404  and coupling component  408  are shown coupling to the bottom of the waveguide. In other examples, the alignment of the attenuation port  404 , PCB  406 , and coupling component  408  may have a different alignment. For example, the coupling may be to a side or end of a waveguide as well. 
     As previously discussed, the coupling component  408  is configured to couple at least a portion of the reflected electromagnetic energy from the waveguide to the attenuation component  410  through the attenuation port  404 . In this way, when the coupling component  408  couples the at least a portion of the reflected electromagnetic energy, the coupling component  408  may essentially act as a receiving antenna. The coupling component  408  receives the at least a portion of the reflected electromagnetic energy from the waveguide and couples it through the attenuation port. 
     In various different examples, the coupling component  408  may take different forms. For example, the coupling component  408  may be a metallic loop-shaped structure, as shown in  FIG. 4A . The coupling component  408  may function similarly to an antenna, that is the coupling component  408  may be able to transmit or receive electromagnetic energy (i.e. a wave). Functionally, in one example, the coupling component  408  may be a component configured to convert a guided wave from a waveguide to a guided wave outside of the waveguide (e.g. couple the wave to an attenuation component). In another example, the coupling component  408  may be a component configured to convert a guided wave from outside the waveguide to a guided wave in a waveguide. 
     In various examples, the coupling component  408  may be made in various ways and with various materials. In some examples, the coupling component  408  may be formed of a ceramic that is coated, plated, or otherwise overlaid with metal. The coupling component  408  may also be formed from stamped metal, bent metal, or other another metal structure. In some additional examples, the coupling component  408  may itself be a metallic strip or component on a second circuit board that may be surface mounted to PCB  406 . 
     Therefore, there are many structures that can function to cause the conversion of the wave from a wave in the waveguide to a wave not in the waveguide and can take the place of coupling component  408 . 
     In some examples, the coupling component  408  may be a bi-directional coupler that functions to both (i) couple a signal from outside the waveguide into the waveguide and (ii) couple signal from inside the waveguide out of the waveguide. 
     In some further examples, the coupling component  408  may be configured to couple a differential mode signal from outside the waveguide into the waveguide. In some additional examples, the coupling component  408  may be configured to couple signal from inside the waveguide out of the waveguide as a differential mode signal. 
     In some additional examples, the coupling component  408  may be configured to couple a single mode signal from outside the waveguide into the waveguide. In some additional examples, the coupling component  408  may be configured to couple signal from inside the waveguide out of the waveguide as a single mode signal. 
     In various embodiments, the coupling component  408  may be designed to have an impedance that optimizes the percentage of electromagnetic energy that the coupling component  408  couples between its input and output. Due to the coupling component  408  being coupled to a circuit board via SMT, the circuit board to waveguide transition can be manufactured more easily and most cost effectively. Rather than having to optimize a waveguide transition, a coupling component  408  may be designed and attached to a circuit board via SMT. Then, when the circuit board is mounted to a back of the antenna unit, the coupling component  408  may extend through a hole or port in the antenna unit into the waveguide. Thus, the transition may be designed more easily and more cost effectively. Further, the SMT-based coupling component  408  also allows more easy repair. If a signal is not coupling correctly the coupling component  408  may be switched out because it mounted via SMT. If the coupling component  408  was omitted and different coupling was used, it may be more difficult to repair the waveguide block structure. 
     The coupling component  408  is shown as a metallic loop in  FIG. 4A . However, the coupling component  408  may take many other shapes, depending on various design criteria. For example, the coupling component  408  may be a component that is shorted to itself, open ended, or shorted to ground. The coupling component  408  may have many different geometries. Any component that can both (i) be mounted via SMT to a PCB and (ii) couple electromagnetic energy between a waveguide and a PCB may function as the coupling component  408 . 
     In some examples, the coupling component  408  may also be designed based on testing requirements for a radar system. The testing requirements for the radar system may include testing defined based on the radar system being used with an autonomous, semi-autonomous, or driver-assistance vehicle. As part of the testing requirements, there may be various system integrity checks. The coupling component  408  may be designed in a way that its operation and or installation can be checked during a testing routine. For example, the coupling component  408  may be connected to a PCB  406  at mounting points  412  (mounting points  412  are discussed further with respect to  FIG. 4B  below). As part of the testing routine, a low frequency or DC electric current may be fed to one of the mounting points  412 . An output current may be measured at the other mounting point  412 . By measuring the current at one mounting point  412  from current input at the other mounting point  412 , the connection of the coupling component  408  to the PCB  406  may be verified. 
     By using a coupling component  408  at a waveguide-to-PCB transition (either as part of a transmission or reception pathway), the manufacturing tolerances required during the construction of a radar unit may be reduced. For example, the alignment of various components, such as the alignment of the PCB and the waveguide block structure, may be able to be less precised when the coupling component  408  is used to couple a signal between the PCB and the waveguide block structure. Further, the loosening of tolerances of the configuration of the waveguide and PCB may enable both the PCB and waveguide to be manufactured more inexpensively. Although the alignment of the PCB and waveguide may not be ideal, the coupling component may offset any effects caused by the less precise alignment. 
     The attenuation component  410  is disposed on a circuit board  406  located outside of, or on an external surface of, the waveguide block structure. The attenuation component  410  may receive the at least a portion of the reflected electromagnetic energy from the coupling component  408 . In some examples, a surface of the attenuation component  410  may be configured to comprising absorb the portion of the reflected electromagnetic energy. In some further examples, the attenuation component may include at least one microstrip line on the circuit board. Yet further, the attenuation component may include conductive ink printed on the circuit board. 
     The attenuation component may be configured to act as a load or termination. When acting as a load or termination, the attenuation component may dissipate, that is reduce and/or get rid of, the reflected electromagnetic energy. The attenuation component may use various different ways to dissipate (or absorb) the reflected electromagnetic energy. In some examples, the attenuation component may be mounted on a lossy PCB  406 . The lossy PCB  406  will dissipate the reflected electromagnetic energy. In another example, a resistive surface of a trace (or other component) may cause dissipation of the reflected electromagnetic energy. In yet another example, the attenuation component may include a differential pair of lines  410  configured to dissipate the reflected electromagnetic energy. In other examples, the attenuation component may include a singled ended line configured to dissipate the reflected electromagnetic energy. In another example, the attenuation component may be made from Nickel Chrome (NiCr), as NiCr dissipates electromagnetic energy. In yet further examples, the attenuation component may be a resistive ink dot that dissipates electromagnetic energy. In other examples, the attenuation component may include microstrip and/or transmission lines on the PCB  406 . 
     In some examples, the PCB  406  may also be coupled to at least one heat sink. Because of the energy contained in the reflected electromagnetic energy, absorbing the energy may increase the temperature of the PCB  406 . A heat sink may be able to dissipate heat from the PCB  406 . 
       FIG. 4B  shows a top-down view of two pairs of mounting points  412  for coupling components surface mounted on a circuit board  406 . The two pairs of mounting points  412  for coupling components may each be coupled to a respective coupling component that extends through a respective attenuation port  404 . Thus, the two pairs of mounting points  412  for coupling components may each receive a different reflected signal from the respective coupling component coupled to a respective waveguide. The two pairs of mounting points  412  may be the SMT points where the coupling component may couple to an absorption component. As shown in  FIG. 4B , the two pairs of mounting points  412  are coupled to differential pair lines  410 . The differential pair lines  410  may be configured to dissipate the reflected electromagnetic energy. The differential pair lines  410  may be, or coupled to components, made from conductive ink. The conductive ink may be resistive and dissipate the reflected electromagnetic energy. Further shown in  FIG. 4B  are grounding points  414 . The grounding points  414  are points that may be used to introduce an electrical ground to the PCB  406 . The grounding points  414  may form an electrical contact with the waveguide block, such as the bottom of waveguide block shown in  FIG. 2D . 
       FIG. 4C  illustrates an example arrangement of waveguide terminations and loads on a circuit board, in accordance with an example embodiment. The example PCB layout shown in  FIG. 4C  may be used with the example waveguide block layout shown in  FIG. 2F . Each of the waveguides (other than the one being fed) of  FIG. 2F  may be coupled to a respective attenuating component in the PCB. The attenuating components of  FIG. 4C  may be similar to those described throughout this disclosure. Further, at least one of the feed and the waveguide terminations may be coupled to a coupling component (as described herein) configured to effectively couple energy in to, or out of, the waveguide. 
     Waveguides L 1 - 1  through L 1 - 5  of  FIG. 2F  may be coupled to attenuating component L 1 - 1  through L 1 - 5  of  FIG. 4C , respectively. Additionally, waveguides L 2 - 1  through L 2 - 5  of  FIG. 2F  may be coupled to attenuating component L 2 - 1  through L 2 - 5  of  FIG. 4C , respectively. Further, waveguides R 1 - 1  through R 1 - 5  of  FIG. 2F  may be coupled to attenuating component R 1 - 1  through R 1 - 5  of  FIG. 4C , respectively. Yet further, waveguides R 2 - 1  through R 2 - 5  of  FIG. 2F  may be coupled to attenuating component R 2 - 1  through R 2 - 5  of  FIG. 4C , respectively. Thus, each waveguide may have an associated attenuating component for attenuating reflected signals. In some examples, both the fed and non-fed waveguides may each have an associated attenuating component. 
     It should be understood that other shapes and dimensions of the waveguide channels, portions of the waveguide channels, sides of the waveguide channels, wave-directing members, and the like are possible as well. In some embodiments, a rectangular shape of waveguide channels may be highly convenient to manufacture, though other methods known or not yet known may be implemented to manufacture waveguide channels with equal or even greater convenience. 
     It should be understood that arrangements described herein are for purposes of example only. As such, those skilled in the art will appreciate that other arrangements and other elements (e.g. machines, apparatuses, interfaces, functions, orders, and groupings of functions, etc.) can be used instead, and some elements may be omitted altogether according to the desired results. Further, many of the elements that are described are functional entities that may be implemented as discrete or distributed components or in conjunction with other components, in any suitable combination and location. 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the scope being indicated by the following claims.