Patent Publication Number: US-2022216608-A1

Title: Apparatus with Partitioned Radio Frequency Antenna and Matching Network and Associated Methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation-in-part of U.S. patent application Ser. No. 15/250,719, filed on Aug. 29, 2016, titled “Apparatus with Partitioned Radio Frequency Antenna Structure and Associated Methods,” Attorney Docket No. SILA381. Furthermore, the present patent application is related to U.S. patent application Ser. No. 16/237,511, filed on Dec. 31, 2018, titled “Apparatus for Antenna Impedance-Matching and Associated Methods,” Attorney Docket No. SILA411. The foregoing patent applications are hereby incorporated by reference in their entireties for all purposes. 
    
    
     TECHNICAL FIELD 
     The disclosure relates generally to radio frequency (RF) signal transmission/reception techniques, circuitry, systems, and associated methods. More particularly, the disclosure relates to RF apparatus with partitioned antenna structures and matching networks to provide improved features, and associated methods. 
     BACKGROUND 
     With the increasing proliferation of wireless technology, such as Wi-Fi, Bluetooth, and mobile or wireless Internet of things (IoT) devices, more devices or systems incorporate radio frequency (RF) circuitry, such as receivers and/or transmitters. To reduce the cost, size, and bill of materials, and to increase the reliability of such devices or systems, various circuits or functions have been integrated into integrated circuits (ICs). For example, ICs typically include receiver and/or transmitter circuitry. A variety of types and circuitry for transmitters and receivers are used. Transmitters send or transmit information via a medium, such as air, using RF signals. Receivers at another point or location receive the RF signals from the medium, and retrieve the information. 
     To transmit or receive RF signals, typical wireless devices or apparatus use antennas. RF modules are sometimes used that include the transmit/receive circuitry. A typical RF module  5 , shown in  FIG. 1 , includes an RF circuit  6 , a resonator  8 , and a radiator  9 . Typically, resonator  8  and radiator  9  are included in the RF module. In other words, the structures that form resonator  8  and radiator  9  are included within RF module  5 . 
     The description in this section and any corresponding figure(s) are included as background information materials. The materials in this section should not be considered as an admission that such materials constitute prior art to the present patent application. 
     SUMMARY 
     A variety of apparatus and associated methods are contemplated according to exemplary embodiments. According to one exemplary embodiment, an apparatus includes an RF circuit to transmit or receive RF signals. The apparatus further includes a loop antenna to transmit or receive the RF signals. The apparatus further includes an impedance matching circuit coupled to the RF circuit and to the loop antenna. The impedance matching circuit includes lumped reactive components. 
     According to another exemplary embodiment, an apparatus includes a module and a substrate coupled to the module. The module includes an RF circuit to transmit or receive RF signals, and a first portion of a loop antenna to transmit or receive the RF signals. The substrate includes a second portion of the loop antenna. 
     According to another exemplary embodiment, an apparatus includes a module, and a substrate coupled to the module. The module includes an RF circuit to transmit or receive RF signals, and one portion of an impedance matching circuit coupled to the RF circuit. The substrate includes another portion of the impedance matching circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The appended drawings illustrate only exemplary embodiments and therefore should not be considered as limiting the scope of the application or the claims. Persons of ordinary skill in the art will appreciate that the disclosed concepts lend themselves to other equally effective embodiments. In the drawings, the same numeral designators used in more than one drawing denote the same, similar, or equivalent functionality, components, or blocks. 
         FIG. 1  shows a conventional RF module. 
         FIG. 2  shows a circuit arrangement for an RF apparatus (or part of an RF apparatus) according to an exemplary embodiment. 
         FIG. 3  shows a circuit arrangement for an RF apparatus (or part of an RF apparatus) according to another exemplary embodiment. 
         FIG. 4  shows an RF apparatus with a partitioned antenna structure according to an exemplary embodiment. 
         FIG. 5  shows an RF apparatus with a partitioned antenna structure according to another exemplary embodiment. 
         FIG. 6  shows an RF apparatus with a partitioned antenna structure according to another exemplary embodiment. 
         FIG. 7  shows a flow diagram for a process of making a module with a partitioned antenna structure according to an exemplary embodiment. 
         FIG. 8  shows a flow diagram for a process of making an RF apparatus with a partitioned antenna structure according to another exemplary embodiment. 
         FIG. 9  shows an RF apparatus with a partitioned antenna structure according to another exemplary embodiment. 
         FIG. 10  shows an RF apparatus with a partitioned antenna structure according to another exemplary embodiment. 
         FIG. 11  shows a circuit arrangement for an RF apparatus (or part of an RF apparatus) according to an exemplary embodiment. 
         FIG. 12  shows a circuit arrangement for an RF apparatus (or part of an RF apparatus) according to another exemplary embodiment. 
         FIG. 13  shows a circuit arrangement for an RF apparatus (or part of an RF apparatus) according to another exemplary embodiment. 
         FIG. 14  shows a circuit arrangement for an RF apparatus (or part of an RF apparatus) according to another exemplary embodiment. 
         FIG. 15  shows a circuit arrangement for an RF apparatus (or part of an RF apparatus) according to another exemplary embodiment. 
         FIG. 16  shows a circuit arrangement for an RF apparatus (or part of an RF apparatus) according to another exemplary embodiment. 
         FIG. 17  shows a circuit arrangement for an RF apparatus (or part of an RF apparatus) according to another exemplary embodiment. 
         FIG. 18  shows a circuit arrangement for an RF apparatus (or part of an RF apparatus) according to another exemplary embodiment. 
         FIG. 19  shows a layout for an RF apparatus (or part of an RF apparatus) according to an exemplary embodiment. 
         FIG. 20  shows a layout for an RF apparatus (or part of an RF apparatus) according to an exemplary embodiment. 
         FIG. 21  shows a flow of currents in an RF apparatus (or part of an RF apparatus) according to an exemplary embodiment. 
         FIG. 22  shows a layout for an RF apparatus (or part of an RF apparatus) according to an exemplary embodiment. 
         FIG. 23  shows a circuit arrangement for antenna matching circuitry according to an exemplary embodiment. 
         FIG. 24  shows a circuit arrangement for antenna matching circuitry according to another exemplary embodiment. 
         FIG. 25  shows a circuit arrangement for antenna matching circuitry according to another exemplary embodiment. 
         FIG. 26  shows a circuit arrangement for an RF apparatus (or part of an RF apparatus) according to another exemplary embodiment. 
         FIG. 27  shows a system for radio communication according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     One aspect of the disclosure relates generally to RF apparatus with partitioned antenna structures to provide improved features, and associated methods. As described below, according to this aspect, in RF apparatus according to exemplary embodiments, the antenna structures are partitioned. More specifically, part of the resonator and radiator structures are included in one device (e.g., a module), and the remaining or additional part(s) of the resonator and radiator structures are made or fabricated or included outside the device (e.g., externally to a module). 
       FIG. 2  depicts a circuit arrangement  10  for an RF apparatus (or part of an RF apparatus) according to an exemplary embodiment. More specifically, circuit arrangement  10  illustrates the electrical connections or couplings among the various parts of an RF apparatus. 
     Circuit arrangement  10  includes antenna structure  15 . Antenna structure  15  includes chip antenna  20  coupled to resonator  25 . Generally, resonator  25  includes devices, components, or apparatus that naturally oscillate at some frequency, e.g., the frequency at which the RF apparatus transmits RF signals or the frequency at which the RF apparatus receives RF signals. In exemplary embodiments, the reactance of one or more features or devices or portion of the substrate (on which various components of circuit arrangement  10  are arranged or fixated) or the substrate layout, matching components (e.g., inductor(s), capacitor(s)) (not shown), and/or chip antenna  20  form resonator  25 . 
     Referring again to  FIG. 2 , resonator  25  is coupled to radiator  30 . Generally, radiator  30  includes devices, components, or apparatus that transforms conducted RF energy (e.g., as received from RF circuit  35  or from a communication medium, such as air or free space) into radiated RF energy. In exemplary embodiments, one or more features or devices or portions of the substrate (on which various components of circuit arrangement  10  are arranged or fixated) or the substrate layout, chip antenna  20 , and/or surrounding ground plane (e.g., ground plane formed in or on a substrate on which the substrate include circuit arrangement  10  is arranged or fixated) form radiator  30 . 
     Referring again to  FIG. 2 , RF circuit  35  couples to antenna structure  15  via link  40 . In exemplary embodiments, RF circuit  35  may include transmit (TX), receive (RX), or both transmit and receive (transceiver) circuitry. In the transmit mode, RF circuit  35  uses antenna structure  15  to transmit RF signals. In the receive mode, RF circuit  35  receives RF signals via antenna structure  15 . In the transceiver mode, RF circuit  35  can receive RF signals during some periods of time and alternately transmit RF signals during other periods of time (or perform neither transmission nor reception, if desired). Thus, the transceiver mode may be thought of as combining the transmit and receive modes in a time-multiplexed fashion. 
     Link  40  provides an electrical coupling to provide RF signals from RF circuit  35  to antenna structure  15  or, alternatively, provide RF signals from antenna structure  15  to RF circuit  35  (during the transmit and receive modes, respectively). Generally, link  40  constitutes a transmission line. In exemplary embodiments, link  40  may have or include a variety of forms, devices, or structures. For example, in some embodiments, link  40  may include a coaxial line or structures. As another example, in some embodiments, link  40  may include a stripline or microstrip structure (e.g., two conductors arranged in a length-wise parallel fashion). 
     Regardless of the form of link  40 , link  40  couples to antenna structure  15  at feed point or node  45 . In some embodiments, feed point  45  may include a connector, such as an RF connector. In some embodiments, feed point  40  may include electrical couplings (e.g., points, nodes, solder joints, etc.) to couple link  40  to chip antenna  20 . Feed point  45  provides RF signals to chip antenna  20  (during the transmit mode) or alternately provides RF signals from chip antenna  20  to link  40  (during the receive mode). 
     In exemplary embodiments, chip antenna  20  may constitute a variety of desired chip antennas. Chip antennas are passive electronic components with relatively small physical dimensions, as persons of ordinary skill in the art know. Referring to  FIG. 2 , chip antenna  20 , together with resonator  25  and radiator  30 , forms antenna structure  15 . As noted above, antenna structure  15  transmits RF signals from RF circuit  35  or provides RF signals received from a communication medium (e.g., air) to RF circuit  35 . In some embodiments, antennas other than chip antennas may be used. The embodiment shown in  FIG. 2  uses chip antenna  20  because of its relatively small size, relatively low cost, and relative ease of availability. 
     Generally, in exemplary embodiments, structures used to fabricate or implement resonator  25  and radiator  30  might overlap or have common elements. For example, as noted above, in some embodiments, resonator  25  and radiator  30  may include one or more features or devices of the substrate (on which various components of circuit arrangement or RF apparatus are arranged or fixated) or the substrate layout. In such situations, resonator  25  and radiator  30  may be combined. 
       FIG. 3  shows a circuit arrangement  60  for an RF apparatus (or part of an RF apparatus) according to an exemplary embodiment that includes a combined resonator and radiator, i.e., resonator/radiator  50 . More specifically, circuit arrangement  60  illustrates the electrical connections or couplings among the various parts of an RF apparatus. Other than the combined resonator and radiator, circuit arrangement  60  has the same or similar features as described above with respect to circuit arrangement  10  (see  FIG. 2 ). 
     As noted,  FIG. 2  and  FIG. 3  show the electrical topology of an RF apparatus according to an exemplary embodiments.  FIG. 4 ,  FIG. 5 , and  FIG. 6  illustrate or add physical features or configuration of RF apparatus according to an exemplary embodiments. More specifically,  FIG. 4 ,  FIG. 5 , and  FIG. 6  show the partitioning of resonator  25  and radiator  30  (similar partitioning may be applied to a combined resonator and radiator, such as resonator/radiator  50  (see  FIG. 3 ). 
     In exemplary embodiments, a physical carrier, device, enclosure, or other physical entity is used to house or include or support antenna structure  15 . In some embodiments, antenna structure  15  (chip antenna  20 , resonator  25 , and radiator  30  in the embodiment of  FIG. 2 , or chip antenna  20  and resonator/radiator  50  in the embodiment shown in  FIG. 3 ) are included or housed in a module.  FIG. 4  shows such a module, labeled as  80 . 
     In some embodiments, module  80  includes a physical device or component, such as a substrate (not shown) to which various components (e.g., chip antenna  20 ) are affixed or which supports various components. In exemplary embodiments, the substrate provides physical support for the various components of module  80 . In addition, in some embodiments, the substrate provides a mechanism for electrically coupling various components of module  80 . For example, the substrate may include electrically conducting traces to couple chip antenna  20  to the resonator and/or radiator. 
     In exemplary embodiments, the substrate may be fabricated in a variety of ways, as desired. For example, in some embodiments, the substrate may constitute a printed circuit board (PCB). The PCB, as persons of ordinary skill in the art will understand, provides mechanisms or features such as traces, vias, etc., to electrically couple various components of module  80 . The PCB mechanisms or features may also be used to implement part of the resonator and/or radiator (or the combined resonator/radiator), for example, traces, matching components, ground planes, etc. 
     In exemplary embodiments, the material (or materials) used to fabricate the PCB may be selected based on a variety of considerations and attributes. For example, the PCB material may be selected so as to provide certain physical attributes, such as sufficient strength to support the various components in module  80 . As another example, the PCB material may be selected so as to provide certain electrical attributes, such as dielectric constant to provide desired electrical characteristics, e.g., reactance at a given or desired frequency. 
     As noted, exemplary embodiments include a partitioned antenna structure. Referring again to  FIG. 4 , antenna structure  15  (not labeled in  FIG. 4 ) includes a partitioned resonator and a partitioned radiator. More specifically, antenna structure  15  includes a part of a resonator in module  80 . Thus, the resonator is physically partitioned into two portions (or parts or pieces). One of those portions is included in module  80 , and is labeled  85 A. In other words, portion  85 A is less than the entire (or complete) resonator. Resonator part or portion  85 A may include a part of the overall resonator structure, for instance, one more matching components, part of an overall ground plane, etc. The second part of the resonator is not included in module  80 , and is fabricated using structures external to module  80 , as described below in detail. The two portions of the resonator together form the entire or complete resonator. 
     Similarly, antenna structure  15  (not labeled in  FIG. 4 ) includes a part of a radiator in module  80 . In other words, the radiator is physically partitioned into two portions (or parts or pieces). One of those portions is included in module  80 , and is labeled  90 A in  FIG. 4 . Thus, portion  90 A is less than the entire (or complete) radiator. Radiator part or portion  90 A may include a part of the overall radiator structure, for instance, one more matching components, part of an overall ground plane, etc. The second part of the radiator is not included in module  80 , and is fabricated using structures external to module  80 , as described below in detail. The two portions of the radiator together form the entire or complete radiator. 
     Note that in some embodiments the resonator or the radiator is partitioned, but not both the resonator or radiator. For example, in some embodiments, the resonator is partitioned as described above, but the radiator is not partitioned and is included in module  80  (even though in this case the radiator may have relatively small efficiency). As another example, in some embodiments, the radiator is partitioned as described above, but the resonator is not partitioned and is included in module  80 . 
     As noted above, in some embodiments, the resonator and the radiator are combined (e.g., a resonator/radiator). In such embodiments, antenna structure  15  (not labeled in  FIG. 4 ) includes a part of the resonator/radiator in module  80 . In other words, the resonator/radiator is physically partitioned into two portions (or parts or pieces). One of those portions is included in module  80 . The resonator/radiator portion included in module  80  may include a part of the overall resonator/radiator structure, for instance, one more matching components, part of an overall ground plane, etc. The second part of the resonator/radiator is not included in module  80 , and is fabricated using structures external to module  80 . 
     Note that in the embodiment shown in  FIG. 4 , RF circuit  35  is not physically included in module  80 . Instead, RF circuit  35  is external to module  80 , and is coupled to chip antenna  20  via link  40 . In some embodiments, RF circuit  35  is physically included in module  80 , as is link  40 .  FIG. 5  depicts an example of such an embodiment. In the embodiment in  FIG. 5 , RF circuit is included in module  80 , and is coupled to chip antenna  20  via link  40  (which is also included in module  80 ). Link  40  may be used externally to module  80  to allow communication with RF circuit  35  (e.g., providing signals to be transmitted or receiving RF signals that have been received). Including RF circuit  35  in module  80  facilitates certification of module  80  for a given standards or protocol, as desired. 
     As noted, antenna structure  15  includes portion of resonator  85 A and portion of radiator  90 A. The remaining portions or parts of the resonator and radiator are fabricated externally to module  80 . In some embodiments, the remaining portions are fabricated using features or devices in a substrate to which module  80  is coupled or affixed.  FIG. 6  depicts an example of such an embodiment. 
     More specifically, apparatus  100  in  FIG. 6  shows an RF module  80  that is coupled to or affixed to substrate  105 . In addition to module  80 , substrate  105  may be coupled to or affixed to other devices, features, subsystems, circuits, etc., as desired. In exemplary embodiments, substrate  105  may be fabricated in a variety of ways, as desired. For example, in some embodiments, the substrate may constitute a PCB (generally labeled as  105 ). The PCB, as persons of ordinary skill in the art will understand, provides mechanisms or features such as traces, vias, etc., to electrically couple module  80  to other devices, features, subsystems, circuits, etc. 
     The PCB (or generally substrate)  105  features (or mechanisms or devices or components or parts) may also be used to implement the second portions of the resonator and radiator (or the combined resonator/radiator). Examples of such features include traces, conductive areas or planes, such as ground planes, etc. In the embodiment shown, features of substrate  105  is used to part of the resonator, labeled  85 B, and part of the radiator, labeled  90 B. Resonator parts or portions  85 A and  85 B are coupled together (electrically and/or physically) to form the overall resonator (e.g., resonator  25  in  FIG. 2 ). Similarly, radiator parts or portions  90 A and  90 B are coupled together (electrically and/or physically) to form the overall radiator (e.g., radiator  30  in  FIG. 2 ). 
     In exemplary embodiments, the material (or materials) used to fabricate substrate or PCB  105  may be selected based on a variety of considerations and attributes. For example, the PCB material may be selected so as to provide certain physical attributes, such as sufficient strength to support the various components coupled or affixed to PCB  105 . As another example, the PCB material may be selected so as to provide certain electrical attributes, such as dielectric constant to provide desired electrical characteristics, e.g., reactance at a given or desired frequency, desired overall resonator electrical characteristics, and/or desired overall radiator electrical characteristics. 
     By partitioning the resonator (e.g., resonator  25 ) and the radiator (e.g., radiator  30 ), antenna structure  15  is partitioned. For example, referring to  FIG. 6 , the resonator is partitioned into portion  85 A and portion  85 B. In addition, or instead, the radiator is partitioned into portion  90 A and portion  90 B. Given that antenna structure  15  includes the resonator and the radiator, antenna structure  15  is partitioned as shown in the figure and described above. In embodiments where the resonator and the radiator are combined, partitioning the resulting resonator/radiator also results in antenna structure  15  being partitioned. 
     Partitioned antenna structures according to exemplary embodiments provide several features and attributes. For example, partitioned antenna structures provide effective tuning of the antenna (e.g., chip antenna  20 ), rather than merely relying on techniques that involve changing the dielectric materials in relatively close proximity of the antenna, changing packaging materials (e.g., molding materials) or dimensions, or changing the dimensions or characteristics of a substrate (e.g., PCB) to which module  80  is affixed. Consequently, efficient or effective tuning of the antenna for a given application that uses module  80  is possible even if relatively significant detuning occurs because of various factors (e.g., molding and plastic layers, whether used in module  80  or externally to module  80 ). Thus, tuning of the antenna may be accomplished in a relatively flexible manner and with potentially lower costs (e.g., because of smaller module sizes, etc.). 
     Moreover, given that module  80  includes portions, rather than the entire, resonator and radiator, the module size is reduced. The reduced size of module  80  provides reduced board area, reduced cost, increased flexibility, etc. For example, resonator portion  85 B and radiator  90 B, which are fabricated externally to module  80  (e.g., using features or parts of substrate  105 ) may be sized or configured or fabricated to accommodate a desired RF frequency without changing characteristics of module  80 . In other words, resonator portion  85 B and radiator portion  90 B, which are fabricated externally to module  80  (e.g., using features or parts of substrate  105 ) may be sized or configured or fabricated to provide effective RF transmission or reception, given the particular characteristics of a module  80 . 
     One aspect of the disclosure pertains to processes for making or using modules such as module  80 .  FIG. 7  illustrates a flow diagram  120  for a process of making a module with a partitioned antenna structure according to an exemplary embodiment. At  125 , the RF circuit (e.g., RF circuit  35 , described above) is fabricated and included in the module, as desired. (In embodiments where the RF circuit is already fabricated (e.g., a semiconductor die including the RF circuit), the fabricated RF circuit may be included in module  80 . Furthermore, in embodiments where the RF circuit is external to the module, block  125  may be omitted.) 
     At  128 , the chip antenna (e.g., chip antenna  20 , described above) is fabricated and included in the module, as desired. (In embodiments where the chip antenna is already fabricated (e.g., as a separate component, obtained in a packaged form), the fabricated chip antenna may be included in module  80 .) 
     At  131 , a portion or part of the resonator (e.g., resonator  25  in  FIG. 2 ) is fabricated and included in module  80 . The portion or part of the resonator may constitute, for example, portion  85 A shown in  FIG. 5  and  FIG. 6 . In other words, the entire structure that forms the resonator is partitioned into two portions, as described above. One of those portions (e.g., portion  85 A) is included in module  80 . 
     Alternatively, or in addition, at  134 , a portion or part of the radiator (e.g., radiator  30  in  FIG. 2 ) is fabricated and included in module  80 . The portion or part of the radiator may constitute, for example, portion  90 A shown in  FIG. 5  and  FIG. 6 . (Note that in embodiments that use a combined resonator and radiator, a portion of the resonator/radiator is fabricated and included in module  80 ). In other words, the entire structure that forms the radiator is partitioned into two portions, as described above. One of those portions (e.g., portion  90 A) is included in module  80 . 
       FIG. 8  shows a flow diagram  150  for a process of making an RF apparatus with a partitioned antenna structure according to another exemplary embodiment. The process shown in  FIG. 8  assumes that a portion of the resonator and a portion of the radiator (or a portion of the resonator/radiator) are included in a module, such as module  80 , as described above (although the process may be used with other embodiments, as desired, by making appropriate modifications). 
     At  155 , characteristics of the portions of the resonator and radiator (e.g., portions  85 B and  90 B, described above) that are external to the module, e.g., fabricated or included in substrate  105  in  FIG. 6 , are determined or calculated. Such characteristics include size of various features (e.g., ground plane), material characteristics (e.g., dielectric constants), etc. 
     At  160 , the portions of the resonator and radiator that are external to the module are fabricated using features of a substrate, e.g., substrate  105 , described above. At  165 , the module is mounted to the substrate. At  170 , the module is coupled electrically to the substrate, for example, coupling portion  85 A to portion  85 B, coupling portion  90 A to portion  90 B, power and ground connections, RF signal paths, etc. Note that in some embodiments, mounting of the module and electrically coupling the module to the substrate may be performed together (e.g., by soldering the module to the substrate). 
     One aspect of the disclosure relates to including circuitry in an RF apparatus using substrate  105  to provide most or all components for an RF communication apparatus (e.g., receiver, transmitter, transceiver).  FIG. 9  illustrates an RF communication apparatus  200  with a partitioned antenna structure according to another exemplary embodiment. 
     As described above, module  80  and portions  85 B and  90 B fabricated/included in or on substrate  105  provide RF circuitry for the RF apparatus. In addition, RF communication apparatus  200  includes baseband circuit  205  and signal source/destination  210 . In the embodiment shown, baseband circuit  205  is included in module  80 . Baseband circuit  205  couples to RF circuit  35  via link  220 . 
     In the case of RF reception, using link  220 , baseband circuit may receive signals from RF circuit  35 , and convert those signals to baseband signals. The conversion may include frequency translation, decoding, demodulating, etc., as persons of ordinary skill in the art will understand. The signals resulting from the conversion are provided signal source/destination  210  via link  215 . In the case of RF reception, signal source/destination  210  may include a signal destination, such as a speaker, a storage device, a control circuit, transducer, etc. 
     In the case of RF transmission, signal source/destination  210  may include a signal source, such as a transducer, a microphone, sensor, a storage device, a control circuit, etc. The signal source provides signals that are used to modulate RF signals that are transmitted. Baseband circuit  205  receives the output signals of the signal source via link  215 , and converts those signals to output signals that it provides to RF circuit  35  via link  220 . The conversion may include frequency translation, encoding, modulating, etc., as persons of ordinary skill in the art will understand. RF circuit  35  uses the partitioned antenna structure to communicate RF signals via a medium such as air. 
     In some embodiments, baseband circuit  205  may be omitted from module  80 , and instead be affixed to substrate  105 . For example, a semiconductor die or IC that contains or integrates baseband circuit  205  may be affixed to substrate  205  and may be coupled to module  80 .  FIG. 10  shows an RF communication apparatus  240  that includes such an arrangement. Link  220  provides a coupling mechanism between baseband circuit  205  and RF circuit  35 , as described above. RF communication apparatus  240  provides the functionality described above in connection with  FIG. 10 . Including baseband circuit  205  in module  80  facilitates certification of module  80  for a given standards or protocol, as desired. 
     Another aspect of the disclosure relates to apparatus for impedance matching circuits (or matching circuits or matching networks or matching circuitry or impedance matching networks or impedance matching circuitry) in RF apparatus, and associated methods. As persons of ordinary skill in the art will understand, impedance matching circuits may be called simply “matching circuits” without loss of generality. 
     Impedance matching or impedance transformation circuits, here called matching circuits, are typically used in RF apparatus, such as receivers, transmitters, and/or transceivers, to provide an interface or match between circuitry that have different impedances. 
     More specifically, in the case of purely resistive impedances, maximum power transfer takes place when the output impedance of a source circuit equals the input impedance of a load circuit. In the case of complex impedances, maximum power transfer takes place when the input impedance of the load circuit is the complex conjugate of the output impedance of the source circuit. 
     As an example, consider an antenna with a 50-ohm impedance (R=50Ω) coupled to a receive or receiver (RX) circuit with a 50-ohm impedance. In this case, maximum power transfer takes place without the user of an impedance matching circuit because the output impedance of the antenna equals the input impedance of the RX circuit. 
     Now consider the situation where an antenna with a 50-ohm impedance (R=50Ω) coupled to an RX circuit with a 250-ohm impedance. In this case, because the respective impedances of the antenna and the RX circuit are not equal, maximum power transfer does not take place. 
     Use of an impedance matching circuit, however, can match the impedance of the antenna to the impedance of the RX circuit. As a result of using the impedance matching circuit, maximum power transfer from the antenna to the RX circuit takes place. 
     More specifically, the impedance matching circuit is coupled between the antenna and the RX circuit. The impedance matching circuit has two ports, with one port coupled to the antenna, and another port coupled to the RX circuit, respectively. 
     At the port coupled to the antenna, the impedance matching circuit ideally presents a 50-ohm impedance to the antenna. As a result, maximum power transfer takes place between the antenna and the impedance matching circuit. 
     Conversely, at the port coupled to the RX circuit, the impedance matching circuit presents a 250-ohm impedance to the RX circuit. Consequently, maximum power transfer takes place between the impedance matching circuit and the RX circuit. 
     In practice, the impedance matching circuit often fails to perfectly match the impedances. In other words, signal transmission from one network to another is not perfect and 100% of the signal power is not transmitted. As a result, reflection occurs at the interface between circuits or networks with imperfectly matched impedances. 
     The reflection coefficient, S 11 , may serve as one measure or figure of merit for the level of impedance matching. A lower S 11  denotes better power transmission (better impedance matching), and vice-versa. 
     In exemplary embodiments, impedance matching circuits or apparatus including impedance matching circuits, and associated methods are disclosed. The impedance matching circuits are relatively low cost, may be used with RF receivers (RX), RF transmitter (TX), and/or RF transceivers. 
     Furthermore, impedance matching circuits according to various embodiments may be adapted to various operating frequency ranges, power levels, and RX circuit or RX and TX circuit impedances. In addition, impedance matching circuits according to various embodiments may be used with a variety of RX or RX and TX circuit configurations (e.g., low-IF receivers, direct conversion receivers or transmitters, etc.), as persons of ordinary skill in the art will understand. 
     According to one aspect of the disclosure, matching circuits are provided in RF apparatus that match the impedance of an antenna (more particularly, a loop antenna in some embodiments, as described below in detail) to the impedance of an RF circuit. The matching circuits provide the impedance matching functionality without using chip or ceramic antennas. In other words, according to this aspect of the disclosure, RF apparatus include an RF circuit, a matching circuit, and an antenna. 
     Instead of using chip antennas, matching circuits are used that use lumped components or elements, such as reactive components (inductor(s), capacitor(s)). In some embodiments, the reactive components constitute surface mount device (SMD) components. Other types of components, however, may be used, depending on various factors, as persons of ordinary skill in the art will understand. Examples of such factors include the frequency of operation, cost, available space, performance specifications, design specifications, available technology, etc., as persons of ordinary skill in the art will understand. 
     The matching circuits obviate the use of chip antennas in such RF apparatus. Avoiding the use of chip antennas provides some benefits. For example, the overall cost of the RF apparatus may be decreased by avoiding the use of or eliminating the chip antenna. 
       FIG. 11  depicts a circuit arrangement for an RF apparatus (or part of an RF apparatus)  300  according to an exemplary embodiment. More specifically, the figure illustrate the electrical connections or couplings among the various parts of RF apparatus  300 . RF apparatus  300  includes loop antenna  310  which, as described below in detail, is formed in or on substrate  105 . RF circuit  35  couples to matching circuit  305  via link  40 . In exemplary embodiments, RF circuit  35  may include transmit (TX), receive (RX), or both transmit and receive (transceiver) circuitry. In the transmit mode, RF circuit  35  uses loop antenna  310  to transmit RF signals. In the receive mode, RF circuit  35  receives RF signals via loop antenna  310 . In the transceiver mode, RF circuit  35  can receive RF signals during some periods of time and alternately transmit RF signals during other periods of time (or perform neither transmission nor reception, if desired). Thus, the transceiver mode may be thought of as combining the transmit and receive modes in a time-multiplexed fashion. 
     Link  40  provides an electrical coupling to provide RF signals from RF circuit  35  to matching circuit  305 , alternatively, provide RF signals from antenna matching circuit  305  to RF circuit  35  (during the transmit and receive modes, respectively). Generally, link  40  constitutes a transmission line. In exemplary embodiments, link  40  may have or include a variety of forms, devices, or structures. For example, in some embodiments, link  40  may include a coaxial line or structures. As another example, in some embodiments, link  40  may include a stripline or microstrip structure (e.g., two conductors arranged in a length-wise parallel fashion). Other types of structures may be used to realize link  40 , as persons of ordinary skill in the art will understand. 
     Regardless of the form of link  40 , link  40  couples to matching circuit  305  at feed point or node  45 . In some embodiments, feed point  45  may include a connector, such as an RF connector. In some embodiments, feed point  40  may include electrical couplings (e.g., points, nodes, solder joints, solder balls, vias, etc.) to couple link  40  to matching circuit  305 . Feed point  45  provides RF signals to matching circuit  305  and, ultimately, to loop antenna  310  (during the transmit mode) or, alternately, provides RF signals from loop antenna  310 , which are provided to link  40  by matching circuit  305  (during the receive mode). 
     In some embodiments, matching circuit  305  may be formed in, on, or using various features of, substrate  105 .  FIG. 12  shows such an embodiment. In some embodiments, a module, such as an RF module, or semiconductor die, is used.  FIG. 13  shows such an embodiment. 
     Referring to  FIG. 13 , a variety of alternatives are contemplated and are possible. For example, in some embodiments, module  80  may have its own package. In such embodiments, the package of module  80  is mounted, affixed, or attached to substrate  105 , either directly (e.g., soldered), by using a carrier, etc. As another example, in some embodiments, module  80  may be formed or affixed or attached to its own substrate. In such embodiments, the substrate of module  80  is mounted, affixed, or attached to substrate  105 , either directly (e.g., soldered), by using a carrier, etc. 
     In some embodiments, matching circuit  305  is partitioned. In other words, a portion (or part) of the circuitry for matching circuit  305  is included in module  80 , whereas another portion of matching circuit  305  is included in or formed in or formed on or formed using substrate  105 .  FIG. 14  shows such an embodiment. In the embodiment of  FIG. 14 , a portion  305 A of matching circuit  305  is included in module  80 . For example, some of the reactive components of matching circuit  305  may be included in module  80 . Referring again to  FIG. 14 , another portion  305 B of matching circuit  305  is realized using substrate  105 . For example, substrate  105  may include conductive traces or patterns to which some of the reactive components of matching circuit  305  may be affixed (e.g., soldered). The conductive traces or patterns (e.g., patters of conductor formed in a PCB used to realize substrate  105 ) couple portion  305 B of matching circuit  305  to loop antenna  310 . 
     In some embodiments, loop antenna  310  is partitioned. In other words, a portion (or part) of loop antenna  310  is included in module  80 , whereas another portion of loop antenna  310  is included in or formed in or formed on or formed using substrate  105 .  FIG. 15  shows such an embodiment. In the embodiment of  FIG. 15 , a portion  310 A of loop antenna  310  is included in module  80 . For example, conductor traces or conductors or conductor patterns in module  80  may be used to implement portion  310 A of loop antenna  310 . Referring again to  FIG. 14 , another portion  310 B of loop antenna  310  is realized using substrate  105 . For example, substrate  105  may include conductive traces or patterns used to realize or implement portion  310 B of loop antenna  310 . The conductive traces or patterns (e.g., patters of conductor formed in a PCB used to realize substrate  105 ) couple portion  310 B of loop antenna  310  to matching circuit  305 . 
     One aspect of the disclosure relates to including circuitry in an RF apparatus using substrate  105  to provide some or all components for an RF apparatus (e.g., receiver, transmitter, transceiver)  300 .  FIG. 16  illustrates an RF communication apparatus  300  with matching circuit  305 , included in module  80  (as described above in connection with  FIG. 13 ), according to an exemplary embodiment. Referring to  FIG. 16 , in addition, RF apparatus  300  includes baseband circuit  205  and signal source/destination  210 . In the embodiment shown, baseband circuit  205  is external to module  80 , and couples to RF circuit  35  via link  220 . 
     In the case of RF reception, using link  220 , baseband circuit may receive signals from RF circuit  35 , and convert those signals to baseband signals. The conversion may include frequency translation, decoding, demodulating, etc., as persons of ordinary skill in the art will understand. The signals resulting from the conversion are provided signal source/destination  210  via link  215 . In the case of RF reception, signal source/destination  210  may include a signal destination, such as a speaker, a storage device, a control circuit, transducer, etc., as persons of ordinary skill in the art will understand. In the case of RF transmission, signal source/destination  210  may include a signal source, such as a transducer, a microphone, sensor, a storage device, a data source, a control circuit, etc. The signal source provides signals that are used to modulate RF signals that are transmitted. Baseband circuit  205  receives the output signals of the signal source via link  215 , and converts those signals to output signals that it provides to RF circuit  35  via link  220 . The conversion may include frequency translation, encoding, modulating, etc., as persons of ordinary skill in the art will understand. RF circuit  35  uses matching circuit  305  to provide the RF signals to loop antenna  310  for transmission via a medium, such as air or vacuum. 
     In some embodiments, a portion or part of matching circuit  305  is included in module  80 , whereas another portion or part of matching circuit  305  is external to module  80 .  FIG. 17  shows such an embodiment. Similar to the embodiment of  FIG. 14 , in the embodiment in  FIG. 17 , a portion  305 A of matching circuit  305  is included in module  80 . Another portion  305 B of matching circuit  305  is external to module  80 , for instance, realized using substrate  105 , as described above. 
     In some embodiments, a portion (or part) of loop antenna  310  is included in module  80 , whereas another portion of loop antenna  310  is external to module  80 .  FIG. 18  shows such an embodiment. Similar to the embodiment of  FIG. 15 , in the embodiment in  FIG. 18 , a portion  310 A of loop antenna  310  is included in module  80 . Another portion  310 B of loop antenna  310  is external to module  80 , for example, realized using substrate  105 , as described above. 
     Another aspect of the disclosure relates to the physical layout of matching circuit  305  and antenna loop  310 .  FIG. 19  shows a layout for an RF apparatus (or part of an RF apparatus) according to an exemplary embodiment. More specifically,  FIG. 19  shows a loop antenna that is implemented as a printed-loop-substrate-edge fringing field antenna. In other words, loop antenna  310  uses a conductive loop, implemented as an example using conductive patterns or traces formed in or on substrate  105  (e.g., a PCB), hence the label printed-loop. The conductive loop (e.g., printed-loop) is implemented at or near an edge (as shown in  FIG. 19 ) of substrate  105 , i.e., either near one or more edges of substrate  105  (as shown in  FIG. 19 ), or at one or more edges of substrate  105 , i.e., with no clearance (or nearly no clearance) between the conductive loop and the edge(s) of substrate  105 . 
     Parts of substrate  105  are not used to implement loop antenna  310 , e.g., parts of the conductive layer on a PCB are stripped or edged to generate voids  330  (i.e., areas not covered by a conductive layer). Conductive patterns or traces  340  and  345  are used to implement matching circuit  305 . In the example shown, the RF feed is accomplished using conductive pattern  340  (i.e., a receiver (not shown) or transmitter (not shown) is coupled to conductive pattern  340 . An inductor L 1  is coupled between conductive pattern  340  and loop antenna  310 . A capacitor C 1  couples conductive pattern  340  to conductive pattern  345 . A capacitor C 2  is coupled between conductive pattern  345  and loop antenna  310 . 
     Thus, a matching circuit is formed that includes inductor L 1  and capacitors C 1  and C 2 . The matching circuit formed in  FIG. 19  is merely illustrative, and no limiting. As persons of ordinary skill in the art will understand, other matching circuits may be implemented, using lumped reactive components or elements, as described above, by using such components and one or more conductive patterns in or on substrate  105  to implement desired matching circuits. Loop antenna  310  is resonated by matching circuit  305 . 
     Referring again to  FIG. 19 , a number of ground vias  335  are used to couple several points of loop antenna  310  to a ground plane (not shown). The ground plane may be formed using one or more internal layers of substrate  105  (e.g., internal layer(s) of a multi-layer PCB), or the bottom layer of substrate  105  (e.g., the bottom layer or reverse side of a PCB).  FIG. 20  shows the layout for such an arrangement. More specifically, ground vias  335  couple loop antenna  310  (shown partially using dashed lines as it does not reside in the layer shown) to conductive pattern  350 . Conductive pattern  350  constitutes a ground plane and, as noted, may be implemented using one or more internal layers or the bottom or reverse side or layer of substrate  105 . 
     As noted above, loop antenna  310  is resonated by matching circuit  305 , which gives rise to RF currents.  FIG. 21  shows an example of RF current distribution in the layout shown in  FIG. 19 . Referring again to  FIG. 21 , RF currents  360  propagate generally along the top side of substrate  105 , along the right side of substrate  105 , along the bottom side of substrate  105 , and along the left side of substrate  105 , thus generating RF radiation. Some fringing currents flow along the top side or edge of substrate  105 , as shown in  FIG. 21 . Such fringing currents generate fringing fields that also generate RF radiation. Note that although generally the conductive loop is radiating, the main radiator is along the edge(s) of substrate  105  because of relatively large size. Thus, without using a chip or ceramic antenna, loop antenna  310  uses the conductive loop and the edge(s) of substrate  105  as radiators, driven by matching circuits that use lumped reactive components or elements. 
     The size of the conductive loop in loop antenna  310  generally depends on the operating frequency (e.g., the frequency of an RF signal transmitted via loop antenna  310 , or the frequency of an RF signal received via loop antenna  310 ). Thus, the size of the conductive loop and/or substrate  105  may be selected in order to accommodate desired operating frequencies. Various shapes of the conductive loop are also possible, and contemplated. Some conductive loops may be shaped and dimensioned so as to increase the bandwidth of loop antenna  310 , or to accommodate relatively limited areas available around module  80  on substrate  105 . 
     Generally, several techniques may be used to improve the performance of loop antenna  310 : (a) using relatively narrow traces, relatively far from module  80 , in order to decrease the loop area/dimensions that gives rise to self-capacitance; (b) increasing the distance between the conductive loop coupling mechanisms (pins, etc.) to reduce the parallel parasitic capacitance with matching circuit  305 ); and (c) increased conductive loop width and length to widen the bandwidth. Note that larger conductive loop areas may be achieved in a variety of ways, for instance, by widening the conductive loop, or by making it longer, which decreases the quality factor (Q) of the conductive loop, i.e., decrease the imaginary part of its impedance compared to the real part of its impedance. 
     As noted above, in some embodiments, a portion of matching circuit  305  (see, for example,  FIG. 17 ) or a portion of loop antenna  310  (see  FIG. 18 ) is included in module  80 . In such embodiments, another portion of matching circuit  305  (see, for example,  FIG. 17 ) or a portion of loop antenna  310  (see  FIG. 18 ), respectively, is external to module  80 , e.g., formed using substrate  105 .  FIG. 22  shows a layout for such embodiments. More specifically, module  80  is positioned (typically mounted or affixed or attached) with respect to substrate  105 . Module  80  is electrically coupled to loop antenna  310 . As noted in some embodiments, a portion of matching circuit  305  is included in module  80 , whereas another portion of matching circuit  305  is laid out externally to module  80 . Furthermore, as noted in some embodiments, a portion of loop antenna  310  is included in module  80 , whereas another portion of loop antenna  310  is laid out externally to module  80 . 
     Another aspect of the disclosure relates to the topology of matching circuits  305 . Loop antenna  310 , for example, a printed-loop antenna, usually exhibits an inductive impedance. More specifically, with increasing lengths, the conductive loop impedance approaches the high impedance point of a Smith chart, as the loop impedance approaches its self parallel resonance point. The parallel self resonator is formed by the loop inductance and by the fringing field parasitic capacitance. To act as an antenna, the conductive loop is usually used below its self resonant frequency, which means it exhibits an inductive impedance. The conductive loop, however, can be used also above its self resonance frequency, where it exhibits capacitive impedance. In either case, a variety of matching circuits may be used with loop antenna  310 . Some examples are described and illustrated in U.S. patent application Ser. No. 16/237,511, cited above. 
       FIG. 23  shows a matching circuit according to an exemplary embodiment. More specifically, matching circuit  305  in  FIG. 23  includes reactive network  450  coupled in series or cascade with reactive network  550 . Reactive networks  450  and  550 , as the name suggests, include one or more inductors and/or capacitors. Reactive networks  450  and  550  may have a variety of topologies, for example, as described and illustrated in U.S. patent application Ser. No. 16/237,511, cited above. 
       FIG. 24  shows a matching circuit according to another exemplary embodiment, which uses a shunt resonant network and a reactive network. More specifically, matching circuit  305  in  FIG. 24  includes resonant network  500  coupled in shunt with the RF port of matching circuit  305 , i.e., between the RF port and ground. Resonant network  500  is also coupled to reactive network  550 . Reactive network  550  is coupled in series or cascade with the antenna port of matching circuit  305 . Resonant networks  500 , as the name suggests, include one or more inductors coupled to one or more respective capacitors to form a resonant circuit or tank or network. Reactive network  550  and resonant network  500  may have a variety of topologies, for example, as described and illustrated in U.S. patent application Ser. No. 16/237,511, cited above. 
       FIG. 25  shows a matching circuit according to another exemplary embodiment, which uses a series resonant network and a reactive network. More specifically, matching circuit  305  in  FIG. 25  includes resonant network  500  coupled in series with reactive network  550 . Reactive network  550  and resonant network  500  may have a variety of topologies, for example, as described and illustrated in U.S. patent application Ser. No. 16/237,511, cited above. 
       FIG. 26  illustrates a circuit arrangement  600  for a matching network  305  coupled to loop antenna  310 . One end of loop antenna  310  is coupled to ground (e.g., using ground vias, described above). Another end of loop antenna  310  is coupled to the antenna port of matching circuit  305 . In the particular example shown, matching circuit  305  generally has a topology similar to the topology in  FIG. 25 . More specifically, matching circuit  305  includes a resonant circuit  500  that uses inductor L 1  in series with capacitor C 1 . Matching circuit  305  further includes a reactive network  550 , which includes a single capacitor split into four series-coupled (or cascade-coupled) capacitors C 2 -C 5  (to reduce sensitivity to component variations or tolerances, for example, as described and illustrated in U.S. patent application Ser. No. 16/237,511, cited above. The example in  FIG. 26  does not use a shunt-coupled network, because in the particular case illustrated, parallel parasitics present in the circuit (e.g., the conductive loop, etc.) shift the impedance close to the nominal resistance (e.g., 50Ω) circle of the Smith chart. In other situations, a shunt network may be appropriate and may be used, for example, as described and illustrated in U.S. patent application Ser. No. 16/237,511, cited above. 
     Matching circuit  305  or loop antenna  310  may be partitioned, e.g., into portions, respectively, where one portion is included in a module (not shown) and a another portion that is external to the module, as described above. Furthermore, although various embodiments are described with respect to loop antennas, other types of antenna may be used, as persons of ordinary skill in the art will understand. The choice of antenna depends on various factors, such design specifications, performance specifications, cost, substrate characteristics and dimensions, module (if used) characteristics and dimensions, available technology, target markets, target end-users, etc., as persons of ordinary skill in the art will understand. 
     Antenna structures or loop antennas (which include a looped conductor and a substrate edge) according to exemplary embodiments may be used in a variety of communication arrangements, systems, sub-systems, networks, etc., as desired.  FIG. 27  shows a system  250  for radio communication according to an exemplary embodiment. 
     System  250  includes a transmitter  105 A, which includes antenna structure  15  (not shown). Via antenna structure  15  or loop antenna  310 , transmitter  105 A transmits RF signals. The RF signals may be received by receiver  105 B, which includes antenna structure  15  (not shown) or loop antenna  310  (not shown). In addition, or alternatively, transceiver  255 A and/or transceiver  255 B might receive the transmitted RF signals via receiver  105 D and receiver  105 F, respectively. One or more of receiver  105 D and receiver  105 F includes antenna structure  15  (not shown) or loop antenna  310  (not shown). 
     In addition to receive capability, transceiver  255 A and transceiver  255 B can also transmit RF signals. More specifically, transmitter  105 C and/or transmitter  105 E in transceiver  255 A and transceiver  255 B, respectively, may transmit RF signals. The transmitted RF signals might be received by receiver  105 B (the stand-alone receiver), or via the receiver circuitry of the non-transmitting transceiver. One or more of transmitter  105 C and transmitter  105 E includes antenna structure  15  (not shown) or loop antenna  310  (not shown). 
     Other systems or sub-systems with varying configuration and/or capabilities are also contemplated. For example, in some exemplary embodiments, two or more transceivers (e.g., transceiver  255 A and transceiver  255 B) might form a network, such as an ad-hoc network. As another example, in some exemplary embodiments, transceiver  255 A and transceiver  255 B might form part of a network, for example, in conjunction with transmitter  105 A. 
     In exemplary embodiments, RF apparatus including antenna structure  15  may include a variety of RF circuitry  35 . For example, in some embodiments, direct conversion receiver and/or transmitter circuitry may be used. As another example, in some embodiments, low intermediate frequency (IF) receiver and offset phase locked loop (PLL) transmitter circuitry may be used. 
     In other embodiments, other types of RF receiver and/or transmitter may be used, as desired. The choice of circuitry for a given implementation depends on a variety of factors, as persons of ordinary skill in the art will understand. Such factors include design specifications, performance specifications, cost, IC, die, module, or device area, available technology, such as semiconductor fabrication technology), target markets, target end-users, etc. 
     In exemplary embodiments, RF apparatus including antenna structure  15  or loop antenna  310  may communicate according to or support a variety of RF communication protocols or standards. For example, in some embodiments, RF communication according to Wi-Fi protocols or standards may be used or supported. As another example, in some embodiments, RF communication according to Bluetooth protocols or standards may be used or supported. As another example, in some embodiments, RF communication according to ZigBee protocols or standards may be used or supported. Other protocols or standards are contemplated and may be used or supported in other embodiments, as desired. 
     In other embodiments, other types of RF communication according to other protocols or standards may be used or supported, as desired. The choice of protocol or standard for a given implementation depends on a variety of factors, as persons of ordinary skill in the art will understand. Such factors include design specifications, performance specifications, cost, complexity, features (security, throughput), industry support or availability, target markets, target end-users, target devices (e.g., IoT devices), etc. 
     Referring to the figures, persons of ordinary skill in the art will note that the various blocks shown might depict mainly the conceptual functions and signal flow. The actual circuit implementation might or might not contain separately identifiable hardware for the various functional blocks and might or might not use the particular circuitry shown. For example, one may combine the functionality of various blocks into one circuit block, as desired. Furthermore, one may realize the functionality of a single block in several circuit blocks, as desired. The choice of circuit implementation depends on various factors, such as particular design and performance specifications for a given implementation. Other modifications and alternative embodiments in addition to the embodiments in the disclosure will be apparent to persons of ordinary skill in the art. Accordingly, the disclosure teaches those skilled in the art the manner of carrying out the disclosed concepts according to exemplary embodiments, and is to be construed as illustrative only. Where applicable, the figures might or might not be drawn to scale, as persons of ordinary skill in the art will understand. 
     The particular forms and embodiments shown and described constitute merely exemplary embodiments. Persons skilled in the art may make various changes in the shape, size and arrangement of parts without departing from the scope of the disclosure. For example, persons skilled in the art may substitute equivalent elements for the elements illustrated and described. Moreover, persons skilled in the art may use certain features of the disclosed concepts independently of the use of other features, without departing from the scope of the disclosure.