Patent Publication Number: US-2023155270-A1

Title: Dyadic radial coupler

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application No. 63/279,602, filed Nov. 15, 2021, and titled “DYADIC RADIAL COUPLER,” the entirety of which is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention generally relates to the field of communications, particularly radio frequency couplings. 
     Description of the Related Art 
     Radio frequency (RF) couplers can be used to carry RF signals from one point in a circuit to another with minimal losses, such as between layers of a printed circuit board (PCB). RF signals can have a frequency in the range from about 450 MHz to about 90 GHz for certain communication standards. 
     RF couplers commonly use parallel-line or planar transmission lines to carry the RF signals. A conventional RF coupler is a four-port device that consists of two adjacent RF transmission lines of sufficient length to couple the RF signal from one transmission line to the other. However, the length and number of ports make it difficult to integrate existing RF couplers into a crowded PCB layout. 
     SUMMARY OF THE INVENTION 
     In certain embodiments, the present disclosure relates to a dyadic radial coupler for coupling RF signals between PCB layers. The dyadic radial coupler includes an input port comprising a transmission line on an input layer of a PCB, a coaxial conductor, an end of the conductor operatively connected to the transmission line, a coupled port located at an opposite end of the coaxial conductor; and an impedance transformer integrated within the transmission line of the input port, wherein the input layer transmission line includes an at least partially annular conducting strip on the input layer of the PCB such that coaxial coupling of an RF signal is achieved between the input port and the coupled port. The dyadic radial coupler can further include wherein the coupled port is included in a transmission line on a coupled layer of the PCB and the coupled layer transmission line includes an at least partially annular conducting strip. 
     In various embodiments, the input layer transmission line or coupled layer transmission line is a transmission line. The dyadic radial coupler can further include an impedance transformer integral to the coupled layer transmission line. In some embodiments, the coupler is configured to operate at microwave frequencies. The coupler can be configured to have about 0 dB of signal attenuation for coupled RF signals in a predetermined frequency band. 
     In other embodiments, the dyadic radial coupler is a frequency selective coupler to attenuate signals in an undesired frequency range. The at least partially annular conducting strip on the input layer of the PCB or an at least partially annular conducting strip on the coupled layer of the PCB can be substantially circular, elliptical, parabolic, or hyperbolic for improved RF signal excitation of the coupler. In the preferred embodiment, the conducting strip is substantially a ring. 
     In a number of embodiments, the dyadic radial coupler has a plurality of coupled ports on various intermediate layers of the PCB for propagation of the RF signal by way of parasitic coupling. The coupler can have a through port and a coupled port on each intermediate PCB layer for parasitic coupling excitation by the RF signal. 
     In another embodiment, the coupled port is disconnected from additional circuit elements to allow the RF signal to radiate into free space. The dyadic radial coupler can include a microstrip patch and at least one ground plane on a PCB layer, causing the coupler to act as an antenna for the RF signal. In yet another embodiment, a plurality of couplers are connected together to form an antenna array having a common ground plane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a schematic representation of an input port in one embodiment of a dyadic radial coupler. 
         FIG.  1 B  is a schematic representation of a coupled port in one embodiment of the dyadic radial coupler. 
         FIG.  2    is a schematic representation of a coupled layer stripline feed of the dyadic radial coupler illustrating various dimensions of the stripline feed. 
         FIG.  3    is a graph of signal attenuation through a dyadic radial coupler for a range of RF signal frequencies. 
         FIG.  4 A  is a schematic representation of an input port of a frequency-selective dyadic radial coupler. 
         FIG.  4 B  is a schematic representation of a through port and a coupled port of a frequency-selective dyadic radial coupler. 
         FIG.  5    is a graph of signal attenuation through a frequency-selective dyadic radial coupler for a range of RF signal frequencies. 
         FIG.  6    is a sectional view of a plurality of PCB layers connected by a dyadic radial coupler. 
         FIG.  7    is a top plan view of an antenna structure comprising an antenna embodiment of the dyadic radial coupler. 
         FIG.  8    is an orthographic projection of an antenna constructed according to the antenna embodiment of  FIG.  7   . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following detailed description of certain embodiments presents various descriptions of specific embodiments. However, the innovations described herein can be embodied in a multitude of different ways, for example, as defined and covered by the claims. In this description, reference is made to the drawings where like reference numerals can indicate identical or functionally similar elements. It will be understood that elements illustrated in the figures are not necessarily drawn to scale. Moreover, it will be understood that certain embodiments can include more elements than illustrated in a drawing and/or a subset of the elements illustrated in a drawing. Further, some embodiments can incorporate any suitable combination of features from two or more drawings. 
     Referring initially to  FIG.  1 A , an example of a dyadic radial coupler (DRC) is shown generally at  100 . An input layer stripline feed  105  is disposed on an input layer  110  of a printed circuit board (PCB). The stripline feed  105  can be formed by etching, photo-lithography, or any other method known to one skilled in the art. In various embodiments, the input layer stripline feed  105  can be a microstrip feed, slotline feed, finline feed, imageline feed, waveguide, or any other type of transmission line known to one skilled in the art. The DRC  100  includes an input port  120 , which is included in the input layer stripline feed  105 , for connecting to a signal source, an input stage, or another component of an RF circuit configured to supply the DRC with an RF signal. The input port  120  is operably connected to an impedance matching transformer  150  for impedance matching and signal conditioning of the RF signal received by the input port. The impedance matching transformer  150  comprises a substantially rectangular portion of the stripline feed  105 . As will be described in detail herein, in certain embodiments, the dimensions of the matching transformer  150  are selected to improve coupling of RF signal components at desired frequencies. In some embodiments, the stripline feed  105  can further include a tapered portion  151  located between the matching transformer  150  and the input port  120 . In other embodiments, an end of the impedance matching transformer  150  connects directly to the input port  120 . 
     An end of the matching transformer  150  opposite from the input port operably connects the matching transformer to a coaxial conductor  130 . The coaxial conductor  130  couples RF signals between different layers of the PCB after impedance matching and signal conditioning is performed by the matching transformer  150 . An at least partially annular conducting strip  155  surrounds the coaxial conductor  130  except where the conductor contacts the input layer stripline feed  105 . A radius of the conducting strip  155  is selected to enhance coupling of the RF signal components at desired frequencies based upon the dimensions of the coaxial conductor  130  and impedance matching transformer  150 . The at least partially annular conducting strip  155  can also serve to isolate the dyadic radial coupler  100  from RF emissions by nearby circuit components. 
       FIG.  1 B  shows the DRC  100  of  FIG.  1 A  from an opposite end of the coaxial conductor  130 . A coupled layer of the PCB  140  has a coupled layer stripline feed  106  which receives coupled RF signal components through the coaxial conductor  130 . In various embodiments, the coupled layer stripline feed  106  can be a microstrip feed, slotline feed, finline feed, imageline feed, waveguide, or any other type of transmission line known to one skilled in the art. The coupled layer stripline feed  106  can be formed by any of the same methods as the input layer stripline feed  105 . The coupled layer stripline feed  106  includes an at least partially annular conducting strip  160  which is concentric with the coaxial conductor  130 . In some embodiments, the annular conducting strip  160  may comprise substantially a ring that separates the stripline feed  106  from a central conductor of the coaxial conductor  130 . The at least partially annular conducting strip  160  couples RF signals from the coaxial conductor  130 , which are extracted from the conducting strip by the coupled layer stripline feed  106 . 
     The coupled layer stripline feed  106  further includes an impedance matching transformer  150 , which in certain embodiments may be identical to the impedance matching transformer of the input layer stripline feed  105 . In other embodiments, the dimensions of the matching transformer  150  may be selected to improve coupling of specific RF frequencies, or to reduce the surface area of the DRC  100  on the input PCB layer  110  or coupled PCB layer  140 . The impedance matching transformer  150  is operatively connected to an output port  170 , which is also included at least partially in the coupled layer stripline feed  106 , for coupling the RF signal to another part of a circuit on the coupled PCB layer  140 . In some embodiments, the stripline feed  106  can further include a tapered portion  151  located between the matching transformer  150  and the input port  170 . The impedance matching transformer  150  and tapered portion  151  on the coupled layer  140  can be substantially the same as those on the input layer  110 , or can be selected for improved signal conditioning on the coupled layer. 
     0 dB Coupling Embodiment 
     Referring now to  FIG.  2   , the coupled layer stripline feed  106  and at least partially annular conducting strip  160  are shown in detail. Beginning from where an end of the central conductor of the coaxial conductor  130  contacts the coupled PCB layer  140 , a radius (r)  210  is measured to an outer edge of the stripline feed  106  that is equal to or greater than the radius of the coaxial conductor  130 . A radial difference (d)  220  is measured from an outer radius of the at least partially annular conducting strip  160  to the edge of a via on the coupled PCB layer  140  that surrounds the stripline feed  106 . 
     In one embodiment, the radius  210  is selected to match a maximum coupled length (La)  230  of the DRC  100  for coupling RF signals with approximately 0 dB of loss. In the 0 dB coupling embodiment, the DRC  100  is configured to couple RF signal components within a desired frequency range with minimal loss. To achieve 0 dB coupling, the radius (r)  210  is determined based on a coupled length (La)  230  selected to couple the desired frequencies, where (r) is given by Equation 1 and Equation 2 below and β even /β odd  are the phase delays of even and odd components of the coupled RF signal. 
     
       
         
           
             
               
                 
                   
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       FIG.  3    illustrates signal attenuation in coupled RF signals over a range of frequencies for one embodiment of the DRC  100 . A graph of signal loss measured by scattering parameters (S-parameters) over a frequency range of 20 to 40 GHz is indicated generally at  300 . Signal loss in the 0 dB coupling embodiment of the DRC  100  is shown at  310 , with minimal losses between approximately 25 and 31 GHz. However, the dimensions of various elements of the DRC  100  (such as, the impedance matching transformer  150 , at least partially annular conducting strip  130 , and tapered portion  151 ) can be selected to achieve approximately 0 dB coupling for an arbitrary range of frequencies of interest. For example, the DRC  100  can be configured to couple specific RF bands in a communications device where unwanted RF noise is present. 
     Return losses  320 / 330  measured from the input port  120  and coupled port  170  are also illustrated in  FIG.  5   . Both return losses  320 / 330  exhibit band stop filter behavior, attenuating the RF signal components at approximately 26 and 31 GHz. 
     Although  FIG.  3    illustrates one example of signal attenuation for a DRC  100 , other results are possible, including results that depend on implementation, application, and/or processing technology. 
     Parasitic Coupling Embodiment 
     Referring now to  FIGS.  4 A and  4 B , a second embodiment of the DRC  100  is shown for frequency-selective coupling of RF signals. In  FIG.  4 A , the tapered portion  151  of the input layer stripline feed  105  is elongated to guide RF signals from the input port  120  across the PCB  110  and into the impedance matching transformer  150 . The impedance matching transformer is advantageously configured for signal conditioning and filtering to attenuate components of the RF signal outside a predetermined pass band. The pass band may also be referred to as a coupling band because the DRC  100  couples only those signals falling within a chosen frequency range. One of skill in the art will conceive of various other embodiments of the of the DRC  100  to selectively couple various coupling bands of interest. 
     In  FIG.  4 B , a coupled layer of the PCB  140  is shown to have a second input port  430  (in some embodiments, the second input port  430  can act as a through port) which is operatively connected to the central conductor of the coaxial conductor  130  by way of the coupled layer stripline feed  105 . The coupled layer stripline feed  105  is elongated similarly to the tapered portion  151  of the input layer  110  to guide the RF signal across the PCB to the through port  430 . Advantageously, the RF signal may not pass through a signal conditioning or filtering stage between the coaxial conductor  130  and the through port  430 , which allows the same RF signal to coupled directly into a second DRC  100  and propagate to multiple PCB layers simultaneously. The through port  430  of a first DRC  100  can be connected to an input port  120  of a second DRC  100  to achieve coupling of the RF signal to an arbitrary number of coupled ports on various PCB layers. 
     Adjacent to the coaxial conductor  130 , a parasitic coupler  410  is provided on the coupled layer  140  to parasitically couple the RF signal as it passes between the coaxial conductor  130  and the through port  430 . In the preferred embodiment, the parasitic coupler  410  is substantially a half-ring axially aligned with the coaxial coupler  130  and separated by a partially annular conducting strip in the via. In various embodiments, the parasitic coupler  410  can be substantially parabolic, hyperbolic, circular, or elliptical, the dimensions of the coupler determined by the desired level of coupling and chosen coupled frequencies. In certain embodiments, the parasitic coupler  410  can be substantially a straight microstrip or stripline segment that terminates at an edge of the via adjacent to the coaxial conductor  130 . In the preferred embodiment, the parasitic coupler  410  attenuates the RF signal by approximately 7.5 dB as the signal is extracted from the coaxial conductor  130 . To reduce the surface area of the DRC  100  on the PCB, the parasitic coupler  140  can be formed at a lesser angle relative to the central conductor at the expense of greater signal attenuation. Conversely, the parasitic coupler  140  can be made substantially a ring to envelop the conductor and increase the level of coupling. 
     A parasitic stripline  440  operatively connects the parasitic coupler  410  to a matching transformer  150  for filtering and signal conditioning of the parasitically coupled RF signal. In the preferred embodiment, the parasitic stripline  440  forms a curve to reduce the length of the DRC  100  on the coupled layer  140  of the PCB. The curvature of the parasitic stripline  440  is selected to mitigate reflections or attenuation of the coupled RF signal. In alternate embodiments, the parasitic stripline  440  can be either substantially straight or otherwise nonlinear to accommodate nearby components on the coupled layer  140  of the PCB. The matching transformer  150  performs additional signal conditioning and filtering before the RF signal is coupled to the coupled port  170 . The parasitic coupler  410 , parasitic stripline  440 , impedance matching transformer  150 , and coupled port  170  can be duplicated on a plurality of coupled layers  140  of the PCB to parasitically couple the RF signal from the coaxial conductor  130 . This parallelization allows the RF signal to propagate simultaneously across intermediate layers of the PCB between the input layer  110  and a final coupled layer  140  without sacrificing performance of the DRC  100 . 
       FIG.  5    illustrates attenuation of coupled RF signals over a range of frequencies for a frequency-selective embodiment of the DRC  100 . A graph of signal loss measured by scattering parameters (S-parameters) over a frequency range of 26 to 42 GHz is indicated generally at  500 . Signal loss for the 7.5 dB coupling embodiment of the DRC  100  is shown at  510 , with a coupling band  540  having minimal attenuation of the RF signal between about 37 and 42 GHz. In the pictured embodiment, the DRC  100  attenuates signals in the coupling band by approximately 7.5 dB and attenuates signals in a stop band  550  from about 26 to 30 GHz by 18 dB or more. Between the coupling band  540  and the stop band  550 , a transition region exists where lower frequency components of the RF signal are gradually attenuated until the frequencies enter the stop band  550 . The performance curve  510  of the pictured embodiment resembles a high-pass filter, but the dimensions of the DRC  100  can be adjusted to include an arbitrary range of frequencies in coupling band  540 . Likewise, the DRC can be configured to include an arbitrary range of unwanted frequencies in the stop band  550 . 
     Attenuation of a through signal  520 , measured at a through port  430 , and return loss  530  are also illustrated in  FIG.  5   . The through signal  520  shows slight losses in the coupling band  540  because a portion of the signal is lost to the coupled port  170 . The return loss  530  remains at less than −10 dB through both the coupling band  540  and stop band  550 . 
     Although  FIG.  5    illustrates one example of signal attenuation for a DRC  100 , other results are possible, including results that depend on implementation, application, and/or processing technology. 
       FIG.  6    shows various intermediate layers  630  of a PCB  600  that are coupled by a DRC  100 . An input layer  610  of the PCB  600  has an input stripline feed  640  that is operatively connected to a first coaxial conductor  130 . The first coaxial conductor  130  couples an RF signal from the input stripline feed  640  to a first intermediate layer  630 . In the pictured embodiment, the input layer  610  is at an elevation of approximately 0.025 mm relative to a base layer  605  of the PCB  600 , and a first intermediate layer  630  is at an elevation of approximately 0.11 mm. A second coaxial conductor  131  operatively connects the first intermediate layer  630  to a coupled layer  620 , the conductor  131  passing through various other intermediate layers  630  which can include coupled ports  170  for parasitic coupling of the RF signal. In the pictured embodiment, the various intermediate layers  630  are at elevations of 0.22 mm, 0.42 mm, 0.67 mm and the coupled layer is at an elevation of 0.87 mm relative to the base layer  605 . Preferably each PCB layer  610 ,  620 , and  630  has a thickness of approximately 200 microns, but the construction of the PCB  600  can be any known to one skilled in the art. Each PCB layer  610 ,  620 , and  630  can include one or more striplines, microstrips, or other transmission lines  640  on an obverse side and a reverse side, allowing multiple embodiments of the DRC  100  to coexist on adjacent layers of the PCB  600 . 
     Antenna Embodiment 
     Referring now to  FIG.  7    and  FIG.  8   , an antenna embodiment of the DRC  100  is shown generally at  700 . In this embodiment, the coaxial conductor  130  is not connected to a coupled port  170 , instead allowing the RF signal to radiate into free space from the conductor  130  acting as an antenna. The antenna embodiment of the DRC  100  advantageously allows for wireless transmission using an antenna structure that covers a compact surface area on the PCB. Multiple antenna structures can be located together in close proximity to create an antenna array for improved performance. 
     In an exemplary DRC  100  constructed according to the antenna embodiment, a first conductive ground layer  710  of the PCB acts as a ground plane for the antenna. The first ground layer  710  can further include a ground layer stripline feed  740  for coupling an input RF signal to the coaxial conductor  130  at one end of the conductor. Vertically above the first ground layer  610 , a microstrip patch  720  exists on a separate layer of the PCB where the opposite end of the coaxial conductor  130  connects to a coaxial via feed  730  on the patch  720  which is included in an at least partially annular narrow empty region  750 . The narrow empty region  750  between the coaxial via feed  730  and the rest of the microstrip patch  720  results in radial coupling excitation of the RF signal and causes the coupled signal to radiate into free space. 
       FIG.  8    illustrates an exemplary antenna constructed according to the principles of the present invention. In the pictured embodiment, a second ground layer  810  exists below the first ground layer  710  and includes the ground layer stripline feed  740 . In the embodiment of  FIG.  8   , the ground layer stripline feed  740  is a stripline feed, with the first ground layer  710  acting as ground for the stripline. The second ground layer  810  is electrically connected to the first ground layer  710  by a plurality of columnar conductors  820 , which are preferably arranged along edges of the second ground layer  810  surrounding the stripline feed  740 . The coaxial conductor  130  connects the stripline feed  740  to the coaxial via feed  730  on the microstrip patch  720 . In certain embodiments, the coaxial conductor  130  includes a shorting via  880  which connects an exterior of the conductor  130  to the first ground layer  710  to provide grounding 
     In the exemplary antenna array, this structure is duplicated with two antennas connecting to two stripline feeds  740  oriented approximately 90 degrees from each other. Preferably, one of the stripline feeds  740  is provided for horizontal polarization of the antenna and the other stripline feed is provided for vertical polarization of the antenna. However, an antenna array can be constructed with the antenna elements arranged in any configuration known to one skilled in the art. 
     Applications 
     Devices employing the above-described schemes can be implemented into various electronic devices and multimedia communication systems. Examples of the electronic devices can include, but are not limited to, consumer electronic products, parts of the consumer electronic products, electronic test equipment, communication infrastructure applications, etc. Further, the electronic device can include unfinished products, including those for communication, industrial, medical and automotive applications. 
     CONCLUSION 
     The foregoing description may refer to elements or features as being “connected” or “coupled” together. As used herein, unless expressly stated otherwise, “connected” means that one element/feature is directly or indirectly connected to another element/feature, and not necessarily mechanically. Likewise, unless expressly stated otherwise, “coupled” means that one element/feature is directly or indirectly coupled to another element/feature, and not necessarily mechanically. Thus, although the various schematics shown in the figures depict example arrangements of elements and components, additional intervening elements, devices, features, or components may be present in an actual embodiment (assuming that the functionality of the depicted circuits is not adversely affected). 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel apparatus, methods, and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. For example, while the disclosed embodiments are presented in a given arrangement, alternative embodiments may perform similar functionalities with different components and/or circuit topologies, and some elements may be deleted, moved, added, subdivided, combined, and/or modified. Each of these elements may be implemented in a variety of different ways. Any suitable combination of the elements and acts of the various embodiments described above can be combined to provide further embodiments.