Abstract:
A microwave frequency signal path crossover apparatus for surface mounting to a circuit board. The signal path crossover including interspaced planar horizontal shielding members, horizontal dielectric members, and vertical shielding vias surrounding horizontal signal carrying members connected to the circuit board by vertical vias. Low errant signal emitting structures including partial half and three quarter arc vias, terminating arms, half circle arc transition apertures, via grounding fingers, and compensating capacitive structures are taught.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and is a continuation-in-part of U.S. provisional application Ser. No. 61/894,663 filed on Oct. 23, 2013. This application is hereby expressly incorporated by reference in its entirety. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not Applicable. 
     RESERVATION OF RIGHTS 
     A portion of the disclosure of this patent document contains material which is subject to intellectual property rights such as but not limited to copyright, trademark, and/or trade dress protection. The owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office patent files or records but otherwise reserves all rights whatsoever. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to improvements in surface mount components for electrical circuits handling microwave frequencies with signal paths that cross in proximity each other. More particularly, the invention relates to improvements particularly suited for multiple layer circuits requiring high signal quality and low profile applications. In particular, the present invention relates specifically to a particular surface mount construction of a crossover apparatus and method minimizing disruptions to the electrical signals. 
     2. Description of the Known Art 
     As will be appreciated by those skilled in the art, signal path crossings or crossovers are known in various forms. Patents disclosing information relevant to signal path crossovers include: U.S. Pat. No. 2,860,305, issued to Bey on Nov. 11, 1958 entitled High frequency transmission line coupling device; U.S. Pat. No. 3,104,363, issued to Butler on Sep. 17, 1963 entitled Strip transmission line crossover having reduced impedance discontinuity; U.S. Pat. No. 3,740,678, issued to Hill on Jun. 19, 1973 entitled Strip Transmission Line Structures; U.S. Pat. No. 4,078,214, issued to Beno on Mar. 7, 1978 entitled Microwave crossover switch; U.S. Pat. No. 4,533,883, issued to Hudspeth, et al. on Aug. 6, 1985 entitled Coaxial transmission line crossing; U.S. Pat. No. 5,003,273, issued to Oppenberg on Mar. 26, 1991 entitled Multilayer printed circuit board with pseudo-coaxial transmission lines; U.S. Pat. No. 5,321,375, issued to Corman on Jun. 14, 1994 entitled RF crossover network; U.S. Pat. No. 5,600,285, issued to Sachs, et al. on Feb. 4, 1997 entitled Monolithic stripline crossover coupler having a pyramidal grounding structure; U.S. Pat. No. 6,097,260 issued to Whybrew, et al. on Aug. 1, 2000 entitled Distributed ground pads for shielding cross-overs of mutually overlapping stripline signal transmission networks; U.S. Pat. No. 6,734,750, issued to Ostergaard on May 11, 2004 entitled Surface mount crossover component; U.S. Pat. No. 6,825,749, issued to Lin, et al. on Nov. 30, 2004 entitled Symmetric crossover structure of two lines for RF integrated circuits. Each of these patents is hereby expressly incorporated by reference in their entirety. 
     These patents teach various structures for crossovers but fail to recognized a simple construction approach with integrated capacitors and a construction that eliminates excess unwanted signal paths. Thus, these prior references are very limited in their teaching and utilization, and an improved microwave crossover is needed to overcome these limitations. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved surface mount microwave crossover for a signal crossing location on an electric circuit board for high frequency lines operating with microwave type signals and frequencies. In accordance with one exemplary embodiment of the present invention, a method and construction is taught for a surface mount multiple layer build up of a three dimensional crossover. The three dimensional crossover utilizes a full triple ground plane sandwiching two different ground surrounded signal paths. A further improvement teaches built in compensating capacitance. Still further, the invention teaches minimization of the excess material to minimize stray signal effects. The invention has the advantage that it operates over a wide band of frequencies and is economical in construction costs. These and other objects and advantages of the present invention, along with features of novelty appurtenant thereto, will appear or become apparent by reviewing the following detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the following drawings, which form a part of the specification and which are to be construed in conjunction therewith, and in which like reference numerals have been employed throughout wherever possible to indicate like parts in the various views: 
         FIG. 1  provides a schematic view of a multiple port portion of a single layer microwave circuit. 
         FIG. 2  shows the first metal layer for the crossover. 
         FIG. 3  shows the second metal layer in plane with the first conducting signal layer and the impedance compensating capacitors. 
         FIG. 4  shows the third metal layer with an uninterrupted ground plane and compensating capacitors. 
         FIG. 5  shows the fifth metal layer in plane with the second conducting signal layer. 
         FIG. 6  shows the sixth metal layer. 
         FIG. 7  is a magnified view of the synthetic transmission line created by the shunt capacitors at each metal layer through which a signal via travels. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in the build up from  FIG. 1  to  FIG. 6  of the drawings and shown completed in  FIG. 6 , one exemplary embodiment of the present invention is generally shown as a microwave crossover  50  (in  FIGS. 2, 5, and 6 ) for surface mounting on a circuit board  10 .  FIGS. 2 through 6  show the construction of the crossover  50  with a first conductive layer  100  (in  FIGS. 2 through 4 and 6 ), first dielectric  150  (in  FIGS. 3, 4, and 6 ), second conductive layer  200  (in  FIGS. 3, 4, and 6 ), second dielectric  250  ( FIGS. 4 and 6 ), third conductive layer  300  ( FIGS. 4, 5 and 6 ), third dielectric  350  (in  FIGS. 5 and 6 ), fourth conductive layer  400  (in  FIGS. 5 and 6 ), fourth dielectric  450  (in  FIG. 6 ), and fifth conductive layer  500  (in  FIG. 6 ) connected by vertical vias  105  (in  FIGS. 2 and 6 ). The layers  100 ,  200 ,  300 ,  400 ,  500  and dielectrics  150 ,  250 ,  350 ,  450  are planar and the conductive vias  105  are vertical. This construction forms shielded paths  600  (in  FIGS. 3 and 5 ), a synthetic transmission line  700  (in  FIG. 7 ), and a cutoff waveguide  800  (in  FIG. 6 ). For the preferred embodiment, the conductive layers were formed from metal, but any substance with the appropriate shielding characteristics and electrical transmission characteristics may be utilized. We can consider each of the elements during the build up from the base circuit  10  (in  FIG. 1 ). 
       FIG. 1  schematically depicts a multiple port portion of a single layer microwave circuit  10 . The microwave circuit board  10  includes a first port  1  with a first signal line  11 , a second port  2  with a second signal line  12 , a third port  3  with a third signal line  13 , and a fourth port  4  with a fourth signal line  14  embedded in a common ground plane  21 . The common ground plane  21  and the term ‘ground’ are to be interpreted as the base potential for the signals in the operating environment for the microwave circuit board that may be considered to be ground in most operating circuits, but it is envisioned that ‘ground’ may take on the meaning of the ‘base signal level’ in some applications where true ‘ground’ is not used in the circuitry. The ground plane  21  may or may not be connected to a second ground plane on the underside of the circuit by plated through-holes, or vias  16 . 
       FIG. 2  shows the first conductive layer  100  electrically bonded and physically bonded to and enhancing the ground plane  21  inside the crossover  50  making the crossover  50  performance less susceptible to misalignment effects. As shown in  FIG. 2  the bottom of the microwave crossover  50  is a first conductive layer  100  that is intended to mimic the direction of the required layout of the signal paths on the microwave circuit  10 . Thus, the first conductive layer  100  serves two main functions: first a means for connecting the crossover  50  to the circuit board  21  via bonding or soldering, thus, both electrically and mechanically; and second the first conductive layer  100  minimizes the electrical effects, e.g. reflections of slight placement errors. 
     The first ground conductive layer  100  is designed with body  102  forming a ground plane  170  having a perimeter  103  defining arm edges  104  and corners  106 ,  111 . Note the symmetric perpendicular cross shape  800  of the first conductive layer  100  with the initial formation of vertical vias  105  on the perimeter  103 . The vertical vias  105  can be simple wires but the preferred embodiment uses half arc vias  107  on the arm edges  104  and three quarter vias  108  on the inner corners  106 , and one quarter vias  109  on the outer corners  111 . The vertical vias are also shown positioned to electrically connect to the board ground plane  21 . The partial arc shape of the preferred vertical vias  107 ,  108 ,  109  is important for the efficient operation of the crossover  50  because the shape minimizes the effect of interference and stray signals. The body  102  is constructed with a first arm  110 , a second arm  120 , a third arm  130 , and a fourth arm  140  with each arm  110 ,  120 ,  130 ,  140  connected to the center body  149 . The first arm  110  includes a first transition end  112  designed with a first via transfer  114  positioned in a first rectangular cutout transition aperture  113  between the first ground fingers  116 ,  118 . The first via transfer  114  supports the first signal via  115 . The second arm  120  includes a second transition end  122  designed with a second via transfer  124  positioned in a second rectangular cutout transition aperture  123  between the second ground fingers  126 ,  128 . The second via transfer  124  support the second signal via  125 . The third arm  130  includes a third transition end  132  designed with a third via transfer  134  positioned in a third rectangular cutout transition aperture  133  between the third ground fingers  136 ,  138 . The third via transfer  134  supports the third signal via  135 . The fourth arm  140  includes a fourth transition end  142  designed with a fourth via transfer  144  positioned in a fourth rectangular cutout transition aperture  143  between the fourth ground fingers  146 ,  148 . The fourth via transfer  144  supports the fourth signal via  145 . 
     The four signal vias  115 ,  125 ,  135 ,  145  are used to create two separate signal paths with the first path  601  in (in  FIG. 3 ) from port  1  to port  2  and the separate second path  602  (in  FIG. 5 ) from port  3  to port  4 . As a reference point, the shorter first via  115  in the lower left of center is electrically connected to port  1 , the shorter second via  125  in the upper right is electrically connected to port  2 , the longer third via  135  in the upper left is electrically connected to port  3  and the longer fourth via  145  in the lower right is electrically connected to port  4 . Note that these vias  115 ,  125 ,  135 ,  145  create a horizontal to vertical change in signal path direction. Reflections can arise whenever something interrupts the characteristic impedance of the microwave circuit which is strongly influenced by the geometric relationship between signal conductors and ground conductors, as well as other material characteristics. Here, it is important to note that the signal vias  115 ,  125 ,  135 ,  145  have caused a change in the geometric relationship between the conductors and ground plane  21  over which the microwave signals are traveling. It can be shown that the vias  115 ,  125 ,  135 ,  145  introduce extra inductance per unit length into the circuit  10  and also a discontinuity inductance caused by the abruptly changing the signals&#39; propagations from plane parallel with the circuit board to normal with the board. 
     Also note the symmetric perpendicular cross shape  800  of the first conductive layer  100  with the initial formation of vertical vias  105  on the perimeter  103  including half arc vias  107  on the arm edges  104  and three quarter vias  108  on the inner corners  106  and one quarter vias on the outer corners  111 . 
     The geometric relationship of the signal lines to the ground plane is important to the performance of the circuit because of characteristic impedance. To completely derive the importance of the signal lines and characteristic impedance relationship is outside the scope of this document, but it can be shown that the characteristic impedance of a transmission line is tightly associated with the differential quantities of inductance and capacitance per unit length. Two measures of microwave signal integrity are reflection and isolation. Reflections distort the signal much the same way as echoes or reverberations distort audio signals. Isolation may be defined as the absence of crosstalk, as when one conversation interrupts another. 
       FIG. 3  illustrates the preferred embodiment of the present invention where the second conductive layer  200  is disposed in parallel with the first conductor layer  100  and is separated from it by a dielectric  150 . Note that  FIG. 3  is rotated in relation to the view shown in  FIG. 2  as shown by the position of the ports  1 - 4 . The dielectric  150  can be selected for the application including those known in the art such as air, oil, glass, plastic, ceramic or the like. 
     The second layer  200  contains three functional elements: a second layer signal line  260  connecting ports  1  &amp;  2 , a ground plane  270  and two impedance compensating capacitors  280  shown as the second layer third port capacitor  281  located at port  3  and the second layer fourth port capacitor  282  located at port  4 . The second layer signal line  260  is one of the conducting paths  600 . 
     The second layer signal line  260  is connected between the first via  115  and second via  125  to reach down to ports  1  and  2 . The second layer signal line  260  extends through the second layer lower line aperture  261  in the second ground plane  270 . Note that the second layer signal line  260  is of reduced cross section along the length of the distance between the ports. The ground plane  270  is a conducting plane with a first plane side  271  and second plane side  272  interrupted by the signal line  260 . Each mirrored side  271 ,  272  includes two path edge arms  273  and also includes one capacitor arm  274  with a capacitor aperture  275 . Thus, the second ground layer  270  includes two capacitor arms  274 , and two capacitor apertures  275 . In this manner, each capacitor arm  274  extends to form the first part of the associated impedance compensating capacitor  280 . 
     The impedence compensating capacitor  280  also includes a semicircular extension  285  shown as a half doughnut or half washer shaped conducting structure. The first second layer semicircular extension  283  is electrically connected to the third via  135  and the second second layer semicircular extension  284  is electrically connected to the fourth via  145  reaching down to the associated ports  3  &amp;  4 . The conducting doughnut semicircular extension  285  serve to contribute capacitance to the signal vias  135 ,  145 , thus helping to offset the inductance associated with the vertical via presence in the crossover  50 . 
     Also shown in  FIG. 3  are the connections of the first ground layer  170  ( FIG. 5 ) connecting half are vias  107 , three quarter vias  108 , and one quarter vias  109  arranged along the edges of the ground plane  270  of the crossover  50  that connect to the second ground plane  270  to the first ground layer  100 . Their purpose is to connect the ground plane  21  to all the ground planes  170  ( FIGS. 5 and 6 ),  270  ( FIG. 6 ),  370  ( FIG. 6 ),  470  ( FIGS. 5 and 6 ),  570  ( FIG. 6 ) of the crossover  50  ( FIG. 5 ). Note how the ground vias  107 ,  108 ,  109 , and the ground planes  170 ,  270 ,  370 ,  470 ,  570  they connect are arranged with an external shape of a cross with edges in proximity to the signal lines, and not some other shape. e.g. in the shape of a square or rectangle. This relationship is also important for preserving the proper characteristic impedance and minimizing reflections. 
       FIG. 4  shows the third conductive layer  300  in parallel with the second conductive layer  200  and separated from the second conductive layer by the dielectric  250 . The third conductive layer  300  contains at least one ground plane  370  with two terminating arms  371  and two capacitor arms  374  each defining capacitor apertures  375 . The third ground plane  370  is connected by vias  107 ,  108 ,  109  to the first ground plane  170  ( FIGS. 5 and 6 ) and the second ground plane  270  ( FIGS. 3, 5, and 6 ). 
     Each capacitor arm  374  extends to form the first part of the associated third layer impedance compensating capacitor  380  shown as the third layer third port capacitor  381  located at port  3  and the third layer fourth port capacitor  382  located at port  4 . 
     Each impedence compensating capacitor  380  also includes a semicircular extension  385  shown as a half doughnut or half washer shaped conducting structure. The first third layer semicircular extension  383  is electrically connected to the third via  135  and the second third layer semicircular extension  384  is electrically connected to the fourth via  145  reaching down to the associated ports  3  &amp;  4 . 
     Additional conductive layers identical to the construction of the third conductive layer  300  can be added when it is inconvenient to make the conductive of the third conductive layer  300  thick enough. These additional intermediate layers can be crucial to controlling isolation between the signal line connecting ports  1 &amp;  2  and the signal line connecting ports  3  &amp;  4 . One preferred embodiment uses two conductive layers which are considered to be combined to form the third conductive layer  300 . 
       FIG. 5  illustrates the preferred embodiment of the present invention where the fourth conductive layer  400  is disposed in parallel with the third conductive layer  300  and is separated from it by a third dielectric  350 . The fourth layer  400  contains two functional elements: a fourth layer signal line  460  connecting ports  3  &amp;  4  and a ground plane  470 . The fourth layer signal line  460  is also one of the conducting paths  600 . 
     The signal line  460  is connected between the third via  135  and fourth via  145  to reach down to ports  3  and  4 . Note that the signal line is also of reduced cross section along the length of the distance between the ports. 
     The ground plane  470  is a conducting plane with a first plane side  471  and second plane side  472  interrupted by the signal line  460 . Each mirrored side  471 ,  472  includes two path edge arms  473  and also includes one terminating arm  474 . 
     Also shown in  FIG. 5  are the connections of the first ground layer  170  connecting half arc vias  107 , three quarter are vias  108 , and one quarter arc vias  109  arranged along the edges of the ground plane  470  of the crossover  50  ( FIGS. 2, 5, and 6 ) that connect to the fourth ground plane  470  to the first ground plane  170 ). 
       FIG. 6  shows the fifth conductive layer  500  that is disposed in parallel with the fourth conductive layer  400  and is separated from it by a fourth dielectric  450 . The filth conductive layer  500  is continuous and is very similar to the first body  102 . The fifth conductive layer  500  forms a ground layer  570  with terminating arms  574  connected by the half arc vias  107 , three quarter vias  108 , and one quarter arc vias  109  arranged along the edges of the ground plane  570  of the crossover  50  that connect the fifth ground plane  570  to the other ground planes  170 ,  270 ,  370 ,  470 . 
       FIG. 7  shows the synthetic transmission line  700  is created by adding shunt capacitors to each conductive layer through which a signal via travels and is created by the above described structure. The synthetic transmission line  700  shown is at port  3 . The connecting via  135  vertically traverses the second and third conductive layers  200 ,  300  and dielectric layers  150 ,  250 ,  350  which behave as inductive discontinuities to the signals intended to travel between ports  1  &amp;  2  (in  FIG. 2 ) and between ports  3  &amp;  4  (in  FIG. 2 ). In order to minimize these inductive discontinuities, capacitors  280 ,  380  have been formed between the signal via  135  and ground planes  200 ,  300 . This creates a ladder network of series inductances and shunt capacitances, forming a so-called synthetic transmission line  700 . By adding shunt capacitance to each layer  200 ,  300  in the form of washer or doughnut-shaped conducting features  283 ,  284  (in  FIG. 3 ),  383 ,  384  (in  FIG. 4 ) aligned in coplanarity with ground plane layers  270 ,  370  and as shown in  FIG. 7 , signal reflections from ports  1 - 4  (in  FIG. 2 ) are greatly reduced. 
     As noted throughout the exterior crossover perimeter shapes of  FIGS. 1 through 6 , a cut-off waveguide  800  ( FIG. 6 ) is created by the cross arm shape of the crossover  50 . As shown in  FIGS. 2-6 , the body of the crossover  50  is shaped like a cross with extending arms. In the absence of any other surface mount device with which to compare this structure that might seem like a normal shape or perhaps a whim of the designer, but this is not the case. Most all surface-mount microwave components are rectangular or square. The tacit but widespread assumption that microwave surface-mount components should be square is subtly reinforced today in the computer-aided design software used to create the components, because they begin with a ‘box’ that may be either rectangular or square. Thus, creating a surface-mount microwave component that is not square is not only not obvious to the competent practitioner, it is also not convenient. But there is a physical reason why a designer might want to shape a crossover this way, namely to attenuate higher order waveguide modes. Although beyond the scope of this disclosure, it can be shown that electromagnetic energy can propagate not only along signal traces, but also inside structures known as ‘waveguide’ which may be made of conductive, conductive plus dielectric or just dielectric. An example of a dielectric waveguide is an optical fiber, which propagates electromagnetic energy in the form of light. Moreover, it is very evident that electromagnetic energy may propagate through free space, because otherwise radios could not physically exist. By making the signal/ground structures of the crossover narrow and creating the intersection of two narrow structures, with signal lines on different isolated geometric planes, isolation is improved. Thus, the present invention teaches unique construction method and apparatus not previously known. 
     Reference numerals used throughout the detailed description and the drawings correspond to the following elements:
         first port  1     second port  2     third port  3     fourth port  4     base microwave circuit  10     first signal line  11     second signal line  12     third signal line  13     fourth signal line  14     plated through hole vias  16     common ground plane  21     microwave crossover  50     first conductive layer  100     first layer body  102     perimeter  103     arm edges  104     vertical vias  105     inner corners  106     half arc vias  107     three quarter vias  108     one quarter vias  109     first arm  110     outer corners  111     first transition end  112     first half circle arc transition aperture  113     first via transfer  114     first ground fingers  116 ,  118     first signal via  115     second arm  120     second transition end  122     second half circle arc transition aperture  123     second via transfer  124     second ground fingers  126 ,  128     second signal via  125     third arm  130     third transition end  132     third half circle arc transition aperture  133     third via transfer  134     third ground fingers  136 ,  138     third signal via  135     fourth arm  140     fourth transition end  142     fourth half circle arc transition aperture  143     fourth via transfer  144     fourth ground fingers  146 ,  148     fourth signal via  145     center body  149     dielectric  150     first layer ground plane  170     second conductive layer  200     second dielectric  250     lower signal line  260     lower line aperture  261     second ground plane  270     first plane side  271     second plane side  272     path edge arms  273     capacitor arm  274     capacitor apertures  275     impedance compensating capacitor  280     second layer third port capacitor  281     second layer fourth port capacitor  282     impedance compensating capacitor  280     first second layer semicircular extension  283     second second layer semicircular extension  284     semicircular extensions  285     third conductive layer  300     third conductive layer  300     third dielectric  350     third ground plane  370     third layer terminating arms  371     third layer capacitor arms  374     third layer capacitor apertures  375     third layer impedance compensating capacitor  380     third layer fourth port capacitor  382     first third layer semicircular extension  383     second third layer semicircular extension  384     semicircular extension  385     fourth conductive layer  400     fourth dielectric  450     upper signal line  460     upper line aperture  461     fourth ground plane  470     first plane side  471     second plane side  472     path edge arms  473     terminating arm  474     fifth conductive layer  500     fifth ground layer  570     fifth layer terminating arms  574     shielded paths  600     first path  601     second path  602     synthetic transmission line  700     cut-off waveguide  800         

     From the foregoing, it will be seen that this invention well adapted to obtain all the ends and objects herein set forth, together with other advantages which are inherent to the structure. It will also be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. Many possible embodiments may be made of the invention without departing from the scope thereof. Therefore, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense. 
     When interpreting the claims of this application, method claims may be recognized by the explicit use of the word ‘method’ in the preamble of the claims and the use of the ‘ing’ tense of the active word. Method claims should not be interpreted to have particular steps in a particular order unless the claim element specifically refers to a previous element, a previous action, or the result of a previous action. Apparatus claims may be recognized by the use of the word ‘apparatus’ in the preamble of the claim and should not be interpreted to have ‘means plus function language’ unless the word ‘means’ is specifically used in the claim element. The words ‘defining,’ ‘having,’ or ‘including’ should be interpreted as open ended claim language that allows additional elements or structures. Finally, where the claims recite “a” or “a first” element of the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.