Vertical grounded coplanar waveguide H-bend interconnection apparatus

Abstract: An interconnection apparatus (50) providing a right angle H-plane bend in grounded coplanar waveguide GCPW transmission line media is disclosed. Respective first and second GCPW lines (60, 80) each include a dielectric substrate (62, 82), on which is formed on a bottom surface (62B, 82B) a bottom conductive ground plane (64, 84), and on a top surface (62A, 82A) is formed a center conductor strip (68, 88) sandwiched between first and second top ground plane strips (66A, 66B, 86A, 86B). The two GCPW lines (60, 80) are disposed orthogonally, forming a corner junction (100) at which corresponding bottom and top ground planes (66A, 86A, 64, 84), and the center conductor strips (68, 88) of the lines (60, 80) are electrically connected. The gaps (70A, 70B, 90A, 90B) between the top ground plane strips (66A, 66B, 86A, 86B) and the center conductor strips (68, 88) have regions (76A, 76B, 96A, 96B) of increased width at the corner junction (100) to compensate for the capacitance resulting from the junction (100).

Description: This invention relates to a vertical coplanar waveguide H-bend interconnect apparatus according to the preamble of claim 1. A grounded coplanar waveguides (GCPW) transmission line is a type of media used in many RF applications. Most GCPW right angle bends occur within a single plane, e.g. a horizontal plane. Conventionally, vertical bends require the transition from a GCPW to another transmission line (such as a coaxial line). Conventionally, circuit boards have been interconnected with cables or ribbons. The disadvantages to these conventional interconnect techniques include excessive size, weight and cost. IEEE Microwave and Guided Wave Letters, Vol. 2, No. 9, September 1992, pp. 370-371, W.A. Artuzi "Laterally Shielded Coplanar Waveguide for Millimeter Waves" discloses a coplanar waveguide. The CPW comprises a center conductor strip and to two top ground planes. The center conductor strip and both top ground planes are arranged on a substrate, each top ground plane being arranged in a distance to the center conductor strip thus defining a gap therebetween. In this paper a right angle bend is shown connecting two CPWs, wherein the center conductor strips and the top ground planes of both CPWs are aligned and in electrical contact. IEEE Transactions on Microwave Theory and Techniques, Vol. 42, No. 9, September 1994, K. Wu et al., "Theoretical and Experimental Analysis of Channelized Coplanar Waveguides (CCPW) for Wideband Applications of Integrated Microwave and Millimeter-Wave Circuits" proposes a quasi-planar structure for wideband applications of integrated microwave millimeter-wave circuits. Compared with the conventional coplanar waveguides, the novel transmission line is has a narrow metallic notch channel located underneath the main guiding part, which is able to provide direct grounding equalization without resorting to via-holes or the use of air-bridges. IEEE Transactions on Components, Hybrids, and Manufacturing Technology, Vol. 12, No. 2, June 1989, pp. 297-302, N. Muthukrishnan et al. "A Thick-Film Coplanar Probe for Time Domain Measurements" discloses a coplanar probe for testing of highfrequency components with planar geometries, such as striplines, microstriplines, and coplanar waveguides. The coplanar probe has a center conductor and split ground planes on either side separated by a gap. DE-C1-44 04 312 discloses an arrangement for connecting a stripline 3, arranged on a substrate 1, with a stripline 4 being arranged on a substrate 1, substrate 1 and substrate 2 extending in different planes. On either side of the striplines 3, 4, lines 41, 42 and 31, 32, respectively, are provided. A chip comprising three lines 6, 61, 62 is provided for connecting the lines 4, 41, 42 on substrate 1 with the lines 3, 31, 32 on the substrate 2. EP-A-0 671 776, which is a prior art according to Article 54(3) EPC, relates generally to microwave directional coupler devices for electromagnetically coupling a plurality of two-conductor transmission lines, each comprising signal conductor means and ground conductor means to provide for transfer of microwave energy between the two lines. The object of the present invention is to provide a vertical coplanar waveguide H-bend interconnect apparatus having an increased operating bandwidth and an improved performance. This object is solved by an apparatus with the features of claim 1. This invention offers a new, compact approach to microwave packaging. Separate, individual hybrid circuit board assemblies can now be packaged vertically, saving valuable real estate. A vertical grounded coplanar waveguide (GCPW) H-bend interconnect apparatus is described, and includes a first GCPW transmission line, comprising a first dielectric substrate having first and second opposed surfaces, a bottom conductive ground plane defined on the first dielectric surface, and a center conductor strip defined on the second surface in a spaced relationship with first and second top conductive ground plane strips. The interconnect apparatus further includes a second GCPW transmission line, comprising a second dielectric substrate having third and fourth opposed surfaces, a second bottom conductive ground plane defined on the third dielectric surface, and a second center conductor strip defined on a fourth surface in a spaced relationship with third and fourth top conductive ground plane strips. The second substrate is disposed transversely to the first substrate and in contact with the first substrate such that the first and second center conductor strips are aligned and in electrical contact, the first and third top ground plane strips are aligned and in electrical contact, and the second and fourth top ground plane strips are aligned and in electrical contact. The first and third top ground plane conductor strips, and the second and fourth top ground plane conductor strips, are respectively electrically connected along a corner junction between the first and second GCPW transmission lines. The gaps between respective top ground plane conductor strips and the center conductor strip are increased in size at regions adjacent the corner junction to compensate for capacitive coupling at the junction. BRIEF DESCRIPTION OF THE DRAWING These and other features and advantages of the present invention will become more apparent from the following detailed description of an exemplary embodiment thereof, as illustrated in the accompanying drawings, in which: FIG. 1 is an isometric view of a vertical, right angle GCPW bend embodying the invention. FIGS. 2A-2C are schematic diagrams showing three different alternate embodiments of the shaping of the H-bend junction groundplane cutouts to improve performance of the GCPW bend. FIG. 3 is an isometric view illustrating an arrangement of stacked MICs. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an isometric view of a vertical, right angle, grounded coplanar waveguide (GCPW) bend interconnect circuit 50 embodying this invention. Conventionally, most GCPW right angle bends occur within a single plane. This interconnect circuit 50 provides a transition from a GCPW 60 in a horizontal plane 52 to a GCPW 80 in a vertical plane 54 without the need of an intermediate interconnect. The two GCPWs 60 and 80 are placed at right angles, forming a vertical, right angle GCPW H-bend. This can be extended to form interconnects between a stacked assembly of microwave hybrids. The horizontal GCPW 60 comprises a planar dielectric substrate 62 having opposed planar surfaces 62A and 62B. A GCPW bottom ground plane 64 is defined by a metal layer applied to the lower surface 62B. A center conductor strip 68 is defined on the top surface 62A between first and second top ground planes 66A and 66B, also formed on the top surface 62A. The top ground planes are separated from the center conductor strip by gaps 70A and 70B. A plurality of plated through holes 72 are formed in the substrate 62 to provide electrical ground connection between the bottom ground plane 64 and the top ground planes 66A and 66B. In some embodiments, the GCPW lines will not include the bottom ground plane layer, in which case it will be unnecessary to provide the interconnection between the top and bottom ground plane layers. The vertical GCPW 80 comprises a planar dielectric substrate 82 having opposed planar surfaces 82A and 82B. A GCPW bottom ground plane 84 is defined by a metal layer applied to the lower surface 82B. A center conductor strip 88 is defined on the top surface 82A between first and second top ground planes 86A and 86B, also formed on the top surface 82A. The top ground planes are separated from the center conductor strip by gaps 90A and 90B. A plurality of plated through holes 92 are formed in the substrate 82 to provide electrical ground connection between the bottom ground plane 84 and the top ground planes 86A and 86B. The two GCPWs 60 and 80 are connected together at a right angle with the top ground plane strips and center conductor strips of the two GCPWs respectively electrically connected together, e.g., by conductive epoxy. This forms a right angle corner interconnection 100 between the top surfaces of the two GCPWs. A section of conductive strips is removed from the horizontal GCPW substrate 62 to expose the dielectric at region 74, and the vertical GCPW substrate 82 is placed on top of this exposed dielectric. The sharp corner of the interconnection 100 will have a great deal of capacitance associated with it, so the corners 76A, 76B, 96A, 96B of the ground planes 66A, 66B, 86A, 86B near the vertical transition 100 are relieved or cut out to increase the gap size between the center and top ground plane conductor strips to help compensate for the capacitance. In an exemplary embodiment, the GCPWs 60 and 80 have a center conductor width of 20.96 mils, a gap size (70A, 70B) of 10 mils, and a 40 mil thick substrate of RT/6010 Duroid (TM) (ε r =10.2). The plated through via holes 72 and 92 have a diameter of 13 mils, centered at a distance of 75 mils from the center of the center conductor strip 68 and 88. Attachment of the two transmission lines 60 and 80 can also be accomplished with reflowed solders, solder bumps, z-axis adhesives, as long as there is DC continuity between the corresponding conductor lines. Analysis shows that reshaping of the H-bend junction will increase the operating bandwidth and improve the performance. FIGS. 2A-2C illustrate three respective different configurations of the ground plane cutouts at the H-bend junction. FIG. 2A illustrates a GCPW center conductor 68' and ground plane conductors 66A' and 66B', wherein the ground plane conductors have flare-out end configurations which are gradual exponential tapers. FIG. 2B illustrates a GCPW line configuration including center conductor 68'' and ground plane conductors 66A'' and 66B'', wherein the latter conductors have ground plane flare-outs which are gradual linear tapers. FIG. 2C illustrates a GCPW line configuration including the center conductor 68''' with ground plane conductors 66A''' and 66B''', wherein the latter conductors have abrupt step cutouts at the ends thereof. All of the configurations can be used to reshape the H-bend junction cutouts to improve the RF performance. FIG. 3 is an isometric view illustrating, as an exemplary application for the invention, an arrangement of stacked microwave integrated circuits (MICs) realized with vertical GCPW H-bend connections in accordance with the invention. Here, two printed wiring boards (PWBs) 150 and 160 are arranged in parallel in a vertical orientation. Extending between the PWBs are several MIC boards 170A-170N. Each MIC board has GCPW input/output connections 180 along its edges as indicated in FIG. 3 on exemplary board 170C. Each PWB board 150 and 160 has vertical GCPW circuits extending along the inner facing surfaces of the boards. For example, board 150 has vertical GCPW circuits 152 formed on surface 154. Vertical H-bend interconnects 100 in accordance with the invention, as more particularly shown in FIG. 1, provide microwave frequency interconnection between the GCPW input/output lines of the stacked MIC boards and the vertical GCPW lines 152 of the vertical PWBs. In this exemplary embodiment, the GCPW input/output lines of the stacked MIC boards do not include the bottom ground plane layer. However, such ground planes are desired, and can be interconnected with plated through holes formed in the dielectric substrates to the corresponding top ground plane strips on the stacked boards, and also to corresponding bottom ground plane strips for the GCPW lines 152 of the vertical PWBs. This invention need not be restricted to two PWBs as illustrated in FIG. 3. For example, one vertical GCPW can connect several stacked, horizontal boards. It would also be possible to skip any boards where connections are not necessary by sizing the boards appropriately or by cutting sections out of the boards to allow the vertical GCPW to pass by without making contact. Further extensions would allow for multiple GCPWs on each board. This would require one vertical GCPW for each different waveguide on the boards. Applications for the invention include vertical interconnections between stacked substrates, which can be found in receiver/exciter circuits, communication subsystems, and other microwave circuitry. Such circuitry can be found in radar systems, satellites, microwave automobile electronics, missile systems, and cellular telephones.

Claims: A vertical coplanar waveguide (CPW) H-bend interconnect apparatus (50) with a first CPW transmission line (60), comprising a first dielectric substrate (62) having first and second opposed surfaces (62B, 62A), and a first center conductor strip (68) defined on said second surface (62A) in a spaced relationship with first and second top conductive ground plane strips (66A, 66B); and a second CPW transmission line (80), comprising a second dielectric substrate (82) having third and fourth opposed surfaces (82B, 82A), and a second center conductor strip (88) defined on said fourth surface (82A) in a spaced relationship with third and fourth top conductive ground plane strips (86A, 86B), wherein said second substrate (82) is discposed at an angle and adjacent to said first substrate (62) such that said first and second center conductor strips (68, 88) are aligned and in electrical contact, said first and third top ground plane strips (66A, 86A) are aligned and in electrical contact, said second and fourth top ground plane strips (66B, 86B) are aligned and in electrical contact, said first and third top ground plane conductor strips (66A, 86A), and said second and fourth top ground plane conductor strips (68B, 88B) are respectively electrically connected along a corner interconnect junction (100) between said first and second GCPW transmission lines, said first center conductor strip (68) is separated from said first and second ground plane strips (66A, 66B) by respective first and second gaps (76A, 768), and said second center conductor strip (88) is separated from said third and fourth ground plane strips (86A, 86B) by respective third and fourth gaps (90A, 90B), characterized in that said first, second, third and fourth gaps (70A, 70B, 90A, 90B) have regions (76A, 76B, 96A, 96B) of increased gap size adjacent said corner interconnection junction (100) to compensate for capacity coupling at said junction (100). The apparatus of claim 1, characterized in that said regions (76A, 76B, 96A, 96B) of increased gap size are rectilinear in configuration. The apparatus of claim 1, characterized in that said regions of increased gap size have a gradual exponential tapered configuration. The apparatus of claim 1, characterized in that said regions of increased gap size have a gradual linear tapered configuration. The apparatus of any of claims 1 - 4, characterized in that said first and second CPW transmission lines (60, 80) are disposed orthogonally to each other. The apparatus of any of claims 1 - 5, characterized in that said first CPW transmission line (60) is formed on a printed wiring board (PWB) (150) and that said second CPW transmission line (80) is formed on a microwave integrated circuit (MIC) board (170) arranged orthogonally to the PWB (150), with said apparatus providing board-to-board microwave frequency electrical interconnection between the PWB (150) and the MIC board (170), the PWB (150) including said first dielectric substrate (62), the MIC board (170) including said second dielectric substrate (82), and a vertical CPW H-bend interconnection (100) being provided at a junction between said first and second CPW lines (60, 80). The apparatus of any of claims 1 - 6, characterized in that said first CPW transmission line (60) comprises a bottom conductive ground plane (64) defined on said first dielectric surface (62B), that said second CPW transmission line (80) comprises a second bottom conductive ground plane (84) defined on said second bottom conductive ground plane (84) defined on said third dielectric surface (82B), and that said first and second bottom conductive ground planes (64, 84) are electrically interconnected to each other. The apparatus of claim 7, characterized by a plurality of conductive plated through holes (72, 92) formed through said respective first and second dielectric substrates (62, 82) and forming an electrical connection between said respective bottom ground planes (64, 84) and said top ground plane strips (66A, 66B, 86A, 86B), so that said top ground plane strips (66A, 66B, 86A, 86B) of each CPW transmission line (60, 80) are in electrical contact with said corresponding bottom ground plane (64, 84).

Inventors: HOFFMEISTER RICHARD M, QUAN CLIFTON, HOFFMEISTER, RICHARD M., QUAN, CLIFTON
Applicants: HUGHES ELECTRONICS CORP, HUGHES ELECTRONICS CORPORATION
Application year: 1996
Main classification: H01P1
IPC codes: H01P3, H01P1, H01P5