Waffle wall-configured conducting structure for chip isolation in millimeter wave monolithic subsystem assemblies

• US 5,065,123 A
• Filed: 10/01/1990
• Issued: 11/12/1991
• Est. Priority Date: 10/01/1990
• Status: Expired due to Fees

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.), Texas Instruments, Inc.
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Heckaman, Douglas, Vought, Ronald, Caraway, Edward
• Primary Examiner(s): GENSLER, PAUL L
• Application Number:
  US07/591,034
• Time in Patent Office: 407 Days
• Field of Search: 333/12, 333/204, 333/205, 333/238, 333/246, 333/247, 333/251
• US Class Current: 333/246
• CPC Class Codes: H01L 23/552 Protection against radiation, e.g. light or electromagnetic waves
• CPC Class Codes: H01P 1/16 for mode selection, e.g. mode suppression or mode promotion; for mode conversion

Abstract

A two-dimensional periodic conductive post array structure is used to suppress higher order wave propagation within a large microstrip housing assembly without attentuating the desired TEM mode of propagation. Substantially vertical conductive posts are spaced at appropriate wavelength periods in the X and Y directions on top of and through a microstrip substrate in a so called "waffle-wall" type configuration. The periodic post structure provides high microwave signal isolation by functioning as a band rejection filter both above the microstrip substrate and within the substrate to isolate between nearby active and passive circuit functions located on the microstrip substrate. The desired TEM mode microstrip transmission line is routed through the conductive post matrix to provide the signal, control and DC paths between circuit chips and other active and passive circuit functions.

Claims

1. A structure for isolating between spaced apart microwave circuit components and transmission media located on a top surface of a microstrip substrate, comprising:

a bottom ground plane provided below said microwave substrate;

a top ground plane located above said microwave substrate substantially parallel to said bottom ground plane; and

a two-dimensional periodically arrayed matrix of conducting posts orthogonally arranged between said top and bottom ground planes for isolating microwave circuit components located between said posts on the microwave substrate, each end of the conducting posts forming said matrix being grounded to one of said top and bottom ground planes wherein each microwave circuit component to be isolated is spaced apart from and surrounded by a number of said conducting posts of said matrix of conducting posts to isolate the microwave circuit component.

2. A structure according to claim 1, further comprising:

a housing metal base supporting the microstrip substrate; and

a housing cover sealed to said housing metal base over the microstrip substrate and forming an air cavity between the top surface of the substrate and said housing cover.

3. A structure according to claim 2, wherein the microstrip substrate is formed of Teflon™

fiberglass.

4. A structure according to claim 2, wherein said matrix of conducting posts are fixedly attached at one end to said housing cover, said housing cover having a metallized underside coupling with said plurality of conducting posts to form said top ground plane;

wherein said plurality of conducting posts extend substantially vertically toward the microstrip substrate at their other ends; and

capacitive air gaps formed between the other ends of the plurality of conducting posts and said microstrip substrate for tuning said plurality of conductive posts.

5. A structure for isolating between spaced apart microwave circuit components and transmission media located on a top surface of a microstrip substrate, comprising

a housing base supporting the microstrip substrate;

a housing cover sealed to said housing metal base over the microstrip substrate and forming an air cavity between the top surface of the substrate and said housing cover;

a plurality of conducting posts forming a periodic array arranged orthogonally to the plane of the microstrip substrate and extending between the microstrip substrate and said housing cover;

wherein said periodic array of conducting posts are configured as a two-dimensional matrix, said structure further comprising;

a plurality of holes formed in the microstrip substrate and housing metal base corresponding to said two-dimensional matrix of conducting posts, said plurality of conducting posts being press fit at their one ends into said plurality of holes and extending toward said housing cover at their other ends;

a conductive layer arranged against the other ends of said conducting posts, and

a compression layer located against said conductive layer on one side and against said housing cover on its other side for keeping said conductive layer in contact with the other ends of said plurality of conductive posts thereby forming a ground connection at each end of said plurality of conductive posts.

6. A structure according to claim 5, wherein the spaced apart microwave circuit components and transmission media are arranged on the microstrip substrate around said plurality of holes.

7. A structure for isolating between spaced apart microwave circuit components and transmission media located on a top surface of a microstrip substrate, comprising

a housing base supporting the microstrip substrate;

a housing cover sealed to said housing metal base over the microstrip substrate and forming an air cavity between the top surface of the substrate and said housing cover;

a plurality of conducting posts forming a periodic array arranged orthogonally to the plane of the microstrip substrate and extending between the microstrip substrate and said housing cover;

wherein said periodic array of conducting posts are configured as a two-dimensional matrix, said structure further comprising;

wherein said housing has a metal underside, the structure further comprising;

a plurality of cover holes formed in said housing cover corresponding to the two dimensional matrix of conducting posts, said cover holes having metal side walls connected to said metal underside;

a plurality of base holes formed through the microstrip substrate and housing metal base and aligned substantially vertically with said plurality of cover holes, said plurality of conducting posts being pressed into an interference fit with the side walls of the cover holes and base holes to provide grounding along the conducting posts circumference at both ends.

8. A structure according to claim 7, wherein said plurality of conducting posts are formed of roll posts.

9. A structure according to claim 7, wherein said plurality of cover and base holes are provided with tapered edges near said hole openings for aiding the alignment and insertion of the plurality of conducting posts.

10. A structure for isolating between spaced apart microwave circuit components and transmission media located on a top surface of a microstrip substrate, comprising

a housing base supporting the microstrip substrate;

a housing cover sealed to said housing metal base over the microstrip substrate and forming an air cavity between the top surface of the substrate and said housing cover;

a plurality of conducting posts forming a periodic array arranged orthogonally to the plane of the microstrip substrate and extending between the microstrip substrate and said housing cover;

wherein said periodic array of conducting posts are configured as a two-dimensional matrix, said structure further comprising;

said structure further comprising;

a plurality of base holes formed in the microstrip substrate and housing metal base corresponding to said two-dimensional matrix of conducting posts, said conducting posts being coupled at one end into said base holes and extending toward said housing cover at their other ends;

a dielectric film arranged against the other ends of said plurality of conducting posts;

a conductive layer stacked atop of said dielectric film;

a compression layer arranged between said conductive layer and housing cover for holding the conductive layer and dielectric film against the other ends of said plurality of conducting posts, said conductive layer, dielectric film and conducting posts forming a series coupled inductance and capacitance for series resonance tuning of said conducting posts.

11. A structure according to claim 10, wherein said dielectric film has a predetermined thickness and dielectric constant for accurate tuning of the plurality of conducting posts.

12. A structure according to claim 11, wherein said dielectric film is a dielectric film sheet bonded to said conductive layer.

13. A structure according to claim 11, wherein said dielectric film is deposited onto the other ends of said plurality of conducting posts.

14. A structure according to claim 11, wherein said plurality of conducting posts have a predetermined length and diameter selected for resonance near a desired frequency band for the structure.

15. A structure for isolating between spaced apart microwave circuit components and transmission media located on a top surface of a microstrip substrate, comprising

a housing base supporting the microstrip substrate;

a housing cover sealed to said housing metal base over the microstrip substrate and forming an air cavity between the top surface of the substrate and said housing cover;

a plurality of conducting posts forming a periodic array arranged orthogonally to the plane of the microstrip substrate and extending between the microstrip substrate and said housing cover;

wherein said periodic array of conducting posts are configured as a two-dimensional matrix, said structure further comprising;

wherein said housing cover has a metal underside, the structure further comprising;

a plurality of cover holes formed in said housing cover corresponding to the two dimensional matrix of conducting posts and having cover hole diameters greater than those of said conducting posts, said plurality of cover holes having metallized side walls connected to said metal underside;

a plurality of base holes formed in the microstrip substrate and housing metal base, said plurality of base holes being vertically aligned with said cover holes, the plurality of conductive posts forming an interference fit at one end with said plurality of base holes; and

coaxial capacitive air gaps formed between the other ends of said plurality of conductive posts and said cover hole side walls for series tuning portions of the plurality of conductive posts within the air cavity.

16. A structure according to claim 15, wherein a selected number of said plurality of conducting posts are custom tuned via adjustment to the conducting posts length and its associated cover hole diameter.

17. A structure for isolating between spaced apart microwave circuit components and transmission media located on a top surface of a microstrip substrate, comprising

a housing base supporting the microstrip substrate;

a housing cover sealed to said housing metal base over the microstrip substrate and forming an air cavity between the top surface of the substrate and said housing cover;

a plurality of conducting posts forming a periodic array arranged orthogonally to the plane of the microstrip substrate and extending between the microstrip substrate and said housing cover;

wherein said periodic array of conducting posts are configured as a two-dimensional matrix, said structure further comprising;

wherein said plurality of conducting posts are fixedly attached at one end to said housing cover, said housing cover having a metallized underside coupling with said plurality of conductive posts to form a top ground connection;

a plurality of base holes formed in the microstrip substrate and housing metal base corresponding to said two-dimensional matrix configuration of the plurality of conducting posts and having base hole diameters greater than those of said conductive posts; and

coaxial capacitive air gaps formed between the other ends of said plurality of conducting posts and the base hole side walls for series tuning said plurality of conducting posts.

18. A structure according to claim 17, wherein said plurality of conducting posts are integrally formed with said housing cover via metal fabrication techniques.

19. A structure according to claim 18, wherein said plurality of conducting posts are integrally formed with said housing cover via metal fabrication techniques.

20. A structure according to claim 19, wherein the spaced apart microwave circuit components and transmission media arranged on the microstrip substrate spaced from said plurality of conducting posts.

21. A structure for preventing in-band guided wave propagation, generated from spaced apart microwave circuit components and transmission media, within a dielectric substrate, comprising:

a top surface metallization for the dielectric substrate;

co-planar transmission lines formed on said top surface metallization for coupling the circuit components;

a bottom surface metallization for the dielectric substrate;

a periodic array of metal plated via holes formed in said dielectric substrate for providing top surface to bottom surface conduction paths to prevent in-band guided wave propagation within the dielectric substrate.

22. A structure according to claim 21, wherein said top and bottom metallizations are electroplated chromium/gold compositions.

23. A structure according to claim 21, wherein an annular air gap is fabricated between the top terminations of said periodic array of metal plated via holes and said top surface metallization to series resonance tune the metal plated via holes to provide increased high frequency isolation.

24. A waveguide mode band rejection filter structure for in-substrate and above-substrate isolation of spaced apart microwave circuit components and transmission media, comprising:

a housing base;

a dielectric substrate having top and bottom surface metallization supported on said housing base;

a housing cover, having a metallized underside, sealed to said housing base over the dielectric substrate;

an air cavity formed between the top surface metallization and the metallized underside of said housing cover;

a plurality of conducting posts configured in a two dimensional periodic array, said plurality of conductive posts fixedly attached and electrically coupling at one end to the metallized underside of said housing cover;

said plurality of conducting posts further extending substantially vertically toward the dielectric substrate;

capacitive air gaps formed between the other ends of the plurality of conducting posts and the top surface metallization for tuning said plurality of conducting posts to reject above substrate waveguide mode propagation; and

a periodic array of metal plated via holes formed in the dielectric substrate for providing top surface to bottom surface conduction paths to reject in-band guided wave propagation within the dielectric substrate.

25. A filter structure according to claim 24, wherein the plurality of conducting posts and the periodic array of metal plated vias are offset from each other.

26. A method for isolating microwave circuit components and transmission media in a monolithic microwave integrated circuit subsystem assembly, the method comprising the steps of:

fabricating the integrated circuit subsystem on a microstrip substrate in a manner to avoid placement of the circuit components and transmission media in a periodic two dimensional array of locations on the microstrip substrate;

forming a periodic two-dimensional matrix of conducting posts having the same dimensions as the two dimensional array of locations on the microstrip substrate;

electrically coupling the matrix of conducting posts at one end to a top ground plane located above said conducting posts and at the other end to a bottom ground plane supporting the microstrip substrate such that the matrix of conducing posts and the periodic array of locations are in alignment.

27. A method for providing a waveguide mode band rejection filter for an air cavity formed in a microcircuit assembly between a metal housing cover and a housing metal base, the method comprising the steps of:

supporting a microstrip substrate with the housing metal base;

arranging a two-dimensional periodic array of conducting posts substantially vertical to said microstrip substrate and extending between said microstrip substrate and the housing cover;

designing a microwave circuit layout around said conducting posts; and

providing capacitances at one end of said periodic array of conducting posts to series tune said conducting posts through the electrical connection formed from the metal housing cover through the capacitance and conductive posts to the housing metal base.