Stripline cable with reduced crosstalk

• US 4,441,088 A
• Filed: 12/31/1981
• Issued: 04/03/1984
• Est. Priority Date: 12/31/1981
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Anderson, Carl J.
• Primary Examiner(s): Gensler, Paul L.
• Application Number:
  US06/336,205
• Time in Patent Office: 824 Days
• Field of Search: 174/35, 174/36, 174/117 F, 174/117 FF, 174/117 PC, 174/126 S, 333/1, 333/238, 333/246, 333/99 S
• US Class Current: 333/1
• CPC Class Codes: H01B 7/08 Flat or ribbon cables
• CPC Class Codes: H05K 1/024 Dielectric details, e.g. changing the dielectric material around a transmission line
• CPC Class Codes: H05K 2201/0191 wherein the thickness of the dielectric plays an important role
• CPC Class Codes: H05K 2201/0715 provided by an outer layer of PCB
• CPC Class Codes: H05K 3/28 Applying non-metallic protective coatings H05K3/0091 takes precedence; methods for intermediate insulating layers for build-up multilayer circuits H05K3/4673
• CPC Class Codes: Y10S 505/866 Wave transmission line, network, waveguide, or microwave storage device
• CPC Class Codes: Y10S 505/886 Cable

Abstract

A transmission line having substantially reduced far-end forward wave crosstalk is characterized by a single layer of dielectric material having a thickness chosen to provide a forward wave coupling constant K_F substantially equal to zero. The dielectric layer is located on a ground plane, and has a plurality of signal carrying conductors embedded in it. The thickness H of the dielectric underlayer below the signal carrying conductors is chosen to provide a transmission line having the selected values of impedance, etc. and substantially reduced forward wave crosstalk. The thickness t of the dielectric overlayer above the signal carrying conductors is chosen (for the selected value of thickness H of the dielectric underlayer) at the finite value critical thickness at which forward wave mutual capacitance and forward wave mutual inductance cancel to a null. The ground plane and the signal carrying conductors can be superconductors.

Claims

1. A transmission line for carrying high speed signals with substantially reduced forward wave crosstalk, consisting essentially of a ground plane layer comprised of a plane of electrically conductive material;

a layer of dielectric material, having a single dielectric constant ε

_r, located on said ground plane;

a plurality of signal carrying conductors located in said layer of dielectric and separated from said ground plane layer by a thickness of dielectric underlayer H, there being a thickness of said dielectric material above said plurality of conductors forming a dielectric overlayer of a thickness t, the thickness H being chosen to yield a transmission line having a desired impedance, and said thickness t of dielectric overlayer being chosen for the value of H such that the forward wave crosstalk components (mutual capacitance and mutla inductance) between adjacent signal carrying conductors are substantially equal and opposite.

2. A transmission line made up of a ground plane, a dielectric underlayer arrayed on such ground plane, a number of conductors arrayed on such dielectric underlayer in a conductor layer substantially parallel to such ground plane, and a dielectric overlayer arrayed on such conductors characterized by

(a) a set of parameters, not including parameter t (thickness of the dielectric overlayer), providing mechanical stability and impedance attributes postulated for an operational objective, which set of parameters together with parameter t define a plot of forward wave coupling coefficient of crosstalk versus thickness of dielectric overlayer, which plot rises through a null at a small finite value and thereafter falls asymptotically toward a second null at infinity;

and

(b) the thickness of said dielectric overlayer is the thickness corresponding to such null at a small finite value.

3. The transmission line of claim 2 further characterized in that the ground plane and the conductors are superconductors.

4. The transmission line of claim 2 further characterized in that the signal carrying conductors are thin films of substantially rectangular cross section, all in the same plane, and substantially parallel.

5. A microstrip superconducting transmission line structure comprising

(a) superconducting ground plane;

(b) a planar array of superconducting signal conductors arrayed substantially parallel to each other and to said superconducting ground plane;

(c) a dielectric layer arrayed on said superconducting ground plane in such fashion that said signal conductors are embedded in a planar central portion of said dielectric layer, defining by its position a dielectric underlayer and a dielectric overlayer;

whereby said ground plane, signal conductors and said dielectric underlayer together delimit mechanical strength and impedance, and have parameters of mutual capacitance and self-inductance which are components of forward wave crosstalk, which components for a postulated thickness of dielectric overlayer define a finite value null and approach at infinity an infinite value null; and

(d) the thickness of said dielectric overlayer is the thickness at which said finite value null occurs.