Optical waveguides – Planar optical waveguide
Reexamination Certificate
1998-05-15
2001-02-06
Sanghavi, Hemang (Department: 2874)
Optical waveguides
Planar optical waveguide
C385S014000, C257S758000, C343S7000MS, C343S786000, C333S246000
Reexamination Certificate
active
06185354
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a printed circuit board including an integral waveguide; and more particularly, this invention relates to an integral waveguide formed of a metallic layer on a substrate, a solid dielectric layer overlying the metallic layer and having channels, and a metallic plate connected to the metallic layer through the channels.
BACKGROUND OF THE INVENTION
In electronic assemblies, it is known to use transmission lines to transmit an electromagnetic signal between components on a printed circuit board. Microstrip and strip line are illustrative examples of transmission lines which are used to transmit electromagnetic signals between components on a printed circuit board. Microstrip and stripline feature planar metallic conductors that are readily amenable to fabrication during the construction of a printed circuit board.
Microstrip comprises a conductive strip separated from a ground plane by a dielectric layer. Stripline comprises a central conductive strip adjoined by two dielectric layers. The two dielectric layers separate the central conductive strip from two ground planes. Microstrip and stripline technology have been improved primarily by the introduction of new dielectrics which offer lower propagational loss. However, because propagation in microstrip and stripline is limited to the transverse electric mode, microstrip and stripline may be cumbersome to tune. Moreover, the single propagational mode combined with dielectric constraints confluence to form practical operating impedance limitations for microstrip and stripline technology.
It is known to use waveguides, such as hardlines, to transmit electromagnetic signals between different circuit boards. Waveguides generally offer lower propagational loss than microstrip and stripline and greater isolation of electromagnetic radiation than microstrip and stripline do. Waveguides may also offer increased ability for controlling impedances than microstrip and stripline line do.
A waveguide typically has a hollow cross-section, which determines the propagation mode and the cut-off frequency of electromagnetic radiation transmitted by the waveguide. The complexity of manufacturing suitable elliptical, circular, and rectangular cross sections has prevented the incorporation of integral waveguides into printed circuit boards. Thus, while metallic waveguides with sundry geometrical cross-sections are commercially available as discrete transmission line components, so far microstrip and stripline technology generally reflect the limited extent of waveguide incorporation into printed circuit boards of commercially available products.
The impedance of microstrip and stripline is determined by the width of the conductive strip, the thickness of the dielectric layer or layers, and the dielectric constant of the dielectric material. If the thickness of the dielectric material is sufficiently thin, such as 50 microns or thinner, then manufacturing tolerances must be carefully controlled to compensate for potential variances in the dielectric thickness. Variances in dielectric thickness may cause line impedance mismatches. Even slight variations in the dielectric thickness of ten to fifteen microns can detrimentally affect the impedance of stripline or microstrip, in which a dielectric layer is 50 microns or thinner. Batch-to-batch variations in the dielectric material properties further contribute to impedance mismatches associated with transmission line using thin dielectric layers of 50 microns or less. While many commercially available discrete waveguides offer uniform impedances, the difficulty and expense of integrating discrete waveguides into printed circuit boards has discouraged the use of integral waveguides to facilitate impedance matching of intraboard signals.
Thus, a need exists for an integral waveguide for intraboard connections of a printed circuit board. In addition, a need exists for an integral waveguide that can provide a substantially constant impedance despite ordinary variations in dielectric thickness from manufacturing procedures.
BRIEF SUMMARY OF THE INVENTION
In accordance with this invention, a printed circuit board comprises a metallic layer on a substrate. The metallic layer has a first strip and a second strip spaced apart from the first strip. A solid dielectric layer overlies the metallic layer and features a first channel exposing the first strip, a second channel exposing the second strip, and a land disposed between the first channel and the second channel. A metallic plate overlies the land, extends through the first channel to the first strip, and extends through the second channel to the second strip.
In this manner, the metallic layer and the metallic plate cooperate to form a waveguide about the dielectric layer. Thus, this invention provides a waveguide on a printed circuit board that is compatible with standard manufacturing techniques for fabricating a printed circuit board. In one aspect of this invention, a horn antenna is connected to the waveguide to transfer electromagnetic energy to and/or from the waveguide.
REFERENCES:
patent: 4966430 (1990-10-01), Weidel
patent: 5227749 (1993-07-01), Raguenet et al.
patent: 5453154 (1995-09-01), Thomas et al.
patent: 5596336 (1997-01-01), Liu
S. Ramo, J. Whinnery, and T. Van Duzer;Fields and Waves in Communication Electronics(Second Ed. 1984), pp. 411-422.
Forse Roger J.
Kronz Jason Andrew
Fekete Douglas D.
Motorola Inc.
Sanghavi Hemang
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