Wave transmission lines and networks – Long lines – Strip type
Reexamination Certificate
2000-03-15
2003-02-11
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Long lines
Strip type
C333S246000
Reexamination Certificate
active
06518864
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a coplanar transmission line, and more particularly to a coplanar transmission line used in a high frequency circuit, wherein the coplanar transmission line is improved in reduction of a transmission loss and also in keeping a sufficient chemical strength.
The coplanar transmission line has been used in the high frequency circuit. The coplanar transmission line has the following structure. A signal conductive layer is selectively formed on a surface of a dielectric substrate, wherein the signal conductive layer allows a signal transmission. Ground conductive layers are selectively formed on the top surface of the dielectric substrate, so that the ground conductive layers extend along opposite sides of the signal conductive layer. A bottom ground conductive layer is formed on a bottom surface of the dielectric substrate for mounting the substrate to an external case, wherein the bottom ground conductive may be made of a metal such as gold or tin. The ground conductive layers on the top surface of the dielectric substrate and the bottom ground conductive layer on the bottom surface of the dielectric substrate do form a parallel-plate structure which allows a parallel-plate mode signal as a leakage signal to be propagated through the dielectric substrate and in a direction perpendicular to a signal transmission direction in which the signal is transmitted in the signal conductive layer or the co-planer transmission line. As a frequency of the signal transmitted or propagated through the coplanar transmission line is high, a signal waveguide mode is coupled to the parallel-plate mode, whereby the signal transmission loss is increased. Further, even if a distance between adjacent two of the coplanar transmission lines is large, the signal waveguide mode is made coupled to the parallel-plate mode whereby coupling of the signal waveguide mode between the adjacent two of the coplanar transmission lines appears through the parallel-plate mode. Namely, it is difficult for the conventional structure of the coplanar transmission line to prevent the signal transmission loss due to the coupling in the parallel-plate mode between the adjacent two of the coplanar transmission lines.
In order to have solved the above problem with the signal transmission loss due to the coupling between the adjacent two of the coplanar transmission lines, another conventional structure of the coplanar transmission line has been proposed, which is disclosed in Nirod K. Das “IEEE Transactions on Microwave Theory and Techniques”, Vol. 44, pp. 169-181, 1996. This conventional structure of the coplanar transmission line has a plurality of metal via which provide connections between the ground conductive layers on the top surface of the dielectric substrate and the bottom ground conductive layer on the bottom surface of the dialectic substrate.
FIG. 1
is a fragmentary cross sectional elevation view illustrative of the conventional structure of the coplanar transmission line, wherein the plurality of metal via is provided for providing connections between the ground conductive layers on the top surface of the dielectric substrate and the bottom ground conductive layer on the bottom surface of the dialectic substrate.
A signal conductive layer
22
is selectively formed on a top surface of a dielectric substrate
21
which is made of a ceramic. Two ground conductive layers
23
are selectively formed on the top surface of the dielectric substrate
21
, so that the ground conductive layers
23
extend in opposite sides of the signal conductive layer
22
, provided that the ground conductive layers
23
are distanced from opposite side edges of the signal conductive layer
22
. A bottom ground conductive layer
24
is formed entirely on a bottom surface of the dielectric substrate
21
. Two metal vias
25
are formed in the dielectric substrate
21
so that the two ground conductive layers
23
are connected through the two metal vias
25
to the bottom ground conductive layer
24
. The metal vias
25
may prevent the signal or power leakage in the parallel-plate mode.
Still another conventional structure of the coplanar transmission line is disclosed in M. Hotta Asia Pacific Microwave Conference 1998 Proceedings, pp. 409-412.
FIG. 2
is a fragmentary cross sectional elevation view illustrative of the still other conventional structure of the coplanar transmission line, wherein a groove is formed. A groove is formed in the dielectric substrate, so that the groove extends under the signal conductive layer and over the bottom ground conductive layer. A signal conductive layer
32
is selectively formed on a top surface of a dielectric substrate
31
. Two ground conductive layers
33
are selectively formed on the top surface of the dielectric substrate
31
, so that the ground conductive layers
33
extend in opposite sides of the signal conductive layer
32
, provided that the ground conductive layers
33
are distanced from opposite side edges of the signal conductive layer
32
. A bottom ground conductive layer
34
is formed entirely on a bottom surface of the dielectric substrate
31
. A groove
36
is formed in the dielectric substrate
31
, so that a bottom of the groove
36
is positioned directly over the bottom ground conductive layer
34
, whilst a top of the groove
36
is positioned indirectly under the signal conductive layer
32
and also under inside portions of the ground conductive layers
33
, provided that the top of the groove
36
is separated by a part of the dielectric substrate
31
from the signal conductive layer
32
and the ground conductive layers
33
. The existence of the groove
36
makes a reduction in thickness of the part of the dielectric substrate
31
under the signal conductive layer
32
, whereby the signal or power leakage in the parallel-plate mode is cut off.
Yet another conventional structure of the coplanar transmission line is disclosed in Japanese Laid-open Patent Publication No. 9-23106. A signal conductive layer is selectively formed on a top surface of a dielectric substrate. Two ground conductive layers are selectively formed on the top surface of the dielectric substrate, so that the ground conductive layers extend in opposite sides of the signal conductive layer, provided that the ground conductive layers are distanced from opposite side edges of the signal conductive layer. A bottom ground conductive layer is formed entirely on a bottom surface of the dielectric substrate. Two metal vias are formed in the dielectric substrate so that the two ground conductive layers are connected through the two metal vias to the bottom ground conductive layer. The metal vias may prevent the signal or power leakage in the parallel-plate mode. Additionally, four recessed portions are formed in opposite edges of the dielectric substrate, wherein the opposite edges are distanced in the same direction as the signal transmission or signal propagation through the signal conductive layer. At the opposite edges of the dielectric substrate, a discontinuity in the transmission or propagation mode is likely to appear. The recessed portions suppress generation of the higher-order propagation mode.
An additional conventional structure of the coplanar transmission line is disclosed in Japanese Laid-open Patent Publication No. 9-23107. A signal conductive layer is selectively formed on a top surface of a dielectric substrate. Two ground conductive layers are selectively formed on the top surface of the dielectric substrate, so that the ground conductive layers extend in opposite sides of the signal conductive layer, provided that the ground conductive layers are distanced from opposite side edges of the signal conductive layer. A bottom ground conductive layer is formed entirely on a bottom surface of the dielectric substrate. Two metal vias are formed in the dielectric substrate so that the two ground conductive layers are connected through the two metal vias to the bottom ground conductive layer. The metal vias may prevent the signal
Ito Masaharu
Maruhashi Kenichi
Ohata Keiichi
Chang Joseph
Michael Best & Friedrich LLC
NEC Corporation
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