Wave transmission lines and networks – Long line elements and components – Strip type
Reexamination Certificate
2001-03-08
2003-07-08
Ham, Seungsook (Department: 2817)
Wave transmission lines and networks
Long line elements and components
Strip type
C333S260000, C439S827000
Reexamination Certificate
active
06590478
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electromagnetic transmission lines, and more particularly to short coaxial transmission lines, and methods for using such transmission lines to interconnect RF ports on mutually parallel printed-circuit boards.
BACKGROUND OF THE INVENTION
FIG. 1
is a simplified perspective or isometric view of a combination
10
of modules, including a main module mated with a plurality of other modules. In
FIG. 1
, a rectangular, somewhat planar housing
12
contains at least one printed-circuit board lying in the plane parallel to dash line
14
, which is to say parallel to that one of the two broad faces, namely near face
12
fn
. A second housing designated
16
a
is one of a set
16
of additional housings, illustrated in phantom, which are adapted to be coupled to housing
12
for the flow of electromagnetic energy therebetween by way of coaxial transmission-line structures.
As is well known to those skilled in the art, a coaxial transmission line includes a center conductor lying within, and concentric with, a cylindrical outer conductor. Coaxial transmission lines take many forms, but all are characterized by the flow of electromagnetic energy in the region or space between the center and outer conductors. The generally accepted meaning of a transmission line, as opposed to simple “wires,” is that the surge impedance or characteristic impedance of the transmission line tends to be constant along its length, or if the impedance changes along its length, the change is effected in a controlled manner which tends to minimize overall reflection of energy, so that energy introduced into one end of the transmission line is “transmitted” to the remote end with a minimum of loss attributable to mismatch. While coaxial transmission lines may be made to have almost any characteristic impedance, two such impedances are most common. The nominal impedance of 50 ohms is theoretically capable of handling the highest power without voltage breakdown, while the nominal impedance of 75 ohms theoretically provides the least loss per unit length. Military equipments such as radar and other transmitting devices requiring high power thus tend to use 50-ohm transmission lines and associated connectors, while some commercial users such as cable television have, at least in the past, operated at 75 ohms.
In the arrangement of
FIG. 1
, the coupling between module
16
a
and a portion of module
12
is provided by coaxial connectors of a set
18
a
of such connectors, not entirely illustrated in FIG.
1
. In
FIG. 1
, portions of four connectors
18
a
1
,
18
a
2
,
18
a
3
, and
18
a
4
associated with module
16
a
are illustrated. It should be understood that this number, and their layout, are illustrative only, and that there may be more or fewer such connectors associated with each module of set
16
of modules.
In order to minimize losses in interconnecting transmission lines, and to minimize the volume occupied by the combined modules
10
of
FIG. 1
, it is desirable to have each module
16
x
of set
16
of modules immediately adjacent the near or facing surface
12
fn
of module
12
. In order to accomplish a close spacing, it is possible to use as connectors type GPO interconnects, manufactured by Gilbert Engineering, whose address is 5310 W Camelback Road, Glendale, Ariz. 85301. These connectors are characterized from DC to 40 GHz.
FIG. 2
a
is a simplified, exploded view of a particular version of the GPO connector, adapted for connecting conductive traces on a printed circuit board to conductive traces on another such board, and
FIG. 2
b
represents a cross-section of a portion of the arrangement of
FIG. 1
in its assembled state. For specificity,
FIGS. 2
a
and
2
b
illustrates connector
18
a
1
of FIG.
1
. In
FIG. 2
a
,
214
a
represents a portion of the printed circuit board lying within housing
12
in plane
14
, and
214
b
represents another printed circuit board lying within housing
16
a
. In this particular layout, the two printed circuit boards
214
a
and
214
b
lie mutually parallel.
In the arrangement of
FIGS. 2
a
and
2
b
, both printed-circuit boards are “stripline” boards, in that the transmission lines within each board lie between ground planes. In
FIGS. 2
a
and
2
b
, printed-circuit board
214
a
includes a near ground plane
214
agn
and a remote or far ground plane
214
agf.
Lying between ground planes
214
agn
and
214
agf
are two layers of dielectric or insulating material, a near layer
214
am
and a far layer
214
aif.
Lying between insulating layers
214
am
and
214
aif
is plane
14
of
FIG. 1
, and lying “in” the plane are a plurality of conductive traces, one of which is illustrated as
214
act.
It should be understood that the “plane”
14
is conceptual, as a plane is dimensionless and therefore cannot contain a three-dimensional object such as trace
214
act,
however thin.
In
FIGS. 2
a
and
2
b
, a circular aperture
214
aga
is defined in ground plane
214
agn,
thereby exposing the near surface
214
ains
of near dielectric or insulating layer
214
ain.
Near the center of aperture
214
aga,
a conductive pad
214
acp
is affixed to the near surface
214
ains
of near dielectric layer
214
ain,
and is electrically coupled, as by a plated-through via
214
av,
to an end of the underlying conductive trace
214
act.
Also in
FIG. 2
a
is another printed circuit board
214
b
, which is similar in its construction to printed circuit board
214
a
, but which appears somewhat different, since it is seen from the rear rather than from the front. Elements of circuit board
214
b
corresponding to those of
214
a
are designated by the same reference numerals, but in the “
214
b
” series rather than in the “
214
a
” series. Thus, printed-circuit board
214
b
shows a near ground plane
214
bgn
, a far ground plane
214
bgf
, a near dielectric layer
214
bin
, a far dielectric layer
214
bif
, with a conductive trace
214
bct
extending therebetween, and ending at the center of an aperture
214
bga
in near ground plane
214
bgn.
The GPO connector
18
a
of
FIG. 2
a
includes two surface connector portions
210
a
and
210
b
, together with a “bullet” portion
216
, some of which is also visible in the cross-section of
FIG. 2
b
. Surface connector portion
210
a
is illustrated as including three portions exploded away from each other. Surface connector portion
210
a
includes an outer conductor or flange portion
210
aoc
, an inner conductor portion
210
aic
, and a cylindrical insulator portion
210
ai
. As illustrated, outer conductor
210
aoc
includes a tubular body portion
210
aocb
, a lower flange
210
aoclf
, and a strengthening flange
210
aocsf
. Body
210
aocb
of outer conductor
210
aoc
defines an inner bore
210
aocbb
which is dimensioned to accept the outer diameter of cylindrical insulator portion
210
ai
. Cylindrical insulator portion
210
ai
contains an axial bore dimensioned to accommodate the body portion of center or inner conductor portion
210
aic
. Assembly of surface connector portion
210
a
to printed circuit board
214
a
is accomplished by soldering or otherwise metallurgically connecting an end of center conductor portion
210
aic
to the center pad
214
acp
. The bore of insulator
210
ai
is then fitted over the protruding center conductor, the outer conductor
210
aoc
is fitted over and around insulator
210
ai
, and the lower flange
210
aoclf
is then soldered to that portion of the near ground plane
214
agn
surrounding aperture
214
aga
defined by dashed circle
214
ac.
Connector portion
210
b
of connector
18
a
of
FIG. 2
a
is similar to portion
210
a
, and is similarly affixed to printed circuit board
214
b
. More particularly, the end of inner conductor
210
bic
is soldered or otherwise metallurgically connected to a pad (not designated) connected to the end of conductive trace
214
bct
so that it projects away from the surface of the board
214
b
. Dielectric insulator
210
bi
is fitted over protruding inner conductor
210
bic
. Outer cond
Duane Morris LLP
Ham Seungsook
Lockheed Martin Corporation
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