Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2000-05-09
2002-05-21
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S238000
Reexamination Certificate
active
06392503
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to strip line or microstrip directional couplers. In particular, the invention relates to sawtooth edge coupled directional couplers.
2
. Description of Related Art
In
FIG. 1
, a conventional directional coupler
10
is depicted as a four port network having ports (
1
), (
2
), (
3
) and (
4
). Coupler
10
includes primary line
12
and secondary line
20
. Primary line
12
includes coupled primary arm
14
, first port feed
16
and second port feed
18
. Secondary line
20
includes coupled secondary arm
22
, third port bend
24
, third port feed
28
, fourth port bend
26
and fourth port feed
30
. Power P
1
is provided to the coupler at first port (
1
), and powers P
2
, P
3
and P
4
are measured as the output of ports (
2
), (
3
) and (
4
), respectively. The coupling factor CF of the coupler for coupling power that has been input in port (
1
) and output from port (
3
) is P
3
/P
1
, the directivity of the coupler is P
4
/P
3
, and the insertion loss of the coupler is P
2
/P
1
, although the coupling factor, the directivity and the insertion loss are usually expressed in decibels (dB). However, other definitions may be used. For example, the coupling factor CF may be defined to be P
4
/P
1
(power coupled from port
1
to port
4
) or P
3
/P
2
(power coupled from port
2
to port
3
) and the insertion loss of the coupler may be defined to be P
1
/P
2
.
FIG. 2
depicts a conventional microstrip transmission line, and
FIG. 3
depicts a conventional strip line transmission line. Conventional coupler
10
is made from either conventional microstrip transmission lines or conventional strip line transmission lines.
FIG. 4
depicts a conventional microstrip coupled transmission line pair, and
FIG. 5
depicts a conventional strip line coupled transmission line pair as is formed between coupled primary arm
14
and coupled secondary aim
22
of FIG.
1
.
In known couplers formed on a homogeneous medium, the solution to the well known Telegrapher's equations (of signal propagation) applied to the transmission line pair of either
FIG. 4
or FIG. S reveals that signal transmission is possible only in one of two eigenmodes that each have electrical and magnetic field components only in a direction transverse to the propagation direction (i.e., TEM modes). These two TEM modes are conveniently labeled o for odd and e for even. For coupled strip lines (FIG.
5
), the characteristic impedence of the two modes are different and are given by:
Z
0
e
,
o
=
30
π
(
b
-
t
)
ϵ
r
(
W
+
bC
f
2
π
A
e
,
o
)
,
A
e
=
1
+
ln
(
1
+
tan
h
θ
)
ln
2
,
A
o
=
1
+
ln
(
1
+
cot
h
θ
)
ln
2
,
θ
=
π
S
2
b
,
and
C
f
(
t
/
b
)
=
2
ln
(
2
b
-
t
b
-
t
)
-
t
b
ln
[
t
(
2
b
-
t
)
(
b
-
t
)
2
]
.
If the power coupling factor per meter k(x) is known or calculated from first principals, the coupling factor of the coupler can be computed by integrating along the length from x=0 to x=l of the coupled transmission lines (
14
and
22
in
FIG. 1
) as follows:
CF=|∫k
(
x
)exp(−
j&bgr;x
)
dx|,
where &bgr; is the propagation factor for the particular mode (odd or even) which may be different for the two modes. Similarly, directivity can be computed to be:
dir
=
1
CF
&LeftBracketingBar;
∫
k
(
x
)
exp
(
-
𝔱2β
x
)
ⅆ
x
&RightBracketingBar;
,
and insertion loss IL=1−CF(1-dir). Typically, the directivity of the conventional coupler of
FIG. 1
is about 14 dB, worst case.
FIG. 6
depicts a known sawtooth coupler. The zig-zag edge increases the power coupling factor per meter k(x) in both the primary line and the secondary line, slows the wave propagation velocity, and the directivity remains dependent on the wave propagation velocity, as well as other factors, along the primary and secondary lines.
SUMMARY OF THE INVENTION
It is an object to the present invention to provide a directional coupler that has improved directivity. It is a further object of the present invention to provide a directional coupler whose directivity is less sensitive to manufacturing process variations.
These and other objects are achieved in a directional coupler that includes a main arm and a branch arm. The main arm includes a first main sawtooth section, a second main sawtooth section and a main straight section coupled between the first and second main sawtooth sections. The branch arm includes a first branch sawtooth section and a second branch sawtooth section. The first branch sawtooth section includes a first side and a second side. The first side of the first branch sawtooth section is shaped to include a zig-zag edge and the second side of the first branch sawtooth section is shaped to include a non-straight edge. The second branch sawtooth section includes a first side and a second side, and the first side of the second branch sawtooth section is shaped to include a zig-zag edge. The zig-zag edge of the first side of the first branch sawtooth section is coupled to the first main sawtooth section, and the zig-zag edge of the first side of the second branch sawtooth section is coupled to the second main sawtooth section.
These and other objects are achieved with a method to make a coupler that includes steps of fabricating a coupler based on a first pattern, modifying the coupler, measuring a performance parameter of the coupler, and revising the first pattern to make a second pattern for use in making more couplers. The fabricated coupler includes a main arm and a branch arm. The main arm includes a first main sawtooth section, a second main sawtooth section and a main straight section coupled therebetween. The branch arm includes a first branch sawtooth section and a second branch sawtooth section. The first branch sawtooth section includes a first side and a second side wherein the first side of the first branch sawtooth section is shaped to include a zig-zag edge. The second branch sawtooth section includes a first side and a second side wherein the first side of the second branch sawtooth section is shaped to include a zig-zag edge. The zig-zag edge of the first side of the first branch sawtooth section is coupled to the first main sawtooth section, and the zig-zag edge of the first side of the second branch sawtooth section is coupled to the second main sawtooth section.
REFERENCES:
patent: 3629733 (1971-12-01), Podell
patent: 3980972 (1976-09-01), Podell et al.
“The Circuits and Filters Handbook”, Wai-Kai Chen, Editor, pp. 1188-1191 and 1239-1242, CRC Handbook Published in Cooperation with IEEE Press, 1995, Boca Raton, Florida.
Banner & Witcoff , Ltd.
Glenn Kimberly E
Nokia Networks Oy
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