U.S. patent number 3,715,689 [Application Number 05/225,041] was granted by the patent office on 1973-02-06 for wideband microwave power divider.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Army. Invention is credited to Gordon J. Laughlin.
United States Patent |
3,715,689 |
Laughlin |
February 6, 1973 |
WIDEBAND MICROWAVE POWER DIVIDER
Abstract
A microwave structure comprising a parallel transmission line
that is bised by a conducting septum to form two independent
microstrip circuits that are in anti-phase; i.e., the conducting
septum becomes a common ground plane for a pair of equal amplitude
microstrip circuits that are in anti-phase relative to the common
ground at points equidistant from the point of bisection of the
parallel transmission line. In one embodiment, the proprosed
microwave structure is utilized as a power divider with input power
being supplied to a conventional microstrip circuit formed of a
pair of spaced parallel conductor strip members which also form the
parallel transmission line and the anti-phase microstrip circuits,
and whose widths are varied to form a reflectionless transition
from the input microstrip circuit to the parallel transmission line
and subsequently to the pair of output microstrip circuits, each of
which receives half of the input power supplied to the device.
Inventors: |
Laughlin; Gordon J. (Columbia,
MD) |
Assignee: |
The United States of America as
represented by the Secretary of the Army (N/A)
|
Family
ID: |
22843274 |
Appl.
No.: |
05/225,041 |
Filed: |
February 10, 1972 |
Current U.S.
Class: |
333/128; 333/21R;
333/246 |
Current CPC
Class: |
H01P
5/12 (20130101) |
Current International
Class: |
H01P
5/12 (20060101); H01p 001/16 (); H01p 003/08 ();
H01p 005/12 () |
Field of
Search: |
;333/10,9,11,84,84M,21R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Saalbach; Herman Karl
Assistant Examiner: Nussbaum; Marvin
Claims
What is claimed is:
1. A microwave structure comprising,
a parallel line transmission line formed of a pair of electrically
conductive line members separated by a dielectric material and
disposed in spaced parallel planes, and
a septum member formed of electrically conductive material disposed
in a plane bisecting the distance between the spaced parallel
planes of said pair of transmission line members and cooperating
with equal lengths of each of said transmission members for
converting said parallel line transmission line to a pair of equal
amplitude, anti-phase microstrip circuits.
2. The microwave structure specified in claim 1 wherein said
parallel line members are in the form of a pair substantially thin
flat strip members having portions disposed one above the other and
extending in the same direction to form the line members of a
parallel line transmission line.
3. The microwave structure specified in claim 2 wherein said pair
of strip members include respective second portions which are of
equal length and which extend in different directions relative to
one another and relative to said same direction and cooperate with
said septum member to form a pair of microstrip circuits with
spaced apart output ports.
4. The microwave structure specified in claim 3 wherein said second
portion of each of said strip members extend in opposite directions
perpendicular to said same direction.
5. The microwave structure specified in claim 1 further including a
pair of spaced elements separated from one another by said
dielectric material and forming a microstrip input operably
connected to said parallel line transmission line elements.
6. The microwave structure specified in claim 3 wherein said
electrically conductive strip members have third portions
configured to form an input microstrip circuit operably connected
adjacent those portions of said strip members forming said parallel
line transmission line.
7. The microwave structure specified in claim 6 wherein said third
portions include a portion of each of said strip members forming
respectively a conductor and ground plane element for said
microstrip input circuit.
8. The microwave structure specified in claim 7 wherein the
respective widths of said electrically conductive strip members is
varied to maintain a constant characteristic impedance between the
input to said input microstrip circuit and the output ports formed
by said strip members and said conductive septum.
Description
BACKGROUND OF THE INVENTION
In recent years, the relatively bulky and cumbersome hollow
waveguide and circular coaxial transmission line have been replaced
by so-called planar transmission line structures, one class of
which is the so-called microstrip circuit wherein electromagnetic
waves propagate along a narrow flat strip conductor element
dielectrically separated from a wider conductive element or ground
plane. In certain applications of these so-called microstrip
circuits or transmission lines; e.g., for use in microwave mixers
or antenna difference channels, it is often desirable to employ a
power divider structure wherein the input power is divided equally
between two output ports in equal amplitude but with voltages that
are 180.degree. out-of-phase. In the past, in order to accomplish
this with the so-called microstrip transmission line, it was
necessary to utilize half wavelength line lengths to achieve the
180.degree. out-of-phase outputs. Unfortunately, such a device is
frequency dependent in that the anti-phase relationship is attained
only at a very select frequency; i.e., the prior art microstrip
power divider was very narrow banded.
DESCRIPTION OF THE INVENTION
In accordance with the present invention, it is proposed to provide
a microwave structure suitable for use as a power divider which is
independent of half or quarter wavelengths lines and therefore
inherently wideband in operation. Moreover, the proposed device
provides naturally or inherently for reflectionless transmission
over the entire operating bandwidth where the output characteristic
impedance for each output is equal to one-half the input
characteristic impedance of the device, and the device can also be
designed so that it is impedance matched to a common impedance
value (e.g. 50 ohms) at all ports. The proposed device is also
amenable to miniaturization for microwave integrated circuit
applications.
Basically, the proposed microwave structure of the present
invention comprises a transmission line of parallel and equal width
strips that is bisected by a thin septum of electrically conductive
material to form two independent microstrip circuits that are in
anti-phase. More particularly, it is well-known to those skilled in
the art that the electric and magnetic fields of a parallel
transmission line conductor pair of equal width mounted one above
the other on an intervening dielectric substrate are mirror images
about a plane midway between the lines.
In accordance with the present invention, it is proposed that a
conducting septum be inserted along a plane midway between the
parallel transmission line conductors without disturbing the
magnetic or electric field configurations. As a result, the power
contained above the image plane (conducting septum) is equal to the
power below the image plane, and relative to the image plane or
conducting septum the electric fields above and below this plane
are in anti-phase. Because the field configurations are not altered
by the presence of the conducting septum, the parallel transmission
line appears continuous. On the other hand, once the conducting
septum is inserted, as proposed in accordance with the present
invention, the upper and lower conductors are no longer required to
lie one directly above the other as is the case with the parallel
transmission line; i.e., the conductors can be taken in separate
directions in their respective plane and the field configurations
above the image plane (septum) will be preserved relative to the
upper conductor and the field configurations below the image plane
(septum) will be preserved with regard to the lower conductor.
As will be described in more detail hereinafter, the field
configurations associated with the upper and lower conductor
elements are those of a microstrip line, and relative to the
conducting septum the voltages of the upper and lower conductors
are in anti-phase at points equidistant from the point of insertion
of conducting septum. Moreover, the power propagated by upper
conductor above the conducting septum is equal to the power
propagated by the lower conductor below conducting septum. The
conducting septum, therefore, becomes common ground plane for a
pair of equal amplitude microstrip circuits that are in anti-phase
relative to the common ground plane.
In view of the foregoing, one object of the present invention is to
provide a microwave structure for converting a parallel
transmission line into a pair of anti-phase microstrip
circuits.
Another object of the present invention is to provide a microwave
structure capable of being utilized to perform broadband, equal
power division of input micro-wave power.
Another object of the present invention is to provide a microwave
structure having application as a reflectionless power divider
whose outputs are in anti-phase relative to a common ground
conductor and which is inherently broadband, compact, of very
simple construction, and amenable to microminiaturization.
Other objects, purposes and characteristic features of the present
invention will in part be pointed out as the description of the
present invention progresses and in part be obvious from the
accompanying drawings, wherein:
FIG. 1 is an isometric view of a power divider structure
constituting one embodiment of the present invention; and
FIG. 2 is an enlarged partial cross-sectional view of the central
parallel transmission line portion of the power divider structure
of FIG. 1.
In the power divider embodiment shown in FIG. 1 of the drawings, a
suitable dielectric member formed of alumina (.epsilon..sub.r
.congruent. 9) or like material and designated at 10 supports a
pair of electrical conductor members 11 and 12 formed of flat
copper strips, for example. These conductor strips 11 and 12 have
substantially L-shaped configurations at the respective right-hand
ends thereof, as viewed in FIG. 1. Also carried in the dielectric
10, midway between the spaced-apart conductor strip members 11 and
12, is a suitable thin sheet or septum 13 formed of suitable
electrically conductive material such as, for example, 0.003 inch
aluminum foil.
The left-hand end of the upper conductor strip 11 is slightly
narrower than the midportion of this member and, together with the
enlarged left-hand end portion of the lower conductor strip member
12 forms an input microstrip circuit for the power divider
structure of FIG. 1. By way of example, in one practical embodiment
of the proposed power divider structure (utilizing 0.050 inch
alumina as the dielectric block 10) for a 50 ohm transmission line,
the width of the left-hand end portion of the upper conductor strip
11 was 0.050 inch; whereas, the enlarged end portion of the lower
conductor strip 12 (which ideally would be infinitely wide) was
found to function successfully with a 2 inch width.
On the other hand, the midportions of the upper and lower conductor
strips 11 and 12 are the same width and form a parallel
transmission line pair. By way of example, a strip width of 0.080
inch was found to be acceptable for this midportion of the strips
11 and 12, during fabrication of the practical 50 ohm line
embodiment mentioned above. The right-hand or output microstrip end
portions of both the upper and lower conductor strips also have a
width equal to that of the center portions of the conductor strips
11 and 12. It should be noted here that the variation in width
between the left-hand end and center portion of the upper conductor
strip 11 is for the purpose of attaining a constant characteristic
impedance transition when proceeding from the left-hand or
microstrip input end of the structure into the central or parallel
transmission line portion. On the other hand, by making the
right-hand or output ends of conductors 11 and 12 of a width equal
to the central portions, the characteristic impedance of each of
the output microstrip circuits is one-half that of the parallel
transmission line, in order to also achieve reflectionless
transmission therebetween.
Referring now to the cross-sectional view of FIG. 2 taken, as
mentioned previously, at the parallel transmission line portion of
the illustrated device, the electric and magnetic fields of such a
parallel transmission line with an intervening dielectric substrate
are mirror images about a plane midway between the line conductors
11 and 12, as shown. In FIG. 2 the electric field lines are shown
in solid line form and the magnetic field lines are shown as dashed
lines. Relative to the designated image plane which is midway
between conductors 11 and 12, the electric fields above and below
the image plane are in anti-phase and the microwave power contained
above the illustrated image plane is equal to the power below the
image plane. Accordingly, the conducting septum 13 can be inserted
along this image plane, as shown in FIG. 1, without disturbing the
field configurations and therefore the parallel line appears
continuous. Once the septum 13 is inserted, however, the upper and
lower conductor strips 11 and 12 are no longer required to lie one
directly above the other, as in the parallel transmission line
portion. Thus, the extending right-hand ends of the conductors 11
and 12 can now be taken in separate directions in their respective
planes; e.g., taken perpendicular to the direction of the parallel
transmission line portions as shown in FIG. 1, and the field
configurations above the image plane (septum 13) will still be
preserved with regard to the upper conductor strip 11 and the field
configurations below the image plane (septum 13) will be preserved
with regard to the lower conductor strip 12. As a result, the
voltages of the upper and lower conductors 11 and 12 relative to
the conducting septum 13 are in anti-phase at points equidistant
from the plane of insertion of the conducting septum 13. The septum
13 thus becomes a common ground plane for a pair of equal amplitude
microstrip circuits that are in anti-phase relative to the common
ground at points equidistant from the plane of bisection of the
parallel transmission line pair.
As shown in the power divider embodiment of FIG. 1, input microwave
power to the divider structure is applied to a microstrip circuit
formed by the left-hand ends of the upper and lower conductor strip
members 11 and 12. In particular, the enlarged left-hand end of the
lower conductor strip 12 functions as the ground plane for the
input microstrip circuit and the width of the upper conductor strip
11 determines the characteristic impedance of this input microstrip
circuit. On the other hand and as mentioned hereinabove, the widths
of the parallel line conductors; e.g., the midportions of the
conductor strips 11 and 12, are equal to one another and to the
width of the output microstrip conductors but different from that
of the input microstrip in order to achieve reflectionless
transmission throughout the structure. Moreover, the fact that the
field configurations are not disturbed by the presence of the
conducting septum 13 also facilitates the reflectionless
transmission of power section to the parallel line section to the
two output microstrip circuits. The resulting three dimensional
microstrip circuit is thus a reflectionless power divider whose
outputs are in anti-phase relative to the common ground plane 13;
it is inherently broadband, compact, very simply constructed and
amenable to microminiaturization; and, requires only that the two
output microstrip arm segments be of equal length. The
characteristic impedance of each of these two output microstrip
circuits is equal to one-half that of the central of parallel
transmission line portion of the device. It should be understood at
this time that the illustrated microstrip input to the transmission
line pair of the proposed structure is only one manner of applying
input microwave energy to the transmission line pair. By way of
example, this input microstrip circuit might be replaced by a
coaxial-to-parallel transmission line pair transition structure,
etc.
Suitable coaxial-to-microstrip transitions on either side of the
substrate 10 can provide a pair of coaxial outputs from the
proposed device which are in anti-phase relative to their outer
conductors, or imaginative transitions could be used for a pair of
anti-phase planar microstrip or strip line outputs. If the input
port and the two output ports of the proposed power divider are to
have the same impedance, tapers or quarter-wavelength impedance
matching transformers can, if desired, be incorporated into the
divider. Tapers would be the better choice here since they tend to
have ultra broad-band characteristics above a cutoff frequency
determined by the length of the taper. Moreover, the taper could be
designed into each microstrip arm or the whole divider could be
formed as one continuous taper.
Various other modifications, adaptations and alterations are of
course possible in light of the above teachings. It should
therefore be understood at this time that within the scope of the
appended claims the invention may be practiced otherwise than as
specifically described hereinabove.
* * * * *