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Патент USA US3048815

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United States Patent Q??ce ,
Patented Aug. 7, 1962
to be converted into the dominant TEM mode by me
chanical and electrical asymmetries in the line, such as
bends, junctions, etc.
Another approach for obtaining ?rst order non-recipro
Robert L. Fogel, Torrance, and Herbert T. Suyematsu, 5 cal e?ects in coaxial transmission line is to provide the
Los Angeles, Calif., assignors to Hughes Aircraft Com
line with ‘an inhomogeneous cross section so that the TEM
pany, Culver City, Calif, a corporation of Delaware
Filed June 8, 1959, Ser. No. 818,919
3 Claims. (Cl. 333-—31)
mode cannot be progagated. The dominant mode for
this modi?ed type of coaxial line is a hybrid mode con
taining both the TE and TM modes, although in a few
The present invention relates to non~reciprocal wave 10 special cases, the dominant ‘mode can be solely the TE
or the TM mode. This principle has been utilized with
transmission and, more particularly, to a coaxial slow
coaxial lines in ‘which the line has been half ?lled with
wave structure, partially disk-loaded, having selectively
a material having a high value of dielectric constant.
magnetized ferrite elements.
The boundary conditions imposed ‘by this ‘geometry re
A number of non-reciprocal wave trans-mission devices
have been developed for microwave frequencies. The 15 quire the existence of longitudinal components of the
radio frequency magnetic ?eld which in combination with
more recent, and most effective of these, utilize mag
the circular components of the radio frequency magnetic
netized ferrite elements suitably mounted in a waveguid
?eld provides the required circular polarization at the
ing structure to provide the required non-reciprocal char
air-dielectric interface. With rods of ferrite material dis
acteristics. The principle of operation upon which these
devices are based is the action of the magnetized ferrite 20 posed along the interface and in presence of a static mag
netic ?eld non-reciprocal wave transmission is achieved.
element to pass energy in one direction and attenuate
Several geometries for the dielectric loading of the co
or absorb the energy in the other direction. For this
axial line have been explored together with the suitable
operation to attain, it is necessary that the ‘ferrite element
of the ferrite elements for non-reciprocal Wave
be mounted Within the waveguiding structure at a position
Where is a net component of circularly polarized radio
In'this latter type of coaxial structure, i.e., a structure
frequency magnetic ?eld of the mode that is propagating.
in which the inhomogeneity is non~circularly symmetric,
In most of the known non-reciprocal ferrite devices,
the relation between the magnitude of the circularly polar
the circularly polarized radio frequency magnetic ?eld
ized radio frequency magnetic ?eld and the characteristics
exists in the mode of the energy that propagates in the
of the dielectric loading material is not rigorously known
absence of the ferrite element. The ferrite is placed in
because the exact solutions to the wave equation have not
a position so that the resulting mode has its maximum
yet ‘been obtained. Experimental and approximate theo
retical results show that the magnitude of the non-recipro
region of the magnetized ferrite. Thus, for a rectangular
cal effects increases as the value of the dielectric constant
waveguide propagating energy in the dominant mode,
the ‘ferrite element is mounted within the waveguide to 35 for the loading material increases.
To more clearly understand the foregoing results in co
include a position located half way between the longi
component of circularly polarized magnetic ?eld in the
tudinal center line and one side of the broad walls. While
this structure is the more common, it is possible under
certain conditions to obtain non-reciprocal wave trans
axial transmission line having an inhomogeneous cross
section, the difference between the free-space velocities
of propagation of the separate media will be assumed to
mission by placing the ferrite element in a position where 40 cause a distortion of the principal mode. If the co
axial line is completely ?lled with either of the different
media, a TEM mode will propagate with the free-space
Upon magnetization of a ferrite so positioned, a compo
velocity of that medium and there will he no longitudinal
nent of circularly polarized magnetic ?eld is created with
of the radio frequency magnetic ?eld. If the
in the ferrite because of the gyromagnetic action. The
cross section of the line is made inhomogeneous, the en
non-reciprocal e?ects resulting from this type of opera
ergy will try to propagate in each medium with the free
tion are second order, however, and less e?icient than the
space velocity of propagation of that medium. Since
previously described operation.
the energy must propagate with the same velocity over
Non-reciprocal devices as described in the foregoing
the entire cross section, however, the velocity of propaga
paragraphs are suitable for operation at the higher micro
tion of the resulting distorted mode (in the general case,
wave frequencies; however, when such devices are de
a hybrid TE plus TM) will have a value between the
signed for operation at the lower microwave frequencies
limiting values of the free-space velocities of propagation
‘and at the ultra-high frequency region, they are extremely
of the individual medium and the hybrid mode, in the
large. Since coaxial transmission lines are smaller, they
case under consideration, will have a component of cir
are more suitable for the propagation of energy at such
referenced lower frequencies and a new approach is re 55 cularly polarized radio frequency magnetic ?eld. It is,
therefore, readily apparent that as the ratio of velocities
quired because the radio frequency magnetic ?eld of the
of propagation of the two media is increased, the amount
dominant TEM mode is linearly polarized. Second order
of distortion of the original mode (and, thus in the pres
non-reciprocal effects may be readily achieved but for the
ent instance, the magnitude of the component of the cir
more e?icient ?rst order non-reciprocal effects, one of
60 cularly polarized radio frequency magnetic ?eld) is also
several other approaches appear to be more ‘feasible.
One of the referenced aproaches for achieving ?rst
While non-reciprocal wave transmission is attainable
order non-reciprocal effects in coaxial transmission line
involves the propagation of the ?rst higher order T=E11
in accordance with the foregoing, it is to be recognized
mode which has a circularly polarized component of
that in dielectric materials, the dielectric loss increases
the radio frequency magnetic ?eld is linearly polarized.
radio frequency magnetic ?eld. In order to propagate 65 as the value of the dielectric constant increases. As a
this TEu mode within a given size coaxial line, the
result of such relationship, the dielectric loss involved
frequency required is much higher than that of the TEM
in using materials having a dielectric constant on the
mode for the same line, or for a given frequency the size
order of 15 or higher begins to degrade the performance
of the line required to support the TEn mode is much
of the non-reciprocal device in which they are used. It
larger. The differences are such that the advantages of 70
follows that the efficiency of the non-reciprocal
the coaxial line over the hollow waveguiding structures
effects is limited in dielectric loaded devices by the ratio
are lost. Also energy progagated in this TEM mode tends
3 .
of velocities of propagation which, in turn, is limited by
in a conventional manner to extend diametrically through
coaxial line 11 parallel to the broad faces of the strips
16 and 17.
the dielectric loss of the dielectric materials.
It is, therefore, an object of the present invention to
provide an et‘?cient, compact and simple waveguiding
With the ferrite strips 16 and 17 suitably magnetized,
structure for non-reciprocal wave transmission having an
inhomogeneous cross section without dielectric materials.
_ In brief, the non-reciprocal wave transmission device
the electron spins within the ferrite and the sense of
rotation of the circularly polarized radio frequency mag
netic ?eld are properly related for only one direction of
vof the present invention is a modi?ed “slow-wave-loaded”
'waveguiding structure with suitably mounted elements of
energy propagation and so provide a non-reciprocal dif
ferential phase shift and attenuation.
agnetized ferrite. The slow-wave-loading is partial and
is accomplished with conductive elements mounted in
A 3” length of modi?ed slow-wave coaxial line, as
described in the foregoing, having a %" outside diameter
and propagating energy at 3000 mc./s. operates as indi
cated in FIG. 2. Such FIG. 2 is a plot of the differential
phase shift in degrees obtained over a substantially low
15 increment of applied static magnetic ?eld of O to 400 gauss
spaced-apart relation within the structure to extend across
one-half thereof to provide an inhomogeneous cross sec
tion and thereby a circularly polarized component of the
radio frequency magnetic ?eld at the boundary of the
loading elements.
The action of the ferrite as mounted
and a resulting curve 26 indicates a range of diiferential
at the referenced boundary then provides non-reciprocal
operation of the device.
phase shift between zero and approximately 150 degrees.
Similar operation of a half-slow-wave caxial line 1.3" in
length has provided a differential phase shift of 90+5
Other objects and advantages of the invention will be
readily apparent in the following description and claims
degrees with a loss of 0.3 db. with the foregoing struc
considered together with the accompanying drawings, in
tures a VSWR of 1.1 or less over a 12% band width has
FIG. 1 is a perspective view, partly in section, of a
modi?ed slow-wave coaxial line having a non-reciprocal
characteristic in accordance with the present invention;
FIG. 2 is a characteristic curve showing the operation
of the device of FIG. 1; and
been obtained by providing matching transformer struc
ture (not shown) at each end of the line.
The results described in the foregoing paragraph show
the usefulness of the present invention as a differential
phase shifter, which has many applications in the micro
wave art.
In such device the ratio of the velocities of
FIG. 3 is a modi?cation of the device of FIG. 1.
propagation for the loaded and unloaded regions is of
Referring to the drawings in detail, FIG. 1 in partic
the order of 10 to 1. From this it follows that to obtain
ular, a section of coaxial line 11 comprises an inner con 30 the same ratio in a dielectrically-loaded waveguiding
ductor 12 and an outer conductor 13. A plurality of
semi-circular conductive disks 14 are similarly and ra
structure, a material having a dielectric constant of the
order of 100 would be required. The losses inherent in
a material having such high dielectric constant would be
prohibitive and are entirely avoided by the structure of
dially mounted in parallel and spaced-apart relation on
the inner conductor 12 to extend transversely with respect
Such disks 14 are electrically connected to the
the present invention. Also, by increasing the static mag
inner conductor 12 and insulated, as by suitable spacing,
from the outer conductor 13. In this con?guration, there
netic ?eld to a value producing gyro resonance in the
ferrite strips 16 and 17, the device is operable as an isola
tor with substantially high values of attenuation for one
direction of propagation and substantially none in the
is provided a modi?ed slow-wave structure wherein energy
propagates in a hybrid mode which is, in the general form,
a combination of the TB and TM modes.
The reason for the propagation of the referenced hybrid
mode has been set forth in the previous discussion and
may be readily understood by considering that the velocity
of propagation in the disk-loaded half-portion of the line
is of one value and that of the unloaded half-portion is
of another value.
Since energy propagates with but one
value of the velocity of propagation in such structure,
the actual velocity of propagation is one having a value
that is intermediate to the two referenced values. Thus,
the inhomogeneity introduced by the partial disk-loading '
of the inner conductor requires that the resulting mode
have a longitudinal component of the radio frequency
magnetic ?eld which is combination with the circular
component provides a circularly polarized radio frequency
magnetic ?eld at or near the boundary between the loaded
and unloaded regions of the line.
The theory of operation of the slow wave coaxial line
having complete disks mounted on the inner or center
opposite direction.
Referring now to FIG. 3 there is illustrated a second
non-reciprocal coaxial wave transmission line 31. In
this embodiment a plurality of conductive half disks 32
are radially mounted in spaced-apart and parallel relation
in contact with the outer conductor 33 and extend toward,
but not in contact with the inner conductor 34. The
resulting structure also constitutes a “slow-wave-loaded”
coaxial line and operates in substantially the same manner
as set forth for the structure of FIG. 1. Thus, elongated
ferrite strips 36 and 37 mounted on either side of and
parallel to the inner conductor 34 on the diametric edges
of the half disks 32 provide a non-reciprocal transmission
characteristic when suitably magnetized. To provide the
required magnetization, a conventional adjustable static
magnetic ?eld structure (not shown) is mounted exter
nally of the line and establishes a magnetic ?eld, H,
through the ferrite strips 36 and 37 parallel to the broad
faces thereof as indicated by arrows 39.
conductor is well-known in the art and is generally appli
The operation of this latter embodiment of the inven
cable to the partially-loaded structure described in the 60 tion is the same as set forth for the structure of FIG. 1.
preceding paragraphs with minor modi?cations. Such
Thus, for substantially low values of applied static mag
partially-loaded coaxial line is reciprocal in operation in
netic ?eld, di?'erential phase shift of the energy, propagat
that waves propagated in either direction are effected in
ing in one direction through the line, is obtained. Also,
the same manner.
by increasing the value of the static magnetic ‘?eld for
Now to provide a non-reciprocal characteristic to the
gyro resonance in the ferrite, non-reciprocal attenuation
partially loaded coaxial line two substantially thin elon
gated strips 16 and 17 of ferrite material are mounted on
With respect to the foregoing non-reciprocal wave
the diametrical edges of the disks 14 to extend parallel
transmission device, it is to be realized that the 50%
to the inner conductor 12 with one on either side of such
loading factor provided by the semi-circular disks is not
conductor. Thus, the strips 16 and 17 are disposed at 70 limiting. Other geometric con?gurations providing an
the boundary between the loaded and unloaded regions
inhomogeneous cross section are within the scope of the
of the coaxial line structure where the circularly polarized
invention set forth. Also, it is to be realized that the
radio frequency magnetic ?eld of the hybrid mode of
waveguiding structure is not limited to circular coaxial
propagated energy is present. An adjustable static mag
lines as the same principles are applicable with respect to
netic ?eld, H, as indicated by arrows 21, is established 75 other structures in which the dominant mode of propaga
tion is the TEM mode such as rectangular coaxial line,
strip line, and slab line.
Structure has, therefore, been described for providing
non-reciprocal wave transmission with minimum losses
and physical dimensions. While the salient features of
such structure have been described in detail with respect
to particular embodiments, it will be readily apparent that
numerous modi?cations and changes may be made Within
the spirit and scope of the invention and it is, therefore,
not desired to limit the invention to the exact details 10
shown except insofar as they may be set forth in the fol
lowing claims.
What is claimed is:
1. A non-reciprocal wave transmission device com
prising: a coaxial type waveguide supporting radio fre 15
quency energy in the TEM mode, said Waveguide having
ductor; said waveguide being operative in a transverse
static magnetic ?eld paralleling the broad surfaces of said
ferrite strips.
2. A device as claimed in claim 1, wherein said discs
are connected to said inner conductor.
3. A device as claimed in claim 1, wherein said discs
are connected to said outer conductor.
References Cited in the ?le of this patent
White _______________ __ Aug. 4,
Suhl et a1. ___________ __ Ian. 19,
Crowe ______________ __ July 26,
Litton _______________ __ Aug. 2,
Seidel ______________ __ Nov. 21,
Australia ____________ _._ Mar. 18, 1957
France ______________ __ Nov. 18, 1957
Australia ____________ _~ Aug. 27, 1958
an inner conductor and an outer conductor; slow-wave
means disposed within said waveguide, said means in
cluding a plurality of spaced-apart conductive half-discs
mounted on one of said conductors and spaced from the
other conductor, said half-discs being similarly mounted
in parallel relation to provide two regions in said wave
Seidel: “Journal of Applied Physics,” February 1957,
guide having di?‘erent velocities of propagation; a pair of
pages 218-226.
elongated ferrite strips mounted on said half-discs parallel
to said inner conductor along the boundary between said 25 Morgenthaler et 211.: “Proceedings of the IRE,” Novem
regions with one strip on either side of said inner con
ber 1957, pages 1S51—1552.
Patent N0. 3,048,801
August 7‘I 1962
Robert L. Fogel et ale
5 in the above numbered pat
It is hereby certi fied that error appear tters Patent should read as
n and that the said Le
ent requiring correctio
corrected below.
insert -— there ——;
Column 1, line 25, after "where"
hybrid ——; line 53'
column 3, line 39, for "hybrid" rea
"caxial" read
for "is" read —- in -—; column 4, line 18?, for
—— coaxial —-; line 19,, for "90+5" read -— 90-i_-_5 ——;
line 20a
for "with"I second occurrence, read —— With -'-—.
Signed and sealed this 22nd day of Januar y 1963a
Attesting Officer
Commissioner of Patents
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