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Nov. 6, 1962
W. A. HUGHES
3,063,027
HIGH POWER MICROWAVE ISOLATOR
Filed Feb. 14, 1955
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3,063,027
Patented Nov. 6, 1962
I
2
The novel features which are believed to be character
istic of the invention, both as to its organization and
3,063,027
‘
HEGHPOWER MICRUWAVE ISOLATOR
Willard Aiien Hughes, Los Angeles, Caiiii, assignor to
Hughes Aircraft Company, Culver City, Caii?, a cor
poration of Delaware
Filed Feb. 14, 1955, Ser. No. 487,996
2 Claims. (Cl. 333-242)
This invention relates to waveguides for unidirectional
microwave transmission, and more particularly to a
broadband high power waveguide isolator.
Many utilizations of microwave energy require a power
source which is very stable in amplitude and frequency
method of operation, together with further objects and
advantages thereof, will be better understood from‘ the
5 following description considered in connection with the
accompanying drawing in which a number of embodi
ments of the invention are illustrated by way of example.
It is to be expressly understood, however, that the draw
ing is for the purpose of illustration and description only,
10 and is not intended as a de?nition of the limits of the
invention. In the drawing:
FIG. 1 is a perspective cut-away view of a simpli?ed
embodiment of the invention to aid in the explanation of
output. For example, the usual microwave generators
the invention;
are susceptible to deterioration with respect to frequency
FIG. 2 is a cross-sectional view through a practical em
and amplitude output if the nature of the load varies. It 15
bodiment of the invention;
follows that their stability is deleteriously affected if
FIG. 3 is a cross-sectional view of a second practical
energy is re?ected from a load which varies in impedance.
embodiment of the invention;
Accordingly, it is highly desirable to isolate the micro
FIG. 4a is a longitudinal sectional along the centerline
wave energy generator from the load. It is also desir
of a third embodiment of the invention;
FIG. 4b is a cross-section taken through the embodi
ment of FIG. 4a at the plane designated as 4b;
wave from the load.‘
FIG. 5 is a cross-section of a fourth practical embodi
In the prior art this was most closely achieved by
ment of the invention; and
mounting one or more ferrite specimens in a waveguide
FIG. 6 is a cross-section of a ?fth practical embodi
and subjecting them' to an externally applied static mag 25
merit of the invention.
netic ?eld. In one form of load isolator a ferrite speci
Referring now to the drawing, in which like numbers
men, preferably ‘of rectangular cross section, is asym~
able to provide such isolation with a low insertion loss
while at the same time exhibiting high loss to the re?ected
represent like elements in the different ?gures, it will be
metrically mounted in a rectangular waveguide parallel
to its longitudinal axis. The static traverse magnetic 30 assumed for purposes of explanation that it is desired to
pass energy from left to right through the isolator. In
?eld is provided by a relatively large permanent magnet
the cause of simplicity certain structural details have
located outside of the waveguide. The magnetic ?eld is
been omitted from the ?gures. For example, secured
channeled through the ferrite, causing the ferrite to pro
to each end of the isolator but omitted from the draw
vide high attenuation for wave energy passing through it
in one direction and low attenuation for wave energy 35 ings is a suitable waveguide ?ange for coupling the de
vice of this invention to other equipment.
traversing it in the opposite direction.
Referring speci?cally to FIG. 1, microwave energy is
It is an object of the present invention to provide a
impressed upon opening 10 of waveguide 12 from a micro
microwave isolator of the type described above which is
wave source in a manner well known in the art. Wave
relatively compact and at the same time is capable of
guide 12 may be a length of conventional waveguide of
handling a large magnitude of power.
40 the character adapted to be used at the desired microwave
It is another object of the present invention to provide
frequency. Ferrite strips 14 and 16 are in a conventional
a high power microwave isolator that is relatively broad
manner rigidly secured to the inner horizontal surfaces
band in its operation and not frequency sensitive.
of waveguide section 12 and are interposed along plane
The desired isolation is achieved in accordance with
this invention in the following manner. In a section of 45 15, which is the plane of circular polarization of the H
?eld of the traveling microwave. Permanent magnet 18
waveguide a slender ferrite strip is placed longitudinally
is constructed and placed so that “north” pole face 20
in a plane of circular polarized H ?eld. This plane in the
and “sent ” pole face 22 focus transverse to the wave
waveguide is one parallel to the electric ?eld and its lo
guide
a narrow magnetic ?eld along the plane 15 through
cation may be calculated by methods well known in the
ferrite
strips 14 and 16 which are, as shown, of substané
art. It is the plane in which the transverse component
tially the same length as the pole faces and of cross
of the H ?eld is equal to the longitudinal component of
section very small compared With the waveguide cross
the H ?eld of the traveling microwave. An external
section.
transverse static magnetic ?eld is caused to be focused
Referring now to FIG. 2, permanent magnet 18, shown
through the ferrite. With this con?guration a forward
going microwave signal has a circularly, with a positive 55 in cross~section, is placed around waveguide'lz in such
a manner that the transverse static magnetic ?eld is
sense, polarized H ?eld and the ferrite exerts no absorp
focused along plane 15 representing the plane of circular’
tion effect upon it. Thus, the insertion loss is extremely
polarization of the H ?eld. Ferrite strips 14 and 16
low. The backward going microwave signal in the same
are secured to the inside walls of waveguide 12 as shown
plane has a circularly, With a negative sense, polarized H
so as to be interposed in the transverse magnetic ?eld
?eld and is absorbed by the precessional resonance of the
along plane 15.
electrons in the ferrite. The undesired re?ected micro
Referring now to FIG. 3, permanent magnet i8 is
wave energy is then converted to heat by precessional
again shown to substantially surround waveguide section
damping losses and the heat is absorbed into the wall of
12 and pole faces 25} and 22 again focus the transverse
the waveguide. The physical theory concerning the
magnetic ?eld along plane 15 which coincides with ‘the
phenomenon of positively and negatively circularly polar
ized magnetic ?elds is a rectangular TEN) mode in a
certain plane in the waveguide and the dependence of I
the sense of the circular polarization upon direction of
65
plane of circular polarization of the propagating magnetic
?eld. Longitudinally dividing waveguide section 12 into
three substantially equal volumes having substantially
equal cross-sections are secured brass cooling ?ns 24
and 26. As in the previous embodiment, ferrite strips
propagation is discussed in “The Microwave Gyrator,”
Bell System Technical Journal, January 1952, pages 1.—3l, 70 14 and 16 are mounted along the inside Wall of wave
by C. L. Hogan.
guide 12 in the plane 15 of circular polarization. Mount
ed in the same plane and on the opposite surfaces of brass
3,063,027
.51.
For purposes of description of the operation of the
invention it will be assumed that the waveguide is excited
in the TB“, mode. The operation of the invention is not
disturbed by this mode. The electric and magnetic ?elds
'3
cooling ?n 24 are ferrite strips 27 and 28; and likewise
on the opposite surfaces of brass cooling ?n 26 and coin
cident with plane 15 are mounted ferrite strips 29 and 30.
Ferrite strips 27—30 are of substantially the same dimen
sions as strips 14 and 16.
are set up as usual with the transverse electric ?eld across
the narrow dimension of the cross-section of the wave
Referring to FIGS. 4a and 4b there is shown in sec
tion an embodiment of the invention which utilizes a
guide and the alternating magnetic ?elds across the
greater dimension of the cross-section of the waveguide
and along the length of the waveguide. The electrons in
microwave impedance transformer having a broadband
impedance matching characteristic.
The transformer
comprises steps 32, 34, 35, 35', 34’, 32’ (left to right) in
the horizontal walls of waveguide section 31. Ferrite
strips 14' and 16’ are secured along the length of the
narrowest portion of waveguide 31 in proportionally the
10 the ferrite strips have an average magnetic moment which
same position of the cross-section as in the other embodi
ments of the invention. The ferrite strips may here be
smaller in cross-section than are strips 14 and 16 in the
previous embodiment.
Permanent magnet 18’ with attached pole faces 29 and
22 is placed in a manner to provide the narrow trans
verse magnetic ?eld along plane 15 through ferrite strips
14’ and 16' across the height of the waveguide section 31.
Glass or other dielectric seals 36 and 36' are placed across
waveguide section 31 at opposite ends of the isolator in a
manner so as to sustain a pressure differential between the
space inside the isolator and the outside waveguide.
Referring now to FIG. 5, magnet 18 is again shown to
substantially surround waveguide 12, and pole faces 20
and 22 focus a transverse magnetic ?eld through the wave
is random in the absence of the external magnetic ?eld.
When permanent magnet 18 is in place to establish the
transverse external ?eld along plane 15, the average
magnetic moment tends to line up with the external ?eld
which is established. In addition, the alternating mag
netic ?elds, due to the waveguide excitation, cause this
average magnetic moment to process. This processing
of the average magnetic moment is attended by the pro
duction in the ferrite of magnetic ?elds which tend to
reinforce the alternating magnetic ?elds. The precession
frequency depends upon the strength of the external
?eld and when the precessional frequency is made equal
to the propagating microwave frequency, precessional
resonance occurs.
Under these conditions microwave energy travelling
left to right in waveguide section 12 in FIG. 1 is not
effected by the precessional resonance and passes un
attenuated to the load or other utilization device of the
microwave energy. Energy reflected from the utiliza
guide coincident with plane 15. Ferrite strips 14 and 16
tion device, however, has circularly polarized magnetic
are placed as before along the inside wall of waveguide 30 fields of opposite sense along plane 15 and in this case
12 coincident with plane 15. The strips are here made
precessional resonance occurs to absorb substantially all
with a substantially half round cross-section. In addition,
the re?ected energy in the ferrite strips 14- and 16 by
cooling ?ns 3S and 40 are secured on the outside of wave
precessional damping losses and the energy is absorbed
guide section 12 along the length of the isolator coincident
as heat in the wall of the waveguide.
with plane 15 and are adapted to conduct and radiate heat
Referring now to FIG. 3, it is seen that the brass cool
away from the ferrite strips 14, 16 and waveguide 12.
ing ?ns 24 and 26 of their attached ferrite strips 27
Referring now to FIG. 6, waveguide section 12 with
through 30 cause the device to be capable of absorbing
ferrite strips 14 and 16 and pole pieces 20 and 22 are
and dissipating even higher amounts of energy ‘by virtue
shown in substantially the same con?guration as in FIG. 40 of the function of the cooling ?ns to conduct heat with
2. However, the magnet 18” is reversed to encircle the
the outside waveguide walls. The principle of operation,
opposite side of waveguide 12; and external cooling ?ns
however, remains exactly the same because the cooling
43 in the form of a length of channel 44 are secured along
?ns are at right angles to the electric vector in the wave
the length of waveguide section 12.
guide and do not effect the magnetic vector because the
Referring to FIGS. 3 and 5, it is seen that slots 41 and
fins are made of brass.
42 are cut substantially through the waveguide to allow
The device shown in FIG. 4 is an embodiment of the
the pole faces to be in closer proximity to the ferrites for
invention which utilizes an impedance transformer to
purposes of improving the focusing of the transverse mag
netic ?eld through the ferrite strips and along plane 15
reduce the dimensions of the waveguide in the region of
the ferrite strips so that a smaller magnet may be used
within the waveguide. The depth of the slot may be the
due to the reduced magnetic gap between waveguide
entire thickness of the waveguide wall or any fraction 50 surfaces through the ferrite strips 14' and 16’. The vol
thereof. The horizontal dimensions are substantially
ume enclosed between glass seals 36 and 36’ may be
those of the ferrite strips. As shown in FIG. 3, pole faces
either evacuated or pressurized to preclude arcing across
20 and 22 are accordingly shaped with tongue projections
the reduced waveguide dimension. This embodiment has
of the same dimensions which are inserted into their re
the further advantage of providing an even lower inser
spective slots. The embodiment according to FIG. 5 55 tion loss because less ferrite material is required to
utilizes iron cooling ?ns 38 and 40 for pole faces; and
achieve a given attenuation.
there are adapted to ?t directly into the slots.
_
The embodiment of FIG. 5 utilizes external cooling
The permanent magnets adapted for use in the inven
?ns to increase the power dissipating capabilities of the
tion may be, for compactness and efficiency, of the well
isolator. Because of the proximity of ?ns 38 and 40
known Alnico type or any similar material having like 60 to the ferrite strips 14 and 16, heat is readily conducted
characteristics. The ferrite strips utilized are fabricated
from the ferrite strips to the cooling ?ns. In this embodi
of material suitable for precessional resonance at micro
ment the cooling ?ns function also as magnetic pole faces
Wave frequencies. For example, ferrites of the general
and thus are shaped in a conventional manner to focus
formula XFe 203 in which X is a bivalent metal ion are
a strong magnetic ?eld along plane 15 through the ferrite
particularly useful for this purpose. A suitable ferrite 65 strips. The half-round cross-section of ferrite strips 14
is described in the patent to Luhrs, No. 2,644,930 which
and 16 provides the advantage of decreasing the tendency
consists of 25 moles of manganese oxide, 25 moles of
of the microwave energy to are between the ferrites be
zinc oxide and 50 moles of ferric oxide. The mixture is
sintered at 1300 degrees C. The composition and man
ner of making ferrites having the necessary structure are 70
cause of the rounded surfaces. Also the rounding pro
vides a broader band of operation because of internal
described in the RCA Review No. 17 for September, 1950
by R. L. Harvey et al. Substances capable of exhibiting
demagnetization due to the rounded geometry.
Referring to the embodiment according to FIG. 6, cool
the precessional absorption phenomenon at microwave
ford another practical means for dissipating the heat from
ing ?ns ‘43 attached as a channel 44 to the waveguide af
frequencies are known in the art as ferro-magnetic dielec
75 the ferrite strips. Magnet 18” is reversed from the pre
tries.
5
3,063,027
vious embodiments in order that the external cooling ?ns
of channel 44 may be closer to the ferrite strips.
6
tion of the magnetic ?eld within the waveguide; a second
embodiment of FIG. 5, the following speci?cations were
plurality of ferrite strips secured along the interior walls
of said waveguide section also coincident with the plane
of circular polarization in the magnetic ?eld; an external
including ?anges; the inside dimensions of the waveguide
focused along and throughout said plane of circular polar
ization.
.070” x 1.7" and were placed so that their centerlines
2. A microwave isolator device in which the effect of
microwave energy loss through heat dissipation due to
In a speci?c structure constructed according to the
used:
The brass waveguide section was 3" in overall length 5 magnet adapted to provide a transverse magnetic ?eld
were 1.122" by .497"; the ferrite strips Were .100" x
were .220” from the closest vertical wall; cooling fin-pole
pieces 38 and 40 were of soft pure iron .18” x .55" x 1.7”
each with a tongue .062" x 1.7" inserted through a lon
electron precessional resonance damping losses in a fer
rite substance is utilized to allow propagation of micro
wave energy in a waveguide in one direction and preclude
gitudinal slot of the same dimensions in the waveguide
propagation of the microwave energy in the opposite
walls to make actual contact with the ferrite strips along
their entire length; the magnet was horseshoe in cross 15 direction, said device comprising: a length of rectangular
waveguide being adapted to be excited in the plane polar
section and 1.7" long and cast of Alnico V material; the
ized mode and having thereby a plane throughout the
magnetic ?eld at the pole faces was 3700 Gauss and at
length of the waveguide section along which the magnetic
the surface of the ferrites opposite the pole faces, 3300
Gauss.
vector is circularly polarized; a pair of slender ‘ferrite
Using a pulsed carrier over the band from 8500 ki1o~ 20 strips secured along the length of said waveguide section
in contact with the inner surface of opposite walls thereof
megacycles to 9500i kilomegacycles, the pulses being 2.4
along said plane and having a semi-circular cross-‘section,
micro-seconds in width and of 4-15 cycles repetition rate
the curved portions of said strips facing each other and
continuous duty, the attenuation in the forward direction
the vilat portions of said strips being disposed perpendicu
was .5 db while the attenuation in the reverse direction
was 12 dbil db over the above band. Thus an attenua 25 lar to said plane; a permanent magnet external to the
waveguide for producing a transverse magnetic ?eld along
tions ratio of nearly 30‘ to l in db was achieved while
transferring power peaks of ‘greater than 300 kilowatts
the plane of circularly polarized magnetic ?eld through
and average power of greater than 300 watts.
Other advantages over the prior art are that a lower
said ferrite strips; cooling ?ns external to said waveguide
section and attached thereto consisting of a material suit
able for serving also as pole faces for said magnet and
voltage standing wave ratio (VSWR) is seen by the micro
wave circuitry on the input side of the isolator; the iso
lator of this invention operates over a considerably broader
band and is, therefore, much less frequency sensitive;
the insertion loss of the device is negligible (.5 db); and
the power handling capabilities are at least 100 times
better than in the prior art systems. It is also seen that
the device is simple in construction so as to o?er economic
advantages.
being attached thereto, each of said cooling ?ns being
secured to said waveguide coincident with the plane of
circular polarization external to said waveguide section
and being secured thereto in a manner such that each of
said cooling ?ns is a?ixed to one of said ferrite strips
for conducting heat therefrom into space.
References \Cited in the ?le of this patent
What is claimed is:
1. A waveguide isolator device utilizing the principle
of magnetic precessional resonance and the inherent
energy dissipation associated therewith in a ferrite sub
stance for unidirectionally absorbing microwave energy
propagating within the waveguide, said isolator device
comprising: a section of rectangular waveguide being 45
adapted to be excited in a conventional plane polarized
mode; a number or" cooling ?ns, said cooling ?ns being
thin heat conductive nonpermeable sheets supported along
the length of said waveguide internal thereto and dis
posed parallel to the magnetic ?eld in a manner to avoid 50
disturbance of the electric ?eld; a ?rst plurality of ferrite
strips supported along and in contact with said cooling
?ns and made coincident with a plane of circular polariza
UNITED STATES PATENTS
2,643,296
Hansen ______________ __ June 23, 1953
2,648,047
2,748,353
2,745,069
2,767,380
2,776,412
2,777,906
2,844,789
2,849,684
Hollingsworth _________ __ Aug. 4,
Hogan _______________ __ May 29,
Hewitt ________________ __ May 8,
Zobel ________________ __ Oct. 16,
Sparling _______________ __ Jan. 1,
Shockley _____________ __ Jan. 15,
Allen ________________ __ July ‘22,
Miller _______________ __ Aug. 26,
1953
1956
1956
1956
1957
1957
1958
1958
OTHER REFERENCES
Journal of Applied Physics, vol. 24, No. 6, June 1953,
pages 816-817.
Fox et al.: “Behavior and Applications of Ferrites,”
Bell Technical Journal, vol. XXXIV, No. 1, January 1955.
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