Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention relates in yeneral to apparatus for non-reciprocal
transmission of electromagnetic wave energy and more particul~rly, the
invention pertains to broadband waveguide y-jlmction circulators.
DISCUSSION OE~ TEIE PRIOR ART
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The conventional three port waveguide symmetrical waveguide circulator
employs three waveguide arms that are arrangecl at angles of 120 with respect
to one another and meet at a common junction. Centrally disposed at the
junction are one or more gyromagnetic members which are situated to preserve
the symmetry of the junction. The gyromagnetic members are subjected to the
influence of a magnetic field in the operation of the circulator to cause the
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device to be a non-reciprocal transmi-tter of electro-magne-tic wave energy
propagating in the waveguide. To improve the operating characteristics of
the symmetrical y-junctlon circulator, modifications in the si~e and shape of
the gyromagnetic members and in the matching the impedance of those members to
the remainder of the structure have been made. The improved circulators have,
in general, preserved the symmetry of the junction and have required gyro-
magnetic members of appreciable volume.
U.S. patent 3,104,361 granted to J.G. Leetmaa, et al, discloses a
circulator having a triangular gyromagnetic member situated between a pair of
triangular transformer plates. The gyromagnetic member is entirely with the
junction and the apexes of the triangular transformer pla-tes extend into the
waveguide arms to provide an impedance match for the gyromagnetic member. The
arrangement preserves the symmetry of the junction while providing an impedance
matching structure that is asserted to be less frequency sensitive than
conventional impedance transformers.
U.S.Patent 36849~3 Aug 15 1972 granted to J.J. Cotter, et al, discloses a
circulator employing a pair of triangular gyromagnetic members separated by an
i~erposqd die~lectricmember.The gyromagnetic members are disposed between a -~
pair of transition elements that reduce the height of the waveguide in two
steps to prbvide impedance matching. The Cotter, et al, circulator preserves
the symmetry of the junction but its construction is somewhat more critical
than the Leetmaa, et al, circulator because Cotter, et al, uses two gyromagnetic
members that must be maintained in alignment to preserve the symmetry of the
junction, whereas Leetmaa, et al, employs a single gyromagnetic member.
However, even in the Leetmaa, et al, device, the upper and lower transformer
plates must be maintained in alignment as well as the dielectric supports
; between which the gyromagnetic member is sandwiched.
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SUMMARY OF THE INVENTION
The invention resides in an improved three-port waveguide circulator
of simplified construction that requires but a single gyromagnetic element
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approximately one quarter wavelength long measured in the gyromagnetic material.
Only one transformer plate is required although two transformer pla-tes may be
used. To minimize the cost of manufacture and avoid the necess:Lty for aligning
two transEormer plates, a one transformer plate construction is preferred. The
gyromagnetic member is disposed at the center of the junction with one face
spaced frorn the waveguide wall by a diel~ctric gap which can be made adjustable
to facilitate tuning of the device. The opposite face of the gyromagnetic
member is disposed upon a conductive member so that that face is short~
circuited whereas the obverse face is open circuited at the dielectric gap.
Because of the asymmetrical arrangement of the gyromagnetic member, an
additional advantage is gained in that the higher order modes are shifted to
a portion of the frequency spectrum outside the band of intended operation of
the circulator. The invention, because it employs a single quarter wave
gyromagnetic element, permits a reduction in weight to be achieved over
conventional circulators which employ three quarter wavelength or one half
wavelength gyromagnetic elements. Moreover, an appreciable saving in cost can
be realized by the reduction in volume of the ferrite or garnet gyromagnetic
material needed for a quarter wavelength element, compared to the material
neeaed for a half wave or three quarter wave length element.
THE DRAWI~GS
The invention, both as to its construction and its mode of operation,
can be better understood from the detailed description that follows when it is
considered in conjunction with the accompanying drawings in which:
Fig. 1 is a perspective view of a conventional prior art waveguide
y-junction circulator in which interior components are depicted in phantom;
Fig. 2 is a cross-sectional view in elevation taken along the line
2-2 in Fig. l;
Fig. 3 is a perspective view of the preferred embodiment of the inventor
in which parts are broken away to expose the interior of the circulator;
Fig. 4 is a cross-sectional view in elevation of the preferred
embodiment of the invention taken along the line 4-4 in Fig. 3;
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Fig. 5 indicates dimensions to be considered in the construction oE
the preferred embodiment;
Fig. 6 depicts a modification of khe preferred embodiment which permits
independent tuning of the in-phase mode by a central tuning post;
Fig. 7 depicts an embodiment of the invention employing a triangular
gyromagnetic element and a triangular transformer plate.
DETAILED DESCRIPTION
Fig. 1 depicts a prior art waveguide y-junction circulator having
three waveguide arms A, s and C meeting at a common junction. Centrally
disposed at the junction are a pair of gyromagnetic disks 1 and 2, which for ;
ease of exposition are assumed to be of ferrite exhibiting gyromagnetic
properties. The ferrite disks are identical in diameter and thickness and
are separated by a gap that in some conventional circulators is filled with a
dielectric material. The ferrite disks are disposed between a pair of circular
transformer plates 3 and 4 that match the impedance of the ferrite disks to the
waveguide structure. In the operation of the circulator, the ferrite disks are
subjected to the influence of unidirectional magnetic field, represented in
Fig. 1 by the arrow designated HDC. The magnetic field can be established by
one or more permanent magnets or may be set up by an electromagnet having the
ferrite disks between its pole pieces.
Electromagnetic wave energy entering waveguide arm A propagates to the
~nction and because of the gyromagnetic properties of the ferrite disks,
substantially all the energy is directed into arm B. In the ideal waveguide `
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circulator, all the wave energy enters arm B and none enters arm C. The `~ ~ -
`j circulator is not a reciprocal transmitter because wave energy entering arm B ~
is directed into arm C and not into arm A~ ~.
By changing the direction of ma~netic field HDC, the circulator can be
operated as a switch in as much as a reversal in direction of that magnetic ~ -~
field causes electromagnetic wave energy entering arm A to be directed into
arm C rather than into arm B.
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Fig. 2 shows a cross-section of the prior art circulator taken along
the plane 2-2 in Fig. 1. The ferrite disks 1, 2 must be maintained in alignment
as well as the transformer plates 3, 4, to preserve the symmetry of the junction.
Construction of the circulator requires relatively precise dimensional control
as there usually is no provision for adjustment of the gap between the ferrite
disks after the device is assembled. Commonly, however, capacitive tuning
screws, as shown in U.S. patent 3,593,210 July 13, 197_, granted to R.F. Skedd
are-provided in each waveguide arm to faci7itate tuning.
Fig. 3 depicts the preferred embodiment of the invention with part of
the waveguide top wall broken away to expose the interior of the circulator.
In the Fig. 3 arrangement the gyromagnetic element 5 is a disk of a mat~erial~
such as ferrite or garnet exhibiting gyromagnetic properties. The length of
the disk along i~s axis is approximately a quarter wave length measured in
the medium of the disk at a selected frequency in the operational band of the
clrculator. The disk is mounted on a cylindrical boss 6 that rises from the
transformer plate 7. As shown in the cross-sectional view of Fig. 4, a memher
8, threaded into the top wall of the`waveguide, is disposed directly over the
gyromagnetic disk 5. The member 8, and boss 6, preferably are of the same
diameter as the gyromagnetic disks. The member 8, essentially is an extension
of the waveguide top wall which permits adjustment of the gap between that wall
and the gyromagnetic disk. Because of that gap, the disk is open circuited at
its upper face whereas the face that lies on the boss is short circuited.
Adjustment of the gap permits tuning of the circulator. To further facilitate
tuning of the device, capacitive tuning screws 10, 11 and 12 are provided as
indicated in Figs. 3 and 4. In each of the three waveguide arms, a capacitive
tunlng screw is situated above the transformer plate.
The more lmportant dimensions to be dealt with in construction of an
embodiment of the invention are indicated in Fig. 5. An embodiment of the
invention of the general type shown in Figs. 3 and 4 was constructed using
WR-90 waveguide arms and a gyromagnetic element constituted of TT390 ferrite.
The dimensions of that embodiment are as follows: a = .080", b = .060",
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c = .160", d = .395", and f = 1.130". The dimension indicated as h in Fig. 5
is .400" or WR-90 waveguide. rrhat embodiment operated with a VSWR (voltage
standing wave ratio) of less -than 1.10 from 8.5 GHz to 9.6 GHz and was tuned
with a capacitive screw in each arm located between the edge of the transformer
plate and the ferrite disk and with the movable gap adjusting plate situated
directly over the disk. Over a broader band extending from 8.0 G~z to 10.0 GHz,
that embodiment operated with a VSWR of less than 1.30. To scale that
embodiment for another frequency band, the Eoregoing dimensions, as a rough ;
calculation, can be multiplied by the factor ~ , where ~ is the center
frequency of the new band. In addition, a ferrite material should be selected
whose magnetization is close to the magnetization of rrT39o ferrite multiplied
by the factor g o5 .
E'ig. 6 shows an embodiment of the invention that is an improvement upon
the Fig. 4 circulator. In the Fig. 6 circulator the ferrite disk 12 is mounted
on a boss 13 that can be moved to adjust the gap between the disk and the
upper waveguide wall. rrhe boss is provided with threads that mate with threads
on the transformer plate 14 whereby upon rotation of the boss, it moves ;
vertically as viewed in Fig. 6. Extending downwardly from the upper waveguide
wall is a tuning post 15 situated over the center of the ferrite disk. The
tuning post is threaded into the waveguiae wall to permit vertically movement
of the post. Thetuning post is a thin, electrically conductive rod whose
presence in the guide affects only the in-phase mode of the circulator. .
It has been established that circulator action depends upon the ; ;
relationship between the responses of the junction to three modes supported
in the junction, viz., an in-phase mode and two counter-rotating modes, the
reflection coefficients of which must be mutually displaced in phase by 120.
'rhe variations in bandwidth exhibited by different ~orms of circulators
depend upon the dgree to which a particular structure maintains the requisite
phase relation as frequency is changed and by the onset of higher order
modes.
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The tuning post 15 permits -the in~phase mode -to be -tuned
independently to cause i-ts rerlec-tlon coef'ficlent to be dls-
placed by 120 with respect to -the o-ther modes. 'rhe in-phase
mode has an electric fleld on the axls of symme-try such that
the resonant frequency depends upon the pene-tratlon of the
pos-t into the waveguide. The coun-ter-rotating modes have
only transverse electric fields in the axis of symmetry and
hence are not affected by the post if that post is slender.
The invention causes higher order modes to be shifted
upward in frequency compared to the conventional prior art
circulator and thereby provides an additional advantage. ;
Fig. 7. depicts an embodiment of the invention employing
a triangular gyromagnetic element 16 mounted on a triangular
boss 17rising from -the triangular transformer plate 18. A
tuning post 19, similar to the post of 15 in Fig. 6, is dis-
posed directly over the center of gyromagnetic element. While
not illustrated in the figure, capaci-tive tuning screws can
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be provided in each of the waveguide arms.
While not illustrated, a mixture of -triangular and cir-
cular elements can be employed at the circulator's junc-tion.
For example, the transformer plate may be triangular and the ,
gyromagnetic element may be a disk disposed on a cylindrical
boss.
, Although the invention has been illustrated as embodied
in a symmetrical y-junction waveguide circulator, it can also
take other forms such as a t-junction waveguide circulator.
In view of the different forms that the invention can take,
it is not intended to limit the invention to the precise
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-' embodiments illustrated in the drawings. -
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