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Патент USA US3056096

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Sept. 25, 1962
Filed Sept. 9, 1959
2 Sheets-Sheet 1
E we
Sept. 25, 1962
Filed Sept. 9, 1959
2 Sheets-Sheet 2
t" ¿free
Patented Sept. 25, 1952
Another object of this invention is a compact and
uncomplicated nonreciprocal maser ampliñer that can be
easily constructed with minimal requirements of pre
cision in the process of manufacture.
A feature of the present invention is an arrangement
Harold Seidel, Fanwood, NJ., assigner to Beil Telephone
Laboratories, Incorporated, New York, NX., a corpo
ration of New York
which includes a -section of conductively bounded hollow
wave 4guide with a ferrite slab in contact with part of
the inner surface thereof.
Filed Sept. 9, 1959, Ser. No. 838,883
5 Claims. (ci. sse-4)
A typical embodiment of the invention is in a simpli
This invention relates to masers and more particularly,
to nonreciprocal traveling wave masers.
lO fied maser which comprises a section of conductively
bounded hollow wave guide of appropriate dimensions
The invention is based on my discovery that, with a
with a slab of gyromagnetic material partially filling the
proper choice of waveguide dimensions, modes of »the
enclosed volume and With the active maser material dis
“ferrite dielectric” type can be used to propagate energy
posed in that part of the contained space which is not
in the form of a slow wave in a manner which is ad
vantageous in some areas of technology. In particular, 15 occupied by the ferrite.
I have discovered that gyromagnetic materials can be
it is found that under certain conditions the `group velocity
loaded into wave guides so that energy will propagate in
of the propagating modes can be reduced by making the
the lferrite dielectric mode in such a manner that the
guide smaller, the reduction being proportional to the
phase constant ß=ß(w) exhibits singulari-ties which may
scaling factor. A slow wave structure of this sort has a
natural application, «for instance, in the design of stable, 20 be designated as -oo and -l-oo. Since the group velocity
of the wave energy propagating in the guide may be ex
high-gain masers where the inclusion of «slow wave struc
pressed as
tures is `dictated Iby the need to extend the interaction
time of the input signal and the maser medium so that
a high degree of amplification can be obtained in a rea
sonable leng-th of Wave guide. In addition, the non 25
reciprocal propagation characteristics of the ferrite di
electric mode can be utilized advantageously to provide
it [follows that for certain values `of w intermediate the
lthe degree of stability required in a high-gain amplifier.
singular points the wave is slowed. Furthermore, I
Workers in the waveguide art have known for some
have discovered that singularities of opposite sign may
time that when an appropriately magnetized 'ferrite slab 30 be produced by arranging the -gyromagnetic material so
is loaded into a rectangular Wave guide `a series of new
that there are at least two magnetically different kinds
modes appear which propagate at large values of the
of interfaces extending along the longitudinal dimension
phase constant ß. These modes are not associated with
of the wave guide.
the normal mode, and over «a large frequency range
In a preferred embodiment in accordance with the in
propagation in the wave guide is exclusively in the extraor 35 vention, a rectangular slab of gyromagnetic material, ad
dinary modes which have been recognized to be non
vantageously yttrium iron garnet, is positioned inside
reciprocal. Propagation in the particular mode employed
a hollow rectangular Wave guide in contact with one of
in this invention, in fact, occurs in only one direction
the walls thereof in such a manner as to «fill about one
until the ferrite slab almost fills the interior of `the guide.
half of the volume enclosed by the guide. The width of
A-t a critical point propagation in the tìrst direction is cut 40 the guide is made small in comparison with the free space
off and propagation in the opposite direction is estab
wavelength of the signal to be slowed, and means are
lished. The term “ferrite ydielectric mode” has been used
provided at each of its ends for coupling the small guide
to describe these “one-way” surface modes in which
to the larger size generally used to transmit ordinary
the magnetic field appears to be concentrated around the
modes so that the signal energy can be applied to the
yferrite-metal and ferrite-air interfaces. This term is de 45 input end of the «device and abstracted at the output end.
rived from the analogous propagation of surface modes
The invention will be more fully understood from the
along dielectric materials.
The theory of Iferrites in rectangular wave guides, with
some reference to the ferrite dielectric modes, is the sub
ject of an article by Button and Lax in I.R.E. Trans
actions, Volume AP-4, pages 531-537 (1956). As the
theoretical background which will be helpful in under
standing the present invention is adequately set -forth in
.following more `detailed description, taken in conjunc
tion with the accompanying drawing, in which:
FIG. l `shows the basic elements of a slow wave struc
50 ture in accordance with the invention;
FIG. 1A is a plane section through the device 10 along
the line 1A;
FIG. 2 is a plot of the relative intensity of the mag
netic field inside the ferrite loaded small rectangular wave
the literature, a :detailed account is not included in this
Ordinarily, slow wave propagation is obtained through
the use of periodic structures. Included in this descrip
guide shown in FIG. 1;
FIG. 3 illustrates diagrammatically one form of a
maser incorporating a slow wave structure according to
tion are the helix types which are thought of in terms
the invention; and
of geometric slowing, and the cavity types which are
FIG. 3A is a plane section through the device 30 along
thought of in terms of dispersion. There are others, in 60 the line 3A.
a sense hybrid to these two types, but nevertheless within
the classification of periodic structures.
Such periodic
structures have generally required precision fabrication
Referring now more specifically to the drawing, there
is shown a nonreciprocal slow wave structure l0 corn
prising a conductively bounded hollow rectangular wave
to close tolerances. Thus they have been costly to manu
guide 12 with a slab or block of gyromagnetic material
facture in addition to being subject to deviations from 65 14 in part of the enclosed space and in contact with one
the calculated and desired characteristics. Furthermore,
when periodic structures are used in masers it is generally
found necessary to introduce complications to `furnish a
degree of nonreciproci-ty or other means of providing for
amplifier stability.
An object of the present invention is, therefore, a new
and improved nonreciprocal traveling wave maser.
of the narrow walls thereof. Following the principles of
the invention it has been found that optimum slowing
conditions occur in this embodiment when the gyromag
netic member substantially fills the interior of the wave
70 guide on one side of a plane dividing _theenclosed space
into two approximately equal rectangular volumes. In
accordance with the invention, the width of the guide is
In the illustrated embodiment 36 the medium 38 typi
made much smaller than the free space wavelength of
cally comprises a paramagnetic solid characterized by
the signal. This choice of dimensions is intended to cut
at least three discrete energy levels. Desired separation
off all of the conventional TE modes. The TE ferrite
of the energy levels may be attained by means of the
dielectric modes, however, may still propagate, their
ability to do so being independent of the dimensions of CII Zeeman effect due to a D.-C. magnetic field Hdc extend
ing through the medium 38. In order to maintain the
the guide, although the characteristics of propagation do
clarity of the drawing the means for establishing the mag
depend on the guide size. In particular, I have discovered
netic field are not shown but its direction is indicated by
that if the wave guide is made arbitrarily small the group
the arrow labeled Hdc. The same field may also be
velocity of the ferrite dielectric mode is reduced in pro
utilized to establish the sense of magnetic properties of
portion to the scaling factor. The group velocity is found
the gyromagnetic member, though in some cases it may
to have a maximum at some defined center of the trans
be desirable to use different values of Hdc for each of
mission band and to decrease uniformly to zero at both
these purposes, in which case magnetic shunting can be
edges of the band.
utilized to achieve the desired distribution of magnetic
Although it is obvious that the group velocity is con
tinuously variable over the operational range of the slow
To operate the maser, pump energy is supplied to the
wave structure, most embodiments of the invention will
normally seek the highest possible slowing factor. Thus
medium 38 at a frequency corresponding to the separa
the waveguide width be no smaller than about one
pliñcation of the input. A high degree of amplification
so greatly in size.
tion, in most cases likely to occur it considerably ex
ceeds the bandwidth of the main resonance line of the
maser crystal.
Various modifications are, of course, feasible within
tion between the appropriate Vpair of the energy levels.
the width of the guide will generally be made as small
By these means a population inversion with respect to
as is convenient in the particular circumstances. The
reduction in size is limited only by the increased losses 20 a second pair of energy levels is produced in the crystal.
Such an inversion is known in the maser art as a negative
in the ferrite and the difi’iculty of transferring energy to
temperature. The signal input is then made to corre
a very small wave guide. To obtain a usable reduction
spond to the separation between such second pair of en
of the group velocity, the waveguide width typically will
ergy levels. Interaction between the signal and the
be no more than about one-half, and preferably no more
than about one-eighth, of the free space wavelength. 25 medium stimulates the return transition and energy of
the corresponding frequency is radiated, resulting in am
Practical considerations usually make it desirable that
is achieved by means of the extended interaction time
twentieth of the free space wavelength. Transfer of sig
of the slow wave with the maser medium. Additionally,
nal energy between the small guide and the guide used
to propagate the conventional modes is effected by the 30 the ferrite dielectric mode lends stability to the amplifier
by virtue of its nonreciprocal characteristics.
coupling arrangements 18 and 19. In the illustration the
Generally, the width W of the wave guide 32 will be
waveguide wall in contact with the ferrite member is ex
too small to support the pumping wave in the absence of
tended and broadened while the other three walls are
any modification in the basic rectangular geometry. In
tapered from the small guide up to the standard size.
order to carry the pump energy to the medium 38, one
The gyromagnetic member may be extended into the
of the narrow walls of the guide is replaced by the ridge
larger guide to achieve a more efficient transfer. Ad
36. The distance S-ì-W is substantially V2A at the pump
vantageously, it may be tapered to avoid undesirable dis
ing frequency, although in most cases W will be some
continuities. Thus the member 14 has constant thickness
what smaller than S and may be disregarded.
while its width increases with the guide width in sections
If the maser is tuned by varying the applied D.-C.
18 and 19. It is extended into the standard guide and 40
magnetic field, the slowing medium will be tuned simul
tapered off in a convenient length. These principles are
taneously. While the bandwidth of the gyromagnetic
known in the waveguide art but under ordinary circum
member decreases proportionally to the slab magnetiza
stances are not called upon to connect guides which differ
Since the degree of slowing is also proportional to
the magnetization of the slab 14, the gyromagnetic ma
terial should usually be selected to have a high mag
netic moment at the temperature range in which the de
vice is to be operated. A well-known ferrimagnetic sub
the spirit of the invention, both in the slow wave struc
stance which has suitable characteristics over a wide
ture of FIG. 1 and in the maser shown in FIG. 3.
In particular, the shape of the wave guide is not re
thermal range, including the liquid helium temperatures
often associated with masers, is yttrium iron garnet.
With a polycrystalline form of this material as the slow
ing medium and with a steady magnetic ñeld of 600
gauss the internal magnetization is about 1700 gauss
and the accompanying useful bandwidth is of the order
of 2 kmc. In a wave guide having a width of 1A inch
and a height of lÁx inch, such an arrangement yielded a
center-band slowing factor of about 10.
stricted to the rectangle shown in the illustrative embodi
Other possible configurations will be apparent
to those skilled in the art.
Additionally, the maser
material and the gyromagnetic medium may each take
a variety of shapes and forms, the better to adapt the
device for operation at a particular frequency or power
level. Following the principles of the invention, a plu
rality of members having different magnetic properties
may be placed in the wave guide with the gyromagnetic
An illustrative embodiment of the invention is depicted 60 member or members and contiguous thereto so as to
create the necessary longitudinal singularities in ß. In
in FIG. 3, wherein there is shown a maser 3€) comprising
such an arrangement the ferrite-metal interface is not
a conductively bounded hollow rectangular wave guide
required and the slab need not be in contact with the
32 with one of the narrow walls replaced by a ridge 36
waveguide wall. Furthermore, a variety of coupling or
which extends into the space enclosed by the guide and
has its sides close to the broad faces thereof. The gyro 65 matching techniques may be used to transfer `energy to
and from the small wave guide.
magnetic material 34 is positioned along the other narrow
What is claimed is:
wall and partially fills the contained space. The maser
l. A nonreciprocal maser amplifier comprising a con
medium 38 is disclosed in the space between the ridge 36
ductively bounded hollow waveguide, an elongated gyro
and the gyromagnetic material 34, the most advantageous
location being determined from data of the kind illus 70 magnetic member disposed within said waveguide, said
trated in FIG. 2 where ö is the coordinate of the ferrite
air interface in the structure shown in FIG. 1. As can
be seen from the curve, most of the flux of the radio
frequency magnetic ñeld is close to the face of the gyro
magnetic member.
member extending longitudinally of said waveguide and
partially ñlling the interior thereof, said member having
a first longitudinally extending surface portion in contact
with and conforming to an interior surface portion of
said waveguide, means forming a negative temperature
medium disposed vwithin said waveguide in the space not
occupied by said gyromagnetic member, a substantial
Volume of said negative temperature means extending
into the region immediately adjacent a second surface
portion of said gyromagnetic member, said negative tem
perature means being characterized by an energy level
system adapted to amplify signals having a frequency
below the cutoif frequency of said waveguide, means for
establishing a unidirectional transverse magnetic ñeld
face portion in contact with the waveguide wall opposite
the interior face of the ridge and a second longitudinally
extending ñat surface portion spaced from the interior
face of the ridge, means forming a negative temperature
medium disposed within said waveguide in the space be
tween said gyromagnetic member and the interior face of
the ridge, said negative temperature means being char
acterized by an energy level system adapted to amplify
signals having a frequency below the cutoff frequency
through said gyromagnetic member, means for applying 10 of a waveguide having a width equal to the distance be
pump energy to said negative temperature means, means
tween the face of the ridge and the opposite side of said
connected to one end of said waveguide for causing sig
waveguide, means for establishing a unidirectional trans
nal wave energy to propagate therethrough in a slow
verse magnetic field through said gyromagnetic member,
ferrite dielectric mode, and means for abstracting an am
means for causing a pump wave to propagate through said
15 ridge `waveguide for inverting the population distribution
in said negative temperature means, means connected
2. A device as in claim 1 wherein said gyromagnetic
to one end of said waveguide for causing signal Wave
member comprises yttrium-iron garnet.
energy to propagate therethrough in a slow ferrite dielec
3. A nonreciprocal maser ampliñer as in claim 1 in
tric mode, and means for abstracting an amplified signal
which said waveguide is of rectangular cross-section, and 20 output from the other end of said waveguide.
said gyromagnetic member has a thickness substantially
plified signal output from the other end of said wave
equal to the height of said waveguide and a width sub
stantially smaller than the width of said waveguide.
4. A nonreciprocal maser amplifier as in claim 1 where
in said negative temperature means comprisesy a para 25
magnetic solid and said gyromagnetic member comprises
a ferrimagnetic solid.
5. A nonreciprocal maser amplifier comprising a con
ductively bounded hollow rectangular ridged waveguide,
References Cited in the tile of this patent
Tien ________________ __ Apr. 2l, 1959
De Grasse et al.: “Bell System Technical Journal,”
March 1959, pages 305-334.
an elongated gyromagnetic member disposed within said 30 Lax et al.: “Journal of Applied Physics,” September
waveguide, said member extending longitudinally of said
1955, pages 118641187.
waveguide and partially iilling the interior thereof, said
Seidel: “Proceedings of the IRE,” October 1956, pages
member having a first longitudinally extending ilat sur
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