Патент USA US3056096код для вставки
Sept. 25, 1962 H. sExDEL 3,056,091 TRAVELING WAVE MASER Filed Sept. 9, 1959 2 Sheets-Sheet 1 OU TWsAENU p E we N L H . Sept. 25, 1962 H. sEIDEL 3,056,091 TRAVELING WAVE MASER Filed Sept. 9, 1959 2 Sheets-Sheet 2 BV .T j AT ORNEV t" ¿free Patented Sept. 25, 1952 2. 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 3,056,091 TRAVELING WAVE MASER 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 i a high degree of amplification can be obtained in a rea 035 sonable leng-th of Wave guide. In addition, the non 25 Vg-dœ 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 specification. 55 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 3,056,091 3 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 field. 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. ments. 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 3,056,091 5 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 guide. 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 UNITED STATES PATENTS 2,883,481 Tien ________________ __ Apr. 2l, 1959 OTHER REFERENCES 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 1410-1414.