[1]United States Patent Office 3@100,287 3,100,237 PHASE SHIFTER UTILIZING VARL4,BLE DELAY E"ARTED TO CIRCULARLY POLARIZED ELECTRIC WAVES BY VARIABLY MAGNTETIZED FERRNE MATERIAL Howard Scharfman, Lexington, and Francis J. OHara, Belmont, Mass., assignors to Raytheon Company, Lexington, Mass., a corporation of Delaware Ffled May 31, 1957, Ser. No. 662,843 9 Claims. (Cl. 333-24.1) This invention relates to phase shifters, and more particularly, to adjustable phaseshifting devices of the nonreciprocal type capable of producing relatively large phase variations in energy traveling from a microwave source in an electromagnetic wave transmission system. Variable phase shifters utilizing the Faraday rotation effect have been constr-ucted which consist of ;a longitudinally-magnetized ferrite rod axially posi@tioned within ,a conductive pip-. or other waveguide structures and preceded and followed by circular polarizers. By means of such devices, a plane or linearly-polarized clectroma.-netic wave @at microwave frequencies is converted to circular polarized ener.-Y in the first polarizer, is phase shifted in the ferrite section, and converted back to linear polarization in the output polarizer; the applied magnetic field strength usually being maintained below the value at which saturatiory or ferromagnetic resonance in the ferrite occurs. Thiis, in such phase-shi@fting devices, the phase angle between the output electric vector of the electroma,-netic wave and the input magnetic wave nlay be varied by shiftin-, the phase of the energy passin.- through the ferrite element positioned within the waveguide structure, depending,upon the relative stren.-th of the applied magnetic field and upon the length of ferrite material. I-lowever, in applications in which a ferrite pihase shifter of this type is us,-d to introduce a desired phase shift, it is desirable in numerous applications to produce a relatively lar-e value of phase shift for a given length of ferrite, and to have the input and output waveguide ports located in relatively close proximity, such as, for example, in certain packa.-ing applications wliere a minimum space is required between the input and outpi-,t waveguide ports. In accordance @with the invention, a doublin.- of the phase shift for a given length of ferrite material and for a given applied ferrite field, which is equivalen-t to doublinthe maximq-im phase shift before saturation of the ferrite material, is accompliqhed by feeding linearlypolarized microwave energy through a two-mode transducer or "@thruplexer," having a pair of polarizationselective side arms or connections in eitler a round or square waveguide, and thence into a conventional circular polarizer. The resultant eirrularly-polarized electrical energy -from said polarizer is fed itno a ferrite phase shifter cornprisin.- a longitudinally-magnetized ferrite rod,axially positioned in the waveguide and is thereby phase shifted proportional to -the applied longitudinal field strength in the ferrite material. The energy emerging from the ferrite phase shift section is directed to a shorting plate or bar positioned at the end of the wave,-Uide adjacent to the ferrite section, the sense of eirelllar polarization of refiected electromagnetic wave energy being reversed by the shorting plate prior to reentering the ferrite phase shift section. The reflected wave moving back throu,-h the ferrite encounters a reversed longitudinal field so directed as to produce a second value of phase shift in the same electrical direction as the first, the phase shift being doubled on the second trip -through the ferrite phase shifter. The circular polarizer then' converts the circularly-polarized reflegted wave en--rgy back to a linearlypolarized wave in a plane orthogonal Patented Aug. 6, 1963 2 or cross-polarized to the input elertromagnetic field, and in this rnanner, t-he side arm or second connection of the twomode transducer may be used as the output of the phase-shifting device. It should be noted that this transmission-type phase-shifting device is nonreciprocal in the sense that a phase advance is realized for one direetion of propagation, and,a delay is obtained for the other direction. Thus, @a rel@atively large value of phase shift can be produced in a @ovel @manner by introducing a first value 10 of phase shift to microwave energy passing in one direction thraugh the phaseshifting system and the same -value of phase shift in magnitude and sign to energy traveling in the op@posite direction of transmission therethrough. Moreover, the resultant value of -ph@ase shift, so produced, 1,5 is capable of beiiig controlled by varying the volta.-e applied to the ferrite lyhase shifter to obtain a nonreciprocal phase shift substantially proportional to the applied magnetic field. The invention further discloses a modification of the 20 above-described, cross-polarized phase shifter in which the input and outpiit linearly-polarized magnetic fields are in the same plane, permitting the device having a siligle port to be used as an elee-trically-controllable short circuit. This can be achieved by replaicing the two-mode 25 transducer in the system with a fixed 45' ferrite Faraday rotator, or isolator, preceding the circ-ular polarizer in the system. By adjusting the phase shift, the effective line length of the device may be changed. Thus, the device may be -used as -a shorting stub of variable length. 30 Other objects and advanta-ges will be more readily perceived upon analysis of the drawing, in which: FIG. I is an isometric view, partly in section, of the first embodiment of a phase shifter according to the invention; 35 FIG. 2 is.a graph showing the phase shift as a function of the strength of theapplied magnetic field; and FIG. 3 is -a side view, partly in section, of a further embodiment of the invention. Referring now to FIG. 1, a phase shift system is shown 40 which includes:a two-mode transducer 12, a circular p,olarizer 14, a ferrite phase shifter 16, ;and a shorting bar 18 positioned @at the end of the waveguide adjacent to the ferrite phase shifter. As indicated, the ferrite phase shifter 16 is similar to the rotator section of the phase 45 shifter disclosed in the co-pending application of Howard Scharfman, Serial No. 648,897, filed March 27, 1957, now United States Letters Patent No. 3,090,015, which issued May 14, 1963. More partirularly, FIG. I shows -a rec50 tangular input section of waveguide 20 having a flange 21 ada_pted to provide a connection with a microwave source of energy, such as a magnetron or klystron oscillator. The rectangular waveguide 20, will accept -and support only TEO, waves in which the electric vector, which 55 determines the plane of polariz@tion of the wave, is parahel to the ghort side of the rectangular waveguide. The two-mode transducer 12 is shown integral with the input section of waveguide and inrludes a rectangular output -arm 23, a flange 24 adapted to connect mirro60 wave energy -to a load, and a secorid arm 25 co-operating with output arm 23 to provide a pair of conjugatelyTelated terminals or branch6s in that a wave launched in either one will not appear at the other, Therefore, microwave energy -of the TEo, mode introduced into wave65 gliide 20 will flow through the two-mode transducer 12 into the circalar polarizer 14. It should be understood that any standard type circular polarizer maybe used, provided the proper polarization @nd mode of @nergy is thereby obtained. Moreover, it is 70 obvious to one skilled in the art that a number of owell-known circular polarization means may be emplo@yed in lieu of the circ ular polarizer @14 las long as the length
[2]3,100,287 3 of the polarizer, and the structure wit-hin the section c@,L waveguide is adapted to convert linearly-polarized energy to circularly-polarized energy. In the present instance, circular polarizer 14 comprises a section of circular waveguide 26 having a card or vane of dielectric material 27 diametrically positioned at 45' to the -plane of thelinearlypolarized ,input field within the circular waveguide for the distance necessary to convert the linearly-polarized field to a circularly-polanzed field. Tbe resultant circularlypolarized fieldis connerted by means of @output Range 28 t,o the ferrite phase swfter 16, which has the property of phase shffting the microwave energy transm-itted therethrough in a direction which is dependent upon the direction of the applied axial magnetic field. More particu@larly, therefore, the -phase shift througti the ferrite phase shifter is described in detail in @an article by Howard ,Soharfman entitled "Three New Ferxite Phase Shifters," in the Proceedings of the I.R.E., vol@ 44, pp. 1456-1459, October 1956. The ferrite phase shifter 16, connerted to the eircula@r polarizer ;14, includes a cylindrical ferrite element 32 positioned witlun the waveguide isection 33 by means of a low4oss dielectric material 34 and 34a, such as Teflon, which acts as a solid-supporting medium for the ferrite element 37,. The Teflon dielectric material may be cut to the inner diameter of the circular waveguide section 33, clivided into t-wo sections as ghown at 35 in the region of the ferrite element, a hole bottom-drilled -into each section, and the ferrite element slidably inserted into the Teflon. Many other methods for mountin.a the ferrite wit@hin the Teflon wiU suggest themselves to those skired in the art. For example, whenthe Teflon is to be inserted into a curved section of the waveguide, the Teflon may be h,eated until soft:and poured into that portion of @tbe waveguide. The ferrite device 16 further includes a magnetic, Reldproducing @means, -such as field coil 36, surrounding the circular,waveguide 33 in the rp-gionof the ferrite element 32. The field coil may consist of 25,000 turns of wire connected to an altemating current source 37 of approximately 100 volts at a frequency of 10 kilocycles by way of leads 38 and 39. As noted, the transmission phase shift -through the fer'te rotator section is a function of the applied long@itudinal field. Therefore, the phase shift 0 can be expressed by the @following equation: (0- + 0+) L 0= 2 where p+ is equal to the phase constant of the circularlypolarized wave rotating in the same sense as current causing the magnetic field; p- is equal to the phase constant of the circularly-polarize,d waverotating in t-he opposite -sense of p+; and L is equal to the length of the ferrite rod. FIG. 2 shows the variation of the phase as a function of the applied magnetic field for @a typical X band niierowave phase,shifter. As the magnetic fieldis increased, the phase shift increases slowly and then passes through anapproximately,linear region and -finally saturates the ferrite element. In the presentmstance, a phase shift of from appr,oximately zero degrees to 45' is obtained before the energy reaches the shorting plate or bar 18, Which is soldered or otherwise connected to the end portion of the Teflon-fiHed circular @waveguide section in the region of output flange 40. As shown in the diagrammatic representation of the path lengths followed by electrical energy traversing the phase shift system of FIG. 1, -a ver tically-pola@nzed wave, shown at 41, is circularly-polarized by the circular polarizer 14 in the, man:Ker -represented at 42,,is phase shifted a predetermined number of degrees represented by the vectorat 43, andreflected from shortin,g bar 40. The reflected wave moving back thtough 4 the ferrite experiences a second phase shift of substantially the same value as the first phase shift, as represented at 44, and consequently, the phase shift is doubled on the second t@rip through the ferrite element. In this instance, the relative phase of the energy is shifted an additional 45' on the serond trip. It should be understood that, @from examinat@ion of the curve shown in FIG. 2, the maxi@mum variation of phase shift of the phase shifter 16 is:a function of ferrite length, 10 diameter, and saturation magnetization; therefore, an arbitrarily large electrically variable phase shift can be obtained by dncreasing the length of the device. However, phase variation up to -1000' can be obtained for use with applications requiring large linear phase varia15 tions with low constant insertion loss. As noted, the reflected wave moving through the ferrite phase shifter reenters the circular polarizer 14 and is converted from a c ir--ularly-polarized reflected wave back to a linearly-polarizedwave in a plane cross-polarized to 20 the input field, as represented by the arrow 45 of FIG. 1. In this manner, the side, arm 23 of the thruplexer 12 may be used as the output of the phase-shifting systeni. In this manner, the phase sl-iift system is capable of producing greater phase variation per unit length than heretofore 25 possible in conventional phase shift systems. It should be understood that tLe ferrite phase shifter 16 can be constructed so as to have two planes of symmetry. 1-t is possible, of course, to utilize a ferrite element of square outer configuration in conjunction with a circ ar 30 waveguide or vice versa. It -is also understood that the thruplexer 12 may consist of -the waveguide of either square or circular cross-section as long as the dimpnsions of each side arm are chosen so that only the dominant mode in each can be propagated. It should be further 35 understood that the length of the fertite element 32- preferably exceeds that of its diameter so that the required magnetic field for a given an.-le of phase shift is held relatively low. It is also desirable -to maintain the diameter of t-he ferrite -rod less than 1/3 the diameter of the 40 waveguide 33 -for low-loss @attenuation of the propagated wave. As noted, a square or circular wave,-uide struet-ure including symmetrical ridged guides in whioh thp, circularly-polarized waves of opposite sense have -the satne phase constant at zero field strength can be used as the 45 -PrOPalatiOn medium@. Referring now to FIG. 3, a modification of the single ferrite de'vice of FIG. I is shown wherein a nonreciprocal 45' ferrite Faraday rotator (>f conventional design may be inserted between the circular polaxizer 14 and the 50 thruplexer 12, @the side arm, 23 of t-he thruplexer being terminated in a wellknown matched ter-zim'nation 47, such as -a section of waveguide fi-Iled with Polyiron, or any sirnilar nonreflecting matexial adapted to absgrb electrical 55 energy. As shown, the 451 ferrite rotator 48 comprises a section of circular waveguide 49 fdled with Teflon or similar dielectric material 29 and su@pporting a second ferrite element 50 axiary positioned wit-hin the low4oss dielectric material. A separate magnetic field-producing means 51 surrounds the circular waveguide section 49 60 in the region of the fetrite element 50. This field-producing means may consist of a permanent magnet of sufficient strength to produce a nonreciprocal 45' rotation of the m@icrowave energy passing -through the ferrite material in the forwa-rd and reverse directions. This angular 65 displacement of the Enearly-polarized fields is represented bY the -arrows 62 and 53 in FIG. 3. In Iike manner, the input and o-utput energy linearlY-Polarized in the sanie plane is represented by the arrows 41 and .55. Consequently, the device may be used as an electricauy-con70 trollable short eirr-uit for Well@known impedance matching applications. Whilethe shorting bar 18, as shown in FTGS. I and 3, is located a short distance from the fem,te element 32, it should be understood that at low frequency modulation 75 of the ferrite, the field coil 36 may be located proximate
[3]5 or in cont-act with the shorting plate 18. This is possible because the eddy current effects produced inthe shorting bar 19 (are -negligible. However, at high modulation frequencies, the shor@ting bar is preferably positioned, as shown, -a short distance from -the field coil 36 and the ferrite element 32 to prevent eddy curren-t losses from dissip,ating the driving field energy apphed to the phase shifter. Also, a smal@ler field coil may be used to prod,uce a specified phase shift using a given amount of field current -,vhen it is desirpd to produce a phase shift m energy waveforms having appreciable high frequency components. Furthermore, a direct ourrent may be used to drivethe field coil -in either FIG. 1 or FIG. 3 to produce a constant phase shift of predetermined value, or a combination of direct current and altemating current may be applied to one or more field coils to produce la constant phase shift in connection with a variable phase shift. For the foregoing reasons, it is to be understood that the above described arrangements are illustrative of the application of the @principles of the invention. Nurnerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention. Moreover, the invention is not Iimited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpreta-tion commensurate 'with -the scope of ithe invention within the art. Wha-t is
