US2486001A - Frequency-stabilizing system - Google Patents

Description

Oct. 25, 1949. G. G. BRucK ET AL FREQUENCY-summum SYSTEM Filed Feb. 12, 194e 2 Sheets-Sheet l PESULTH/VT .S/OCBH/VD CARR/Ef? y @Mal/JTW jatentec'lJ ct. 2.5., 1949 FREQUENCY-STABILIZING SYSTEM George G. Bruck, East Orange, N. J., and Philip E. Volz, Auburndale, Mass., assignors to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application February 12, 1946, Serial No. 647,008

(Cl. Z50-36) 11 Claims.

This invention relates to automatic frequencystabilizing systems, and more particularly to apparatus for maintaining a predetermined, fixed relationship between the frequency of a carrier wave, especially, but n; necessarily, a carrier Wave in the microwave region of the electromagnetic spectrum, and a selected reference frequency.

While not limited thereto, the present invention is admirably adapted to the control of the carrier wave of a communication system comprising, for example, two widely separated terminal stations and a plurality of intermediate relay stations, the system permitting two-way transmission of intelligence between any and all of the stations included therein, with the carrier wave emanating from each relay station under the control of the carrier wave received at each relay station, and all under the master control of the carrier wave originating at one of the terminal stations.

In a system of this general description, it is apparent that the frequency of the carrier wave originating at the master terminal station must be controlled within very close limits, and it is the main object of the present invention to provide apparatus satisfying this requirement.

This, and other objects of the present invention, which will become more apparent as the detailed description thereof progresses, are attained, briefly, in the following manner.

A portion of the carrier wave to be stabilized is applied to an energy-transmission system, for example, a Wave guide having a plurality of branches extending from a common junction. One of said branches terminates in a non-linear impedance, such as a crystal, to which modulation is applied whereby a portion of the carrier wave entering said rst branch from said common junction is mixed with the modulation in said crystal, and becomes amplitude modulated, the resultant sidebands travelling along said first branch, back toward said common junction.

A second Wave-guide branch, along which a portion of the carrier wave likewise travels from said common junction, is terminated in a tuned circuit, such as a cavity, resonator, which is designed to be resonant to a selected reference frequency with respect to which it is desired to main tain the frequency of the carrier wave in a predetermined, fixed relationship,

Preferably, the lengths of said first and second wave-guide branches are such that the difference therebetween is equal to where n is an odd integer and x is the wave-guide wavelength corresponding to said selected reference frequency. As a result of such an arrangeand cavity-reflected portions of said carrier wave at said last-named crystal produces a substantially constant-amplitude resultant wave provided there has been no deviation from the aforesaid predetermined, nxed relationship between the frequency of said carrier wave and said refer'- ence frequency. On the other hand, if there has been a deviation from said fixed relationship, the amplitude-modulated portion of said carrier wave and the portion thereof reflected from said cavity resonator do not arrive at said second crystal in phase quadrature, and, therefore, the in-phase component of the modulated portion causes the cavity-reflected portion to become substantially amplitude modulated.

The modulation envelope of the last-named resultant wave has a phase, relative to the modulation initially applied to the carrier wave, and a magnitude, which dep-end, respectively, on the sense and magnitude of any deviation from the above-mentioned fixed relationship between the frequency of said carrier wave and said selected reference frequency. Preferably, said modulation envelope is either in phase with said initially applied modulation, or it is in phase opposition thereto.

If there has been no deviation from said fixed relationship, and, as a result, a substantially constant-amplitude wave' is produced at said second crystal, there is no modulation envelope to recover, but if there has been a, deviation, the modulation envelope of the amplitude-modulated resultant wave produced at said second crystal, Whether it is in phase with the initially applied modulation, or in opposition thereto, is recovered, the sense and magnitude of the recovered envelope depending, respectively, on the sense and magnitude of said deviation.

The recovered modulation envelope is combined, for example, in a differential-amplitude detector, with a portion of the initially applied modulation to obtain a unidirectional output whose direction and magnitude likewise depend, respectively, on the direction and magnitude of the deviation of the frequency of the carrier wave from its fixed relationship with respect to the selected reference frequency.

Said unidirectional output is applied to any preferred electronic or mechanical tuning control To to adjust the source of the carrier wave to compensate for the frequency deviations above referred t0.

Now, it is desired to point ut that the fixed relationship herein referred to can be either a zero frequency difference, as is preferred, or any predetermined actual difference; and it; is further desired to point out that the normal phase relationship between the first above-mentioned amplitude-modulated portion ofthe carrier wave,

and that portion thereof which is reflected-'from the cavity resonator, need not be 90. Where said phase relationship is other than 90, theresultant wave at the second crystal will not be a substantially constant-amplitude wave, but, instead, will have a certain recoverable amplitude characteristic, and upon a frequency deviation occurring, said resultant wave will have `a different amplitude characteristic. In this case, the recovered modulation envelope will have an amplitude characteristic which is a function of the difference between the amplitude characteristics -of both said last-named Vresultant waves, and such a difference-characteristics wave may also be used to control the tuning of the source of the carrier wave.

Inthe accompanying specification there Vshall be'described, and'in the annexed drawings shown, an illustrative embodiment of the frequencystabilizing system of the present invention. It is, however, to be Vclearly understood that the present invention is not to be limited to the details herein shown and described for purposes of illustration only, inasmuch as changes therein may be made without the exercise of invention, and within the true spirit and scope of the claims hereto appended.

1n said drawings,

Fig. 1 is a partial block, partial Vschernaticdiagram of a frequency-stabilizing system assembled in v'accordance with the principles of the present invention;

Figs. Y2 and 3 are vector `diagrams illustrating phenomena occurring in certain of the components of said system;

y Fig. 4 is a schematic diagram of one type of detector 'which may be utilized in the system; and

Figs. 5 and 6 are vector diagrams explanatory ofthe operation of said detector.

Referring now more in detail to the aforesaid illustrative embodiment of the present invention, with particular reference to Fig. 1 of the drawings, the numeral I0 designates a carrier-wave generator, for example, a microwave loscillato'r whose.-frequency it is desired to control as above indicated, and whose carrier-wave output -is iapplied to an energy-transmission system including, for example, a Wave-guide Isection I'I. The latter communicates with another wave-guide section branches I3 and I4, the junction of said branches being hereinafter considered, for mathematical analysis purposes, as the energy-injection point of the system.

The wave-guide branch I'3'I'n`ay beter'rninated in any desired matched load, such'asanappropriate antenna system for radiating the greater portion of the energy developed by the oscillatorl I0, and the wave-guide branch'ld, which is receptive of a'small portion of said energy'through an iris I5, may be terminated in a so-called magic T I6 comprisingthree wave-guide branches f1, I8 and I9 extending from a'commonjunction at right angles to each other.

I2 terminating in oppositely-directed mixer to which is applied, in series with a source 12| of direct current, the relatively lowfre'quen'cy output of an 'oscillator 22 which is intended to modulate that portion of the carrier wave entering the branch I'l from the above- I `mentioned 'common junction, the addition of the frequency, for example, of 50 megacycles.

yThe wave-guidebranch 18 v'may be terminated,

' through 'an iris ?2`3,`in a cav-ity resonator 24de- Ll (l signed 4to be vresonant at the selected reference frequency withrespect to wh-ich it is desired to maintain the frequency of the carrier wave in a predetermined, xe'd relationship. As stated in earl-ierportions o'f Athis specification, the desired carrier-wave frequency may be the resonant frequency of the cavityresonator,- and this relationship is preferred, "or theremay be an actual predetermined difference `between-said frequencies.

The lengths -of thebranches f'l'l and I8, or, 'more accurately, the distance (a) between the center line of the wave-guidesection I4 andthe crystal 20, on the o'ne hand, andthe distance (b) between'the center lline of th'e 'wave-guide section I4 and the iris 2'3, on'thevo'ther, are such that thediiference therebetween (ct-b) is, preferably,

where 11. is 'an lodd 'integer and x is the -waveguide wavelength corresponding to the selected reference frequency. By proper choice of the length and cut-olf 'frequency 'of fthe branches Il and I8, the .phase difference can be 'maintained practically constant -over a substantial frequency band. It willbe understood by those skilled in the art that, desired, other relationships may be used, `provided appropriate modifications are made in the components to be later 'described herein.

vThe wave-guide ybranch I9 may be terminated ina second crystal y2'5 which is receptive of vthe modulated portionof .the carrier wave coming from the rst crystal `20, and another portion of said carrier wavereiiected 'from 4the cavity resonator 724. As hereinbefore indicated, and as will become more apparent `from the mathematical analysis to be hereinafter set forth, the combination of these two waves at fthe second crystal produces a substantially constant-amplitude or a substantially amplitude-'modulated resultant wave, depending upon whether the frequency of the carrier wave hasfdriftedl fromits fixed relationshipwith respect `to the reference frequency, and if it has driftedthe resultant wave willhave a phase, relative tovthat of the initially .applied modulation, and a-magnitude, depending, respectively, on the direction and magnitude of said to the frequency of the modulation `oscillator A2'2,

and which is capable of yrpassing an appreciable frequency band with a -substantially constant phase shift, and the output of said amplifier is applied to a differential-amplitude detector 2'1. The latter `is also receptive-'of -a portion vof the The branch I1 may be terminated in a crystal 75 output'of the modulation oscillator 'f2-'2,iand fthe combination of the modulation-frequency amplifier output and said modulation oscillator output in said detector results in a unidirectional output whose direction and magnitude likewise depend, respectively, on the sense and magnitude of any deviation from the fixed relationship between the frequency of the carrier wave and the selected reference frequency.

The unidirectional output thus obtained is applied to any appropriate tuning control 28, which may be electronic or electro-mechanical, to tune the carrier-wave oscillator I0, and compensate for any drift in the frequency thereof.

Except for the details of the differential-amplitude detector 2l, one form of which, shown in Fig. 4 of the drawings, will later be described, this completes the description of the physical aspects of the systemA of the present invention, and the following is presented as a mathematical analysis of the operation of said system.

It will be assumed that the energy travelling toward the matched load from the energy-injection point is completely absorbed, and any leakage across the magic T will be neglected.

At the energy-injection point, the output en of the carrier-wave oscillator I may be represented by:

8h=Eh SD (wht-F01) (1) where En is the peak value of the carrier wave, wht is the angular velocity thereof, and 01 is a reference phase.

Across the crystal 20, the output e1 of the modulation oscillator 22 may be represented by:

where E1 is the peak value of the modulation wave,

w1 is the angular velocity thereof, and 0n is a reference phase.

That portion of the carrier wave travelling along the wave-guide section I4 from the energyinjection point splits at the common junction, part travelling along the wave-guide branch l1 toward the crystal 20, and part travelling along the wave-guide branch I8 toward the cavity resonator 24.

At the crystal 20, there arrives a portion of the carrier wave which may be represented by:

where 7c is a proportionality constant and c is the phase shift introduced between the energy-injection point and the crystal.

The voltage eh expressed by Equation 3 and the voltage e1 expressed by Equation 2 are mixed at the crystal 2|), as crystal current, and an amplitude-modulated resultant wave travels back along the wave-guide branch I l toward the common junction. The carrier portion of the reilected wave is, however, zero if the crystal is properly matched to the wave-guide branch.

Now, the reection coefficient of the voltage y Relection coeicient=g Reflection coeficient= pressed, and for ael, a carrier component is reiiected, with a -lphase where a 1 and a phrase where a l. Furthermore, any reflected carrier component has an amplitude depending upon the value of a, and has the following form:

@Fkgah sin (wht-M+@ (6) The action at the crystal 20 generates sidebands which are the result of mixing the incident en and the injected e1. Considering only the first order terms, these sidebands have the form:

(7 where the first term immediately above is the upper sideband, and the second term immediately above is the lower sideband.

These sidebands, plus reflected carrier, if any, travel back to the common junction, from whence part goes toward the matched load and is absorbed, and part goes toward the crystal 25 which terminates the wave-guide branch I9.

At this point it is desired to digress momentarily to develop the reiiection coecient of the cavity resonator 24. Over a narrow frequency band, and where the iris 23 is thin compared to the wavelength of the energy being handled by the system, said iris is equivalent to an ideal transformer between the wave-guide branch I8 and the cavity resonator 24. The cavity resonator itself may be represented over a narrow frequency band as a parallel resonant circuit having a constant shunt resistance.

The parallel impedance of the uncoupled resonator is:

where Z0 is the parallel impedance of the uncoupled cavity resonator, at resonance, =r, and

' S Qdfoav in which latter expression Qd is the dissipative Q of the cavity resonator, Af is the difference between the frequency of the injected carrier wave and the resonant frequency of said cavity resonator, and fm is the resonant frequency of said cavity resonator.

Now, considering the iris coupling between the wave guide and the cavity resonator, the parallel impedance of the coupled cavity resonator at the wave-guide side of the iris becomes:

I TLZZ() l-l-jS where n is the ratio of an ideal transformer.

'I'he reilection coeicient for the wave-guide, terminating in the impedance Zp represented by Equation 9, is:

y l Reflection coefficient Z p- Z g where Z'g is the impedance of the wave-guide' 7 the rela-*tive match v:between the fcaNity :resonator Miami thewave-guide branch I 8 v(.al-l-lV-l-,S12 Forithe specialA case where the cavity.resonator and the 'wave-guide branch are matched at resonance, i. e., a1=1, the reflection coefficient reduces to:

-S-QJ'S ll-S2 Returning 'now-to the'analysis of the system as a whlethere arrives Aat thecavity'resonator 24, from the common junction, a yporti'on'of the 4carrier wave 4which'may be represented by:

eh=k1E..sin (ot+01+) (l5.) where k1 is a proportionality vconstant-and c' -is the phase shi'ftintroduced from the energy-injection poi-nt to fthe'cavity resonator.

lfWith la reflection coeicient as expressed in Equation 13,':a17Land for small S, so that said reflection-'coefcient-'is nearly constant in magnitude andtheangle 'thereoflis nearly proportional to'fS, =the voltage reflected from the cavity resonator'24 hasfanangle which'is nearlyproportional 'to' S, andhasthe 1form:

we kial-'L-Sq-Qjals h- 1 (arl-1)2+S2 where Reflection coefficient: (14) 2.. ,s a-12- 7% 2Tad8/I1S Practically, therefore:

where i162* is'a proportionality constant and, vas above stated, Af is the diference between the frequency of "the injected carrier wave and theselected reference frequency, which is the resonant frequency of the cavity resonator.

The Ycarrier wave reflected 'from the vcavity resonator 2:4' travels back tothe common junction of the magic T, from whence part goes toward the matched load and iscabsorbed, and part goes toward the crystal 25, said cavity-rected wave havingtneform:

Thus, there arrives at the crystal 25,'frorn-the crystal 20, upper and lower sidebands and, possibly, a carrier-wave component Vdepending in amplitude on the relative match of the crystal 20 with the Wave-guide branch ll, and reversing in phase as said crystal and guide go through match. Also arriving at the crystal 25, from the cavity resonator 24, is a carrier wave which is nearly constant in amplitude but has a phase angledepending onthe deviation'of its frequency from the predetermined, fixed relationship thereof with respect to the selected reference ifrequency of the cavity resonator 24.

The various voltages arriving at the crystal 25 have the following forms:

where fp" is the phase shift introduced 'between thescrystals 3Mami 25. Carrier. from. cavity resonator` 24- Now, 'any Acarriercomponent from the crystal 20 -conibines "with V'the ycarrierv Iwave 'from theA cavityresonator v'24 vectorially, 'and so, at the crystal '25,-o1i1y'one'fcarrierfinput need be lconsidered.

The combination, `at said 'crystal' 125, vof V"the upper sideban'dyas represented 4by the Expression 21,-ani 'the 'carrier'waveyasrepresented by the Expression'23,`isjasfollows:

in which the low-frequency or modulation en--A velopeiterm cos mzle'f-lfoaLW-w-omena) I(25) 'The combination, atrthe'crystal 2 5, of the lower sideband, ras xreiluesented :by Athe :Expression `A22, andthe lca-rrier wave, Easir-.epresentedfby the expression 23, is as follows:

. Sin'-'CwiWeM--at-Je-tw) .ms @wenn me) (2.8i

-even harmonics, I'or ra 'substantially :constantthe carrier-wave input.

This has been illustrated vectorially in Fig. 2w

of the drawings. The upper sideband may be considered as a vector rotating in a counter- Clockwise direction at the frequency ofthe carrier wave plus that of the modulation wave, and the lower sideband may be considered as a vector rotating in the same direction at a frequency of the carrier wave minus that of the modulation wave. These two vectors periodically become in phase and so, they may also be considered as oppositely-rotating vectors combining to produce a non-rotating vector, which is the resultant sideband. The latter, actually, is the carrier wave varying in amplitude at the modulation frequency, and when combined with the cavity-reflected portion of the carrier wave, with which it is 90 out of phase, said cavity-reiiected portion of the carrier wave remains substantially unaffected. Therefore, no modulation envelope is recovered at the crystal 25.

Where, however, Aa is not zero, in other words, the frequency of the carrier wave has drifted from its iixed relationship with respect to the reference frequency, a recoverable output does appear across the crystal 25, the phase of said output depending on the sign of Aa, i. e., the direction of the frequency drift, and the amplitude of said output depends on the magnitude of Aa,

i. e., the extent of the frequency drift.

This, too, has been illustrated vectorially, in Fig. 3 of the drawings, from which it can be seen that where the carrier frequency drifts above the resonant frequency of the cavity resonator 24, as indicated by the dashed vector to the left of the full line labelled Carrier (wh=fcav) the carrier wave from said cavity resonator acquires, at the crystal 25, amplitude modulation, and,

where the carrier frequency drifts below the resonant frequency of the cavity resonator, as indicated by the dashed vector to the right of said full line, said carrier wave acquires amplitude modulation, said -land modulation referring, of course, to the phase of the modulation envelope. The modulation thus produced results from the effect of an in-phase portion of the resultant sideband acting upon the carrier wave whose frequency has been altered by Aa.

In any event, the output of the crystal 25, after passing through the modulation-frequency amplifier 25, is applied to the detector 21 to extract the sense thereof, depending on whether Aa is or and obtain a unidirectional output of the proper sense and magnitude to operate the tuning control 28.

Referring to Fig. 4 of the drawings, it will be seen that the detector 2l may comprise a pair of diode vacuum tubes 29 and 3o the anodes of which are connected to the opposite ends of the secondary winding 3| of the transformer 32, the primary winding 33 of said transformer having ,applied thereto a signal E, the output of the modulation-frequency amplifier 26. The cathodes of the tubes 29 and 30 are connected to ground, respectively, through resistors 34 and 35, and the secondary winding 3| of the transformer 32 is center-tapped, whereby a portion of the output E of the modulation oscillator 22 may be applied between said center-tap and ground. The output of the detector is taken from across the cathode ends of the resistors 311 and 35,

The input signal E appears across the secondary winding 3| of the transformer 32 as the sum of the voltages E1 and E2. Assuming that Ac is the input to the tube 29, diode I, is the vector sum of E+E1, producing the output Edi shown in Fig. 5 of the drawings. At the same time, the input to the tube 30, diode 2, is the vector sum of E-E2, producing the output Eaz shown in the same gure.

The voltages Edi and Edz appear across the resistors 34 and 35 in opposition to each other, and the algebraic difference therebetween, AE, constitutes the final output of the differential-amplitude detector, as shown in Fig. 6 of the drawings.

This nal output, a unidirectional voltage whose direction and magnitude depend, respectively, on the direction and magnitude of the deviation of the carrier frequency from the frequency desired thereof, is applied to the tuning control 28, which, in turn, acts upon the carrier wave oscillator I0 to compensate for any such deviation.

While the detector- 21 has been shown to include diode vacuum tubes, triodes may be used, in which case the center-tap of the secondary 3| may be omitted, and the output from the oscillator 22 may be applied to the grids of the triodes in parallel.

This completes the description of the aforesaid illustrative embodiment of the frequencystabilizing system ci' the present invention. It will be noted from all of the foregoing that the present invention enables the maintenance, within close limits, of a predetermined xed relationship between the frequency of a carrier wave and a selected reference frequency.

Other objects and advantages of the present invention will readily occur to those skilled in the art to which the same relates.

What is claimed is:

1. Apparatus for stabilizing the frequency of a carrier wave comprising: means for amplitude modulating a portion of said carrier wave; means for shifting the phase of another portion of said carrier wave through such an angle that, upon combination of said amplitude-modulated and phase-shifted portions thereof, a wave having a selected amplitude characteristic results; means, responsive to any drift in the frequency of said carrier wave, for altering the phase of said phase-shifted portion thereof; means for combining said amplitude-modulated and phaseshifted portions of said carrier wave whereby, in the event no frequency drift has occurred. the resultant wave has the aforesaid selected amplitude characteristic, and, in the event a frequency drift has occurred, the resultant wave has a substantially different amplitude characteristic; means for deriving from said last-named resultant wave a wave having an amplitude characteristic which is a function of the difference between the amplitude-characteristics of both said resultant waves; and means, receptive of said difference-characteristics wave, for so tuning the source of said carrier wave as to compensate for said frequency drift.

2. Apparatus for stabilizing the frequency of a carrier wave comprising: means for amplitude modulating a portion of said carrier wave; means for shifting the phase of another portion of said carrier wave through such an angle that, upon combination of said amplitude-modulated and phase-shifted portions thereof, a Wave having a selected amplitude characteristic results; means, responsive to any drift in the frequency of said carrier wave, for altering the phase of said phaseshifted portion thereof, the sense and magnitude `11 of said phase-shift. alteration' depending, respec- .tively,= on thesenses.and'.magnitude,` off. any such frequency drift;l means-for combining the amplitudeemodulated and-1 phase-shifted portions of said: carrierwave Wherebmgintheevent no frequency drift has occurred, the resultant wave .hasfthe aforesaid selected amplitude. character- 1 isticand, in-the eventa` frequencydrift has occurrerl,A the resultant: Wave has, a substantially -di'erent amplitude characteristic; means-'for deriving; from said last-named resultant wave a Wave having an amplitude characteristic which vis a: function of' thefdifferencef between the; amplitude; ehara'cteristicsf` on both sairesultant'waves,

ydifferencefcharacteristicss wave. relative, to the modulation: initially.' appliedtc; said` carrien wave, and'` `the magnitude; thereof.,- depending, respectively, on the sense-and magnitudey 'of'. .said frequency drift; means for combining saiddifference;-characteristicsawave withia .portion of said initially applied modulatiomA tez-obtainA a unidirectional output. whose sense and magnitude-.likewise depend; .respectiveimn thesensesandmagnitudefoi saidfreqi-iency`1 drift; andi means, .rreceptive of said unidirectional wave, .fon'sof tuningg the-,sourceJr ofi. saidv carrier: Wave: as to; Icompensatey for said.I frequency4 drift:

3. Apparatusforstabilizing `thef-trefluency,"of a -tl'ie'phaseofA the-amplitudecharacteristic ofi said j l.

carrier wave comprisingzi means for amplitude ff,

modulatingga portionwofsaid cami'er'wavesimeans forshifting the phase-ofi anotherr'portion ofi sai-d carizier wave througnfannangleof:909; meansglresponsive.J to any; drift. -irn the; ,frequency vor said carrier Wavegfor altering-thefphasefofisaid :phase- '5' shifted-portion thereof: meansffon comb iningthe amplitude-modulated. and' plriaseeshifte(,li portions of said carrier wave wherebmginzxtheevent no; 'frequency 'drift1 has: loccurred;Y the resultant Wayeis: a substantially constant-amplitude' wave, and; in: the: eventta frequencyf has 1 occurred, the resultant wave isfai.substantially.7 amplitudemodulated wave; meansion recoveringethe .fmodulation envelope` of' .said last-named1 resultant wave; and: means, receptive ofi :sa-id modulation envelope, .for .sotuning the. source of said? carrier .wave-as to compensate lfor said'frequency drift.

`4. Apparatusg-for stabilizing the frequency-*of at carrier wave-comprising; meansfor amplitude modulating a portionA of said carrier wave; meansfor shifting the `phase-of vanother portion of said carrier: wave through an-.angle-l off90; means,v responsive: te any v`drift Sinthe frequency of' .saidfcarrier waye;for altering; .the pha'senof #laude-vof." saidfrequencyfdrit; r means for'recoverin'g :'said modulation envelope; 'means for combining said modulation envelope with a\portion' Iof said initially, applied modulation toobtain -a unidirectional'f output whose sense andimagnit'ude like- Wise-depend', respectively, onthe sense and-"magnitude otsaidl frequency drift.; and means, .receptive of said unidirectional Wave, for :so tuningfthe source of said carrier wave as to com- ,pensatefifcr said frequency drift.

#5; Apparatus for maintainingy a-ixed relationship-between thefrequency of a `carrier waveand aselected reference frequencyv comprising: :an energy-transmission system, receptive of.' said' carrier. wave, and having a plurality of branches extending frfomia common junction; means, terminating aV firs-.tofy said. branches, for-amplitude modulatingv` that.. portion cfsaid. carrier wave entering--thesa-me; atuned circuit, resonant, to said selected reference frequency, terminating -a-.second of said-branches; said first and second branches being ofsuch lengthsythatthe difference therebetweeny isi equal. to

where an odd integer and )i is theW-avefguide wavelength corresponding to saidgselected referencefrequency., whereby, at said common junction, said amplitude-modulated portion of said carrier. waveand that portion of-fsaid-carrer wave reflected from said tuned circuit are 90o out of phase; means, terminating a third of said branches, for combining said amplitude-,modulated .and reflected portions of *.saidcarrierwave whereby, in the event theaforesaidl xed relationship between the frequencyl of:l saidcarrier Waveland said selected reference frequency has been maintained, `tlie'resultant wave-isa substantiallyconstant-amplitudewave, and; inthe event saidfixed relationship has.v been altered; theresultant wavel isa substantially amplitude-modulated wave; means for recovering the ln-iodulationenvelope of,saidwlast-namedv resultant wave; and meansreceptiveof saidmodulation envelope,

l for so A'tuning f the.A source of. saidfcar-rier-fwave as to reestablishy saidxed relationship.v betweenv the frequency of saidcarrierwave and. saidy Iselected reference'frequency.

6; Apparatus.. for maintaining-la ,iixed Arelation- ,shipfbetweeni the frequency of atcarrier. wavefand la. selected reference frequency comprising: a

waveag-uide, receptive of said. carrier wave, and

,having` all plurality,- of` branches extending from a common; junction; means, terminating a first of,` said branches-and includingfavsourcerof mod- 0 ulation and a4 mixerl adaptedv to.l be.- energized thereby, for vamplitude modulating that portion -ofr said carrier Wave enter-ing the-same; a cavity resonator, ,resonantto said selectedreference frequency, terminating` a .second of said branches; said first and second branches being5 of.-. such ,lengths-that :the difference.A therebeftvveenfv is :equal where n .isj aniodd integer and` NlistheWai/.ev-,gllde Wavelengthvcor-responding to: said selected reference frequency, whereby, at sa-idcommcn'junction,.said amplitude-modulated .portion of said carrier waveA and4 that portion of saidcarrier wave reectedfrom said cayityresonatoraiie" out` of phase; means, terminating va:thirdfof'said branches andincluding a secundfmixer, `forcom bining said amplitude-modulated, andv reflected portions of said carrier wave whereby, in the event the aforesaid. xed relationship between the frequency of said carrier, wave ,and.,said selected. reference frequency has Ybeen maintained, the resultant wave is ,a substan,tiallyY constant- 2i' amplitude wave, and, in the event `said xed relationship has been altered, the resultant wave is a substantially amplitude-modulated wave; means for recovering the modulation envelope of said last-named resultant wave; and means, receptive of said modulation envelope, for so tuning the source of said carrier wave as to reestablish said fixed relationship between the frequency of said carrier wave and said selected reference frequency.

'7. Apparatus for maintaining a fixed relationship between the frequency of a carrier wave and a selected reference frequency comprising: an energy-transmission system, receptive of said@ carrier wave, and having a plurality of branches extending from a common junction; means, terminating a first of said branches, for amplitude modulating that portion of said carrier wave entering the same; a tuned circuit, resonant to said selected reference frequency, terminating a. second of said branches; said first and second branches being of such lengths that the difference therebetween is equal to 2 where n is an odd integer and X is the wavenitude of the latter amount depending, respectively, on the sense and magnitude of the deviation from said fixed relationship; means, terminating a third of said branches, for combining said amplitude-modulated and reflected portions of said carrier wave whereby, in the event said fixed relationship has been maintained, the resultant wave is a substantially constant-amplitude wave, and, in the event said fixed relationship has been altered, the resultant wave is a substantially amplitude-modulated wave, the phase of the modulation envelope of said lastnamed resultant wave, relative to the modulation initially applied to said carrier wave, and the magnitude thereof, depending, respectively, on the sense and magnitude of said deviation from said fixed relationship; means for recovering said modulation envelope; means for combining said modulation envelope with a portion of said initially applied modulation to obtain a unidirectional output whose sense and magnitude' likewise depend, respectively, on the sense and magnitude of said deviation from said xed relationship; and means, receptive of said unidirectional output, for so tuning the source of said carrier wave as to reestablish said fixed relationship between the frequency of said carrier Wave and said selected reference frequency.

8. Apparatus for maintaining a fixed relationship between the frequency of a carrier Wave and a selected reference frequency comprising: a wave guide, receptive of said carrier wave, and having a plurality of branches extending from a common junction; means, terminating a first of said branches and including a source of modulation and a mixer adapted to be energized thereby, for amplitude modulating that portion of said carrier wave entering the same; a cavity resonator, resonant to said selected where n is an odd integer and A is the wave-guide wavelength corresponding to said selected reference frequency, whereby, at said common junction, said amplitude-modulated portion of said ,carrier wave and that portion of said carrier wave reflected from said cavity resonator are 90,0 out of phase if the aforesaid xed relationshipy between the frequency of said carrier wave and said selected reference frequency has been maintained, and a diiferent amount if said fixed .relationship has been altered, the sense and Amagnitude of the latter amount depending, re-

spectively, on the sense and magnitude of the deviation from said fixed relationship; means,

terminating a third of said branches and including a second mixer, for combining said amplitude-modulated and refiected portions of said carrier wave whereby, in the event said xed relationship has been maintained, the resultant wave is a substantially 'constant-amplitude rvwave, and, in the event said xed relationship has been. altered, the resultant wave is a substantially amplitude-modulated wave, the phase of the modulation envelope of said last-named resultant wave, relative to the modulation initially applied to said carrier wave, and the magnitude thereof, depending, respectively, on the sense and magnitude of said deviation from said fixed relationship; means for recovering said modulation envelope; means for combining said modulation envelope with a portion of said initially applied modulation to obtain a unidirectional output whose sense and magnitude likewise depend, respectively, on the sense and magnitude of said deviation from said xed relationship; and means, receptive of said unidirectional output, for so tuning the source of said carrier Wave as to reestablish said fixed relationship between the frequency of said carrier wave and said selected reference frequency.

9. Apparatus for stabilizing the frequency of a carrier wave comprising: means for amplitude modulating a portion of said carrier wave, a tuned circuit having a resonant frequency with respect to which it is desired to maintain the frequency of said carrier wave in a xed relationship, said tuned circuit being receptive of another portion of said carrier wave to produce a reflected wave whose phase and magnitude are functions, respectively, of the direction and magnitude of any deviation of the frequency thereof from that desired of said carrier Wave; means, receptive of said amplitude modulated portion of said carrier Wave and said reflected wave, for detecting the phase of said reected wave and deriving a unidirectional control voltage whose direction and magnitude are, likewise, functions of said frequency deviation; and means, receptive of said control voltage for tuning the source of said carrier wave to compensate for any such frequency deviation.

10. Apparatus for stabilizing the frequency of a carrier wave comprising: means 'for amplitude modulating a portion of said carrier wave, a cavity resonator having a resonant frequency with respect to which it is desired to maintain the frequency' of: said carrier WaveA in= a: fixed relationship, said cavityl resonator lceing'l receptive of i another portion of said carrier wave to produce a reected Wave whose phase and magnitude are functions, respectively, of the direction and magnitude offt any deviation of the frequency thereof from that desired of said carrier Wave; means, receptive of said: ampliftnde modulated portion of said carrierv Wave and said reflected Wave, for detecting the phase of' said reflected wave and deriving a unidirectional control voltage Whose' direction and'magnitudev are, likewise, functions of said frequency deviation; and means, receptive of said control Voltage for tuning the source of said carrier wave to compensate for any such frequency deviation.

11. Frequency-stabilizing apparatus comprisingz'avsource of" relatively high-frequency oscillations; a source of relatively 10W-frequency oscillations; a circuit, receptive of said relatively high andI 10W-frequency oscillations., and in,- cluding a cavity resonator having. a resonant frequency with respect to which itV is desired to maintain the frequency of said high-frequency oscillations inl a fixed relationship, for modulating said high-frequency oscillations with said 10W-frequency oscillations to producefa modulated wave the phase and magnitude of' whose modulation. envelope are nmctions;v respectively,

the direction, andgf-magnitude of,l any deviation ofwthe'fftrequency off said high-frequency oscillations; fromitnat desired-thereof; means, receptive of, said Vmiocli-ilateczl` Wave, .for recovering said y modulation envelope; means', receptive `ofr said modulation"envelope-anda portion of7 the` output of'saidfisource` of relatively lowwfrequency oscillations, for comparing the phases tlfieieof*z and deriving therefrom-faiunidirectional control voltl REFEREN(JESy CIT-ED The following references are of record in the le of this patent:

UNITED STATES PATENTS Num-her Name Date 2.1051096 Peterson` v Jan. 1 1, 1938 2,3,12QQ'Z9 Crosby Feb. 2 3, 1 943 v2i101'l Ginzton Nov. 12, 1946 Certificate of Correction Patent No. 2,486,001 October 25, 1949 GEORGE G. BRUCK ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 1, line 47, after the Word cavity strike out the comma; column 6, lines 67 and 68, for that portion of the equation reading and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 21st day of February, A. D. 1950.

THOMAS F. MURPHY,

Assistant Uommz'ssz'oner of Patents.

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