US2548836A - Electromagnetic field phase determining apparatus - Google Patents

Description

April 1951 H. R. WORTHINGTON, JR 2,543,336

ELECTROMAGNETIC FIELD PHASE DETERMI NING APPARATUS Filed July 9, 1945 FIG.|

"\ l2 l4 l3 *1 OSGlLLATOR L 2| VARIABLE 22 \ATTENUATOR 24 32 3| AMPLIFIER 4s 42 44 43 x v A 2 2 OSCILLATOR I r 52 AMPLIFIER /45 54 M 55 AMPLIFIER e2 FIG.2

INVENTOR HARVEY R.WORTHINGTON, JR.

ATTORNEY Patented Apr. 10, 1951 v PATENT-"MPEG5 ELECTRdMAGhlETIC FIELD PHASE 1 .l DETERMINING APPARATUS Harvey R". Worthington; a; Cambridge, Mass., A a'ssig'r'ior, by -mesne"assignrrients ;to the" United States of America as represented-by the Secrefiarypfwar 1 "sin pt :r-f," 11'. 1 l

" AimfilicationJuly 9, 1945, Serial No. 504,032

1 2 This invention relates to electrical apparatus and Robert H. Dicke, S. N. 581,695, filed March and-moreparticularly to apparatus used in rela- 8, 1945, and- S} N l 586,413fiiled April 3, 1945 The 'tive phase measurementyand determination of magic-T is also described -on pages; 306-308 of surfaces-having a wavefront of" unifdrm' phase in Principles of Microwave Circuits by C. G. electromagneticenergy"radiating devices. 5 Montgomery, 'RTH; Dicke and E. M. Purcell. A Inthedesignof electromagnetic energy radiatmagic-T has -four waveguide branches; the first ing elements it -isdesirableto be 'abletoexphre two branches bing'colinear, the third being per- -"and-plot'the uniform phase wavefront of the enpendicular to the first two branches, and the ergy emanating therefrom. 'Suclrplotsof uni-.l {fourth "branch bemg e pnaieuiar 't'othe-plane form phase wavefront aid in the design of the '10"forrned by'thedther'threebranches. Kpickup radiating element "and of its point and 'inanner section of line 23- iscdiinted tdtheT InZagic-T of feed; I H 22 at one end and'thfree end thereof is used An object of the present invention is, theref0re','-"' to explore the wavefront surfaces? f th ttoprovide'an electrical device for e tploring "with'a 'ingelernent" [3. The pickup line 23 Inaybe mehigh degree of se'nsitivityand accuracy-the elec-rs chanically adapted to be moved" in a are or tromagnetic wavefront surfaces surrounding a straight line as desired. A'square law type deradizitingelenient. tector 24, preferably-ofthe siliconcrystal type,

' For abetter understanding or the invention, tois inserted in one branch of the magic-T 22 in gethe'r withother and further objects thereof, ---su'ch a manner'asto receive energyfrom line I5 "reference is" bad t'ojthe= following descriptio -26 and line 23.' The remaining branch of the "taken 'in" connection 'with the "accompanying". f i gi i r 221 t t rm t ma h d 2 5 drawing in which: 5 "The dotted portion'26 of the line; l5, Fig". 1, in-

Fig. 1 shows schematically one embodiment of dicates that line l5is very' long compared 'to line =a phasameasuririg device; *and l2 plus line 23. The detector 2 ifeeds an -ampli- Fig; 2' shows another embodiment of a phasefggfier 3| which inturncontrols the vertical deflecmeasuring device; f t'ion-of a cathode ray oscilloscope. The saw- Referring now particularly to Fig. 1 of the tooth-sweepvoltageof the oscilloscope 32 is fed drawingthere is 'shown a phase measuring de-j to theoscill'atorll in such a manner asit'o provicev'vhich comprises-an*oscillator H which feeds duce frequency modulation of' this oscillator.

radio frequency energy through a transmission so In the operation of the device'of Fig. 1 energy line I2 to a radiatingflment -13. he 1ine"l2 '-fromthe "oscillator ll travels through line l2, maybe open wire, coaxiaPor-waveguidedepend- A 'element"l'3," the 'free space between element 13 p n the frequency f he oscillator H1 The" and line-23, a'rid'lin 2'3, and arrives more detector radiating element [3 is any desired type oli-radi-" 24; The total p'a'thlength enumerated above will -ator, dipole; horn; p'arabol'ai -etc.',--the' wavefront bedes'ig'na'tedDl. At the same time energy from surfaces of which it is desired to investigate.- The the oscillator ll arrives at the detect or"24 via line 12 is provided with-a'phase shifter' l4 and coupler lli an'd unezs. The lengthof'this path connects to a second similar transmission line"' is denoted D2.

t -l5by means of a direction coupler l6 which may With'the pickup section 23 at some fixed point be-a waveguide section having twoirise's spaced {and at a particular frequency f the phase 's'hifter so'as to x'natch line I5 to line 12am permit en "I4 canbe'adjusted so that the energies arriving E e'rgyfrom oscillator llto'be' coupled to line 15, i 'a't the detector "24 are 180 out of phaseithe reyet not permitenergy from radiating element I3f sultbeingthat'the' output of the detector 24 will -'to-be' coupled to 1inel5'. Any-other of the sevbe fa minimum and hence the defiectionof the eral well known'types of directional couplers mayiis oscilloscope 32' will be a mini mum. It is well be used. Direetional coupler l6 isdisposed inknown that if two energies of the same frequency "termediate the oscillator H and radiator l3. The" a're c'ombinjed,theamplitude of the resultant is -line-t5 is provided with-a-fiap-typ'e attenuator 2| dependent'upon'the relative phases of the two and connects to one branch of a magic-T 22. A" energies}Furthermore it will be noted'that if the magjcaT is a-well-known type ofmatched direc- 50 relativepha se of the two energies is varied contional coupler for microwaves and is an a'na-1og-uef tihub-dsly; and linearly with timethrough one *ofthe'hybrid coil" used forlo'w'frequenci'es'. The'com'pltecycle, the output of the detector will magic-T coupler is described in the following vary sinusoidally withtime; T0 accQl ripl h this pending applicationsz *R'obertL. KyhlfS. N. "variation'of relative phase itlis" propos ed toyary --580,014,-filed' l ebruary'27;1945,"now abandoned, bathe-oscillator 'frequency linearly With time. It

can be shown that the relative phase between two energies at the ends of two lines of length D1 and D2, where the difference of D1 and D2 is denoted by L, is given by:

In the above expression A is the change in relative phase of the energies at the ends of the lines of length D1 and D2, AI is the change in frequency which brought about the change in relative phase, j is the initial frequency, L is as specified above and Ag is the electrical wavelength as measured within the transmission line. Equation 1 can be simplified to the following expressions:

and for rectangular wave guides to (4) 2'n'LAf In the above equations, in addition to the symbols already designated, A is the wavelength in air, C is the velocity of light and a is the broad dimension of the rectangular guide.

As before stated, if the relative phase of the two energies is varied through one cycle, the output of the detector will complete a one-cycle variation. Therefore, by setting in Equation 3 or 4 above, a solution may be obtained for either the length L, which is the difference of D1 and D2, or M, the frequency change. One of the two dependent variables must of necessity be chosen arbitrarily.

It can be seen that the frequency of the sinusoidal output of the detector depends upon the modulation frequency of the oscillator The sweep voltage of the oscilloscope 32 is used to modulate the oscillator with the result that one complete sine wave will be observed in the oscilloscope.

If now the pickup section of line 23 is moved, the shift of the oscilloscope pattern will indicate the change in phase in the field of the radiating element. If the pickup section 23 is moved in such a manner as to prevent movement of the oscilloscope pattern, the movement will be along a uniform phase wavefront surface.

Referring now to Fig. 2 there is shown an improved phase measuring device which comprises an oscillator 4|, similar to oscillator H, which feeds radio frequency energy through a transmission line 42, similar to line l2, to a radiating element 43, similar to element 3. The line 42 is provided with a phase shifter 44 and is connected to a second transmission line 45 by means of a directional coupler 46. The line 45 is provided with a standing wave detector 5| and connects to a mixer 53 by means of directional coupler 54. An iris 55 is inserted in the line 45 at point C to provide reflection therefrom. The dotted portion 56 of line 45'indicates a very long line. A pickup section of transmission line 6| is adapted to be moved in the field of the element 43 to permit investigation of the constant phase patterns. The line 6| connects to the mixer 53. The output of the mixer 53 feeds through an amplifier 62 to the horizontal set of deflection plates of a cathode ray oscilloscope 63. The output of the standing wave detector 5| feeds through an amplifier 64 to the vertical set of deflection plates of the oscilloscope 63. Sweep voltage from the oscilloscope is fed to the oscillator 4|.

The operation of the device of Fig. 2 is similar fundamentally to that of the device of Fig. 1 and therefor only the points of difference will be discussed.

Energy from the oscillator 4| passes via the two paths hereinbefore described to the mixer 53. If the frequency of the oscillator changes in accordance with the previous discussion, the output of the mixer 53 will be a voltage of sinusoidal waveform. The phase of this result sine wave is dependent upon the phase plane in which the pickup line 5| lies. It is desired to obtain a reference sine wave having the same frequency but which is independent of the position of the pickup line 6|. With the pickup line 6| in a fixed position, which will be taken as the reference position, there exist two points A and B at which energy from the oscillator 4| exhibits the same properties as at A and B at the mixer 53. The distances A to A and B to B are equal. There also exists energy at a point A" which has all the properties of the energy at point A, A and A" being equidistant from the oscillator 4|. The iris 55 is placed at a point C which is equidistant from point A" and point B. The energy which is reflected from the iris 55 will arrive back at B with the same properties it would have had at B. As a result of the foregoing, there appear at the standing wave detector 5| two energies whose relative phases are not dependent upon the position of the pickup line 6| but which behave in the same manner as the energy at the mixer 53 to produce a voltage which is sinusoidal. When the pickup line BI is in the reference position, the outputs of the mixer 53 and detector 5| will be in phase and the resultant pattern in the oscilloscope 63 will be a straight line. When the pickup line BI is moved and does not remain within a surface having a wavefront of uniform phase the oscilloscope pattern will become an ellipse. lhe standing wave detector 5| can be moved to reduce the ellipse to a straight line and the amount of the deviation can be read from a calibration on the detector 5|.

While there has been described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention.

What is claimed is:

1. A phase measuring apparatus comprising, in combination with a cathode ray oscilloscope and a radiating element, a variable-frequency oscillating means, means connected to said oscillating means for varying the frequency thereof repeatedly and linearly with time, first transmission means connecting said oscillating means to the radiating element, a magic-T having two symmetrical and two asymmetrical branches, mixer means inserted in one of the symmetrical branches of said magic-T, matched loading means terminating the remaining Symmetrical branch of said magic-T, second transmission means connected to one of the asymmetrical branches of said magic-T, directional coupler means for connecting said first transmission means to said second transmission means, third transmission means connected tothe remaining asymmetrical branch of said magic-T and movable with respect to said radiating element and in the field of the radiating element for exploring the wavefronts of said field, and amplifier means connecting the output of said mixer means to the oscilloscope whereby indications of surfaces of uniform phase in the field of the radiating element may be observed thereon.

2. A phase measuring apparatus comprising, in combination with a cathode ray oscilloscope and a radiating element, a variable-frequency oscillating means, means connected to said oscillating means for varying the frequency thereof repeatedly and linearly with time, first transmission means connecting said oscillating means to the radiating element, second transmission means, first directional coupler means for connecting said first transmission means to said second transmission means, mixer means, third transmission means connected to said mixer means and movable with respect to said radiating element and in the field of the radiating element for exploring the wavefront thereof, second directional coupler means for connecting 'said second transmission means to said mixer means, standing wave detector means coupled to said second transmission means, reflector means in said second transmission means intermediate said standing wave detector means and said mixer means, first amplifier means connecting the output of said mixer means to the oscilloscope, and second amplifier means connecting the output of said standing wave detector means to the oscilloscope whereby indications of surfaces of uniform phase in the field of the radiating element may be observed thereon.

3. A phase measuring apparatus comprising, in combination with a cathode ray oscilloscope and a radiating element, a variable-frequency oscillator, mixer means, first transmission means for applying signals from said oscillator to said radiating element, second transmission means movable with respect to the radiating element and in the field of said radiating element for exploring the said field and for receiving and ap-- plying said signals to said mixing means, third transmission means for applying signals from said oscillator to said mixer means directly, and means for connecting the output of said mixer to the oscilloscope whereby indications of wavefronts of uniform phase in the field of the radiating element may be observed thereon.

4. A phase measuring apparatus comprising, in combination with a cathode ray oscilloscope adn a radiating element, a variable-frequency oscillator, mixer means, first transmission means for applying signals from said oscillator to said radiating element, second transmission means movable with respect to the radiating element and in the field of said radiating element for exploring the said field and for receiving and applying said signals to said mixer means, third transmission means for applying signals from said oscillator to said mixer means directly, means for connecting the output of said mixer to the oscilloscope, standing wave detector means coupled to said third transmission means, reflector means in said third transmission means intermediate said standing wave detector means and said mixer means, and means for applying the output of said standing wave detector to the oscilloscope whereby indications of wavefronts of uniform phase in the field of the radiating element may be observed thereon.

5. A phase measuring apparatus comprising, in combination with a cathode ray oscilloscope and a radiating element, an oscillator, mixer means, first transmission means for applying signals from said oscillator to the radiating element, second transmission means for applying signals from said oscillator to said mixer means, third transmission means connected to said mixer means and movable with respect to the radiating element and in the field of the radiating element for exploring the wavefronts of said field, means connected to said second transmission means for varying the relative phase of the signals arriving at said mixer means from said second and third transmission means repeatedly and linearly with time, and means for applying the output of said mixer means to the oscilloscope whereby indications of surfaces having a wavefront of uniform phase in the field of the radiating element may be observed thereon.

6. An electromagnetic field mapping apparatus comprising a variable frequency oscillator, a radiator, mixer means, means for coupling said oscillator to said mixer means and said radiator, a'radiation receiving probe movable with respect to said radiator and. from point to point in the field of said radiator, means connecting said probe to said mixer means, means connected to said oscillator for varying its frequency cyclically, to thereby produce an alternating current at the output of the mixer means, and a phase indicating means connected to the output of said mixer means, whereby a wavefront of the field of said radiator may be determined by moving the probe over a surface in the field of the radiator without changing the phase of the alternating current output of the mixer means.

'7. An electromagnetic field mapping apparatus comprising a variable frequency oscillator, a radiator, mixer means, a first means for coupling said oscillator to said mixer means and said radiator, a radiation receiving probe movable with respect to said radiator and in the field of said radiator, second means connecting said probe to said mixer means, a cathode ray tube oscilloscope connected to said mixer means, said oscilloscope including means for cyclically sweeping the electron beam of its cathode ray tube, third means connected to said oscillator for cyclically varying the frequency of said oscillator linearly with time and in synchronism with the sweep of the cathode ray tube beam to thereby produce an alternating current output from the mixer means, said third means varying the frequency of said oscillator throughout a range sufficient to produce an integral number of half cycles of said alternating current at the output of the mixer during each sweep of the cathode ray tube beam, whereby a wavefront of the field of said radiator may be determined by moving the probe over a surface in the field of the radiator without changing the phase of the alternating current output of the mixer means as indicated on the oscilloscope.

HARVEY R. WORTH'INGTON, JR.

REFERENCES CITED The following references are .of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re.21,955 Chaifee Nov. 25, 1941 2,198,113 Holmes Apr. 23, 1940 2,261,272 Newhouse Nov. 4, 1941

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