US2415088A - Radio direction finder - Google Patents

Description

e. 4, 1947. E. N. DINGLEY, JR 2,415,08

RADIO DIRECTION FINDER Filed Dec. 16, 1938 PHASE IIY-DICBTOJE Jh-EECE/VER RECEIVE/ 55 57w PHASE [IVE/6737112.

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INVENTOR EDWARD N. DINGLEY JR.

BY m

Patented Feb. 4, 1947 UNITED STATES PATENT OFFICE aamo DIRECTION FI DER- 7 Edward N. Dingley, Jr., Arlington, Val Application December 16, 1938, Serial No..246,109

8 Claims.

My invention relates broadly to radio direction finder systems by means of which the direction of arrival of radio waves may be determined accurately.

My invention relates chiefly to circuit arrangements in which the phase difierences between the voltages induced in a plurality of immobile wave collector systems is indicated.

One of the objects of my invention is to provide a radio direction finder system by means of Which the direction of arrival of radio waves may be determined regardless of the polarization of such waves and regardless of th vertical angle of incidence of such waves.

Another object of my invention is to provide means by which the phase difierences of the voltages induced in a plurality of collector systems is indicated thus making it possible to determine both thetrue azimuth and the vertical angle of incidence of the wave which induced the saidvoltagesinthe said collectors.

Still another object of my invention is to provide a radio direction finder system which will be capable of determining accurately the direction of arrival of radio waves having any frequency used in radio communication and to achieve this objective without the necessity of rotating or moving the collector system. i 1

' Other and further objects of my invention will be understood from the following specification and by reference to the accompanying drawing in which:

Fig, 1 diagrammatically illustrates a fundamental circuit arrangement of 'myinvention.

Fig. 2 diagrammatically illustrates a modified circuit arrangement of my invention.

Fig. 1 illustrates one embodiment of my invention wherein the vertical antennas, or collectors i, 2; 3, 4 and 20 are mounted in fixed relation to the earth; Antennas I, 2 and 20 lie in a vertical plane which is perpendicular to the vertical plane containing the antennas 3,4 and 20. Antennas H2, 3 and 4 are equidistant and not more than one -half wave length from antenna 20 and are respectively connected to the antenna tuning units 9, I0, I l and [2, which are respectively connected to the radioreceivers l3, l4, l5 and I6, bymeans, respectively of the transmission lines 5; 6,-1"and B. The audio output circuits of receivers l3 and Ill are connected to the phase indicating device U and the audio output circuits of receivers I 5 and I6 are connected to the phase indicating device I85 The source of radio frequency energy,"oscillator I9, is connected to the antenna which'serve's to radiate said energy.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 O. G. 757) The circuits of radio receivers l3, l4, l5 and [6 are not shown for the reason that any type of radio receiver such as a common broadcast receiver used for home "entertainment capable of receiving a modulated radio frequency signal and of delivering at its output terminals the detected audio frequency component thereof will serve the desired purpose and such receiver circuits are well known to .the radio art. i

The audio frequency amplifier circuits ,of the radio receivers should be matched, that is, a si nal of any audio frequency between the approximate limits of 300 to 4000 cycles per second should encounter equal phase shifts in transversing each audio frequency amplifier. This requirement may be fulfilled by mean well known to the art;- The circuits of the antenna tuning units 9, II], II and I2 are not shown for the reason that any type of tuning unit will serve1 the purpose; or the tunin units may beomitted with some sacrifice ofsige.

nal strength, and such tuning units-are likewise well known, as for example those described in the Proceedings of the Institute of Radio, Engineersgt volume "23, November 1935, pages 1268 to 1307.

The circuits of the oscillator l9,are not shown.

for the reason that any well knowntype of oscil lator capable of delivering a few microwattsof; radio frequency energy to the antenna 20 will.

serve the desired purpose. v

q The antennas I, 2, 3 and 4 may be at distances greaterthan one-half wave length from antenna 20 but'fsuch spacing results in multiple bearings As used. herein, at ,two spaced points? is defined as meaning approximately one-half wave length but preferably less than one-half wave length of the highest operating frequency.

- In the following, the wave originat ng at a dis tant pointythe azimuth of which is to be'deterj mined, willhe'tenn'edthe fdistant wave.

In order to demonstrate the advantages of my invention as compared to well known types of direction finders'utilizing immobile antennas, it .is desirable to show wherein, large errorsare produced in the well known types, by waves which arrive not along the ground siderably elevated above the horizon.

In practically all of the well kn'o'wn types of direction finders using four immobile antennas, as for example those described in the Proceedings of the Institute of Radio Engineers, volume 17, March 1929, pages 425 to 478; the'transmission'line 5 is transposed and connected in'pai allel with transmission line 6 and a} means "is provided to measurethe' voltage produced "at their junction.- This'voltageis proportional'tobut at angles con the difference between the voltages induced in antennas I and 2 provided that the impedances of the two antennas and of the two transmission lines are identical, a condition difiicult of achievement. In the same manner, the voltage between the junctions of transmission lines 1 and 8 is measured; Inthefollowing let:

Etiuation 'Tindicates that if the spacing'a is fixed; if "the azimuth z isfixedjand if the angle of '"incidencdh is variable; the ratio M willnot be a'constant exceptwhen'the azimuth '2 is 45 de-. grees or'any-multiple thereof. In the well known typeset directionfinders utilizing the aforestated .prin'cipIatheaZimuth of the wave is determined b y 'theratio It has "been demonstrated that for*a* given azimuth other than multiples 'of 45 degrees; M varies with. the angle ofincidence h and "because "h isiunknown, the direction finder. cannot be "calibrated .to eliminate these. errors.

This variation results inserious. errors of .in-. dicated; azimuth unlessth'ejpacing .0.is..made.. very small'under which conditions the..voltages.

e1-ez and 83-64 become very smalland the sensi- D tivity.of.'the directionfinder .is thereby greatly reduced. Furthermore. Equations l'thr'ough. '7 are based onthe assumption thatthe-impedances. of. allffour antennas and. of. all. four transmission liiiesareequali. Since this condition: is not usually attainable overwidatuning ranges, the magnitudes and .phases .of the voltages delivered from the tfansmissidndines -will ;not-.-be-.equa1ly., proportio'naldto. ttfeimagnitudes andphases ofthe voltages .indii'cedi in.. the. antennas. 1 Equations 1 through'...7demonstrate that such a. lack .of pro-f porti'bnality= williproduce .largeerrors in the value oLM 'andborrespondi'ng large errors in: theindi-.. cated-lazi'rhuthionbearing My invention, assdescribed-hereinafter, elimi.-- nates the errorsand.disadvantages,asrabove-set forth.-. by providing. a. direction .finder. system which-sdoes snot .requireethat the antennas and transmission! 'linesqhaveiidentical: characteristics. Thisiis accomplished: :byq introducing the energy 1 derived from-.zthe sheterodyningaoscillator I 9 into the-.antenna 'of each radio receivers-instead of into the receiver itself. Introducing- .theheterodyning. signalaat=tha antenna subjects-the heterodyning signal mos-essentially. theesame :attenuation and.

phase shift as is encountered by the distant wave or signal in traversing the antenna and transmission line because the two signals differ in frequency by only a fraction of a percent or by 300 to 4000 cycles per second in a total of 1000 to 100,000 kilooycles per second.

If two waves .or signals such as. Ensin (wt+1) and Ed sin .(Pt+2) are combined and detected or demodulated, their difference-frequency signal will be It is to be noted that the phase of the differencefrequency signal is determined by 51- 02. If #11 and z..are both increased or decreased by the same number of electrical degrees, the phase of the: difference-frequency signal remains unchanged- It is;for.this reason that the antenna, the transmission line or the radio receiver, being traversed. simultaneously. by, the heterodyning signal. (Em and by thedistant .wavecr signal. (Ed). may be -tuned Lentirely through resonance. without increasing or decreasing the phase of the.

difference-frequency. signal. from the.value .it

would have had it bothradio frequency. signals hadencountered-.no-phase shift at all... The only result of 'mis-..tuning theantenna, trans! mission line or-radi'o' receiver is.a.loss of detected signal magnitudeas would be'expected.

The last-stated formulae also prove that if the phase (2) of .the distant signal. in..increased .orv decreased. by a given amount, due toa change in. azimuth of the distant source, while1 remains.

fixed, then the phase oithe difference-frequency signal is increased or decreased'by. the same.

amount.

In my invention the phase (1). of the heteroe dyning-signal isheldQconstant and equal-at each.

of the four antennas l, .2, 3 and 4 of Fig. l-by radiating the signalirom an: antenna. (20 of Fig.

1) which. is..located=at a point-equidistant from the aforesaidfour antennas.

If all-time and-spacephases are measuredwith.

nals (audio output signals) oftwo receiverssuch.

as-l3 and I 40f Fig.4, willlbe exactly equal to'the phase difference between the. radio. frequency voltages-induced, on.their-antennas 1 and .2 of.

Fig. 1. by the distant wave or signal.

In consequence of.the foregoing, Equationstl through 4, whichnwerexdefinedin termsof the radio frequency voltages induced in antennas l,

2, 3 and 4 bythe distant wave. apply with equal rigor to the audio.output voltages delivered by the receivers I3, l4, l5 and I6, except that the magnitudes of theaudio voltages will be altered: and will not necessarily'be equal to each other: and except that wt-isnow taken to represent the instantaneous :phase Lat. the timei of the audio. output. of. a receiver which 'might be connected: to antenna:20.- No receiveris'connectedto 'antenna-20; this (point. is .used solely forreferencet phase.

.dicates the phase-angle between. es. and c4.

5 In Equations 1 through 4, the instantaneous phase of e1 is 1=(wt+0 cos 2 cos h) and the in stantaneous phase of e; is ca: (wtcos 2 cos h) and therefore the phase difierence between c1 and c2 is:

12=20 cos 2 cos h (8) And the instantaneous phase difference between es and 84 is:

a4=20 sin 2 cos h (9) And the ratio of on to p is:

qb sin z 2 tan 2 (10 Equation 10 demonstrates that when using my invention, it is only necessary to observe the phase angle cm as indicated by the device l8, and to observe the phase angle 12 as indicated by the device H, to divide cm by on and to find the angle 2 whose tangent is equal to this quotient in order to determine the azimuth z with great accuracy. The values of the spacing 0 and of the angle of incidence h, do not enter into this determination. Furthermore, having thus determined the azimuth 2, its value may be substituted in either Equation 8 or in Equation 9 and the value of the angle of incidence h may thus be determined if desired.

Figure 2 illustrates another embodiment of my invention wherein the vertical antennas 52, 53 and B0 are mounted in fixed relation to the earth. Antennas 5|, 52 and 53 are equidistant from antenna 60 and are spaced 120 arc degrees from each other. The antennas 5|, 52 and 53 are connected to the radio receivers 54, 55 and 56 respectively by means of transmission lines and antenna tuning units which are identical to those described in connection with Figure l. i The audio output circuits of receivers 54 and 56 are connected to the phase indicating device 58 and the audio output circuitsof receivers 55 and 56 are connected to the phase indicating device 51. The source of radio frequency energy (oscillator) 59 is connected to the antenna 60 which serves to radiate said energy. The oscillator 59 is identical to the oscillator I9 of Figure 1. The radio receivers and phase indicating devices of Figure 2 are identical to the radio receivers and phase indicating devices described in connection with Figure l.

The equations for the voltages induced in the antennas 5!, 52 and 53 (or for the audio voltages delivered by the receivers) are somewhat similar to Equations 1 through 4 as follows:

e1=E1 sin (wt+0 cos 2 cos h) (11) e2=Ea sin (wt-H9 cos [e-120] cos h) (12) e3=Ea sin (wt-+0 cos [z+120] cos h) (13) tan 2: 0.866

Equation 1'? demonstrates that when using my invention, it is only necessary to observe the phase angle 1:1; as indicated by the device 58, and to observe the phase angle 9523 as indicated by the device 51, to divide due by 23, to subtract 0.5 from this quotient and to divide the resultant into 0.866 in order to find the tangent of the azimuth z and from the tangent to determine the azimuth z with great accuracy. The values of the spacing 0 and of the angle of incidence h, do not enter into this determination. Furthermore, having thus determined the azimuth 2, its value may be substituted in either Equation 14 or in Equation 15 and the value of the angle of in-.

cidence h may be thus determined if desired.

The phase indicating devices [1, b8, 51 and 58 may be of any kind or type. The use of certain types requires that the magnitudes of the two voltages must be closely identical. This requirement can be fulfilled by the use of well known types of automatic volume control circuits in conjunction with the radio receivers. Certain other types of phase indicating devices require that the frequencies of the voltages must be nearly constant.

matic frequency control circuits in connection with the radio receivers.

The invention herein described and claimed may be used and/or manufactured by or for the Government of the United States of America for governmental purposes without the payment of' any royalties thereon or therefor.

I claim:

1. A method of determining the azimuth angle between a selected line and the path of an incoming distant radio wave, comprising the steps of collecting energy from said wave at two spaced-- points on said line, determining a first phase angle between the waves at the two said points of collection, collecting energy from said wave at two other points spaced from each other the same distance as are the first mentioned two points and on a line normal to said selected line midway between the first mentioned two points, determining a second phase angle between the waves at the second mentioned two points, determining the ratio between the said second phase angle and said first phase angle, which ratio evaluates the tangent of said azimuth angle, and' waves at said second point and said third point,

determining the ratioof said first phase angle to said second phase angle, which ratio evaluates the tangent of said azimuth angle, and from said tangent determining said azimuth angle.

3. A method of "determining the azimuth angle between a selected line and the path of an incoming distant radio wave, comprising the steps of collecting energy from said wave at a plurality of points symmetrically disposed about a central point, said selected line passing through said central point and at least one of said collection points, determining a first phase angle between the wave at one of said collection points and the wave at a second collection point, likewise deter- This requirement can be fulfilled by the use of well known types of auto- 7 miningza second phaseangle between the waves at a different; two of said collection points, determining the ratio between the said phase angles, which'ratio evaluates a function of the said azimuth angle, and from said function determining the said azimuth angle.

4. A method of determining the azimuth angle between a selected line and the path of an incoming distant radio wave, comprising the steps of collecting energy from said wave at a plurality of points symmetrically disposed about a central point, said selected line passing through said central point and at least one of said'collection points, radiating from said central point energy of a frequency to beat with said incoming wave to produce audio frequency, determining a first phase angle between the audio frequency waves derived from energy collected at two respective said collection points, likewise determining a second phase angle between the audio frequency waves derived from energy respectively collected at a different two of said collection points, determining the ratio between said phase angles, which ratio evaluates a function of the said azimuth'angle, and from said function determining said azimuth angle.

5. A system for determining the azimuth angle between a selected line and the path of an incoming distant radio wave, comprising means to radiate a local wave at a frequency to produce an audio beat frequency with said incoming wave, two collectors equidistantly spaced from said local radiating means on said selected line, means respectively connected to each of said collectors to detect the beat frequency derived from energy of said distant wave collected at each of said collectors, means connected to indicate a first phase angle between the said two beat frequencies, two other like collectors equidistantly spaced from said local radiating means on a line through said local radiating means perpendicular to said selected line, means respectively connected to each of said two other collectors to detect the beat frequency derived from energy of said distant wave collected at each of said two other like collectors, and means connected to indicate a second phase angle between the beat frequencies from said two other collectors, the ratio of said second phase angle to said first phase angle being the tangent of said azimuth angle.

6. A system for determining the azimuth angle between a selected line and the path of an incoming distant radio wave, comprising means to radiate a local wave at a frequency to produce an audio beat frequency with said incoming wave, a first, a second and a third collector disposed equidistantly from said local radiating means and from each other, one of said collectors and said local means lying on said selected line, means respectively connected to each of said collectors to detect the beat frequency derived from energy of. said distant wave collected at each of said collectors, means connected to indicate a first phase angle between the beat frequencies from said first and second collectors, and means to indicate a second phase angle between'the beat frequencies "from said second and third collectors, the ratio of said first phase angle. to said second phase angle evaluatingthe tangent of said azimuth angle.

7. A system for determining the azimuth angle between a selected line and the path of an incoming distant radio wave, comprising means to radiate a local wave at a frequency to produce an audio beat frequency .with. said incoming wave, a plurality of collectors symmetrically disposed around said local radiating means, said local radiating means and at least one of said collectors lying on said selected line, means to detect the beatfrequency derived from energy of said distant wave collected at each of said collectors, means connected to two of said detecting, means to indicate the phase angle between the beat frequencies detected thereby and means connected to another two of said detecting means to indicate the phase angle between the beat frequenciesdetected thereby, the ratio of one of said phase angles to the other evaluating a function of said azimuth angle.

8. A system for determining the azimuth angle between a selected line and the path of an incoming distant radio wave, comprising means to radiate a local wave at a frequency to produce an audio beat frequency with said incoming wave, a plurality of collectors disposed around said local radiating means equidistantly from said radiating means and from each other, said local radiating means and at least one of said collectors lying on said selected line, means to detect the beat frequency derived from energy of said distant Wave collected at each of said collectors, means connected to two of said detecting means to indicate the phase angle between the beat frequencies detected thereby, and means connected to another two of said detecting means to indicate the phase angle between the beat frequencies detected by said other two detecting means, the ratio of one of said phase angles to the other evaluating a function of said azimuth angle.

EDWARD N. DINGLEY, JR.

REFERENCES CITED The following references are of recordv inthe file of this patent:

UNITED STATES PATENTS British Jan. 20, 1937

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