US2476977A - Radio direction finder - Google Patents

Description

July 26, 194%.

Filed June 24, 1944 P. G. HANSEL RADIO DIRECTION FINDER 1O Sheets-Sheet 3 FIG. 1.

N\ 20 j E fl 2| r-" 5 so 49 41 To 48 r v PATTERN ROTATING DIFFEREN- DIFFEREN- cmcun 3e mrsansw- DIFFEREN- TIATING TIATING Hm vmrms TIATING cnncurr cmcul'r as cmcurr cmcun l 7 AUDIO 1 A, & OSCILLATOR 5a & 5 A

PHASE 9 EGREE PHASE INVERTER PHAEE SPLITTER mvsm'zn BALANCED BALANCED BALANCED BALANCED MODULATOR MODULATQR MODULATOR MODULATOR comamme IMPEDANCE INVENTgfiSEL RECEIVER PAUL H ATTORNEY July 26, 1949, P. e. HANSEL Filed June 24, 1944 FROM OSCILLATOR 2a RADIO DIRECTION FINDER PATTERN ROYATING ae F'G. 2. CIRCUIT 55 /4O 32 PHASE ROTATION CONTROL AMPLIFIER k E FILTER 43 42 r4 8 PHASE PHASE PHASE INVERTER SPLITTER INVERTER 236 VM ,3! BALANCED CONTROL BALANCED I MODULATOR MODULATOR MODULATOR as as [57 BEARING R-F M RIIAsE AMPLIFIER OSCILLATOR sIIIFTER I FROM BLANKING 'Y 58 REcEIvER a1 SIGNAL GENERATOR INVENTOR.

PAUL G. HANSEL ATTORNEY July 26, 1949.

Filed June 24, 1944 I 10 Sheets-Sheet 3 FIG. 3.

E=E SIN U i -REFERENCE FIELD AT CENTER 2| OF ANTENNA SYSTEM 20.

' e h s|N (w 4 g cos a) OUTPUT OF NORTH ANTENNA N.

e =E h sm (u t cos q) -OUTPUT or SOUTH ANTENNA s.

e =e h SIN (m t g- SIN q)- OUTPUT or EAST ANTENNA E,

e =2 h slN (w t 1 SIN q) OUTPUT OF wssr ANTENNA w.

e :A SIN u t -OUTPUT OF A-F OSCILLATOR as;

e =-A,cos u t -UNBALANCED OUTPUTS OF PHASE SPLITTER 29.

a A'SIN u e, =-A2CO8 u t -aALANcso OUTPUTS or PHASE mvzmcn so.

e A3COS u t -BALANCED OUTPUTS OF PHASE lNVERTER 3|.

IN VEN TOR. PAUL G. HANSEL ATTORNEY July 26, 1949.

Filed June 24, 1944 P. G. HANSEL 2,476,77

RADIO DIRECTION FINDER 1o Sheets-Sheet 4 FIG. 4.

=2 h on (I A cos u t) 2 sm (g t 4 cos 0W OF UPPER TUBE OF MODULATOR 2a.

e',, =-s h Gm (|-A,,pos w t) z sm (w t F cos dD-OUTPUT OF LOWER rum: OF MODULATOR 22.

e' =25, h Z A' Fm cos u t sm (w t 1- cos q)- FINAL OUTPUT or MODULATOR 22.

(2' =-E h Gm (n+A pos u u 2 am (u t cos Q)-OUTFUT OF LOWER TUBE OF MODULATOR Z3.

e' mz h Gm (I-A COS u nz sm (mg- 3 coso-ouwm'r 0F UPPER TUBE or MODULATOR 2a.

e as, h z d cm cos u t sm LQ -t- E-Qcos dJ-FINAL ou-rPu-r OF MODULATOR 2a.

e' E h ew a sm u t) z sm (w t a -"5m o-quwur or w rm run: or- MODULATOR a4.

e' e h cm (l-A SlN u t) z sm m n a- 5m m-ou'rwt OF LOWER "rue: OF MODULATOR 24.

A SIN U-FINAL OUTPUT OF MODULATOR 24.

INVENTOR. PAUL c. HANSEL ATTORNEY Filed June 24, 1944 1o Sheet-Sheet 5 FIG. 5.

a -s h Gm clm sm u x) z sm cu 't g sm q )-ou1' PUT OF LOWER TUBE OF MODULATOR Z5.

a, h e o-A sm u n z sm (U tgsm a) OUTPUT OF UPPER was OF MODULATOR 2s.

e =-2 a h l-tA fim sm u t sm (w ti sm Q)-F,INAL OUTPUT or MODULATOR as.

$.21 K cos (oz-w t) cos u t -|NPUT TO RECEIVER 21.

mpur TO almanac mmcrron a2.

OUTPUT OF R-F OSCILLATOR 33.

OUTPUT OF F CONTROL MODULATOR 34.

mmvrok.

PAUL c. HANSEL' ATTORNEY Jy S, 1994. s. HANSEL RADIO DIRECTIOR FINDER 10 Sheets-Sheet 6 Filed June 24, 1944 4 INVENTOR. PAUL G. HANSEL 8 BY z/ WW2 wl ATTORNEY July 26,

Filed June 24, 1944 To RECEIVER 21 P. G. HANSEL RADIO DIRECTION FINDER FIG. 71

l0 Sheets-Sheet '7 ZIVVENTOR.

I PAUL. G. HANSEL ww w br/f ATTORNEY July 26, 1949, P. G. HANSEL RADIO DIRECTION mvww Filed June 24, 1944 10 Sheets-Sheet 8 Ill} ' HANSEL ATTORNEY 3949, P. e. HANSEL 2,4763

RADIO DIRECTION FINDER .Filed June 24, 1.944 10 Sheets-Sheet 9 FIG. 9.

FROM OSCILLATOR as T0 MODULATOR$ TO MODULATORS a2 a 23 TO MODULATORS as g 31 igf POM R-F OSCILLATOR 3a Fit? In mom PHAs: R-F CONTROL INVERTER cAw-eana RAY MODULATOR s4 43 OR 44 WM :56

INVEN TOR.

PAUL. G. HANSEL ATTORNEY 2%, 3M9. P. e. HANSEL fi v mmo mmacnou FINDER Filed June 24, 1844 l0 Sheets-Sheet l0 FIG. i2.

} fir I137 I45 To To AMPLIFIER & PATTERN ROTATINGH FILTER 4| CIRCUIT as FIG. 53.

FROM To OSC'LLATOR 2B l-mst ROTATION CONROL a0 C-R was INTENSITY cmo m-F OSCILLATOR mum cmcurr 'ro R-F CONTROL MODULATOR 34 i,

INVENTOR.

PAUL G. HANSEL ATTORNEY Patented July as, me

REED DIRECTION FINDER Paul G. Hansel, Red Bank, N. 3.

Application .liune 24, 19%, Serial No. 541,950

30 Elaims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

My present invention relates to radio direction finders, and more particularly, to direction finders of the electronic goniometer type.

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

One of the objects of my present invention is to provide a radio direction finder with a novel, omnidirectional, fixed antenna system, capable of operation over a relatively wide band of frequencies; which permits the taking of bearings on a plurality of sources of radio-frequency energy simultaneously; which avoids the structural problems and high costs ordinarily connected with directional systems; and which eliminates the tedious operating techniques and the inaccuracies usually associated with antenna systems requira ing physical orientation.

Another object of my present invention is to provide a radio direction finder with an antenna system of such novel design as to decrease the number of transmission channels necessarily employed therein, thus reducing to a minimum, phasing and impedance-matching problems.

Still another object of my invention is to pro vide a novel, aperiodic, electronic goniometer, which includes means for modulating the output of the antenna system thereof, whereby the modulation envelope of each signal in the spectrum of signals contained in said output assumes a phase which is a function of the bearing of the source of each of such signals.

A further object of my present invention is to provide a novel bearing indicator for an electronic goniometer, in the form of a phase meter of the cathode-ray type, for comparing the phase of the output of the antenna system, modulated as above described, with the phase of the modulating energy; whereby an accurate bearing of the source of radio-frequency energy instantaneously under consideration is obtained; and this, even where the wave front of such radio-frequency energy is such as would ordinarily be considered unfavorable for direction finding.

A further object of my present invention is to provide such control over the indicator display as to enable modification of the normal pattern able Phase and amplitude for sense-determining amended April 30, 1928; 370 0. G. 757) purposes, without the use of an auxiliary sense antenna.

A still further object of my present invention is the advancement, generally, of the art of radio direction finding. I 7

While the antenna system and phase meter to which references have been made are particularly suitable for use in the radio direction finder of my present invention, they are not restricted to such use; but are thought to have general application wherever the need may exist for' instrumentalities having like characteristics, as will later become more apparent.

These, and other objects and advantages of my present invention, which will be better understood as the detailed description progresses, are attained, broadly, in the following manner:

I provide an antenna system consisting, preferably, of four omnidirectional antennas, one located at each of the corners of a square, the four corners of said square corresponding to the compass points north, east, south, and west. The output of each of said antennas is independently and differentially modulated in a balanced modulator, preferably located at the base of each antenna, at an audio-frequency rate, the modulating energy applied to the north and south antenna outputs being in quadrature with that applied to the east and west antenna outputs. The four, carrier-suppressed, modulated outputs thus obtained are then combined in a common impedance, preferably located at the center of the antenna system, the energy derived from the north and south antennas and their associated modulators being applied to said impedance in opposition, as is the energy derived from the east and west antennas and their associated modulators. The result of the combination is a carriersuppressed, low-frequency modulated, radio-frequency signal whose envelope phase is a function of the bearing of the source of said radio-frequency signal. This signal is then detected in a standard radio receiver, and the demodulated output of said receiver is applied to a bearing indicator, consisting of a phase meter, to enable comparison of the phase thereof with a reference phase, for example, the phase of the above mentioned modulating energy.

Said bearing indicator is, preferably, of the.

cathode-ray type, and includes a sweep generator for "producing a diametral-line trace, which is caused to assume an instantaneous length inversely proportional to the instantaneous amplitude of theoutput of the above mentioned receiver, said trace being rotated about its central point at an angular velocity equal to that of the above mentioned modulating energy. This produces upon the screen of the cathode-ray tube a propeller-shaped pattern the tips of which, when said screen is properly calibrated in terms of azimuth, indicate thedirect and reciprocal directions of arrival of the radio-frequency signal instantaneously under consideration. However, this display is characterized by a 180 ambiguity, and, in order to resolve this ambiguity, it is necessary to add a sense voltage to the modulated input to the above mentioned common combining impedance. Such a sense voltage is preferably obtained by shifting the phase of a portion of the output of each antenna by 90, so as to obtain a final voltage which is cophasal with the receiver input, adding the phase-shifted voltages, and adjusting the amplitude of the resulting signal to correspond with the amplitude of the modulated portion of the input to said receiver. At the same time, a blanking signal is supplied to the indicator whereby the diametralline trace is converted into a radial-line trace. The resulting cardioid r half-propeller patterns now appearing upon theindicator screen point to the true bearing of the radio-frequency signal instantaneously under consideration.

In the accompanying specification there is described, and in the annexed drawings shown, what is at present considered a preferred embodiment of the radio direction finders of the present invention. It is, however, to be clearly understood that the present invention is not limited to said embodiment, inasmuch as changes therein may be made without the exercise of invention and within the true spirit and scope of the claims hereto appended.

In said drawings:

Figure 1 is a block diagram of a portion of a radio direction finder assembled in accordance with the principles of my present invention, said diagram including the major components of said direction finder from the antenna system to the receiver;

Figure 2 is a block diagram of a bearing indicator assembled in accordance with the principles of my present invention, and intended, primarily, for use with that portion of the system generally shown in Figure 1;

Figures 3, 4, and 5 show the wave shapes of the outputs of some of the more important components shown in Figures 1 and 2;

Figure 6 illustrates various types of indicator displays resulting from the operation of the radio direction finder of my present invention under varying circumstances;

Figure 7 is a perspective view of the antenna system preferably utilized with the radio direction finder of my present invention;

Figure 8 is a circuit diagram of the balanced modulators and sense-voltage amplifiers preferably used for independently modulating the output of each of the four antennas comprising the antenna system shown in Figure 7, and deriving therefrom an appropriate sense voltage;

Figure 9 is a circuit diagram of a phase splitter and two phase inverters for controlling the phase relationships between the inputs to the modulators of Figure 8;

Figure 10 is a circuit diagram or a modulator for controlling the input to the balanced modulators, one of which is shown in Figure 11.

Figure 11 is a circuit diagram of one of the two balanced modulators used to provide the indicator of my present invention with a rotating trace;

Figure 12 is a circuit diagram of a phase-rotation control for properly initially orientingv the indicator display with respect to a preselected reference direction;

Figure 13 is a circuit diagram of a. patternrotating circuit for reorienting the normal indicator display during sense determination; and

Figure 14 is a circuit diagram of a blanking signal generatoiafor appropriately altering the normal indicator display during sense determination.

Referring now more in detail to the aforesaid preferred embodiment of my present invention, and with particular reference to the. block diagram of Figure 1 of the drawings, and the wave shapes of Figures 3, 4, and 5 of the drawings, the numeral 20' generally designates an antenna system consisting of four individual, horizontally-omnidirectional antennas N, E, S, and W. These antennas are disposed one at each of the corners of a square and correspond, respectively, to the compass points north, east, south, and west.

The radio frequency field (E), Figure 3A, existing at the center 2| of such antenna system, which will be taken as reference throughout this description, is represented by the equation:

E=Em sin wet (1) where Em is the maximum value of the field strength, and we is the angular frequency thereof.

The voltages (en, es, 6e, ew), Figures 33, 3C, 3D, and 3E, respectively induced in the antennas N, S, E, and W are, therefore:

e,,=E,,,h, sin (aw? cos a) 2 cl=Emh, sin (wJ- cos a) (3) e,=E,,h, sin 1 sin a) 4 e,,,=E,,,h. sin (mii sin a) s where he is the eifective height of each antenna, 11 is the distance of each antenna from the center 2| of the system, 7 is the wave length of the carrier, and a is the angle of wave arrival measured clockwise from north.

These antenna voltages are respectively applied to balanced modulators 22, 23, 24, and 25 preferably disposed one at the base of each antenna. As will later be described in detail, each antenna modulator consists, generally, of a pair of parallel-fed, vacuum tube amplifiers the outputs of which are combined, push-pull fashion, in a common combining impedance 26 which, in turn, feeds a conventional receiver 21.

Now the plate currents (i i, i z) of the amplifiers of the modulator 22 flow through the combining impedance 2B in opposite directions and may be represented by the equations:

where a is the amplification factor of each tube, e is the voltage acting at the grid of each tube, Rp is the plate resistance of each tube, and Gm is the instantaneous grid-to-plate transconductance.

Substituting the value of the voltage en (2), de-

rived from the north antenna. N, for a (6 and '8), and applying the resulting plate currents (ipl, ipil) to the common combining impedance 26, two component voltage drops (8m, ens) are obtained across the receiver input:

e,,='E,,h,Gm.z sin (c t-F cos a) (8) where Zr is the transfer impedance of the load on the modulator.

The sum of the component voltages em and ass (8 and 9), in the absence of any modulating voltages being applied to the modulator 22, obviously is zero.

modulator, I sinusoidally vary the transconductance (G m) of each of the amplifiers. This is accomplished in the following manner:

I provide a conventional oscillator 28 for gen erating an audio-frequency voltage (es); Figure 3F, of about 150 C. P. 5.:

'ea=A sin (mi (10) where A is the maximum value of the modulating voltage, and mm is the angular frequency thereof.

This voltage is fed to a 90 phase splitter 29 to obtain two unbalanced outputs (car, car), Fig= ure 3G, as follows:

These outputs are applied, respectively, to phase inverters 3D and 3!, to obtain two pairs of balanced outputs (e'1, 8'2; e"1, e"2), Figures 33 and 31, each pair having its components in 180 phase opposition, and the pairs bein in quadrature with each other:

ea2=A1 sin wmt e'2=A2 cos wmt (is) e"1=Az Sin wmt (15) e"z=-A2 sin wmt (is) As above stated, the effect of applying modulating voltages to the balanced modulators is to vary the transconductance of the amplifiersthereof.

The instantaneous transconductance (Gmi, Gmz), therefore, of the tubes of the modulator 22 can be expressed:

Gm1=Gmo(1+Am cos wmt) Gm2=G7TLO(1Am cos wmt) where Gmn is the average transconductance, and

Am is the modulation factor.

Equations 8 and 9, representing the unmodulated voltage drops (em, e112) across the receiver input resulting from the modulator 22, then, as shown in Figure 4A, become:

e',.l=smh.amou +21... s m Z. sin (w.+ cos a) However, by difierentially applying an audio-frequency modulating voltage to said The result of combining these voltages, the final output (e'n), Figure c3. of the modulator 22; in other words. the input to the receiver due to the north antenna N, is:

l =2EmkzlA Gm ccsusl sin(tiet+% cosa) (21) In a similar. manner the voltage drops (e'nx, eta), Figure to, due to the amplifiers. or

the modulator 23 become:

8'n= mM ofl 'Am (:05 wMOZ i sin (a t cos a) r 21rd e E h Gm u +A... cos o,,,t)Z am (a t T cos a) And the input e'n, Figure 4D, to the receiver due to the south antenna S, becomes: I

e =2Emh,Z A Gm cos w,,.t sin (w tcos or) Likewise, the amplifier outputs of the modulator 2t (e'e1, 8'e2), Figure 4E and the amplifier outputs of the modulator 25 (6 1111, e'wz), Figure 5A,are:

an: Emh.Gm, 1+-A,, sin w t) 2. sin (aw? sin a) e',,,= -2E,,.h,z,A,,cm, sin a t sin (w ti sin a) (s I now substitute an antenna constant (K) in Equations 21, 24, 29, and 30:

K =2heZtAmG-m0 (31) Adding the four carrier-suppressed, modulated outputs of the antenna modulators 22, 23, 24, and

25, represented by said Equations 21, 24, 29, and

30 to obtain the resultant input to the receiver (e .-=8' ;+'s+e'e+ e'w) 2 w e,=2E,,,K[sin cos a) cos w,,.t+sin sin a)sin w t] cos mi (32) In practice, and as previously stated, the spacing d is small compared with the wave length The following approximations may therefore be employed to simplify Equation 32 and to make its physical significance more apparent:

21d I sin cos a) T (:08 a)% 21rd 2 1r d (T 8111 a): 811] A 3111 a The final input to the receiver (er), Figure 5C, therefore becomes:

From Equation 33 the following may be deduced:

1. When a signal is being received, the radiofrequency input to the receiver is a carrier-suppressed modulated signal having an envelope frequency of 2. The phase of the modulation envelope is a antennas from the center of the system and the 3 frequency of the radio-frequency signal instantaneously under consideration,

Now the output of the receiver 21, a demodulated and, preferably, negative-going voltage, as shown in Figure 5D, will be zero when cos (a-wmlf) in other words, nulls occur when:

(a-w,,.t) (2n-1 radians where n is any integer.

This fact is availed of in the bearing indicator 32 of my present invention, generally shown in Figure 2 of the drawings, which, as previously stated, is essentially a phase meter for comparing the phase of the rectified envelope obtained from the receiver with a reference phase, namely, the phase of the modulating voltage.

For this purpose, I provide a conventional oscillator 33 for generating a relatively low, radiofrequency voltage, Figure SE, for example, about 200 kc., which is applied to a control modulator 34, later described in greater detail. Here, said radio-frequency voltage is modulated with the output of the receiver 21, which has been passed through an amplifier 35, to obtain the modulated output shown in Figure F. Said modulator output has an envelope phase which is a function of the bearing of the signal source instantaneously under consideration, and an amplitude which is instantaneously inversely proportional to the amplitude of the negative-going output of the receiver 21.

This output is applied, through balanced indicator modulators 36 and 31, which will later be described more in detail, to the deflecting plates H and V of a cathode-ray tube 38, thereby providing the latter with a diametral-line trace whose length is dependent upon the instantaneous fill amplitude of the output of the receiver. The diametral-line trace thus obtained is-caused to scan a circular area on the screen of the cathoderay tube 38 at the angular velocity of the modulating energy applied to the modulators of the antenna system 20.

For this purpose, a portion of the output of the audio-frequency oscillator 28 is passed through a pattern-rotating circuit 39, a phaserotation control circuit 40, and an amplifier and filter 4|, the purposes and functioning of which will later be described? and applied to a phase splitter 42 to obtain two voltages in quadrature. These quadrature voltages, after being passed through phase inverters 43 and 44, are applied, differentially, to the balanced modulators 36 and 31. The result is to provide the cathode-ray tube 38 with a rotating field which, in turn, causes the diametral-line trace with which said cathode-ray tube has been provided as above described, to be rotated about its center point.

There now appears upon the screen of the cathode-ray tube a propeller-shaped pattern 45, Figure 6A, comprised of a rotating diametral-line trace, the instantaneous length of which is a function of the amplitude ofthe output of the receiver 21, and the tips of which correspond to the nulls of the output of said receiver and point. on a calibrated scale 46 with which the screen of said cathode-ray tube is provided, to the direct and reciprocal bearings of the source of the radio-frequency signal instantaneously under consideration.

The pattern is initially properly oriented with respect to the calibrated scale by suitably adjusting the phase of the portion of the output of the oscillator 28 applied to the modulators 3G and 31 by means of the phase-rotation control 40.

Now the display thus far obtained includes an ambiguity of 180, as have the normal displays of existing radio direction finding systems. It has heretofore been the' practice to employ a separate sense antenna to resolve this ambiguity, but I propose to accomplish the same result without the use of such a separate antenna.

From an inspection of Equation 33 it is apparent that if a voltage (8c) of the form:

e E K -i cos w t (35) is added to the voltage (e'r) represented by said Equation 33, nulls will not be obtained when cos (a-wmt)=0. Instead, nulls will be obtained when cos (a-wmt)=--1; in other words, when:

(uwmt) =1r(2n-1) radians; (36) where n is any integar The spacing between the nulls of the rectified envelope, constituting the output of the receiver 21, will now be equal to 21r radians of the modulating cycle, and I utilize this result to alter the indicator display to resolve the above mentioned ambiguity.

To this end, and returning once again to Figure 1 of the drawings, I apply a portion of the output of each of the antennas N, S, E, and W, respectively to differentiating circuits 41, 48, 50, and 49 whereby signals are obtained which are substantially out-of-phase with the inputs to the respective antenna modulators 22, 23, 24, and 25. These signals are added to each other, upon closing switches 5|, 52, 53, and 54, in the combining impedance 26, with the result that a sense signal is applied to the receiver 21 which is substantially cophasal with the modulated signal a, (33). The plitude of the sense signal is adjusted to a value equal to that of the expression in Equation 33.

Simultaneously with the addition of the sense voltage (Cc) to the receiver input (e':), the pattern appearing upon the screen of the cathoderay tube 38 is rotated through 90 by operation of a switch 55, Figure 2, associated with the pattern-rotating circuit 39, and thediametralline trace resulting in the propeller-shaped indicator display 45 is converted into a radial-line trace. This is accomplished by utilizing a portion of the output of the radio-frequency oscillater 33 to generate, in a blanking signal generator 56, a blanking signal lasting for approximately one-half of the period of the output of said oscillator, which is applied to the intensity grid G of the cathode-ray tube 38. The blanking signal is suitably phased by interposing a phase shifter 57 between the oscillator 33 and the generator 56, and the'application of this signal to the tube 38 is controlled by a switch 58. The switches 52, 53, and 5 3, Figure 1, and the switches 55 and 58, Figure 2, are preferably ganged forsimultaneous operation.

The result of applying the sense voltage, ob-' tained as above, to the receiver input is to convert the ambiguous propeller-shaped pattern 45 of Figure 6A to the sense-determining, cardioid pattern 59 of Figure 6B.

As above indicated, if the sense voltage ice) is equal to the normal receiver input (e':) the receiver output will have a single null per modulation-signal cycle and thedisplay of Figure 615 results. If, however, the sense voltage (ea) is the pattern .68. shown in Figure 6E. However,

.this does not interfere too greatly with obtaining an accurate bearing on the source; for, by averaging the indications of the two unequal propeller-shaped patterns, the difliculty is largely overcome and a fairly accurate reading is obtained. Or, if the signal is fading, the operator can wait for the instant when the patterns superimpose or become symmetrical and then take a reading as described above for normal operation.

Before passing to a detailed description of the circuits which may be employed in the various maybe controlled by adjusting the band-pass less than the receiver input (e'r), the receiver 40 output will have two minima per modulationsignal cycle, but said minima will be unequally spaced in time. The result will be the dual sensedetermining pattern fill, shown in Figure 6C. In either case, the ambiguity above referred to will have been resolved.

I have found in practice that sometimes, as a result of low signal intensity or because of unfavorable wave front characteristics the bearing indication is not sharply defined. In order to enhance accuracy of observation under such circumstances I provide the balanced modulators 36 and 37 of the indicator with means to be further explained during the description of the modulator circuit shown in Figure 11, for purposely unbalancing said modulators. Such unbalancing causes the pattern 55 of Figure6A to become symmetrically split, resulting in the pattern Bl, shown in Figure 6D. This display is read at the intersections 82 of the two displaced propeller-shaped patterns rather than at the tips thereof,-such manner of reading the display characteristics of the combining impedance 2%. The modulated output, therefore, can be connected to any desired number of receivers and associated indicators, thereby enabling simultaneous direction finding on any desired number of individual signal sources.

This completes the general description of the direction finder of my present invention and I shall now describe some specific circuits which may be utilized in the main components thereof.

As shown in- Figure 7, each of the antennas N, E, S, and W of the antenna system 29 preferably comprises a plurality of telescoping elements 6% rising from housings N, E, S, and'W. Said housings are disposed, in the form of a square,

at the outer ends of mutually perpendicular conduits 65, and are receptive, respectively, of

the balanced modulators 22, 25, 23, and 25 (Figure input circuit of each of said'tubes includes a' coupling capacitor 7 i and a grounded grid resistor 72; the screen gridsthereof are connected to the positive terminal of relatively low-voltage B" materially increasing the effective operating sensupply, through a dropping resistor 73 of appropriate value, by-passed by a capacitor it; and the suppressor grids thereof are grounded, as shown. Plate voltage to each of said tubes is supplied through a center-tap in the combining impedance 26, and the plate outputs thereof are combined in said impedance, in opposition.

The tubes of each modulator are parallel fed from the corresponding antenna of the system 20, and have ,diflerentially applied thereto, through resistors '85, appropriately phased; balanced modulating energy from the inverters 8d and 3! (Figure 1). The relative gains of the tubes of each modulator are adjusted by means of the variable resistor 69, and the over-all gain of sistor 89 and a variable resistor 90.

11 each modulator is adjusted by means of the variable resistor 10. v

The means for deriving the sense voltage necessary to resolve the ambiguity normally present in the bearing display of any selected signal, referred to in earlier portions of this specification, are associated with the antenna modulators just described. Such means include the differentiating circuits 41, 48, 50, and 49, each such circuit comprising, preferably, a capacitor 16, a resistor 11, and an inductor 18, connected in series between each antenna N, S, E, and W, and ground. The drops across the inductors are applied to pentode vacuum tubes 19, the cathodes of which are grounded through bias resistors 30, and the respective switches 52, 54, and 63. The screen grid of each of these tubes is connected to the low-voltage B supply, above mentioned, and the plates of said tubes are all connected to the same side of the combining impedance 26 through coupling resistors 8|. In order to maintain proper balance in each antenna modulator, the plate circuits of those tubes thereof which are connected to the opposite side of the impedance 25, include compensating networks, consisting of resistors -82 which are grounded through capacitors 83.

Because of the differentiating actions of the circuits 41 to 50 inclusive, the signals acting at the control grid of each tube 19 are substantially 90 outof-phase with the received signals at the grids of the modulator tubes 51 and 68. However, the addition of the sense signals in the impedance 26 results in an omnidirectional signal which is substantially cophasal with the resultant modulated signal fed to the receiver 21.

The phase splitter 29 and the phase inverters 30 and 3 I utilized to apply properly phased modulating voltages to the antenna modulators 22 to 25 inclusive, may take the form of the circuits shown in Figure 9. As there shown, a portion of the output of the audio-frequency oscillator 28 is applied, in parallel, across a resistor 84, and two networks 85 and 86, the latter constituting said phase splitter 29. The network 85 includes a capacitor 81 and a resistor 88 connected, in series, with a parallel combination of a fixed re- The network 86 includes a resistor ill and a capacitor 92 connected in series. The values of the capacitors 81 and 92 are equal, and the value of the resistor 9I is equal to the equivalent resistance of the resistor 88 and the parallel combination of resistors 89 and 90.

The drop across an appropriate portion of the resistor 90 is applied to a vacuum tube amplifier 93, and the drop across the capacitor 92, which is substantially 90 out-of-phase with the drop across said resistor 90, is applied to a vacuum tube amplifier 94. The cathodes of the tubes 93 and 94 are grounded, respectively, through resistors 95 and 96, and plate potentials are applied to said tubes, respectively, through resistors 91 and 98. The plate output of the tube 93 is applied, through a coupling capacitor 99 and grid resistor I00, to a vacuum tube IIII, constituting the inverter 3I, and the plate output of the tube 94 is applied, through a coupling capacitor I02 and grid resistor I03, to a vacuum tube I04, constituting the inverter 30. The cathodes of the tubes MI and through pairs of series connected resistors I05 and I06, and I01 and I08, and plate voltage is supplied these tubes, respectively, through resistors I09 and H0. Plate and cathode outputs I04 are grounded, respectively,

- grid resistor H9.

' II4, to the antenna modulators 22 and 23.

phase with each other, and the dual output of the tube IIII is in quadrature with the dual output of the tube I04.

The radio-frequency control modulator 34, for mixing the bearing-indicating output from the amplifier 35 and the radio-frequency oscillations generated by the radio-frequency oscillator 33, may take the form shown in Figure 10. As there shown, the modulator 34 includes a pentode vacuum tube II5, the cathode of which is groundedthrough a bias resistor .I I6 and a variable resistor I I1, the latter having applied across the same, the output from the oscillator 33. The output of the bearing amplifier 35 is applied to the control grid of the tube H5 across a grounded The screen grid of said tube has a positive potential applied thereto through a resistor I20, by-passed by a capacitor I2l, and the suppressor grid thereof is grounded, as shown. Plate potential is applied through a tuned circuit which includes the parallel combination of an inductor I22 and a variable capacitor I23, said parallel combination being resonant to the radiofrequency output of the oscillator 33. The output of the modulator 34 is applied to the indicator modulators 33 and 31.

The indicator modulators 36 and 31, one of which is illustrated in Figure 11, each comprise a pair of pentode vacuum tubes I25 and I26, the cathodes of which are connected to the opposite ends of a variable resistor I21 whose adjustable arm is grounded through a resistor I28.

The variable resistor I21 controls the relative gains of the tubes I25 and I28 and, as indicated in earlier portions of this specification, is used purposely to split the bearing indications on signals which are difficult to read, to enhance the accuracy of observation thereof. The resistors I21 and I28 are by-passed by capacitors I29 and I30.

The control grids of the tubes I25 and I26 are grounded through resistors I3I and I32, and; in addition to being receptive of the output of .the control modulator 34, through coupling capacitors I24, are receptive, through resistors I33 and I34, of properly phased modulating voltages from the inverters 43 or 44.

The screen grids of the tubes I25 and I20 have positive potentials applied thereto through a resistor I35, by-passed by a capacitor I35, and the suppressor grids thereof are tied to the cathodes. The plates of said tubes are supplied with positive potentials through a center-tapped tuned circuit which includes inductors I31 and I38 shunted by a capacitor I39, said tuned circuit being resonant to the radio-frequency oscillations fed to the modulators from the radio-frequency control modulator 34. The outputs across the tuned circuit, which are in phase opposition, are applied, through coupling capacitors I40 and Hi, to the deflecting plates of the cathode-ray tube 38. Of course, the envelopes of the dual outputs of the modulators 36 and 31 are in phase quadrature.

A satisfactory form for the phase rotation control circuit 40 is shown in Figure 12. It includes a vacuum tube I42, connected as a phase inverter, having its cathode grounded through resistors I43 and I44, its input circuit including a coupling s13 capacitorlllt and grid resistor ass, and its output circuit including capacitors-M7 and M8, and a variableresistor' I49 in series therewith. Plate potentialisiapplied througha resistor l50.

The phase of the output across the resistor I49 is controlledby adjusting the value of said resistor, and the control range is governed by the relative impedances of the capacitor Ni and said resistor. V V stantially constant over said control range, provided the values of the resistors Md and i511 are small compared to the impedance values of the capacitor I47 and the resistor see.

Figure 13 shows an appropriate form which the pattern rotating circuit 39 may take. its there shown, the switch 55, which 'is associated with said circuit, is a double-pole double-throw switch The magnitude of said output is subhaving outer contacts l5l, l52, I53, led and central contacts I55 and F56. The output of the audiofrequency oscillator 28 is conveyed to the contacts l5! and Hi l by conductors E57 and 158, and the contacts 852 and H3 are grounded. Connected between the central contacts I55 and I53 are a capacitor l59 and a resistor I60, the reactance of the capacitor being equal to the resistance of the resistor. The output of the circuit, which is applied to the phase rotation control circuit to, is taken between the junction .of the capacitor and resistor, and ground, so that when the switch is thrown to the right, the phase of the input thereto is retarded 45, and when the switch is thrown to the left, the phase is advanced 45. There is, therefore, a relative phase shift of 90 when the switch is thrown from left to right.

I shall now. describe a satisfactory circuit for converting the diametral-line trace, normally displayed on the screen of the cathode-ray tube 38 of the indicator, to the radial-line trace, which is observed during sense determination. This circuit, shown in Figure 14, includes the phase shifter 51, switch 58, and blanking signal generator 56.

As hereinbefore stated, the radio-frequency oscillator 33 is conventional, the output thereof being obtained from a tank circuit llil tuned to the desired frequency. Said output is inductively coupled, through a link I62, to the phase shifter 51. The latter comprises an inductor 863 which is center-tapped to ground, as shown, said inductor being shunted by a series connected variable capacitor I65 and resistor I85. The output of said phase shifter'is taken between the junction of said capacitor and resistor, and ground, and is applied, through a coupling capacitor l66'and a grid resistance network I51, to a pentode vacuum tube 168. The cathode of said tube is grounded through the switch 58, and the time constant of the input circuit to the control grid is such as to develop appropriate bias to obtain a substantially negative-going output from the tube. The screen grid is supplied with a proper positive potential through a resistor I69; the suppressor grid is grounded, as shown; and plate voltage is applied through a resistor H0 and radio-frequency choke H l. The output of this circuit is applied through a capacitor NZ to the intensity grid of the cathode-ray tube 38.

This completes the description of some of the circuits which may be employed in the major components of the direction finder of my present invention. Circuits for the remaining components may be entirely conventional and therefore have not been described herein.

It will be noted from all the foregoing that I have provided a radio direction finder which init corporates, among others, the following novelv and advantageous features:

1. I have provided an omnidirectional, fixed antenna system which is capable of operation over a relatively wide band of frequencies. By means thereof I am able to take bearings on a plurality of sources of signals simultaneously. I have avoided the structural problems and high costs ordinarily associated with conventional directional systems; and I have eliminated the laborious operating techniques and the lnaccuracles usually associated with systems requiring manual orientation.

2. I have provided an antenna system which is so designed as to maintain the number of transmission channels employed therewith at a minimum, thereby reducing phasing and impedance matching problems.

3. I have provided an aperiodic, electronic goniometer incorporating .means for so modulating the output of the antenna system as to obtain a spectrum of signals the envelope phase of each of which is a function of the bearing of the source thereof.

4. I have provided a bearing indicator, in the form of a phase meter, by means on which an accurate bearing of the source of energy instantaneously under consideration is immediately obtained, and such indicator is so designed that signals, which ordinarily would be considered unfavgrable for direction finding, may be accurately rea 5. Finally, I have provided a direction finding system in which sense determination is readily made without the necessity of utilizing an auxiliary sense antenna.

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

I claim:

1. In the method of determining the direction of arrival of wave energy, those steps which include: deriving a plurality of signals from said wave energy at a plurality of points, said points being so physically disposed with respect to a predetermined reference point and with respect to each other that the phase of each of said signals is a continuous function of the bearing of the source of said wave energy with respect to a fiducial line extending from said reference point in a predetermined direction; sinusoidally modulating each of said signals independently at a single frequency which is a minor fraction of that of said wave energy, with the modulation applied to at least one pair of said signals differing in phase from that applied to at least one other pair; combiningthe resulting modulated components to obtain a resultant modulated signal having an envelope phase which is a function of the bearing of said source with respect to said flducial line; and comparing said envelope phase with the phase of the modulating energy.

2'. In the method of deter-mining the direction of arrival of wave energy, those steps which include: deriving. a plurality of signals from said wave energy at a plurality of points, said points being so physically disposed with respect to a predetermined reference point and, with respect to each other, that the phase of each of said signals is a continuous function of the bearing of the source thereof with respect to a fiducial line extending from said reference point in a predetermined direction; sinusoidally modulating each of said signals independently ata frequency which is a minor fraction of that of said wave energy, with the modulation applied to at least one pair of said signals in quadrature with that applied to at-least one other pair; combining the resulting modulated components of each of said signals to obtain a plurality of equal-amplitude, carrier-suppressed signals, one corresponding to each of said first-named signals; combining said carrier-suppressed signals to obtain a resultant modulated signal having an envelope phase which is a function of the bearing of said source of said first-named signals with respect tosaid flducial line; and transforming said resultant modulated signal into a visual indication of the bearing of the source of said wave energy.

3. In the method of determining the direction I of arrival of Wave energy, those steps which include: deriving a plurality of signals from said wave energy at a plurality of points, said points being so physically disposed with respect to a predetermined reference point and with respect to each other that the phase of each of said signals is a continuous function of the bearing of the source thereof with respect to a fiducial line extending from said reference point in a predetermined direction; sinusoidally modulating each of said signals independently at a single frequency which is a minor fraction of that of said wave energy, with the modulation applied to at least one pair of said signals differing in phase from that applied to at least one other pair; combining the resulting modulated components of each of said signals to obtain a plurality of modulated signals, one corresponding to each of said first-named signals; combining said modulated signals whereby a resultant modulated signal is obtained, the phase of whose modulation envelope is a function of the bearing of the source of said first-named signals with respect to said fiducial line; transforming said resultant modulated signal into a visual indication of the direct and reciprocal bearings of the source of said wave energy; so combining unmodulated portions of an even number of said first-named signals as to derive a sense-determining signal; and combining said sense-determining signal with said resultant modulated signal to resolve the ambzguity in said visual indication.

4. A radio direction finder comprising: an antenna system for deriving a plurality of signals from a single source of wave energy, said antenna system including four independent collector elements, one at each corner of a square and each adapted to receive from said single source of Wave energy a signal having a phase which is a continuous function of the bearing of said source of Wave energy with respect to a predetermined reference direction; means for sinusoidally and independently modulating each of said signals to obtain a plurality of carrier-suppressed signals the phase of each of which is a progressive function of said bearing; means for combining said carrier-suppressed signals to obtain a resultant modulated signal the phase of whose envelope, relative to the phase of the source of said modulating means is a function of said bearing; and a phase meter for comparing the relative phases of said envelope and said modulating means.

5. A radio direction finder comprising: an antenna system for deriving a plurality of signals from a single source of wave energy, each signal so derived having a phase which is a continuous function of the bearing of said source of wave energy with respect to a predetermined reference direction; means for applying sinusoidal modulation of a single frequency to each of said signals independently and to pairs of said signals in different phases and thereby obtain a plurality of modulated signals the phase of each of which is a function of said bearing; means for combining said modulated signals to obtain a resultant modulated signal the phase of whose envelope, relative to the phase of the source of said modulation, is a function of said bearing; a radio receiver; and a cathode-ray tube provided with a rotating field having an angular. velocity harmonically related to the angular frequency of said source of modulation and receptive of the output of said receiver for comparing the relative phases of the envelope of said resultant signal and said source of modulation.

6. A radio direction finder comprising: an antenna system for deriving a plurality of signals from a single source of wave energy, said antenna system including four independent, omnidirectional collector elements, one at each corner of a square and each adapted to receive from said single source of wave energy a signal the phase of which is a continuous function of the bearing of said source of wave energy with respect to a predetermined reference direction; means for applying sinusoidal modulation of a single frequency to each of said signals independently and to pairs of said signals in phase quadrature to obtain a plurality of modulated, carrier-suppressed signals the phase of each of which is a function of said bearing; means for combining said carriersuppressed signals to obtain a resultant modulated signal the phase of Whose envelope, relative to the phase" of the source of said modulation, is a function of-said bearing; a radio receiver upon which said resultant signal is impressed; and a cathoderay tube provided with a rotating field under the control of said sinusoidal modulation and having an angular velocity equal to the angular frequency of said source of modulation, and receptive of the output of said receiver, for comparing the relative phases of the envelope of said resultant signal and said source of modulation.

'7. A radio direction finder comprising: an antenna system for deriving a plurality of signals from a single source of wa e energy, each signal so derived havinga phase which is a function of the bearing of said source of wave energy with respect to a predetermined reference direction;

means for applying sinusoidal modulation of a single frequency to each of said signals independently to obtain a plurality of modulated signals the phase'of each of which is a function of said bearing; means for combining said modulated signals to obtain a resultant modulated signal the phase of whose envelope, relative to the phase of the source of said modulation, is a function of said bearing; means, receptive of said modulation envelope, for transforming the same into visual indicia of the direct and reciprocal bearings of said source of wave energy; and means for resolving the ambiguity in said visual indicia; said last named means including means for deriving a sense-determining signal from a combination of unmodulated portions of an even number of said first-named signals, and means for mixing said sense-determining signal with said resultant modul-ated signal.

8. A radio direction finder comprising: an antenna system for deriving a plurality of signals from a single source of Wave energy, each signal so derived having a phase which is a function of the bearing of said source of wave energy with im'ate relation ently and to pairs of said signals in phase quadrature to obtain a plurality of modulated, carrier-suppressed signals the phase of each of which is a function of said bearing; means for combining said carrier-suppressed signals to obtain a resultant modulated signal the phase of whose envelope, relative to the phase of the source of said modulation, is a function of said bearing; a cathode-ray tube, provided with a rotating field having an angular velocity equal to the angular frequency of said source of modulation, and receptive of said modulation envelope, for transforming the latter into visual indicia of the direct and reciprocal bearings of said source of wave energy; and means for resolving the ambiguity in-said visual indicia, said last named means including means for deriving a sense-determining signal from a combination of unmodulated portions of v an even number of said first-named signals, and means for mixing said sense-determining signal with said resultant modulated signal.

9. A phase meter comprising: a cathode-ray tube; means for providing said cathode-ray tube with a rapidly recurring diametral-line trace; means for rotating said trace at an angular velocity harmonically related to the angular frequency of the wave whose phase is to be determined; means for altering the instantaneous length of said trace in proportion to the instantaneous amplitude of the wave whose phase is to be determined; and means for comparing the angular position of'said trace, with respect to a predetermined reference line, when the length of said trace is a maximum or minimum.

10. In a radio direction-finding system, wherein the direct and reciprocal bearings of the source of a selected carrier are implicit in an output voltage (6'!) expressed by the approximate relation K and d are constants of said system, A is the wave length of said carrier,

carrier,

a is the angle of arrival of said carrier with respect to a predetermined reference direction,

mm is the an ular frequency at which said carrier is locally modulated, and t we is the angular frequency of said carrier;

means for resolving .the ambiguity in the indicated direction of arrival of said carrier comprising: spaced-aerial means for deriving from said carrier, and adding to said output voltage, a sensedetermining voltage (8c) expressed by the approxe gE K cos w t zioltage (e'r) expressed by the approximate rela-' eflgE K r cos (aw,,.t) cos cat 18 where Em is the maximum value of said carrier,

K and d are constants of said system,

A is the wave length of said carrier,

a is the angle of arrival of said carrier with respect to a predetermined reference direction,

on is the angular frequency at which said carrier is locally modulated, and

we is the angular frequency of said carrier;

means for resolving the ambiguity in the indicated direction of arrival of said carrier comprising: means for deriving from said carrier an even number of signals each of which has a phase which is a function of the direction of arrival of said carrier; and means for combining said signals with each other to obtain a sense-determining voltage '(ee) expressed by theapproximate relation where the symbols are as defined above, and adding the same to said output voltage.

12. In a radio direction-finding system, wherein the direct and reciprocal bearings of the source of a selected carrier are implicit in an output voltage (e'r) expressed by the approximate relation e',gE,..K cos (oz-m t) cos w t where Em is the maximum value of said carrier,

K and d are constants of said system, A is the wave length of said carrier,

0: is the angle of arrival of said carrier with respect to a predetermined reference direction, wm is the angular frequency at which said carrier is locally modulated in said system, and we is the angular frequency of said carrier;

@QIAX? cos at where the symbols are as def inedabove, and add ing the same to said output voltage.

13. An antenna system comprising: four independent antenna elements, one at each corner of a square; a balancedmodulator associated with 0 each of said antenna elements; a common imthe modulation applied to said one pair of said pedance; and transmission lines for conveying signals between each of said balanced modulators and said common impedance; and a source of sinusoidal modulating potentials of a single frequency for controlling said balanced modulators, and means to phase displace with respect to each other the potentials fed to alternate balanced modulators.

t 14. -A system as set forth in claim 13, wherein said phase displacement is 15. The method as set forth in claim 3, wherein the step of sinusoidally modulating each of said signals also suppresses the carrier.

16. The method as set forth in claim 3, wherein 19 n signals is in phase quadrature with the modulation applied to said other pair.

17. The method as set forth in claim 3, wherein the step of sinusoidally modulatingeach of said means for combining the signals so derived,

means for adjusting the phase and amplitude of the. combined signal and means for combining said combined signal with the output of said antenna system.

'19. In a direction finder having an antenna system comprised of spaced collector elements, means for deriving a sense-reference signal without the use of an auxiliary sense antenna including means for deriving a signal from each of an even number of said spaced collector elements, means for shifting the phase of each signal so derived and means for combining the phaseshifted signals with the output of said antenna system.

20. A phase meter as set forth in claim 9, including means for resolving the ambiguity of the indication including means for converting said diametral-l ine trace into a radial-line trace and means for shifting the phase of rotation of said radial-line trace.

outputs of said balanced modulators to deflect the beam of said cathcde ray tube to produce visual bearing indications.

24. An indicator of the relative phase between a first periodic signal and a second periodic 818- nal, comprising: a cathode-ray tube, a source of deflection signal having a frequency higher than the frequency of said first and second signals. means for controlling the amplitude of said deflection signal in accordance with the amplitude of said first periodic signal, two balanced modulators, each receptive of the output of said lastnamed means, means for deriving a pair of phasedisplaced signals from said second periodic signal, means for controlling said balanced modulators with said phase-displaced signals, respectively, and means responsive to the outputs of said balanced modulators for deflecting the beam of said cathode-ray tube.

25. An indicator as set forth in claim 24, including means for unbalancing said balanced modulators.

21. A phase meter as set forth in claim 9, in-' resolving the ambiguity of the indication including means for converting said diametral-line trace into a radial-line trace, and means for shifting the phase of rotation of said radial-line trace.

.23. A radio direction finder comprising: four independent collector elements having identical horizontal response characteristics, identically oriented; four balanced modulators, one associated with each of said collector elements; a twophase source of modulating signals of substantially sinusoidal waveform; means for applying said modulating signals to each of said balanced modulators in such a manner that alternate balanced modulators receive modulating signals of different phase; a radio receiver; means for connecting the outputs of said balanced modulators to the input of said receiver; and a-bearing indicator receptive of the output of said receiver, said bearing indicator comprising; a cathode-ray tube, a source of high-frequency signal, means for controlling the amplitude of said high-frequency signal in accordance with the output of said receiver; two balanced modulators receptive of the controlled high-frequency signal; a two-phase source of low-frequency modulating signals, harmonically-related to said first-named modulating signals and applied to said balanced modulators in different phases; and means for utilizing the 26. An indicator as set forth in claim 24, including means for blanking the beam of said cathode-ray tube during a portion of the period of said deflection signal.

27. An indicator as set forth in claim 24, including means for unbalancing said balanced modulators, and means for blanking the beam of said cathode-ray tube during a portion of the period of said deflection signal.

28. An indicator of the relative phase between a first periodic signal and a second periodic signal comprising: a cathode-ray tube having a pair of, orthogonally-related beam deflecting means, a source of deflection signal having a frequency higher than the frequency of said signals. means for controlling the amplitude of said deflection signal in accordance with the amplitude of said first periodic signal, a pair of balanced modulators, each receptive of the output of said lastnamed means, means for deriving a second pair of phase displaced signals from said second periodic signal, means for exciting each of said balanced modulators with a different one of said second pair of signals, and means for applying the output of each balanced modulator to a different one of said beam deflecting means for deflecting the beam of said cathode-ray tube.

29. An indicator as set forth in claim 28, wherein said second pair of signals is phase displaced 30. An indicator as set forth in claim 29, including means for unbalancing said balanced modulators.

PAUL G. HANSEL.

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

UNITED STATES PATENTS

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