[1]Patented Dec. 12, 1950 295339229 UNI@TE.D@ STAT'E,S@ PATENT OFFICE 21533"229 OMNIDIRECTIONAL RADIO BEACON Effward' N. Diiig-jey, Jr., ArUngton, Va. Ap .plicatio,n:June 25,1947, Serial No. 757,042 lOr Claims. (Cl., 343-105) (.Gr.anted under the.. act of. March 3, 1883, as ajnen&d- April. 30, 1928" 370 0. G@ 757) 2@ radiator 3 duringz th& period T3, and then the cycle repeats. These periods inay, withiii certain limits. bp-. as long, as desired. In the following speciication, the @ periods wiH he assigned as follows Ti=21 r.,ulliseconOs, T2=T3=1 millisecond. The radiations from the three antennas are in time phase with each other. Although any., desired iradiation@ frequency may be used in@ the pract-ice@ of- this invention, it is preferable to use low frequencies to achieve the inost useful results at. digtance as great a.% 1500 to 2000 mi-les@ Frequencies in the band@ 100 to 250 ke./s. are. preferred-. In the following, description, an. assigned freq@iency.. of 200 ke./s. viill b-,: assumed. In Fi.-@ 1, let@ P be a poin-t@-at or near the earth's slirface su--@Ticiently d,stant from. radi@Ltor I so that lines joining @point@ P to radiators f, 2 and 3 are substantially pa-rallel@ In the following, these li-nes will@. be @ considered @ to, beparallel. In Fig. 1, let Z bp-, the@ angle@ between the line joining point P with,antenna t ' and the extended li@ae join-ng antennas t and 3; With reference to north@ this may be@ termed the. azimuth angle of point P ' The @ signals@ receiied@ at point P from the three antennas may b,- expressed as follows: El=Klefwt]Tl E2=lflej(wt+l -n -I)IT2 E3=Klej(wt-- cos z)IT3 NVhere El, E2, E3=instantaneous field intensity due to antennas7 I., 2, and, ' respectively. Where K@a constant Where I=current in antenna I or 2 or 3 Where;e=base@of Naperian,legarithms Where W=radiated frequency in radians per seeond@. Where Z=azimuth of po"nt P Where ]Tl indicate,-, that tl-ie value holds during period Ti but at other t-imes the value Is zero. In more simple teri-r@s,.tbe field intensity at the point P. is constant re,,ard-,-e@,s of which radiator is radiating and the phase of the eloctromagnetic field due to radiato,.-- 2@ referenced to that previously rece 4 ved.@ om radiator .1 is: r O.-@?r sill. Z And' the phase of the- electromagnetic field due sent bl-,ried coaxial transmission lines which are r)O to radi@itor 31 referred to that previously refurther depicted in PLg. 2. ceived from radiator I is@: 0 3 @ - 7 r C O S Z @ ( 2 ) This: will become apparent from a study of Fig' radiator 2 during @ the period' T2. . and@ only@ from 5.5 lo,.v7hich is a geom.-trical representation of the This invention relates to an improved: long range: omnidirectional. radio beacon system whereby the bear-ing or azimuth, of the moving body may b,- dg@termined in relation to the knov%7n location of 'Llhe beacon@ 11, One@of the objects of the@ invention i,% to pro'vide an improved means for, radiating in space an electroma.@netic L-ield having@ a characteristic 1;vhich@ varies as a kno@vn function of the azimuth f@om the radiating sotrce;@. J@(I Another o'aject of@ the invention is to provide an improved. means@ for recaiving a-,id'detecting- an electromagnetic field'which varl'es as a function of azimuth, and @ for utilizin.- the-variable@ characteristic of@ the! electroma-,netic@ field 15 to; -indicate the azimuth: o-', thL-.@ receiver f!7orn the trai,ismitter or@beacon. Other- and further objects,, of@ the invention will be understbod from the@ fo'@lov@ing specifi@ation and by reference to @the accompanyii2g drawings@ 20 of which: Fig. I is a plan vie@v of tb-e@transmittin.- site.. Fig' la@ is a, di@,gram i.liustrating certain phase r,elationshipsFig. 2 is @ a blaclc diagram @ of, the i tr ansmitting 25 equipment. Fig. 3 is a block@ d4lagram: of the receiver, and indicator. in F-ig 1 the vertical rad'ators 2 and 31 are situated so ihat thir bases; referred to the hori- 30 zontal piane, are at eaual dista-nces ftDP- and in spage quadrattira to the base@ of the veitical radiator, 1. Although various spacin.-s and spac-. angular r@-'Lationships may be used, it is preferable ta use radfators@ of equal@height@ situated as stated 35 above and with rad'ators, 2 and' 3@ each spaced froin radiator I by a, distance equial to 1/2 wa-velength=-i/'Z at t-he ass-igned trnasm. ission frequency' @ This spacing is equiva'ent to ar@ electrical phase difference of r@ radians or 180 electrical, de- 40 grees for@ a, v,,ave traveling from radiator I to radiator,, 2 and 3, respectively. For convenience in@ later I discussion, a line conneeting radiators 3 and f@ is shown to bear tru.- norlh. In Fig. 1, symbol 5 represent-s the house@ or en- 4r) closure fbr ali o@ t.ie transm-itting equipment shmvi,i iTi Fig. 2; syr@ibol-4@rei3resents@a short vertical receiving ),.Titenna situat--d@ equidistant from @adiators 1, 2 and 3 and symbols 6, 7 and 8 repreT@:he transi--Qittirg equipment is arranged so that rad-atiort of the assi.-ned frequency@ occurs only froni@radiator I during the period Ti@ only from
[2]3 phase relationslaips b,,tween the various electroma.@netic fields as they arr-lve a'@- point'-P. Point P has been assumed to b,- so far away th ' at the lines 40, 41 and 42 joiliing point P to radiators 1, 2 and 3 respectively are sifiostantially parallel, as shown. By drawing the line 43 at ri-ght a-igles to line 4,9, it is aiaparent that the electromagiletic field from radiator 2 will lead that from radiator I when both fields arrive at point P by an electrical angle 952 which is seen, by inspection, to be equal to 7r sin Z. Similarly, the electromagnetic field from radiator 3 lags the electroma-netic field from radiator I upon arrival at poin@P by an ele(,trical aiigle 03 which, by inspection, equals Cos Z. If point P is 45 wavelengths removed from radiator 1, the error in the above expressions will be less than I electrical degree. At a frequency of 200 ke./s., 45 wavelengths is approximately 35 nautical miles. At greater distances the error in the above equations is negligible. Mg. 2 is a block diagram of the apparatus required at the transmitting station. In this figure, symbol 9 r--presents a crystal controlled oscillator of conventional design such as is described on Page 496 of "Radio Engineers Hand;book," first edition, by F. E. Terman, published by McGraw-Hill Co. Symbol 10 represents a keyed amplifier or "gate" such as is shown in Fig. 4d, page 628 of Terman, supra, except that the -keying or gating voltage is obtained from the multivibrator 15 to be later described. The output of gate 10 is transmitted through transmission line 6 to the frequency doubler power 'amplifier I I which is Iocated at the base of radiator tower I and is of conventional design. The use of half carrier frequency in the transmission line eliminates feedback therein from the radiated field. The power amplifler I I energizes the radiator I during period Ti. During periods T2 and T3, gate R2 (symbol 10) blocks the passage of energy to transmission line 6. In Fig. 2, phase shifters C and D are of conventional design such as is shown in Fig. 56c on page 949 of Terman, supra. Signals from the crystal oscillator 9 pass through phase shifter C and through gates Cl and C2, which are similar in design to gate R2, throughtransmission line 7 to ihe frequency doubler power amplifier I 6 which energizes radiator 2 only during the period T,- for the reason that exciting energy is blocked from transmission line 7 during the period T, by gate C2 and during the period T3 by gate Cl. Radiator 3 is energized in a similar manner by the frequency doubler power amplifier 17 through the phase shifter D. Its radiation is stopped during the period T, by the gate D2 and during the period T2 by the gate Di. In Fig. 2, symbol 12 represents an oscillator of conventional design which drives a p,,ilse shaper 13 of conventional design such as is shown in Fig. 34a on page 514;of Terman, supra. Pulse shaper 13 drives multivibrator 14 at half the oscillator frequency and multivibrator 14 drives the multivibrator 15 at one-quarter the oscillator frequency. In this example the frequency of oscillator (2 is taken as 1000 C. P. S. and the half cycle period of multivibrator 14 is I milliseconcl and that of multivibrator 15 is 2 milliseconds. The plate of one tube of multivibrator 15 suppiies blocking voltages to gates C2 and D2 during period Tl=2 milliseconds aiid the plate of the other tube of multivibrator I 5 supplies blocking 2,533,229 4 seconds. The plate of one tube of multivibrator 14 supplies blocking voltage to gate Di during the first half of period Ti and during period T2. The plate of the other tube of multivibrator 14 supplies blocking voltage to gate C, during the second half of period T, and during period T3. Thus signals will reach transmission line 7 during period T2 and will reach transmission line 8 during period T3 but those signals are blocked 10 during the period T, by the action of gates C2 and b2. In Fig. 2, some of the signal output of oscillator 9 is passed through the frequency doubler I 8, the phase shifter E (symbol I 9) and to the 15 horizontal deflection plates of cathode ray tube 2,0. This signal is displayed in space quadratur,. with the signal collected by antenna & which is equidistant from antennas 1, 2 and 3. The frequency doubler IS consists of a conventional 20 biased vacuum tube circuit in which the plate circuit is tuned to the second harrionic of the input frequency. The phase shifter E is similar to phase shifters C and D. The -L-igure displayed oii 'Ohe screen of the cath25 ode ray tube 20 will be a measure of the phase relationships between the electromagnetic fie'ds radiated by r@diators 1, 2 and S. If these fields are in time phase, then tl-ie voltage of collector 4 will have a fixed phase relationship to the 30 output V@ phase shifter 19, regardless of whi@.h radiator is energized. This phase relationship may be made zero by adjusting phase shifter 19 and the - figure displayed on the cathode ray tube 23 will be a straight line as shown under the gr) heading "Phase Difference = 0", in Figure 55, page 948 of Terman, supra. If the fields of radiators 1, 2, and 3 are not in time phase, then the voltage of collector 4 will have differ-ng phase relationships with the output of phase 4Lno shifter 19, depending on which radiator is energized. 'For example, these phase relationships might be 45', 90', and 135' respectively for radiators 1, 2, and 3. Since the radiators are energized sequentially, the vision persistence of the 45 eye, and the image persistence of tb-e screen, would make it appear that the cathode ray tube figure comprised three superimposed -figures such as would result from the superpositioning of those figures shown in Figure 55, page 948 of 50 Terman, supra, which are designated respectively as "Phase difference, 45', 90o, and 1351." Under these circumstances, phase shifters C ar-d D may be adjusted to co-phase radiators 2 and 3 with radiator@ I and phase shifter 19 may be 55 adjusted to co-phase its output with that of radiator 1, whereupon the radiators, when sequentially energized@ will produce superimposed straiht line figures on the cathode ray tube 20. Under these conditions, any small phase d-iffer00 ence between the energy radiated from radiators 1, 2, and 3 wi-ii be, apparent by a tendency of one or more of the apparently superimposed figures to become elliptical and this tendency can be corrected by an adjustment of phase shifters 65 C, D, or 19. A required condition for the preferred mode of operation of this radio b,,acon is that the fields radiated by radiators 1, 2, aiid 3 shall be in time' phase. Fig. 3 is a block diagram of the equipment to 70 be carried in a moving body, aircraft, or surface vessel by means of which the phase angles 02 and 03 may be d--termined ' 02 and q53 respectively are defined as the phase angle of the radis.tion field received at the point P, where the movvoltage to gate R2 during, period T2+Ti=@ miui- 75 ing body is situated, from radiatbrs 2 and 3 re-
[3]spectively both of which are measured in relarg3f tube. This wili occur only when the timo tion to the phase@ of the radiation received at point P frcim radiator 1. In Fig. 3, the ascillotor 32, pulse shape-,,@ 33, multi-vibrators 34 and 3 5, all gates, and all p' iase shifters are similar in design to those prevously described as utilized in the circuits of Fi,@. 2. Tlie@ supei-heterodyne receiver 30 is of conventional design such as is described on page 636 of Terman except that the second detector and a,udio frlequency section is oinitted and the intermediate ftequency (I. F.) output is passed through gate S to@ the vertical deflection plates of the cathode ray ose.,,llr;scope tube 36. In Flg. 31 the oscillator 31 is of con-ventional design' The output si.-nal of this oscillator, at fr.equency. IF is connected to the horizontal deflectiori plates of tlie oscilloscope tube 36 through thr'ee parallel chantiels as follows: 1. Through gate @Ri; 2. Through phase shifter A, gate Ai and gate A2; 3. Through plase shifter B, r.,ate Bi and gate B2. Alth6u,-h the intermedi-ate frequenc,7 IF may have any desired iialue, in the followin@ specificatioti th4s valu.-- iE-., assiimed to be 75 ke./s. In Fig. 3, tliet oscillator 32, pulse shaper 33, and multivibrators 34 and 35 bpetate in a manner identic:@,l to that de8cribed in connectio,-q with the similar devi-les of Fig, 2. Assume tliat. tl-.e switch SW-1 (in twci parts) is open, theri gate S passes signals continua;lly and locally generated IF signais from oscillator 31 pass through gate Ri only during the period Ti and are blocked by gates A2 and B2 during this period. These !F signals pass tlirough gates Ai and@ A@ duripg period T2 and are biocked by gat,-s Pi and Bi during this period. These T. F. si,@nals pass through gates Bi and 132 during petiod T31 and ate blockod by gotes Ri and Ai: durinq- this period. Sviitch SW-1 is rrovided to, perip:it the t'me@ retiods Ti, T2 and Ti to be synchrori-ed with the similor transmi,,sion periods at the transmitter. When switch SW-1 is closed, sij,@nals pass froni the receiver 30 to the verti-caj deflection piat6s of oscilloscope 38 only diiring the period Ti during which tirn,- signals from oscilla@tor 9-1 also pass through gate Ri to the horizontal deflection piates of the oscilloscope. SignMs froin the' local oscillator 3:1 are prevented fro-.rn reaching the horizontal defection pl,,tes of the oscilloscope 3a during t-he periods, T2 and T3 by the second section of switch SV,7-1 vrhich places a permanent blocking bias on gates Ali' and B2. Under the conditions described above, if tha oscillato'r 32 is not properly phased with the oscilILl,tor 112 qt the ttatisrnitter, transmitted signals di).ritig portions of transmitter period8 Til T@ and T@ will 9,11 be received during receiver pe-flod Ti (receiver periods T2 and T3 having been blanked out by the closing of switch SW-1). Because the signals transmitted dur" ing these periods are not in phase (at poii-it P), three (or sometirnes two) separate superimposed figures will appear on the screen of the oscilloscope 36@ The resultant will appear as if any two or throe of the figureg of Fig. 55, page 943 of Termari, supra, were surerimposed. If these fi,-ures changel shape or "roll" too ra,,oidly, tie ,,rernier ftequency control o,.l the recei.ve,- 30 ,3hould be adjusted to make thci IF frequey -icy of the receiver 30 more nearly equal tcy that of oscillator 31. Next t,ie vernier freqtiency control of oscillator 32 should be adjusted unti! only or-e figure such as: any one of the figures of Fig. 55, pa-ge periods Ti, T2, and T3 at the receiver are exactly synchronized with the corresponding periods at the transmitter, Under the conditions described above, the switch SW-1 is opened and three superimposed oscilloscope figures will be observed. They w-'@ll appear as if any three fiaures of Mg. 55, pag-. 943 of Terman, supra, had been superimposed. Phase sliifter A should now be rotated until one of the three figures@ is exactly superimposed on the one figure which exists ,vben switch SV@T-1 is closed. Next, phase shifter B should be rotated iintil the rei--qaining figure is exactly super15 iinposed on the other two. Under these conditions, phase shifter A indicat@-s directly the number of electric@al degrees by which the- phase of tho radiation from radiator 2 (as received at po,'-nt P) leads or llq,-s the phase of the radiation 20 from radiator 1. If at ali transmitting stations, radiator 2 is due east and 180 electrical degrees distai-it from, and in tini2 phase with, radiator 1, phase shifter A may bo cali'j3rated directly in qzimuthal@ degrees with a doui)le scale reading 25 on one 8cale@ from 270 through 0 to 90 degrees true bearing and on the other scale from. 270 through 180 to 90 degrees of true bearing. The azin,,ut-hal degrees correspondin@o,, to electrico-I degrees are readily computed from Equation 1 de3,) 2-i@7ed above@ Any one posit-,on of the phase shifter virill indicate two possible bearings, In a s,@milar manner,. phase shifter B may be calibrated directiy in a-z-1muthal degrees viith a double sc@ale reading on one see(.le frorp 0 through 35, 90 to 180 degrees of true bearing and ori the other scale from 0 through 270 to 180 de@-rees of true bearing, the azir@iuthal degrees for the double scale being computed from Equatiop- 2 in this case. Of the two possible bearings indi40 cat-,d by phase shifter A and ef t-he tV,7o possi!)Ie bearings indicated by phase shifter B, two of th@-se bearings will be identical and represent the true bearings without air-biguity exceut on bearings 0, 90, 180 and 270 degrees. If, howeve@-, 4.-, the spacings of the radia-tor towers is stand-ardized qt, say, 175 electrical degrees ar-d the phas@, sh-"fters are calibrated accordingly, there will be no ambiguity whatsoever. in the early discussion herein, a spacin@ of 180 electrica, degrees was used to clerify i@@e description. A@sume that the short 3eriod stability of the trapsmi-tter freiquency and of the freqlzency of the ffrst oscillator of tlie receiver 30 i-s one part per rp-illiofi and that th,@6se f,,-", uencie8 ati@,,ays drift iii opposite, direct;lons, then the freqiiencies vii'@l drift apart 2 cycles per million cycles or 0.4 cycl , e p,--r secovid at a carrii--r frenuencS7 of 200 ke./s. Pssume that the, short period stqbi,ity of os,-,il'ator St is one pp-rt per millio-.l or 0.075 cycle per second at an IF frequency of 75 ke./s., a-.id that this frequency ellways drifts in opposite direction to the drift of the IF fre,,Iuency of the ieceiver 30, then the figures on the screen of the 6scillos.-.o-,Oe will tevol@.-e or "roll" a,t the rate of 0.475 revolution. per sec,,ond. The ibove stated osciliator stabilities ar6 easily achieved and the figures on the screen of the oscillosco,,ue eftii be eagily obstrved v,7hile rolling as rap;dly as 0.475 revolution per second. Careful adjust7' -rq@@nt (if t,ie frequency col'itrol vernier oi-i the roceiver 30@ will reduce this roll to much less than t',ii8 val,.Ue. If the OSCillOS-bpe figures rol - 1 0.475 revoliition per second=171 electrical degrees P. Second,. then in the four milliseconds re048 of Tetman, supra,, is@ displayed by the cathode' 1--5 quired @for each complete comparison. of pbases,
