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Sept. 3,1946. C, B_ WATTS, JR ' 2,406,676 INSTRUMENT NAVIGATION SYSTEM Filed May 29, 1942 « 1 4 sheets-sheet 1 . l A , , . §71/ 9>\V/ I Vy» \ _ Maul/¿A701? Fo/P 5 Z4 ,2f mmc/N6 NETWQRK . ‘ía’ -L "f4/16:5?2 Q2.; mmm/JE - comma INVENTOR CHESTER 5. Mfrs, c/f?. ‘BY ATTORNEY Sept. 3, 1946. 2,406,876 C. B. WATTS, JR INSTRUMENT NAVIGATION SYSTEM Filed May 29, 1942r 4 sheets-sheet 2 '21 ANPL Irl/DE AMPL/Tz/DE ' CoA/m01. CHESTER B. WATTS, L/R. BWM@ @L4M ATTORNEY Sept" 3, 1946» c. B. WATTS, JR 2,406,876 INSTRUMENT NAVIGATION SYSTEM Filed May 259,I 1942 4 Sheets-Sheet 3 @fg-7 0/3456789/a/1/2/3/4-/s/617/e -~ELEVATION ANGLE° INVENTOR CHESTER B. MTN, d?. BYpW/f Ü? Mw@ ATTORNEY Sept. 3, 1946. 2,406,876 C. B. WATTS, JR INSTRUMENT NAVIGATION SYSTEM Filed May 29, 1942 4 Sheets-Sheet 4 CHESTER B. Mfrs, de, www/52%@ ATTORNEY Patented Sept. 3, 1946 2,466,876 UNITED STATES PATENT OFFICE 2,406,876 INSTRUMENT NAVIGATION SYSTERI Chester B. Watts, Jr., East Orange, N. J., assigner to Federal Telephone and Radio Corporation, a corporation of Delaware , Application May 29, 1942, Serial N0. 444,988 16 Claims. l ( Cl.' Z50-_11) 2 This invention relates to directive antenna structures and more particularly to such systems for producing the radiation patterns of Fig. 3 with the antenna apparatus of Fig, l; as are employed for the instrument landing of Fig. 5 diagrammatically represents another suitable antenna arrangement; aircraft. The invention is considered to be equal ly adaptable to transmitting and receiving pur Fig.> 6 is a schematic block diagram of a circuit poses and, in this connection may be useful in for feeding the antenna structure of Fig. 5 to radio locating systems-especially where discrim yield substantially the radiation characteristics ination as to elevation angles of low magnitude is of particular importance. It is an object of the invention to provide an im proved and safer instrument landing system. shown in Fig. 3; Figs. 7, 9 and 11 are graphical plots of signal 10 strength as a function of the elevation angle for further illustrating features of the invention; and Another object is to provide such a system wherein small deviations up or down from the true Figs. 8, 10 and 12 are schematic block diagrams glide path will be characterized by relatively large signal strength. A more specific object is to provide means for 15 of appropriate circuits yielding substantially the radiation characteristics shown in Figs. 7, 9 and 11 respectively. Antenna structures of the so-called vertical type are known for use in connection with set ting up radiation fields suitable for instrument throughout the region from zero elevation angle landing purposes. Referring to Fig. 1, it has here to a substantial fraction of the angle at which 20 tofore been proposed that the antenna for defin the iirst major lobe occurs. ing a glide path by the equi-signal principle In accordance with a feature of the invention, should comprise two antennae A, B disposed one I provide means for radiating a vertically direc above the other. radiatingr a vertically directional pattern char acterized by relatively weak signal strength tional pattern (suitable for use as one of two over According to the system heretofore proposed, lapping patterns of an equi-signal glide path ra 25 the higher antenna A is fed with a signal repre diation) and including an undesired lobe of lower senting a “too low" airplane position (preferably elevation than the first (i. e. lowest) useful lobe a carrier modulated with 90 c. p. s.) while the of said pattern but having a maximum magni lower antenna B is fed with a “too high” signal tude less than four percent of the maximum sig (preferably a carrier modulated with 150 c. p. s.) . nal strength of said ñrst useful lobe. 30 The two patterns thus produced overlap and ef In accordance with another feature of the in fectively intersect along several conical surfaces, vention, I provide means for radiating~ a verti where the axes of said conical surfaces are con cally directional pattern characterized, in the ele sidered as passing vertically and symmetrically vation angle region about the desired glide path, through antennae A and B. by a signal strength which varies with elevation 35 In order better to compare these two diiîerent angle 0 roughly in accordance with the following patterns, radiation signal strength R. has been function; plotted as a function of the elevation angle 0 in Klcos @fi-cos (Ice-00)] Fig. 2. In the case illustrated by this ñgure, it was assumed that the ratio a:b of the respective 40 elevations (with respect to ground) of antennae where K and Ic are constants and 6o is less than A and B was such that each lobe I0 of radiation twenty-five degrees (positive or negative). due to antenna B comprises a total elevation angle Other objects and further various features of equivalent to that comprehended by lobes ll, Il', novelty and invention will hereinafter be pointed out or will become apparent to those skilled in the 45 ll", etc. of radiation due to antenna A. With this type of system, if maximum radiation due to art from a reading of the following specification each óf vantennae A and B is substantially equal in connection with the drawings included here (as illustrated by the lobes ID and Il), the first with. In said drawings intersection l2 of radiation due to antenna A with Fig. 1 diagrammatically represents an antenna that due to antenna B, occurs at an angle well structure suitable for use in accordance with the 50 above that at ywhich the first maximum of radi invention; ation due to .antenna A occurs. This circum Figs. 2 and 3 are graphical plots of signal stance is significant in that, for a given antenna strength R as a function of e (the elevation angle) height, the glide path angle is too large; or, con for illustrating features of the invention; versely, for a desired glide angle, the antenna Fig. 4 is a schematic block diagram of a circuit 55 height must be unnecessarily large. In addition 2,406,876 3 to this fact, there are further intersections I3, I4 for angles very close to that represented by in tersection I2. Since each intersection represents an angle which landing instruments aboard an aircraft may indicate as an appropriate glide an Ul gle, intersections I3 and le may be sources of considerable confusion to a pilot. It is accordingly necessary in this type of system to increase the magnitude of current fed antenna B with respect to that fed antenna A a substantial amount so as to produce a “swamp 4 fore, the overall 15G-cycle radiation pattern will be seen to have substantially zero radiation for these small angles as well as substantially zero slope (i. e. rate- of increase oí radiation per de gree elevation) . Thereafter, between 2 and 3 de grees this radiation will markedly increase (due to the rapid divergence of the two curves after the one due to antenna A passes its maximum and starts to decrease). Thus the resultant radiation of the 15G-cycle or “too high” signal will present substantially the characteristics of curve Il in Fig. 3, while the 90 ing” lobe l5 of radiation. It will be noted that cycle or “too-low" radiation, being due to antenna the 90-cycle radiation pattern due to antenna A A alone, will have the simple substantially hali intersects lobe l5 of the 15G-cycle pattern at only sine slope of curve l, l', 1” in the same iigure. one point in the ñrst 20 degrees namely, at point 15 The curves of Fig. 3 represent radiations from Ikfà, near the maximum of the first lobe Il. an array like Fig. 1 where the elevation ratio However, although any diiiiculty of confus arb is 3 so that at low angles there are three lobes ing intersection i6 with further adjacent inter of radiation due to antenna A lfor each lobe due sections of the radiations due to both antennae to antenna B. Curves 'i-l'-'i”, il, &--%’-‘9", and 20 A and B has been removed, certain other diiiî il relate to a system wherein the “too high” .culties are presented 'by this type of radiation. signal current in B, the “too high” signal cur For example, it will be noted that the differences rent in A, and the “too low” signal current Yin between radiation l5 due to antenna B and radia A are proportional to the values 1, 1A?, and 1 re tion ll due to antenna A for angles of elevation spectively. Curve 8 represents the “too high” lower than the glide path are relatively small as signal component from antenna BÍ. . Curve compared with corresponding differences at ele 9--9’--9” represents the “too high’y component vationV angles just above the correct glide path. from antenna A. Curve Il represents the re This condition is considered undesirable in view sultant I “too-high” pattern of slow-rise form. of the fact that a pilot will not be sumciently Curve 'l-‘i’-1” represents the simple pattern oi warned of deviations below the latter. A safer - the “too-low” signal as radiated from antenna glide path should be characterized by relatively A only. Point I-ß is the intersection of vcurves Il great differences in amplitude of the two types of radiation for deviations below the glide plane, so that there will be no danger of running into high ground obstacles as a result of miscalculat ing the true glide path. Furthermore, a safe glide path should exhibit the feature illustrated by lobes il and l5 of presenting no false glide paths for angles which may reasonably be con fused with the true glide angle. In accordance with the invention, these desir able features may be realized by producing the “too high” radiation pattern as a vector sum of two or more elementary radiation patterns from two or more antennae of different heights above the ground. In accordance with a specific fea ture of the invention two elementary radiation patterns to be combined have their strengths pro portioned to make their slopes about equal at or and 'a'. Curves l1’ and Il” are slow-rise curves produced from the same array but with the cur rent proportions adjusted to 111/511 and 1:2/511 respectively instead of 111/311 as in curve il. It will be noted that intersection I8 is formed from one rapidly falling curve l and onerapidiy rising curve Il and that therefore, deviations above or below the correct glide plane will be characterized by abnormally large signal recep tion. It is further to be noted in connection with the arrangement illustrated in Fig. 3, that the next intersection i9 of the two signals char acterized by these two types of radiation occurs at an elevation angle well above the true glide plane. There will accordingly be little or no danger in this >case of a reasonable pilot mis taking the true glide plane. A relatively simple circuit for simultaneously near the zero point and are oppositely phased. 5.0 obtaining the two types of radiation in Fig. 3 is Thus the resultant “too high” pattern produced by combining them has a substantially zero slope shown in Fig. 4. This circuit is designed for pro ducing an equisignal glide path wherein devia at or near zero and is therefore delayed in rising tion below the true glide plane is detected by a , to its ñrst large maximum value. Such a pattern predominance of one steady signal and deviation may for convenience be referred to as a slow-rise 55 above is characterized by a predominance of an pattern. Y other steady signal. In the form shown, a car -A glide path system having a “too high” pattern rier frequency fu is supplied from a common of the slow-rise type may be constructed with_ source Ztl and fed to one terminal of a conjugate a two-antenna-element structure of the nature network. 2i of the type disclosed in the U. S. shown in Fig. 1 by applying to antenna A not 60 Patent 2,147,807 to A. Alford. In accordance only the usual 90-cycle signal but in addition some with the teachings or" the said patent, network 15G-cycle signal (exactly like that supplied to 2i serves to supply equal amounts of carrier en antenna B but in phase opposition thereto). 1n ergy into two transmission lines 22, 2e for sep other Words, considering the radiation pattern of arate modulation by the respective signals F1 65 the 15G-cycle signal, the radiation thereof will and F2 (which may be 9i) and 150 c. p. s. respec be modified considerably due to an effective can tively). Also in accordance with the said pat cellation of radiations from antennae A and B ent, this modulation is preferably effected by for very small elevation angles in the vicinity of continuously' varying the tuned states of a pair of zero elevation. In accordance with the inven tion the magnitudes of the 15S-cycle signal corn 70 coupled sections 2i, 25 associated respectively with lines 22 and ‘23. The “too-low” signal (oon ponents fed toV antennae A and B are such that, when plotted, the two curves are substantially tangent at the lowest elevation angles, say be tween zero and 1 degree. Upon combining these two 'components for effective subtraction, there sisting of carrier .modulated by the iXi-cycle sig nai F1) is then fed from line 22 to one terminal of another conjugate network 26, and the diag 75 onally opposite terminal thereof is similarly con 2,406,876 nected to line 23 to receive the “too-high” sig nal (consisting of 15G-cycle or Fz-characterized carrier). Other terrminals of network connected respectively to antenna A and ing network 21. Between the terminals work 26 connected to antenna A and to 26 are balanc of net line 23, there is a phase reversal element 28 (e. g. a trans 6 the simple ñrst embodiment above taken for illus tration, the power radiated at 6° is (1.33)2+(1) 2:2.78 and the power radiated along the glide path is (.55)2+(.55)2=.6 Thus the wastage ratio is 4.6. By slightly varying the ratio of the “too high” mission-line transposition) for assuring that none signal currents fed to antennae A and B the of the “too high” or E12-characterized signals will be fed into line 22 and, conversely, that none of 10 elementary patterns corresponding to patterns 8 and 9-9’--9” will become less accurately tan the "too low” or .F1-characterized signals will be gent and the combined pattern will change from fed into line 23. Amplitude control means 29 is the form shown in curve I1 to the form shown provided in the line supplying the signal F2 to in curve l1’ or I7". network 26, whereby the amount of signal F2 to If for example the 150-cycle-modulated cur be radiated from antenna A may be controlled 15 rents are fed to antennae B and A in the ratio with respect to the amount of signal F1 radiated 1:1/5 (instead of 1:1/3 as before) the elementary ?therefrom.Y .As explained above, antenna B is pattern due to antenna A will be of smaller am fed with only one signaland, in the form shown, plitude than curve 9--9’--9” and therefore the it is connected to line 23 so as to radiate carrier characterized with F2 modulation. For purposes 20 combined pattern l1’ instead of having a zero slope at the origin will start rising immediately. of controlling the magnitude of radiation from If such a pattern I1' is substituted for pattern antenna B with respect to that from antenna A, I'l (the pattern 'I-1’-1” being retained without suitable amplitude control means 3i! are pro change for the “too low” signal) the resulting vided in its supply line. In the embodiment above described as a ñrst 25 system will be a little better than the first em bodiment in respect of lowness and power wast age ratio but a little less desirable in sharpness. More speciñcally for this second embodiment rep resented by curves I‘l’ and 'l-'V-'I" the low 9-9’-9” (representing the “too high” signal energy from the antenna A) had such an inten 30 ness is !3.2% per wave length of height, the illustration, it was assumed for simplicity, that patterns 8 and T_T-1" each had an intensity of one unit while the elementary radiation pattern wastage ratio is 3.4 and the sharpness angle sity as to be substantially tangent to pattern 8 for two to one signal ratio is about 0.65 degree. (representing the “too high” signal energy from If on the other hand the A antenna’s share of the antenna B). This latter assumption required the 150-cyc1e-modu1ated signal is raised instead that pattern 9--9’--9" be about 1/3 the ampli tude of pattern 8 since the spread between two 35 of lowered, so that the current ratio is 1:2/5 for this signal, the resulting embodiment will be successive nulls of pattern 9-9’-9" was about slightly less advantageous in respect to lowness ’,/3 the corresponding spread for pattern 8. These of glide path _for a given antenna height as well simple assumptions led to the postulation of cur as in respect to the power wastage, but the rent strengths proportionate to 1:1/3r1 as above sharpness will be improved. More specifically for set forth. 40 such third embodiment (having a 1:2/5z1 propor The two intersecting patterns H and T_T-7” tion for the “too high” current in antenna A the which result from these simple assumptions prove “too high” current in antenna B and the “too to be reasonably useful from the most essential low” current in antenna B respectively) the pat standpoints. Considering ñrst the important cri terns will correspond to curve il” and curve terion of how low a glide angle can be defined " T_T-ï”. It can be computed that these pat with a given antenna height, it will be seen from terns give about 12.6 percent lowness per wave Fig. 3 that a glide angle can be established at length of height, a power wastage ratio of 5.5, and 3.25". Now the curves of this ligure are based a sharpness of about .47 degree. upon antenna heights a and b of about 7.2 wave In. accordance with the invention, the lowness 50 lengths and 2.4 wave lengths respectively. Thus per wave length of height can be increased by if the percentage of lowness of the glide be taken as I3Q() times the reciprocal of the path elevation in degrees (so that a glide of 3° has 100% lowness while a glide path path glide path of 6° providing for the “too low” signal, in lieu of .the conventional half-sine pattern ’I-«T-V' a modi fled pattern which will cause the intersection de fining the glide plane to occur at smaller angles has only 50% lowness) the simple embodiment 55 for given antenna heights. This modified half above described gives 92.4% lowness for an over sine is illustrated in Fig. ’7 as the curve 130. Curve all height of 7.2 wave lengths or 12.8% lowness 4B is the resultant of a vectorial addition of some per wave length of height. radiation from both antennae A and B in a phase relationship similar to that required to produce Considering next the sharpness of the glide path, this may usefully be deñned by the number 60 the slow rise type of curve (such as curves il, I "I", I1” in Fig. 3 and curve lil in Fig. 7) but with the of degrees divergence downward from the true relative magnitude greatly altered. To produce glide path required to yield a two-to-one intensity the slow-rise type of pattern previously described ratio between the 150 and 90 cycle signals. Using this criterion, itwill be seen from Fig. 3 that at 65 the amplitudes of the two elementary 15G-cycle radiations are so adjusted that in the low angle 275° the 90-cycle-modulated signal has an inten region below 11/2" or 2° they are roughly equal and sity of about 0.78 while the 150-cycle-modulated in the region near the glide angle the slower vary signal has an intensity of about 0.39. Thus since ing radiation from the lower antenna B is pre the glide path I8 is at 3.25", the sharpness is ap dominant so that around the glide angle the proximately 0.5 degree. resultant 15G-cycle radiation may be said to con Finally, consideration may be given to the sist o1" the 150-cycle radiation from B minus the power wastage which will be roughly indicated 15G-cycle radiation from A. To produce the by the ratio of the maximum power radiated in modified half-sine curve 40 for the 90-cycle signal any one direction oil the glide path to the power on the other` hand the elementary 90-cyc1e pat radiated along the glide path. In the case of » tern from antenna A should predominate over 2,406,876; 7 8 therefore adjusted to >effect a- 50% current‘mag nitude reduction. The Frsignal is usedto produce? curve 4l! by of the 90-cycle radiation from A minus the 90 directly connecting line 22 to terminal 46’ of netcycle radiation from B. For convenience the for work ¿lliy and also through appropriatev ampli mer procedure of combining radiations to yield a a tude control means` A8 to terminal 44' of net slow-rise pattern consisting of Bradiation minus work 44. As above indicated, curve 4l] was obv-` Aradiation may bey hereinafter referred to as a tained by a reversed subtraction involvingranti normal subtraction proces-s, and the latter proce phasal radiation of the F1 signal from both the; dureV of combining radiations to yield a modiñed antennae. Th-e phase reversalk element in both half-sine pattern consisting of. A radiation minus. networks 'it and ¿ill are- therefore so disposed' B radiation may be referred to as a reversed sub that the'Fl signal isïconveyed to both‘ antenna thaty from B so-thatzaroundtheglide anglefthe-î resultant S30-cycle radiation may beisaid to consistf traction process. The curves illustrated in Fig. 'ï'relateto a two element antenna array as illustrated in Fig. l, elementsin such manner thatY one is‘in phase: opposition with respect to thek other. Since thef magnitude of theFl signalsupplied to antennal wherein. antenna A is disposed at> anelevationof. 15: Bis toy be one half that of the same signal sup5.y Wave lengths while antenna B Y is V2.2 wave plied to antenna A, amplitudecontrol means 48 lengths above the ground. At. 330 megacycles, is so adjustedas tol eifect a 50%-reduction' in F1 these. heights are 4.5 meters and 2 meters. The modulatedcarrier currentv magnitude. With re-elementary radiation. pattern from antenna A spect to'the'F2 signal current fed antenna B, alone is therefore> a half-sine curve consistingof which current has Ybeen considered as of unit a series of lobes such as 5 occurring alternately magnitude, theF1 signal fed antenna A is three inphase opposition atperiods-of about 5.8°. The quarters this value, and that fed to antennal B elementary radiation pattern from antenna B is three-eighths thereof. Accordingly, ampli- alone is characterized by somewhat fatter lobes E5 tude `control means t9 is included in line 22 prior 25.' havingv a periodicity of about 13.1°. Curve to its branch connections to networks 44 and 46. 4 l '--4 I'is a slow-rise pattern similar to curve Il” When control means 49‘ is adjusted in accord ofFig. 3. In the system represented in Fig. '7, ance‘with this three-quarters factor, it is clear curve lll is characterized by the F2 signal and is that bothI antennae will be supplied with signals obtained by radiating the same at unit magnitude from antenna B and` substantially half unit mag 30 F1: and F2 in correct proportion and phase simul taneously to produce‘the F1 signal in accordance nitude in opposed phase relationship from an withi radiation curve fili andthe F2 signal in ac tenna A, while the F1 signal is fedy to antenna A cordance with curve 1H. in three-quarters unit magnitude andto antenna It will be observed that inherent in the oper B in phase opposition `to that fed antenna A and atsubstantially half the magnitude of the latter, ‘ that is, about three-eighths unit magnitude. The result of' both these normal and reversed subtraction processes with respect to signals‘Fi ation of the circuits of' Figs. 4 and 8 above de scribed, is the undesirable feature', due to the arrangement of network 26er 46, that for eachY watt of power supplied to antenna A for radia-`v tion, approximately one watt is dumped `or lost and F2 will be observed as yielding, a pair of curves ¿lli and lll which are well separated from 40 in the balancing network (e. g. network 2l of Fig..4 or network 55A of Fig. 8). Such ineffi ciency may be avoided while still yielding sub-Y stantially the same type of radiation characintersection point of curves ¿El and ¿li more near teristics as above described. in connection with` ly approaches the maximum of curve 5 whereby a more desirable glide angle of approximately 3.7° is 45 Figs. 3 and 4. To accomplish this, the antennav structure of Fig. 1 should be. replacedby an an obtained with the above-indicated antenna di tenna structure of the nature shown in Fig. 5 mensions at the specified carrier frequency. This eachother for substantialïarcs both sides of the glide angle. It will further be observedthat the represents a lo‘wnes-s of 16.2% per wave lengthoi height. The sharpness is about .5 degree, i. e. practically the same as before. It is to be noted, connected as shown in Fig. 6. This alternate an tenna structure comprises an additional radiat . ing element so that there are in all three antennae A, B', and B” dispo-sed one above the other. An tennae A andB’ may be relatively close to each. other but vnot so rclose as to exhibit undesirable in teraction. If the elements A and B have directiv power on co-urse to maximum power in any one 55 ity in themselves, they may be tilted orV displaced horizontally (perpendicular to the flight path) so direction off cour-se is a little less than 1:12. that each may have its null aimed at rthe other to An appropriate circuit for obtaining the radia decrease interaction even with the antennae quiteV tion patterns illustrated in Fig; 7 is shown in Fig. close t0 each oth-er-or at least at nearly the 8, wherein the common carrier frequency source same height. In order to obtain substantially 2O and modulator means Zê and 25 for modulating 60 however, that this improvement as to lower glide angle for given antennae heights has been gained at the expense of radiating eñîciency, for, with the arrangement according to Fig. '7, the ratioof, carrier with the signals Fi and F2, respectively, will be recognized. In order to produce curve 4l, line 23 is directly connected to antenna B .through the effects shown in Fig. 3, the elevations- of one arm of a conjugate network Afl, and to-an Thus the arrangement is approximately equiv alent to that’shown in Fig; 1, as‘will be clear. tenna A by way of appropriate amplitude> control means 455 and another conjugate network d6. Since it'was necessary in the production of curve 4i that the F2 signal be supplied to antennae A and antennae A and B' may be almost alike and the mean height of antennae A and B’ is made equal to the height computed for antenna A in Fig. 1. A circuit for feeding the array of Fig. 5 to produce effects similar to those produced by the circuit of Fig. 4 is shown in Fig. 6 wherein the B in reversed phase relation, the phase reversal >element 4l of network 46 is included in the arm 70 common carrier source 2i] and modulators 24 and 25 will be recognized. Since antennae A thereof adjacent antenna Aand line In the and B' are sufficiently spaced so as to have rel assumed case, the magnitude of F2-modulated Sig atively little interaction, there is no need for a nal fed toantenna A is one half unit (where a fur-ther‘conjugate network. The Fi-character unit represents .the magnitude of the F2 signal fed to antenna B). Amplitude control means ¿55 is 75 izedsignalmay- therefore, lbe fed- directly- to an-V 2,406,876 9 . tenna A and the 1lb-characterized signal direct ly to antennae B’ and B” in appropriate am plitude relation as controlled by amplitude con trols 3|, 32. Again in order to obtain the de sired effective subtraction in connection with radiation of the F2-characterized signal, the line feeding antenna B’ includes a phase reversal ele ment 33. Instead of considering the array of Fig. 5 as being merely an approximate equivalent of Fig. 1 (an approximation which is valid only if antennae A and B’ have nearly the same heights), the array may be more rigorously analyzed as comprising one pair of antennae B’, B” used for radiating the “toohigh” signal in accord ance with a slow-rise type of pattern and one 10 above the ground, antenna B’ is at 1.5 meters elevation, and antenna >B” is at one meter, the curves shown in Fig. 9 result for an operating frequency of 330 megacycles. In this iigure, curve 50, representing radiation of the F2 signal, is a composite of radiation from all three of the antenna elements, and curve 5|, representing radiation of the Fi signal, is formed by using the upper two antennae A and B’. In order to ensure that oscillations of curve 50 sub sequent to the initial rise thereof occur so safely above those of curve 5| as not to permit an intersection of these two curves except at point 52 (for the glide angle), curve 50 has a com ponent of radiation from the lowest antenna ele ment B” of a magnitude approximately 2.4 times unit magnitude. Due to the fact that radiator B” is but a meter from the ground, lobes of radiation therefrom are relatively fat and have a periodicity of the order of 30°. Thus curve 50 is prevented from intersecting curve 5| for sub stantially that range of elevation angles. In order to promote a steepness in the first rise of curve 50, the F2 signal is supplied to antenna B’ in substantially 1.1 current magnitude and t0 antenna A in unit magnitude and opposed phase relation with respect to its supply to the lower two antenna units B’ and B". In order to ensure that the ñrst lobe of curve further lone antenna used for radiating the “too low” signal in accordance with a conventional half-sine pattern. 4When computing the radia tion patterns o-n this basis, the actual heights of B’ and B” may be used in plotting the slow rise radiation pattern of the F2 or “too high” signal, and the actual height of antenna A may be used in plotting the conventional pattern of the Fi or “too low” signal. In a preferred embodiment of the invention the form of array shown in Fig. 5 is proportioned with antennae B” and B' at heights of 2.17 and 6.5 meters respectively and the 150-cycle-modu lated 330 megacycle “too high” signals are fed 30 5| representing radiation of the F1 signal, will be into these antennae with current strengths of 1 of substantial magnitude and at the same time unit, and 2/5 units respectively, thus producing in order to prevent subsequent lobes thereof from for this signal a slow-rise pattern exactly like attaining such magnitudes as may be likely again curve 17" of Fig. 3. The A antenna used for to intersect with curve 50, the former is com radiating the 90-cycle-modula|ted 330 megacycle posed of two components radiated from the upper “too low” signal in this system is 7.5 meters two antenna elements A and B’ in aiding phase high thus giving a conventional pattern of sub for their lowest elevation lobes. In the form stantially half-sine form, similar to the pattern shown, curve 5| is the resultant of Fi signal cur l, l', “l”, but narrowed so that its first null is rent of 0.7 unit magnitude supplied to antenna at 31/2" instead of 4°. If this signal is fed into 40 A and 0.3 unit magnitude supplied to antenna antenna A with a current strength of 1 unit the B’. The resultant of such radiation of the Fi “too low” pattern will be practically the same as and F2 signals is thus seen to define a reasonably curve '1_-T_T’ except for the narrowing above low glide angle (3.7") for a given maximum arimentioned. Thus, no special set of curves are tenna height (4.5 meters at 330 megacycles, i.e. shown to illustrate this embodiment since curves 5 wave lengths). It is quite clear from an in il" and ‘|-1’--'|” of Fig. 3 may (by disregard spection of the trend of curves 50 and 5| for ing the calibrations in degrees) be regarded as larger elevation angles that these two curves will rough illustrations of the general form of the not intersect one another to form a confusing or radiation patterns of this embodiment. The in secondary glide path until some abnormally large tersection of the two patterns of this embodiment 50 angle, of the o-rder of 25 to 30 degrees, is reached. occurs very nearly at 3°, thus giving a somewhat An appropriate circuit for supplying the three lower glide path than the patterns of Fig. 3.` The antenna elements A, B’ and B" simultaneously antenna height assumed, however, is substan to generate radiation patterns 50 and 5|, is tially higher (e. g. 8.2 wavelengths) than in the shown in Fig. 10 wherein the circuit for produc case of Fig. 3. The percentage of lowness per ing the F1 and F2 modulated carriers will be rec wave length of antenna height is therefore only ognized from the several foregoing circuit dia about 12.2% being thus slightly less than for grams, In the form shown, the B12-characterized Fig. 3. carrier is supplied in a line 53, and the Fi-char It will be observed that in all of the above acterized carrier in a line 54. Line 53 is Con described radiation conñgurations, false courses 60 nected to one terminal of a conjugate network are bound to occur at elevation angles within 55, and the latter serves to relay the F2 signal about three times the glide angle defined thereby. in unit current magnitude to antenna A, as will As indicated above, this condition is not ordi be clear. As indicated, the supply of the F2 sig narily serious, for a reasonable pilot will nor nal to antenna A is in reversed phase relation; mally be able to distinguish between a proper 65 accordingly, the phase reversal element 56 of net glide angle of about 3° and a false one three work 55 is in the arm thereof joining antenna times as steep. However, in order unmistak A and line 53. The F2 signals are also simul ably to deñne a glide angle without there being taneously supplied to antenna B’ through ap any secondary or false angles at anywhere near propriate amplitude control means 51 and an the proper magnitude, I propose to employ three other conjugate network 58, and to antenna B" vertically disposed radiating elements to produce through amplitude control means 59. As indi patterns substantially as shown in Fig. 9. To cated, the supply of F2 signals to antenna B’ this end, an antenna structure of the nature is at 1.1 unit magnitude; accordingly, amplitude shown in Fig. 5 may be employed. In a specific control means 51 is adjusted to eiïect this am case wherein antenna A is disposed 4.5 meters plification. In the same way, amplitude control 12 '1li means 59 ís set to efîect a 2.4 increase in mag: nitude of the F2 signals supplied to antenna B”. The F1 signals are supplied to antennae A and B' simultaneously by branchesV of line 54 con Y nected respectively to terminals oi networks 55 and 58, which'terminals are opposite those at which the F2 signals are furnished. In order to effect the appropriate proportioning of these sig nals with respect to the above-mentioned unit current magnitude, amplitude control means El] and El are included in the respective branches of line '51E connected to conjugate networks 55 and 53. In order to produce the curve 5i of Fig. 9, control network Si] is adjusted to eiTect a reduc tion in Fi-signal current to 0.7 unit magnitude, and control network 6I is adjusted to eiiect a 'ren glide plane. ' . „ In order to illustrate an alternate method of supplying the radiating elements with appropri ate mixtures oi the two Vsignals Fi and F2 for radiation in accordance with the invention, the form of circuit arrangement shown in Fig. 12 is used to illustrate how this alternate method may be adapted to produce the radiation patterns oi Fig. l1. In accordance with this form, signal Fi modulates a first carrier fi, >and the signal F2 modulates a second carrier f2. Appropriate mix ing means vare provided for radiating the two signals F1 and F2 in accordance with the inven-` tion, Vand when an aircraft is equipped with re duction thereof to 0.3`unit magnitude. In connection with the radiation patterns of Fig. 9, it will be noted that the comparatively great >degree of .freedom from false glide angles ceiver means having suñicient band width of response -to vcomprehend both carriers fi and f2, it is clear that the original characteristic signals F1 and F2 may be detected and then separately has been obtained with a substantial sacrifice in radiating eniciency, for, in that case, the ratio of power on course to maximum power olii course path-indicating signals. is of the order of 1:14. Actually, however, much closer false courses may be tolerated and in ac cordanceV with a further embodiment, this ehi» ciency expression is vastly improved and at the same time, the glide angle is still further re duced for the same maximum antenna height. This latter embodiment produces the radiation - characteristics of Fig. 11 by means of a circuit such as shown in Fig. 12. The antenna structure for producing these patterns is substantially the ‘ will be impossible for a reasonable pilot to mis take this second ’coursefat 12° ior the proper same as that required to produce the patterns of Fig. 9 with the. exception that the middle antenna element'B’ is at twice its former height, that is, three meters for the assumed case of 330 Radiation oi the F1 megacycle operation. characterized carrier is of the form shown by curve ‘652, and the Fzwsignal radiation is repre sented by curve The latter is, as in the case of Fig. 9, formed as the resultant of radiation from all three antenna elements in the same discriminated as by filter means to derive glide In the form shown, the carrier f1 modulated by signal F1 is supplied in a line ffiä having three branches leading respectively'to antennae A, B', and B”. The ñrst of these branches includes a phase reversal element Sii and ñlter means 6l passing only the signal supplied in line 65, that is, the carrier fi together with the F1 side-bands. The second branchihcludes vamplitude control means 'Sil and another iilter @8 passing the same frequencies as filter 8l. The 'third branch in cludes merely amplitude control means l0. As explained above, the fi carrier and its Fi side bands are supplied to`antenna A in unit current magnitude, to antenna B’ in 1.1’times unit mag-' nitude, and to antenna B” in 2.4 times unit magnitude. Amplitude control means 58 and 'lll are Yappropriately adjusted with respect to each cther’and Atothe magnitude of current supplied to antenna A to lsecure this proportioning of current‘magnitud'es, as will be clear. The f2 carrier as modulated by the signal F2 is supplied ina line 'H having two branches magnitude and phase relation proportions as ' above-‘considered for Fig. 9. Curve V52, however, 45 connected respectively to the upper'antenna ele is formed by a so-called reversed subtraction process >of the nature above described in con nection with curve il@ in Fig. 7. In the form shownthe F1 signal is supplied te antenna A in twice vthe unit current magnitude and to antenna B’ in unit magnitude and opposed phase relation with respect to the F1 signal fed antenna A. -The result oi this reversed subtraction (curve ments A and B’. The i'lrst 'of these branches in cludes amplitude control means ’E2 and a ñlter network 'ld lpassing only the frequencies present in line "M_ rI‘he' other branch Vincludes a phase reversal element ‘i3 and another filter 'E5 similar to filter lli. YCarriers f1 and f2 are preferably relativelyclose to each other `in the frequency spectrum, ‘and their Yproximity is governed by the ability ‘of `iilters 6l ande?) to discriminate radiation having a shorter periodicity than that 55 against the frequencies present in line li and by the converse ability of filters "M and 'l5 to dis of radiation due to the highest antenna element criminate against the frequencies presentïin line (see lobe Gil). lIîhus, if radiation of this lobe $5. Amplitude control means l2 is adjusted to d2 were controlled to be approximately the same reffect an ampliñcation oi substantiallytwice the maximum magnitude as that of lobe ed, it follows that the intersection deñning the glide angle 60 unit current magnitude. When this adjustment is made, it is clear that the circuit of Fig. 12 will be lower than the corresponding intersection will be effective to radiate simultaneously in which would result from use of Vthe simple lobe accordance with “curves S2 and §53 substantially 64. Also it is evident that the reversed sub as shown in Fig. 1l. traction gives a greater sharpness than would be It is to be noted in connection with the embodi 65 obtained by use of the simple lobe Gli. ment shown in Fig. 12 that it has been possible It is to benoted that the second lobe of curve to avoid the above-noted ine'îiiciency (due to a 62 is of greater magnitude than the ñrst. This power dumping) arising out oi >the usefof a num factor, _while detrimental from the standpoint of ber of conjugate networks and that relative lit power wastage ratio, clearly in no way affects the sharpness or unmistakability of the proper 70 tle additional apparatus'is necessary. If desired, the carriers fi and `;f2 may be maintained in sub glide course. The nrst false course as set up by stantial alignment with respect to each other by the second intersection of curves §32 and ‘53 oc means of appropriate frequency stabilization curs at virtually 12°, that is, ‘almost four times means lâ associated with both "the respective the proper glide angle. It is considered that even under the most adverse headwind conditions, it 75 sources of carriers `irland f2 whereby the total E2) will he seen to produce a first lobe of Fi 13 2,406,876 14 band-Width required for the system may be‘made subtraction process, that the proportioning of the a minimum. component of this signal radiated from the lower antenna element with respect to the component of this signal radiated from the upper element of the forms shown in Figs. 4, 8 and 10 to give Ul occurs in a preferred relationship. More speciñ patterns such as illustrated in Figs. 3, 7 and 9. cally for the F1 signals the ratio of the current Similarly, the principle (described in connection in the lower element to that in the upper should with Figs. 5 and 6) of using two separate anten be C’ divided by the corresponding height ratio, nae close together instead of one antenna fed where C’ is between 0 and 0.75. The preferred with two signals, may be applied to all the em somewhat narrower limits for C’ are between 0 bodiments illustrated as having two signals ap-` and 0.60. It will be clear that the form of feeding ar rangement shown in Fig. 12 maybe used in place plied to one element of an array. It will be noted that some of the above de Although this invention has been described in connection with transmitting apparatus, it is not scribed embodiments have fairly low radiating to be interpreted as limited to that type 0f use efiîciency as .. measured byY the power wastage ratio; butin many cases this decrease in e?ciency may be justified by the very substantial improve ment in the sharpness and in the maximum 90 to'150 cycle signal ratio observable below the glide plane. In the case of the radiation pattern 20 shown in Fig. 11, for example, the efiiciency power ratio dropped only to 117.6. It is particu larly to be emphasized that at the very reasonable operating wave length of 330 megacycles the re» sults shown, for example, in Fig. 11 were ob tained with a maximum antenna height of 4.5 meters, that is, about 14.5 feet. From an examination of all of the figures graphically showing radiation patterns in ac cordance with the invention, it will be observed that the slow-rise type of curve formed by what has been termed a normal subtraction process (e. g. curve M in Fig. '7) is generally S-shaped for V,angles up to and in the neighborhood of the glide path; the lower end of the S commencing , sometimes with a> Zero slope (e. g, curve I1), sometimes with a small downward slope (e. g. curve Iï”) and sometimes with a small upward but ratherit is adaptable both to transmitting and receiving purposes. In the latter case, it may find utility in radio locating systems of the type wherein radiations emitted (or reñected) from a plane are received on two receivers (or on one A-N-keyed receiver) making use of the equality of two reception patterns for determining the direction of the plane. While I have particularly described my inven tion in connection with systems producing tone l» modulated signals for an equi-signal course, it is clear that its principles are equally adaptable to other known course-defining systems, such as for example, the well-known aural indicating sys tem wherein the two patterns defining the glide course are alternately radiated in accordance with a keyed pattern. vIn connection with the above-described circuits keying means may be substituted for the modulators. Furthermore, in keying systems the use of power dumps may be altogether avoided by merely switching over the antennae so that in one key position they receive the relative powers above described for signal F2, and in the other position they receive slope (e. g. curve Iï’). Roughly the S-shaped the relative powers described for signal F2. Un form of the curve resembles the first half cycle 40 der such conditions, the keying means may be of a cosine curve; and to a fair approximation said to couple the antennae to the transmitter in the shapes 0f the various possible forms of so called “slow-rise” curves shown and described hereinabove may be conveniently defined by the cosine function one relation (i. e. with one set of amplitudes) “in respect of one signal” while coupling the same antennae thereto in a different relation “in K[cos flo-cos (R04-00)] respect of a second signal.” Likewise, in the earlier described illustrations of feeding the an tennae in accordance with the invention by the where K, lc and 0o are constants. If this expres sion is used to describe the shapes of the slow use of a common carrier separately modulated in two branch lines in accordance with two sig rise pattern, the preferred shapes can be said 50 nals, it may also be said that the antennae are to be those corresponding to a value of 0o be coupled to the common carrier source in one rela tween +20° and --20°. If on the other hand tion “in respect of a first signal,” and in another the slow-rise patterns are to be considered as relation “in respect of a second signal.” made up of a slowly periodic elementary curve Although I have described my invention in de from which there is subtracted a smaller more 55 tail in particular connection with the preferred rapidly periodic elementary curve, then the pre forms illustrated, it is to be understood that many ferred forms of such slow-rise patterns may be modifications, additions and omissions may be said to be those whose initial slope is roughly be made fully within its scope, as defined by the tween -i-l/g the slope of the slowly periodic ele appended claims. mentary curve and -1/2 this slope. Generally 60 What is claimed is: ` speaking, satisfactory results may be obtained 1- Glide path apparatus suitable for instru when the ratio of Fz-signal amplitudes in the ment landing of aircraft, comprising a first an lower antenna element B> with respect to ampli tudes of the F2 signal in the upper antenna ele ment A is C times the inverse ratio of respective elevations of these elements above ground, where C is between 0.7 and 1.9. In other words the F2 signal current ratio (i. e. of the lower element to the upper) is C times the ratio of the height of the upper element to that of the lower ele ment. tenna means and a second antenna means dis posed one generally above the other, a first wave-translating means operating at a predeter mined carrier frequency, means coupling said first and said second antenna means to said wave-translating means, a second wave-translat ing means also operating at said frequency, and means coupling said second wave-translating Preferred conditions, however, call for means solely to said first antenna means. slightly stricter limits of C as between O. 8 and 1.6. 2. Apparatus according to claim l wherein said It will further be observed in connection with ñrst antenna means is disposed above said second the above described figures, in which the F1 sig antenna means. nal was formed by what is termed as a reversed .75 3. Apparatus according to claim 1 wherein said 2,406,876 16 to said ñrst antenna means more energy than said second signaling meansl but said second sig naling means being adapted toY feed to said sec ond antenna means more energy than said first signaling means, whereby said iirst antenna radi first antenna means is disposed above said second antenna means and wherein said first antenna means includes-two antennae, one of said two antennae »being »connected to said last-delined coupling means, and the other of said antennae ates predominantly energy characterized by said being connected to said first-defined coupling first> signal and said second antenna radiates pre dominantly energy characterized by said second means. 4. Apparatus according «to claim 1 wherein said first antenna means is disposed above said sec ond antenna means and further wherein said iirst antenna means includes two antennae, >one of signal. » ' 8. Glide path antenna apparatus suitable for instrument landing of aircraft, comprising a first antenna means and a second antenna means dis-V said two antennae being connected to said last posed one generally above the other and above deiìned coupling means and the other of said a ground, a wave-translating means, and means antennae being connected to said first-defined coupling means, said two antennae being less 15 coupling said nrst and said second antenna means Yto said wave-translating means, said cou spaced with'respect to each other than the spac pling _means including amplitude control means ing between Veither of said two antennae and said coupling said first >antenna means to said wave translating means in a first energy transfer rela second antenna means. 5. Glide path apparatus suitable for instru ment landing of aircraft, comprising a first an 20 tion and amplitude control means `coupling said tenna means and a second antenna means dis posed one generally above the other, a ñrst wave translating means operating .at a given modula tion frequency, means coupling said ñrst and said second antenna means to said wave-translating second antenna means to said wave-translating means in a seco-nd energy transfer relation, and thetwo amplitude control means being adjusted ` so that the ratio of magnitude of said first energy transfer relation to that of said second energy transfer relation is of the same order of magni tude as the ratio of the elevation above said ground o-f said second antenna vmeans to that of means, a second wave-translating means oper ating ¿at a modulation frequency different from said given'frequency and means coupling only said first antenna means to said second wave-translat ing means, said first-mentioned coupling means including means coupling said first wave -translat ing >means to said first antenna means in a first energy transfer relation and means coupling said first wave-translating means to said second an tenna'means in a second energy transfer relation said first antenna means. Y Y V9. Apparatus according to claim 8 wherein the two amplitude control means are adjusted so that the ratio of the magnitude of said energy transfer relations is between .7 and 1.9 times the ratio of the elevation of said seco-nd antenna means to Vthat of Ysaidiìrst antenna means. Y l0. Glide path antenna apparatus suitable for instrument landing of aircraft, comprising a ñrst differing in‘phase from said -iîrst energy transfer relation. Vt. Glide path apparatus Vsuitable for instru antenna means and a second antenna means dis posed one generally above the other and above a ment landing of aircraft, comprising a ñrst an ground, a wave-translating means, :and means tenna means and a second antenna means dis coupling said first and said second antenna means posed o-negenerally above the other, añrst wave translating means, means co-upling said iii-st and said second-antenna means to said wave-translat ing means in substantially opposite phase, a sec ond wave-translating means, and means coupling said first antenna means and said second >an tenna means to said second wave-translating means'in substantially opposite phase, said ñrst to said wave-translating means, said coupling means including amplitude control »means cou pling said first antenna means to said wave translating means in a first energy transfer rela tion and amplitude control means `coupling said second antenna means to said wave-translating means in a second-energy transfer relation, and the two vamplitude control means being adjusted mentioned coupling means »including means cou pling said first wave-translating means to said 50 so »tnat the magnitude of said first energy trans fer relation with respect to said second energy transfer relation is such that _for smallelevation angles above said ground the magnitude of the first antenna means in a first energy transfer relation and means coupling said first wave translating means to said second antenna means in-a second energy transfer relation different in magnitude and phase from said firstV energy characteristic curve `of saidV first antenna means substantially equals that of said second antenna means. transfer relation, said second-mentioned coupling :11. Apparatus according to claim 1 wherein means including means coupling >said second said `first antenna means comprises two radiating wave-translating lmeans to said first' antenna elements spacedone above the other, wherein said means in a third energy transfer relation and means coupling said second wave-translating 60 first-mentioned coupling means includes means coupling said first wave-'translating means to one means to said second antennameans in a fourth of said radiating elements ina first energy trans energy transfer relation different in Imagnitude fer >relation kand means coupling said ñrst wave and phase Vfrom both said third energy transfer transiating imeans to the other of said radiating relation and said second energy transfer relation. '7. Glide path apparatus suitable for instru ment landing of aircraft, comprising a first an tenna means and a second antenna lmeans dis ' posed one generally above the other, ñrst signal ing means for feeding said first andrsecond an tenna means in substantially opposite -phase with 70 elements rinia secondenergy transfer relation, and furtherY lwherein said second-mentioned coupling means inoludes’means coupling said second wave translating' means toA one of said radiating ele naling means for feeding said first land seco-nd ments in _a vthird energy transfer relation and meansk `coupling said second wave-'translating means .to said other radiating element Vin* a fourth cnergytransîer relation, said first energy transfer antenna means in substantially opposite :phase ' relation Lbeing .of `substantially opposite-phase 'to energy characterized byra first signal, .second sig said ssecond V'energy transfer relation »and said said first signaling means'being adapted to feed 75 thirdienergy `transfer relation'being of substan with energy characterized by a A’second signal, 17 2,406,876 tially opposite phase to said fourth energy trans fer relation. 12. Glide path antenna apparatus for operation at a given carrier frequency and suitable for in strument landing of aircraft, comprising a ñrst antenna means, a second antenna means, and a third antenna means disposed one generally above the other and spaced with respect to each other at least a half Wave-length at said operating fre 18 the combined characteristic of both said antenna means is of the general. form of the function [cos lio-cos (ICH-00)] where 0 is the elevation angle, and k and 0o are constants, 0n being between +20° and -20°. 14. Glide path antenna apparatus suitable for instrument landing of aircraft, comprising a ñrst antenna means and a second antenna means dis quency; a first wave-translating means; means 10 posed one generally above the other, a wave coupling said wave-translating means to said first antenna means in a first energy transfer relation, to said second antenna in a second energy trans fer relation, and to said third antenna means in a third energy transfer relation, all said energy transfer relations being different; a second wave translating means; and means coupling said sec ond Wave- “anslating means to said first antenna translating means operating at a predetermined carrier frequency, means coupling said first an tenna means and said second antenna means to said wave-translating means in respect of a ñrst signal at said carrier frequency, a further means coupling substantially only said first antenna means to said wave-translating means in respect of a second signal at said carrier frequency, means in a fourth energy transfer relation and 15. Glide path antenna apparatus according to to said second antenna means in a fifth energy 20 claim 14, wherein said wave-translating means transfer relation different from said fourth en ergy transfer relation. 13. Glide path antenna apparatus suitable for instrument landing of aircraft, comprising a first antenna means and a second antenna means dis posed one generally above the other and above a ground, a wave-translating means, and means coupling said first and said second antenna means includes keying means, said first-mentioned cou pling means being responsive to said keying means to couple said first antenna means and said second antenna means to said wave-trans 25 lating means in respect of said ñrst signal, said further coupling means being responsive to said keying means to couple substantially only said first antenna means to said wave-translating means in respect of said second signal. to said wave-translating means, said coupling means including means coupling said ñrst an 30 16. Glide path antenna apparatus according to tenna means to said wave-translating means in a claim 14, wherein said first-mentioned coupling first energy transfer relation and means coupling means includes modulating means operating in said second antenna means to said wave-translat accordance with said first signal, and wherein ing means in a second energy transfer relation, said further coupling means includes modulating said ñrst and said second energy transfer rela 35 means operating in accordance with said second tions being of substantially opposite phase and of such magnitude with respect to each other that signal. CHESTER B. WATTS, JR.