US2425303A - Antenna system for radio drift indication - Google Patents

Description

Aug. 12,' 1947. P. s. CARTER 2,425,303

ANTENNA SYSTEM FOR RADIO DRIFT INDICATION Filed May 26, 1943 5 Sheets-Shea?l 1 l v Y INVENToR H/L/ 6. CAAQTE/ ATTORNEY Aug. 12, 1947. P. s. CARTER ANTENNA SYSTEM FOR RADIO DRIFT IDICATION I Filed May 2.6, 1943 5 Sheets-Sheet 2 INVENTQR figa/up 5. CARTER.

BY.. y

vATTORNEY Aug 12, 1947 Ff. s. CARTER 2,425,303

ANTENNA SYSTEM FOR RADIO DRIFT INDICATION Filed May 26, -1943 5 Sheets-Sheet 3 DEGREES INVENTOR PHIL/P 5. CARTER.

ATTORNEY Aug- 12v, 1947 P. sjcAR'rER 2,425,303

ANTENNA SYSTEM FOR RADIO DRIFT INDICATION Filed May 26, 1943 5 sheets-sheet 4 Tlcl. y Y T:.CIL

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BY g/www ATTORNEY Aug. 12, 1947. P. s. ARTER 2,425,303

ANTENNA SYSTEM FOR RADIO DRIFT INDICATION Patented Aug. 12, 1947 ANTENNA SYSTEM FOR RADIUDRIFT INDICATION Philip S. Carter, Rocky Point, l\I-..Y., assignor to Radio Corporation. of America, a corporation of Delaware Application Mayl 26,v 1943, Serial yNo. 1188;584

14 Claims. (C1. 12504-115) The l.present invention relates to short wave'antennas and, `more particularly, to antennasystems adapted for use with a radio drift indicator for airplanes.-

An object of'thepresent invention is the provision of .an antenna system for radio drift measurement and indication.

Another object of thepresent inventionis the provision ofa directive' antenna system `adapted to be mounted on the sidesof an airplanefuselage.

StillA another object ofI the present invention is the.v provision of a highly directive antenna system.

A further object of thepresent invention is the provision of a directive antennasystem adapted` tot bemounte'd on a-conductive sheet and having its .maximum effectiveness at an acute angle to the plane of said sheet.

Still a further object is the provision of a directive antennasystem for use with seaplanes` which does not disturb the-aerodynamics of the.y plane and Which is not lable'to water damage-in taking oi from` or alighting upon the surface of the sea.

In determining the drift of the airplane, that is, its vmotion at right angles to the indicated come pass'course of radio means, it is proposed to transmit high frequency energy ina pair of sharply directive beams to port and starboard. ofA the planefand directed downwardly atan angle of 45 degrees from the horizontal; The beams, strik,- ing a somewhat diffuselyreflecting surface, such as thesurface of the earth, or. thesea below the plane,l are reflected and the energy may bepicked up by receiving equipment on the plane.y I f the plane is not drifting the frequencies picked up. from Veach radiated beam `are equal and their mixture produces a Zerobeat indication. If the planefisdrifting, due-to a Doppler effect, the-received frequency from one beam is increased and that from-the other is decreased. Their mixture produces a beat, the frequency of vvlnch is proportional tothe drift speed with relation tothe surface loelow` The antenna `rsystem ofy the presenti invention for producing thesharply directive beams, normal tothe direction of -travel of the plane anddif rected'downwardly at` angles of 45 degrees, includesawedge radiator system on each fuselage side wall. The antennae of. eachwedge system.. include conductive flaps fastened to the conductive-side wall ofthe pla-ne Valongtheir upper edgev and-forming a small angle therewith so that an Opelflnslot-is formed-- alone the bottom. A. plurality, of antennas in Vhorizontal alignment: along.

thesidewallfmay be used so as to increase 'the4 fore andaft .directivity ofthe beams. Parasitic` reectorwedges may also be provided toconcentratezthe-radiating-energy in a single downwardly y directed' beam. Each wedge antenna lmaybe en-r ergizedby connecting `the central conductor-of aconcentric'transmission lineto the innery sideV of the ap. atits longitudinal midpoint whilethe i outer. casing of the transmission line'lisv The present invention will be morefullyunderf stood byrv reference to the following detailedvr description, which-'is accompanied Vby a drawing wherein Figuresl and..2 illustrate .the relation-V ship .ot-the`- desired radiation patterns of the antennaof the. present inventionwith respect -to aplane` onilwhich. theY antennas-'may .be mounted,

while Figure 3 illustrates kanend -view of an ein-V bodiment of the presentinventiomwhile Figure 4 is` aside view lof the embodiment and-.Figure 5 is adirectivity pattern Voftheantenna; Figure 6 illustrates a modi'iication ofthe present invention and 4Figure .'7 is a vertical directivityA pattern of the modification of Figure, while Figure Blillustrates a further. modification. ofthe .present invention; Figure v9-is ahoriz'ontal directivity. pat'- tern ofthe .modification of Figure 8,- Figures. 10

andlll are side and vend views of' a .portionf of 'a-y frther modification ofthepresent. invention,

Figure 12is adiagram'of. a transmission linefassembledfr use with the antenna ofVv Figures 10 '-and. 11," Vwhile Figures 13 and 14 illustrate the radiofrequency field distribution in a wedge resonantfchamber and Figure 15 is a curve useful injdeterminingthe proper dimensions of the anv tenna elements.

Inv Figures 1 and 2 'are shown plan and eleva.-

tilon views of .ani airplane. Shaving mounted onthe portland'starboard'sides-of thev hull*r antenna systerrisl 'and 3. As beforepointed out, it' is desired'to. transmithi'gh frequency energyin a pairof sharplyv directive beams suchas the beamsy pb andsbto port and starboardfof the plane l and directed downwardly at' an. angle. of i5-degrecs, as'A Vshown inFigure 2in the. elevational view.. The beams of energy striking asomewhat diffi'isely"v reiecting surface such asf.the'surface ofi sea S; below the plane are 1 reflectedl and -the energymay. bepickedfupfbythe antennas 2- andv 3 Y and? appliedto suitable receiving equipment; onfthe picked up from each radiated beam pb and sb are equal and their mixture in the receiving equipment produces a zero beat indication. If the plane is drifting to port, for example, the energy transmitted from antenna '2 is reected from surface of S and again received by antenna 2. Due to the antenna traveling in the opposite direction to the returning waves a Doppler effect causes the frequency of the returning energy to be higher than when radiated. The opposite eect takes place on the energy radiated and received from antenna 3. The mixture of the two received energies of different frequencies produces a beat note the frequency of which is proportional to the drift speed with relation to the surface S.

In Figures 3 and 4, reference numeral I0 indicates, generally, a vertical conductive sheet which may be considered to be a side wall of the fuselage of a plane. The dimensions of sheet l preferably are at least .3 wavelengths in height by 4 wavelengths long in order to obtain the desired directivity patterns. An elongated conductive flap I2 is fastened along its upper edge to the conductive sheet I0 and is bent outwardly to form a small angle with respect to the outer face of sheet Il). The ends are preferably closed, as shown by end walls I2 but may be open if desired. The length of flap l2 is preferably of the order of one wave length. When the ends are closed th'e width depends upon the length. The relationship between the length of flap I2 and its width will be made more clear with reference to the curve of Figure 15 which will be described later. At approximately the longitudinal midpoint of iiap I2 is connected the central conductor I4 of a concentric transmission line I5, while the outer casing I6 thereof is connected to the conductive sheet I0. The Vertical distance between the lower edge of ap I2 and the point of connection of conductor I4 maybe so chosen as to obtain an impedance of a particular value at the termination of line I5.

In Figure 5 curve 20 indicates th'e directivity pattern of the antenna of Figures 3 and 4in terms of power versus angles from a line normal to the intersection of sheet I with a reference plane indicated by line 5, 5 of Figure 4.

It will be readily apparent, from an inspection of Figure 5, that even though only a single radiator element is used in the modification of Figures 3 and 4 there is obtained a directivity pattern which is sharply directive in the plane identified by line 5, 5. It will be noted that in this plane there is an entire absence of secondary lobes or ears. However, the pattern in the vertical plane contains, in addition to a downwardly directed main beam, an upwardly directed lobe of considerable amplitude. It is desirable that all, or substantially all, of the radiated energy be directed downwardly where it may be usefully employed and for this reason supplemental parasitic radiating elements may be added to the antenna of Figure 4. This modification is shown in Figure 6 wherein, in addition to the nap I2 and the associated transmission line, a parasitic reflector flap 22 is used. The reflector nap is disposed in a plane parallel to the plane of flap I2 and spaced therefrom a short distance. The lower free edges of ilaps I2 and 22 are, in this modication, provided with adjustable edge pieces I3 and 23 for ne adjustment ofV the tuning of the flaps. Their position may be adjusted during tests and then soldered or clamped in position by suitable xing means. Due to the presence of the reflector ilap 4 22 th'e directivity pattern of the antenna in the vertical plane is improved in that radiation in upward directions is reduced. The pattern is shown in Figure 7, curve 25. It will be noted that the maximum of the curve occurs at an angle of about 40 degrees below the horizontal in substantially a single beam. The energy which, in the previously described embodiment was wasted in the upwardly directed lobe, is now combined with the energy radiated in the desired direction and contributes to the desired useful result. The incidental small ears appearing above the horizontal axis of the curve are not seriously objectionable since they are not only very small but are at such an angle that in most cases they will not reach the surface below the plane from which the energy is to be reflected unless, of course, the antenna system is placed directly beneath the wings of the plane. It is generally not necessary that the antenna system be so placed.

The modication of the present invention shown in Figure 8 utilizes a longitudinal array of four of the wedge antennas and parasitic reiiectors which were shown in vertical section in Figure 6. The elements are arranged in horizontal alignment, in two pairs, in order to increase the fore and aft directivity of the radiated beam. In the particular modification shown in Figure 8, it will be noted that the spacing between the individual wedge antennas is not uniform, the spacing between the center pair being greater than that between adjacent pairs. This variation in spacing was necessary because of the particular construction of a plane with which this antenna system was designed to be used. If possible to do so, it is, of course, preferable to arrange all of the antennas and their associated reflectors as close together in the horizontal plane as possible. The directivity pattern of the antenna of Figure 8 is shown in Figure 9, curve 35 indicating the theoretical directivity pattern, while 36 indicates the actual measured directivity pattern. The presence of the small side ears in the directivity pattern of Figure 9 are due to the increased spacing between the two middle radiators and may be eliminated when all radiators are spaced as closely together as possible.

It will be noted that the measured and theoretical patterns agree quite closely, one with the other, both being characterized by the absence of large supplemental or side ears and an extremely sharp main lobe.

A further modification of the present invention is shown in the side View of Figure 10 and end View of Figure 11. This modification utilizes a different means for tuning the parasitic reflector nap 42 than that shown in Figure 6. Here a capacity plate 43 is mounted on a threaded stud T screwed through a bushing at the outer edge of flap 42 between the flap and the portion of flap 52 which is overlapped by flap 42. By adjusting the spacing of plate 43 with respect to nap 52 the capacity may be adjusted so as to tune the parasitic radiator to resonance. The energized antenna 52 is connected to a transmission line TL having an inner conductor 5I and an outer shellV 5U. This antenna is tuned as shown in Figure l2 by means of a tuning stub v6l! connected across transmission line TL. The inner conductor 6I of stub 60 is arranged to be shorted t0 the outer wall ,by a slidable bridge 62. By properly sliding slider' 62 the reactance of the stub lmay be either capacitive or inductiveas desired, thus in effectv tuning the wedge antenna 52. The transmission line feed system for the antenna 5.1iv of Figures and 11 in addition to tuning stub 60, has connected thereacross an impedance matching stub l!) having an inner conductor 1l and an adjustable snorting slider 12 for adjusting the impedance of the transmission line to a value equal to that of the antenna to Which it is connected. The antenna elements are coupled together in pairs and connected in a parallel relationship to transmission line TL'. At substantially the midpoint of transmission line TL is placed a slidable T piece 80 having within the leg. of the T an inner conductor 8l adapted to contact the inner .conductor 5I of transmission line TL. The leg of the T piece 80 and the inner conductor 8| therewithin are connected tota final transmission line TL which is connected togthe transducer equipment. The purpose of having the slidable T piece 80 at the midpoint of transmission line TL' is to permit final adjustment of the balance of the antenna on each side of the plane after installation.

Due to the presence of the wings of the plane and other causes, it may be found that the radiated beams pb or sb of Figures 1 and 2` are not truly vertical to the line of travel of the plane. By shifting T piece 80 along the length of transmission line TL the horizontal angles of the corresponding beam may be slightly shifted to assume perpendicularity. It should be noted that only slightly over half of the transmission line system for energizing the antennas on one side of the plane is shown. The portion not shown is exactly similar to that shown, the layout being substantially symmetrical about the midpoint of transmission line TL'.

Since the antenna shown in Figures 10 and 11 is mounted on the exterior of the plane Where it is exposed to weather conditions and., more particularly, to a great deal of spray when the plane is leaning on or taking off from the surface of the sea it is desirable that the open edge of the wedges be closed to prevent the entrance of moisture. This may be done by means of closing walls it of high quality dielectric material such as methyl methacrylate. As in the previously described embodiments, the ends of the wedge antenna and reliector are closed by walls li which also act as supporting means to maintaining the angular relationship of the aps with respect to the side wall Ill.

The theory of operation 'of the wedge antenna may be more easily understood if the theory of operation of cavity resonators energized in the lowest order transverse electric mode is considered. A cylindrical cavity resonator energized in this mode has its electric eld transverse to the axis of the cavity, the lines of force forming concentric circles, and the magnetic iield parallel to the axis in the form of closed loops in radial planes. Theoretically, a small section of the cavity lmay be considered by itself if the section considered is bounded by conductive walls normal to the electric field lines, said walls forming a completing path for the lines. Likewise, the outer edge of the section should be completed by a boundaryr such that no magnetic eld may escape, a sort of ctitious magnetic short circuit. The small sector will then operate exactly the same as though it still formed a part of the whole cavity.

This situation is shown in Figure 13, wherein is represented a Wedge shaped sector of the field within a cylindrical cavity resonator, the arrows H representing the magnetic field and terminate along boundary surface MS indicating a magnetic short-circuit. There is, 'of course, no actual magnetic short-circuit but the magnetic lines of force H having boundary MS atp-the bottom of the figure progress across to Athe inner side of the wedge upwardly along the length of the wedge and back to the right and again terminate along boundary MS. Curve Hh along the left-hand side of the figure Aindicates the distribution of the magnetic field in a graphical form. The electric ield indicated by arrows E and curve En is, of course, a maximum at the midpoint of the wedge and must be zero at each end due to the end walls being closed.

The distribution of the magnetic and electric' lields as though viewed from the end of the Wedge of Figure 13 are shown in Figure 14. It will be seen from curve HA lthat the magnetic field decreases from a maximum at the apex o'f the wedge to a minimum at the outer part of the wedge. It will be noted from curve E of Figure 14 that the electric eld increases smoothly from a zero value at the apex of the wedge to a `maximum at the open side of the wedge. The relationship of the length of the wedge resonator to the wavelength and the relationship of the Width of the wedge resonator to the wavelength are interdependent and with either given the other may be determined by curve of Figure 15. Within certain limits either the distance a or h may be arbitrarily chosen and the other dimension obtained from the curve. It will be noted that the curve is asymptotic to a value of of .5 and a value ofV of .383 so it will ordinarily be more desirable to choose values so that the midportion of curve 9U is used.

In the foregoing description and inthe accompanying drawing, some specic dimensions which have been found in practice to Work well' have been indicated. However, it should be distinctly understood that my invention is not to be limited to these particular dimensions, nor tothe particular vembodiments described, but that modications VWithin the scope of the invention may be made.

I claim:

1. A directive antenna including a conductive base sheet having a radiator element associated therewith in the form of a long narrowv conductive flap attached along one edge to said base sheet and forming a small angle with respect to the plane of said sheet and a two conductor transmission line having one conductor connected to said sheet and the other to said ap ata point intermediate its ends.

2. A directive antenna including. a conductive.

7 point intermediate'its ends, said sheet having dimensions of the order of several times the operating wavelength of said system.

3. A directive system including a conductive base sheet having a radiator element associated therewithin the form of an elongated conductive flap attached along one edge to said base sheet and forming a small angle with respect to the plane of said sheet and means for coupling high frequency transducer means to substantially the longitudinal 'midpoint of said flap and to said sheet, said sheet having dimensions of the order of several times the operating wavelength of said system, said flap having a length of the order of the operating wavelength, and a width of the order of .3 to .5 of the operating wavelength.

4. A Vdirective antenna including .a conductive base sheet having a, radiator element associated therewith in the form of an elongated conductive flap attached along one edge tosaid base sheet and forming asmall angle with respect to the plane of said sheet, and a parasitic reflector element including a second flap attached to said sheet along one edge and lying in a plane parallel to the plane of said rst flap and closely adjacent thereto.

5. A directive antenna including a conductive base sheet having a radiator element associated therewith in the form of an elongated conductive flap attached along onejedge to said base sheet and forming a small angle with respect to the plane of said sheet, and a parasitic reflector` element including a second flap attached to said sheet along one edge and lying in a plane parallel to the plane of said rst flap and closely adjacent thereto, and means for tuning each of said elements including an adjustable edge piece associated with the free edges thereof.

6. A directive antenna including a conductive base sheet having a radiator element associated therewith in the form of an elongated conductive flap attached along one edge to said base sheet and forming a smallangle with respect to the plane of said sheet, and a parasitic reflector element including a second flap attached to said sheet along one edge and lying in a plane parallel to the plane of said first flap and closelyadjacent thereto, and an adjustable capacityplate connected to the free edge of at least one of said elements for tuning said element.

7. A directive antenna including a conductive base sheet having a'radiator element associated therewith in the form of an elongated conductive fla'pgattached along one edge to said base sheet and. forming a small angle with respect to the plane'ljofQsaid sheet, and a parasitic reector element 'including a second nap attached vto said sheet along one edge and lying in a planeparallel to the plane of said rst flap and closely adjacent thereto and a transmission line coupled to said radiator element, said transmission line having a shunt branch connected thereto for tuning said radiator element, and means for tuning each of said elements including an adjustable edge piece associatedY with the free edges thereof.

8. A directive antenna array including a plurality of systems, as set forth in claim 4, arranged in end to end alignment, all the said systems be-A ing energized in an in phase relationship.

9. An antenna system for drift indication including an antenna as set forth in claim 4, so mounted on a side wall of the fuselage of an airplane that a sharply directive beam of high frequency energy is directed downwardly a1; an angle of substantially 45 degrees in a plane normal to the direction of flight of said airplane.

10, An antenna system for drift indication including a pair of antennae as set forth in claim l, so mounted over each side wall of the fuselage of an airplane that a pair of sharply directive beams of high frequency energy are directed downwardly at an angle of substantially 45 degrees in a plane normal to the direction of flight of said airplane..

11. An antenna system for drift indication including a pair of antennae as set forth in claim 4, so mounted over each side wall of the fuselage of an airplane that a pair of sharply directive beams of high frequency energy are directed downwardly atan angle of substantially 45 degrees in a -plane normal to the direction of flight of said airplane.

l2. A directive antenna including a conductive base sheet having a radiator element associated therewith in the form of an elongated substantially rectangular conductive iiap attached along one edge thereof to said base sheet within the area of said sheet, and forming a small angle with respect to the plane of said sheet and means for coupling high frequency transducer means between said flap and said sheet at a point near the longitudinal midpoint of said flap.

13. A directive antenna including a conductive base sheet having a plurality of radiator elements associated therewith, each of said radiator elements being in the form of a long narrow conductive flap attached along one edge of said base sheet within its area and forming a small angle with respect to the plane of said sheet, said radiator elements being arranged in end-to-end alignment, all of the said elements being energized in an in phase relationship.

14. An vantenna system for drift indication including a long narrow conductive liap attached along one edge to a conductive side wall of the fuselage of an airplane and forming a small angle with respect to the plane of said side wall, said flap being so arranged that a sharply directive beam of high frequency energy is directed downwardly at an angle of substantially 45 in a plane normal to the direction of night of said airplane.

PHILIP S. CARTER.

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

Y UNITED STATES PATENTS Number Name Date 1,670,553 Sharp May 22, 1928 FOREIGN PATENTS Number Country Date 462,466 Great Britain May 10, 1937

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