US2293694A - Directive radio system for guiding arrangements - Google Patents

Description

Au hzs, 1942.

A. ALFORD 2,293,694

DIRECTIVE RADIO SYSTEM FOR GUIDING ARRANGEMENTS Filed Nov. 7, 1939 4 Sheets-Sheet 2 was. w 101 116' 117 f j 14 F I65. X 115 5 121 IR/l/VSM/i'if/P INVENTOR.,

AMP/76771446 F000 Aug. .25, 1942.

A. ALFORD 2,293,694

DIRECTIVE RADIO SYSTEM FOR GUIDINGARRANGEMENTS Filed Nov. 7. 1959 4 Sheets-Sheet s l atented Aug. 25, 1 942 DERECTIVE RADIO SYSTEM FOR GUIDING ARRANGEMENTS Andrew Alford, New York, N. Y., assignor to International Telephone & Radio Manufacturing Corporation, a corporation of Delaware Application November 7, 1939, Serial No. 303,206

18 Claims.

My invention relates to directive radio systems and more particularly to directive radio systems suitable for guiding beacons and similar arrangements,

One form of radio beacon commonly used as a localizer beacon at an airplane landing field comprises an arrangement for producing a two directional guiding course along the direction of the landing runway. In such beacons it is desirable that the course be made quite sharp so as to avoid interferences due to reflection of energy from objects in the vicinity of the landing field. Should reflections occur from any such objects, distortion of the course and consequent errors in the guiding line may result.

It is an object of my invention to produce an array of radiant acting units, either transmitters or receivers, for obtaining a sharp guiding line to reduce probability of such errors or to form a direction finding receiver. This may be accomplished in accordance with the teachings of my invention by utilizing three radiant acting conductors spaced in a line and energized in suitable phase relation for producing the desired patterns for defining the guiding line.

A further difiiculty with guiding beacons when used for course localizers results from reflecting objects in the path of the back radiation causing variations in the front or principal guiding course which will cause false courses usually termed multiple courses. This trouble may be reduced by constructing an arrangement such that the radiation in the direction of the principal objects causing these disturbances is reduced to a minimum.

It is accordingly 2. further object of my invention to design a transmitting array for guiding beacons wherein radiation in the backward direction is reduced or suppressed in directions toward reflecting objects so as to obviate the above difficulties.

With radio beacons installed at particular landing fields it is often desirable to produce signals indicating the quadrant in which the receiver is located with respect to the beacon so that the proper direction for landing may be readily attained.

It is also desirable that a particular signal identifying the landing field be transmitted so that the pilot may be informed of the identity of the landing field.

, In accordance with further objects of my invention I provide means for producing signals for quadrant identification at the localizer beacon 5 5 and may also provide means for identifying the particular landing field.

In general, direction finders at present in use utilize the principle of a single signal received on the crafts by means of a directive antennae system for indicating the direction line between the receiver and the transmitting station.

In accordance with a still further object of my invention I provide a system utilizing an antenna arrangement similar to that used for a guiding beacon for receiving signals from a broadcasting station so that a line of direction toward the station may be positively established.

Further objects and advantages of my invention will be apparent from the particular description thereof made in accordance with the accompanying drawings illustrating a few preferred embodiments thereof, in which Fig. 1 is a schematic diagram of a radio beacon v transmitter in accordance with my invention,

Figs. 2, 3 and 4 are radiation diagrams used for explaining the operation of the beacon of Fig. 1,

Fig, 5 is an illustration of a preferred type of antenna wherein radiant action is obtained only for substantially purely horizontally polarized raditions,

Fig. 6 illustrates a preferred embodiment of my invention for producing a two-course landing beacon,

Fig. '7 schematically shows a diagram of a twocourse beacon provided with auxiliary means for reducing the radiation in certain directions,

Fig. 8 is a diagram illustrating the radiation patterns which may be obtained with the beacon system of Fig. '7,

Fig. 9 is a schematic illustration of a radio beacon in accordance with my invention provided with means for producing quadrant identification,

Fig. 10 is a radiation pattern useful for explaining the operation of the system of Fig. 9,

Figs. 11 and 12 are alternative keying arrangements for use with the system illustrated in Fig. 9, and

Fig. 13 is a schematic diagram of a direction finding receiver utilizing the principles of my invention.

Turning now to the drawings and particularly Figs. 1 to 4, a brief explanation of the principles of my invention will be given. Throughout this discussion the explanation is made with respect to transmission of signals, it should be distinctly understood, however, that the same principles apply to receiving systems, since receiving antennae operate substantially with the same type of radiant acting patterns as the radiation patterns of a transmitting system.

In Fig. 1 is illustrated a beacon comprising three vertical dipoles IOI, I02, I03. Each of these dipoles is tuned by means of corresponding transmission line sections I 05, I06, I01. Antenna I! is arranged in the center and is energized over one diagonal of a hybrid bridge arrangement by energy from two sources II 0, I I I, modulated at two different frequencies F1, F2. The energy supplied to antenna IOI from the two sources is in phase. Energy is also supplied to the outer antennae I02, I03 over transmission lines H0, H1 from the same two sources of energy over the opposite diagonal of the bridge network IIE. By reason of the hybrid network the output terminals of sources IIO, III are independent of each other and similarly the loads connected over lines H4, and H6, H1 are independent one of the other. A 180 phase shift is provided in transmission line H6, for example by transposition II, so that antennae I02, I03 are energized directly in phase opposition.

In order to explain the operation of the system we may first presume that only antenna IOI is directly fed and that antennae I02, I03 are parasitically energized by radiation from I0 I. In such case a pattern of dumbbell form, such as shown in Fig. 2, is obtained. The shape of this pattern may be varied by adjusting the spacing of parasitically energized antennae I02, I03 with respect to the energized antenna IOI. Furthermore this shape may be modified by the variation in the tuning of parasitic antennae I02, I03.

I have found that the preferred pattern forms may be obtained by spacing antennae I 02, I 03 substantially between 165 and 178 from radiator I 0| the preferred spacing being substantially 165. In this case the sections I06, I01 are made slightly longer than is necessary in order to tune the radiators to resonance, so that they are slightly inductive in reaction.

If now we energize antennae I02, I03 in phase opposition in such a manner that the phase relation of antennae I02, NH and I03 is 90, 0, +90, respectively, a radiation pattern is obtained somewhat of the form illustrated by the solid line curve 30 of Fig. 3, neglecting for the moment the effecting of direct energization of radiator IOI. When the energization of the outer radiators is reversed so that an antenna I02 is energized at +90 and antenna I03 at -90 with respect to antenna IN, the curve shown at 3i in dotted lines at Fig. 3 is obtained. This effect may be produced in accordance with my invention by means of the bridge network. Thus, energy from N0 is fed to antenna IOI directly, and is fed to antennae I02 and I03 in phase opposition over lines H6 and H1. Energy from source III is similarly fed directly to antenna IOI in phase but by reason of a 180 phase shifter I20 in network I I antennae I02, I03 are energized in opposite phase with respect to the energy from source H0. Accordingly, the two patterns 30, 3I are simultaneously obtained, one modulated with frequency F1 and the other with frequency F2. These patterns superimposed with the dumbbell shaped pattern of antenna IOI produce an overlapping radio beacon having two distinguishable patterns 40 and III of Fig. 4. In this connection it is pointed out that transposition I20 in network H5 should be so located that the carrier energy from sources III), II I is not opposed in phase upon feeding to antenna IOI. Were the transposition I20 arranged at a point between the sources I I0, III and the antenna IOI, then the carrier would be substantially suppressed on course. It is more satisfactory to have a strong carrier on course and for this reason the network should be arranged so that the carrier is not suppressed at antenna I 0 I.

As discussed above, it is pointed out that the radiation pattern of Fig. 4 is obtained when the patterns of Fig. 2 and Fig. 3 are combined. In order that the combination may be properly made, it is desirable that the parasitic operation of antennae I02, I03 be preserved when the transmission lines H6, I I1 are connected thereto for direct feeding of the energy. This may be accomplished by proportioning lines H6, H1 so that they form a high impedance with respect to parasitic energy from antenna IOI. Energy radiated from I III energizes antennae I02, I03 in phase, since it travels equal distances to the last named radiators. The line I2I leading from the network to the junction point of lines H6, H1, is made preferably at the midpoint of these lines so that H6, II"! are equal in length. Accordingly, energy induced in antennae I 02, I03 from IN, reaches the junction point of lines H6, H1 in phase opposition because of the transposition in line H0. Therefore, this junction point is at a voltage node which corresponds to a short circuit across the transmission lines. If then, lines H6, III are each made equal electrically to an odd number of quarter wavelengths long, then they will present substantially infinite impedance to energy incoming from antennae I02, I03 and will, therefore, have no effect upon the tuning of the transmission line sections I06, I01. Antennae I02, I03 will, therefore, operate as parasitic antennae in so far as the direct energization by radiation IOI is concerned, but will operate as fed antenna energized in phase opposition in so far as the feed over line I2I is concerned. Accordingly, a radiation pattern of suitable sharpness as shown in Fig. 4 will be obtained. By adjusting the connection points of lines H6, H1 on sections I00, I 01 the feeding of energy to antennae I02, I03 may be controlled.

Because of the detuning of I06, I01 from resonance, a complete impedance matching of the transmission line is not obtained, although the arrangement produces very little mismatch. To match transmission lines with respect to energy fed over line HI. I ma provide an impedance matching means such as element I25 connected across transmission line I2I.

If, instead of making lines IIB, II1 of length L equal to an odd number of quarter wavelengths, these lines are made equal to a multiple of a half-wavelength, then the junction points of these lines with sections I06, I01 will act as though there were a short circuit across the sections I61, so far as energy from IIJI is concerned. If this connection is made then the parasitic antennae I02, I03 may be tuned by adjusting the point of connection of lines H6, H1 thereto instead of adjusting an actual short circuit bar. In this case the short circuiting bar must then be used for the purpose of adjusting the impedance or phase of the directly fed energy to radiators I02, I03. However, the odd quarter wavelength connection is considered preferable for this purpose.

The principles discussed in connection with Fig. l are generally applicable independently of the exact nature of the antenna used as the radiator.

A preferred form of antenna for use is illustrated in Fig. 5. This antenna unit is designed to produce substantially purely horizontally polarized waves. The antenna unit is made up of four radiating arms 50 to 53, inclusive, each of the arms 50 to 53 being of such a length that from the feeding point 54 to the terminal end of the conductor is substantially equal to a halfwavelength electrically. The outer ends of the conductors t to 53 are turned inwardly at their points adjacent the other conductors so that the radiant acting portion of each conductor is energized substantially uniformly throughout. This type of antenna when arranged in a horizontal position produces a substantially purely horizontally polarized radiation. For a more particular description of this type of antenna, reference is made to my co-pending application Serial No. 270,173, filed April 26, 1939.

In Fig. 6 is illustrated a beacon antenna similar to that shown in Fig. l but utilizing radiators of horizontally polarized waves of the type illustrated in Fig. 5. In this figure, antennae IOI, I02 and H13 are connected over lines H8, H1, HQ and I2l to a bridge network H5 over the bridge to a common transmitter 69 l. Transmitter Bill may be utilized in place of the separate sources shown at H3, III in Fig. 1. The energy from this transmitter may be modulated by any known means illustrated as 5&2, 563 to produce differently modulated waves for identifying the beacon courses. This type of beacon transmitting horizontally polarized waves has been found to be successful for producing a sharp course along a particular direction and one in which apparent shifting of the guide line is not caused by banking of the airplane. The sharpness of the course may be adjusted similar to the arrangement disclosed in Fig. 1 by adjusting the spacing and tuning of antennae W2, W3.

A further sharpening of the course may be obtained by arranging further parasitically excited antennae units EM, 605 on either side of the beacon arrangement. The spacing between 604, 665 and I02, N13 is preferably in the order of a quarter wavelength in an actual installation made wherein the beacon was operating at 109 meg-acycles. The spacing of the auxiliary parasitic antenna was made equal to 3' 6". The addition of these parasitic radiators tends to narrow down the width of the radiation patterns so that the energy radiated from the beacon does not diverge so much to either side thereof and therefore is less subject to reflection from nearby objects. Accordingly, the additional sharpness of the course is enhanced as well-as a reduction in disturbances due to reflections in nearby objects.

When radio beacons of the type shown in Figs. 1 to 6, are located near the end of a landing runway, the radiations therefrom in one direction ma be termed the forward course which the airplane follows in coming to a landing. The radiations in the opposite direction may be termed the backward course or back course and serve merely to indicate to an aircraft the direction toward the landing field, but primarily for guiding the craft along the landing line. These back radiations, however, are generally subject to reflection to a higher degree than the forward radiations, since the beacon is usually located at one end of the field and nearby objects are more likely to be located in a region of the back radiations. Reflection of energy from the back course into the forward path causes distortions of the energy as received on the airplane and may produce several false or multiple courses. In.- order to overcome this difficulty I provide a set of parasitic radiators arranged in the back of the beacon, as shown in Fig. 7. These additional radiators may be utilized either with the three element beacon illustrated in Fig. 1, or with the five element beacon shown in Fig. 6.

In Fig. 7 the radio beacon itself is illustrated as being composed of units such as shown in Fig. 5. It should be understood, however, that any type of radiator may be used therein. Similar reference characters are used to apply to the elements of the main transmitter to those used in Fig. 6. Directl behind radiators Hll, I92 and I03 are provided auxiliary parasitically energized antenna units 10!, I02, 103, respectively. These units are arranged preferably a distance in the order of a quarter of the working wavelength, the exact distance being subject to adjustment dependent upon the angle at which the troublesome reflecting objects are to be found. In general this spacing is somewhat diiferent from a quarter of a wavelength. Units Nil, 152, 103 are each tuned substantially to resonance at the working frequency. This tuning may be accomplished by adjusting short circuit bars on transmission line sections Hi, f 52 and 1 [3 connected to the respective antenna. As shown in the figure, transmission line sections H2, H3 are provided with an effective or virtual short circuit, rather than real short circuiting bar.

Assuming first that units fill to Hi3 have been tuned to resonance and no further steps have been taken, it can be seen that energy from radiator NH will operate to drive not only 10E arranged directly behind it but will also energize radiators W2, 163. Thus, the unit will not act to merely weaken the back course by reflection of energy at Nil, but will cause distortions in the form of the back course as well. In order to overcome this effect a transmission line is connected between units 102, 153. In line 120 is provided a means, for example, a transposition I21, for shifting the phase along this line. If line 126 is then made equal to a half-wavelength long at the operating frequency, energy impressed upon antennae 102, 103 in phase from radiator It! and parasitic antenna till, will then produce an apparent effective short circuit at the midpoint of this line. This short circuit will occur at a point one-half wavelength from units m2, H63. Thus, the parasitic operation of these units with respect to any phase energy from antenna lfil and unit it! may be effectively avoided. Energy derived in units 152, 103 and I02, E53, however, will be in phase opposition so that at the midpoint of transmission line 120 a voltage loop will occur. Accordingly, the line 120 will operate as though the open ended halfwave transmission line section were connected across the antenna and will present substantially infinite impedance. Accordingly, line I20 will have no effect with respect to the energy induced from units I02, I03. In order to tune units 152, N33 to resonance, an additional short circuit may be provided, for instance, by means of the transmission line 130. This transmission line is made equal to an integral multiple of wavelengths and is not provided with a transposition. Accordingly, energy from H32, I03 impressed upon antennae 102, 103 will operate to produce a virtual short circuit at the midpoint of 103 causing a substantially similar effect at the junction points of line I30 with transmission line sections H2, H3. By adjusting line 130 vertically with respect to the antennae units I02, I03, these reflectors may be tuned to the desired amount. In place of line 130 actual short circuiting bars may be substituted.

In Fig. 7, lines I20 and I30, I20 is shown above line 130. It should be understood, however, that the relative positions of these lines may be varied depending upon the actual tuning effects that are desired for the separate units. Accordingly, each may be adjusted independently, it being merely necessary that the units be tuned to secure the desired cancellation effect for the rear course. Likewise, it may be noted that reflector unit MI is driven only from radiator IOI, since energy reaching it from the other radiators I02,

I03 will be directly in phase opposition. With the.

system as shown herein, tuning for the purpose of controlling the direction patterns may be effected in any desired manner.

In Fig. 8 is shown, by way of example, a radiation diagram obtained using a system similar to that illustrated in Fig. 7. In this figure, 00, I show the various patterns on each side of the course caused by the radiation from the beacon. The radiation fields are considerably shortened due to the use of the reflecting antenna structure and may be adjusted to have a minimum, substantially at any desired angle 0, corresponding to the direction of the location of a reflecting object. Thus multiple courses due to reflections from the backward radiations may be substantially eliminated. It should be understood that this angle 9 may be varied by the tuning and adjusting of the parasitic radiators 10! to 103, inclusive, so as to assure neutralization of reflected energy from any particular direction.

In an actual test installation of apparatus in accordance with my invention, an arrangement similar to that shown in Fig. 7 was made utilizing three loops, that is, omitting the side parasitic reflectors 600, 605. With this arrangement, elimination of troubles due to reflection from an object located at an angle of substantially 54 from the line of equal signal in the rearward direction was achieved. The back course, however, still was of suflicient strength to extend any usable quantities several miles to the rear of the airport.

With beacons utilized for guiding purposes it is often desirable that means be provided for indicating on the aircraft if an approach is made to the side of the beacon so as to indicate the presence of the landing field in the vicinity. In accordance with my invention such an arrangement may be provided by use of a system such as illustrated in Fig. 9. In this figure a beacon comprising three antennae IOI, I02, I03, is illustrated diagrammatically in plan view. This beacon may be similar to that shown in Figs. 1 or 5, and if desired, modulation identifying the courses may comprise low frequency signals, for example 90 and 150 cycle signals. On either side of central radiator IOI are provided two auxiliary antennae 90, 9|. These auxiliary antennae are preferably parasitic loops and means for modulating or keying the energy by operation on these loops is provided as indicated at 92. The loops 90, 9!, may be arranged so that they are alternately tuned and detuned tending to reduce the energy radiated first in the forward and then in the backward direction. The keying may be made in the form of interlocking Morse signals, for example, the well known AN signals may be used. The operation of the system may be more clearly understood by reference to Fig. 10. In this figure the curves IOI4, IOI5 represent the patterns produced when neither of the reflectors or 9| are efiective. When 90 is made effective, the patterns represented by curves IOI I, IOI3 are formed on each side of the course, so that the predominating energy is in the for- ,ward direction. When 90 is rendered inefiective, 0| is rendered effective, the radiation pattern will then correspond to the curves I000, I 0I2, producing a strong radiation in the backward direction and a weak radiation in the forward direction. This keying may be accomplished in accordance with a known code so that in effect overlapping equi-signal patterns are formed on each side of the beacon producing in efiect another course. This course, however, is very wide and does not constitute a narrow guiding course but merely serves to indicate to the pilot that he is at one side of the beacon. However, when the pilot circles and approaches the beacon from either end he can then maintain his course by means of the 90l50 cycle modulation and can identify his direction of approach by the presence of a strong signal corresponding to the keying frequency for that particular direction.

In Fig. 11 is illustrated one form of keying system suitable for use with the arrangement of Fig. 9. In this figure, the two parasitic antennae 90, 9I, are shown connected over lines H00, IIOI to terminals. Movable contacts H02 are provided so as to connect a section of transmission line H03 across either H00 or IIOI so as to tune and detune the sections. Contact arms I I02 may be controlled by a relay H05 from any known keying means such as indicated at I I06.

In Fig. 12 is shown a further embodiment of a keying means which may be used in accordance with my invention. In this figure the units 90 and SI are shown controlled by a keying means I200 which serves to alternately connect lines I20I, I202, to a tuning transmission line I203 or to a further control circuit indicated generally at I204. Movement of the relay contacts is controlled by relays I205, I 206, so that when antenna 90 is connected to lin I 203, antenna 9| is connected to the circuit I204. This type of arrangement may be utilized with a beacon of the type shown in Fig. 9, and may provide a further identifying signal for indicating the identity of the station. This additional means is the circuit shown at I204 and comprises a pair of vacuum tubes I 2| 2 connected in parallel to the contact terminals and energized from an audio-frequency source I2I3 so that tubes I2I2 are alternately brought and rendered conductive. Source I2I3 preferably operates at an audio frequency, for example, 300 to 1000 cycles so that a particular frequency identified with the station is alternately transmitted from antennae 90, 9| in the direction of the stronger field of the course. It is clear that if desired the identifying frequency may be applied directly as a modulation frequency to the beacon antennae IOI, I02, I03 instead of being applied to the reflectors.

In event that a beacon is utilized wherein the main course is of the alternately energized type, for instance, the well known A-N beacon, the identifying signals should be applied to the reflecting arrangement in the manner shown in Fig. 12. In this manner the dot-dash frequency may be applied to the reflectors 90, SI and simultaneously the identification frequency may be applied thereto without interrupting either of the courses. The line connecting the circuit I204 to the antennae 90, 9|, should preferably be made equal to substantially a quarter wavelength or odd multiple thereof electrically so that at the time the tubes are blocked, the unit connected thereto is working into substantially an infinite impedance, Whereas when the tubes are unblocked the unit 9| is working into substantially zero impedance so that a suitable modulation of the signals may be obtained.

Although, in the example illustrated, an array using only three units is shown, it should be understood that any of the arrays using five, six or eight antennae, as described in the foregoing portions of the specification, may be used, depending upon the directive effect desired.

The antenna arrangement such as illustrated in Figs. 1, 6 and '7 may be utilized for the purpose of direction finding if desired, without any substantial change in the circuit other than the substitution of a receiver for the transmitter. One such arrangement is illustrated in Fig. 13. In this figure the three antennae IOI, I02, I03 are shown diagrammatically as being of the type for receiving horizontal polarized waves, although it is clear that any type of antennae may be used. The energy received over antenna IOI and antennae I02, I03, are separately fed through a hybrid network to lines I3I0, I3II. In lines I3I0, I3I I then energy from the two sides of the course, as illustrated by the patterns of Fig. 4, will be obtained. This energy may then be separately detected and the detected currents applied in opposing relation to an indicating instrument. However, it is usually necessary to amplify the received energy before a useful indication is obtained. In such a case if the energy is to be directly compared, two separate amplifiers would necessarily be provided in which case it is difiicult to assure equal amplification of both signals. Accordingly, a preferred form of receiver as shown in Fig. 13, constitutes modulating means I3I2, I3I3, in lines I3I0, I3II. The modulated energy is then fed over a conjugate network I3I4 to an amplifying receiver I3I5 where the energy is amplified and detected to produce the modulation envelopes. These output modulation envelopes are then fed through device ISIS which constitutes a filter for separating modulation waves and for rectifying these modulations, the rectified energy being then applied to indicator I3II. A balancing network I3I8 is provided so that the conjugate bridge I3I4 may be maintained balanced. With a receiver of this type it is clear that whenever the antenna is adjusted so that I02, I03 are equi-distant from the radiation source, equal signal output at the two frequencies will be obtained so that the meter will indicate the orientation of the antenna group. If energy comes to the antenna group from either side, then the signal corresponding to that side of the course will be received more strongly than the other signal whereby an indication that the craft is not traveling toward the station, will be obtained. It is clear that many other forms of this receiving apparatus utilizing the antenna arrangement of my invention may be built, it being merely necessary to keep in mind that separation of the signals must be provided for at the receiver.

Whle I have described a number of specific embodiments of my invention in connection with the attached drawings, it should be distinctly understood that these showings constitute merely a preferred structure in accordance with my invention. What I consider to be my invention is embodied in the accompanying claims.

What I claim is:

1. A directive radiant acting system comprising a. central radiant acting member, other radiant acting members on either side of said central member and spaced therefrom a distance greater than a quarter wavelength at the working frequency, means for energizing said radiant acting members such that said central member produces radiant action and said other members produce radiant actions displaced 180 electrically with respect to each other and displaced 90 electrically with respect to said central member, means for tuning said other members to oscillate parasitically with respect to cophasally supplied energy, translating apparatus, and conjugate coupling means comprising a bridge network for coupling said central member and said other members to said translating apparatus independently of any interaction between said central member and said other members.

2. A directive radiant acting system according to claim 1, wherein said system operates as a radio beacon, said translating means comprising a transmitter and means for modulating said transmitted energy with diiferent distinctive signals, further comprising means for applying said separately modulated signals to said conjugate coupling means in conjugate relation, for feeding said central member and said other members.

3. A directive radiant acting system according to claim 1, further comprising parasitically energized radiant acting members arranged in spaced relation on the outer side of each of said other radiant acting members, whereby the directive sharpness of said system is increased.

4. A directive radiant acting system according to claim 1, further comprising a further parasitically energized radiant acting member spaced from said central member in the direction substantially at right angles to the line formed by said other members.

5. A directive radiant acting system according to claim 1, wherein said translating means comprises a receiver and an indicator, separate input circuits for said receiver coupled to conjugate points on said conjugate coupling means, Whereby energy from said radiant acting members is separately supplied to said input circuits, and means in said input circuit for imparting dis- 7 tinctive characteristics to energy supplied to said receiver from said circuits.

6. A directive radiant acting system according to claim 1, further comprising an additional central radiant acting member, other additional radiant acting members arranged on either side of said additional central radiant acting member, said additional radiant acting members being spaced in the same direction from corresponding ones of said radiant acting members, means for tuning each of said additional radiant acting members to resonance for parasitic energization from corresponding radiant acting members, and means for detuning said other additional radiant acting members from resonance for energy derived from said central members.

7. A directive radiant acting system according to claim 1, further comprising additional radiant acting members arranged on opposite sides of said central radiant iacting member and spaced therefrom, and means for alternately tuning said additional radiant acting members to resonance at the working frequency.

8. A directive radiant acting system according to claim 1, wherein said system constitutes a transmitting radio beacon, further comprising additional radiant acting members arranged on opposite sides of said central radiant acting memher and spaced therefrom, means for altern ately tuning said additional radiant acting members to resonance at the working frequency, and means for imparting to said beacon a further signal for identifying said transmitter.

9. A radio beacon comprising means for radiating overlapping fields having distinctive signal characteristics in each of two directions to define a course line, reflector means spaced on both sides of said radiating means in the direction of said course line on opposite sides of said radiating means, and means for rendering said reflector means alternately effective in predetermined relation to identify the opposite sides of said course line.

10. A radio beacon comprising a first radiator, a pair of radiators spaced a distance between a quarter wavelength and a half wavelength at the working frequency on either side of said first radiator, a four armed bridge network, means for connecting said pair of radiators in phase opposition to an apex of said network, means for connecting the opposite apex of said bridge network to said first radiator, a pair of energy sources of the same frequency modulated with distinctive signals, means for connecting said energy sources to respectively opposite corners of said network whereby energy from said sources is fed to said first radiator cophasally and to said pair of radiators in phase opposition, means for phasing the energy from one of said sources in phase opposition to the energy from the other source in said pair of radiators, and means for tuning said pair of radiators to oscillate parasitically with respect to energy absorbed cophasally.

11. A radio beacon according to claim 10, further comprising a first reflecting antenna and a pair of reflecting antennae spaced therefrom and spaced from said respective ones of said radiators, means for tuning said reflecting antennae to the operating frequency for parasitic energization from the corresponding radiator, means detuning said pair of reflecting antennae with respect to cophasal energization from said first radiator whereby parasitic action from this source is eliminated, and means for transmitting from said beacons further signals for identifying said beacon.

12. A radio beacon according to claim 10, further comprising a first reflecting antenna and a pair of reflecting antennae spaced therefrom and spaced from said respective ones of said radiators, means for tuning said reflecting antennae to the operating frequency. for parasitic energization from the corresponding radiator, and means detuning said pair of reflecting antennae with respect to cophasal energization from said first radiator whereby parasitic action from this source is eliminated.

13. A radio beacon according to claim 10, further comprising a reflecting antenna system spaced from said beacon radiators, said system comprising three antennae corresponding to respective radiations, adjustable means for tuning said antennae for parasitic operation as reflectors, and adjustable conductor means physically a multiple of wavelengths long and electrically an odd multiple of wavelengths long interconnecting the tuning means to said antennae corresponding to said pair of radiators, whereby an ef fective short circuit may be produced for detuning said antennae with respect to cophasal parasitic energization.

14. A radio beacon according to claim 10, further comprising parasitic antennae spaced from said first radiator on opposite sides thereof and substantially equi-distant from the radiators of said pair of radiators, means for tuning and detuning said antennae alternately to produce interlocking signals transversely of the course defined by said beacon.

15. A radio beacon according to claim 10, further comprising parasitic means spaced from said first radiator on opposite sides thereof and substantially equi-distant from the radiators of said pair of radiators, means for tuning and detuning said antennae alternately to produce interlocking signals transversely of the course defined by said beacon, and means for imparting to said antennae a distinctive audio frequency modulation for identifying the station during the detuned alternate period thereof.

16. A radio direction finder comprising an energy receiving antenna system including, a first antenna, and other antennae spaced on either side of said first antenna, a bridge network having four arms, one of said arms being electrically half a Wavelength greater than the other arms, means connecting said first antenna to one corner of said bridge, means connecting said other antennae in phase opposition to the diagonally opposite corner of said bridge, transmission lines connected respectively to the other diagonally opposed corners of said bridge, means for imparting distinctive characteristics to energy received from said antenna system in said transmission lines, and means responsive to the received energy with said different characteristics for indicating the orientation of said antenna system with respect to a source of received energy.

17. A radio direction finder comprising an energy receiving antenna system including, a first antenna, and other antennae spaced on either side of said first antenna, a bridge network having four arms, one of said arms being electrically half a wavelength greater than the other arms, means connecting said first antenna to one corner of said bridge, means connecting said other antennae in phase opposite to the diagonally opposition corner of said bridge, transmission lines connected respectively to the other diagonally opposed corners of said bridge, means for detecting the energy impressed in said transmission lines, and means responsive to the detected energy for indicating the orientation of said antenna system with respect to a source of received energy.

18. A radio direction finder according to claim 16, further comprising means for amplifying and detecting said distinctively characterized energy and means for separating said detected energy in accordance with said distinctive characteristics interposed between said means for imparting distinctive characteristics and said means for indicating.

ANDREW ALFORD.

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