US2411518A - Electromagnetic wave transmission system - Google Patents

Description

NOV. 26, 1946. G, BUSlGNlES 2,411,518

ELECTROMAGNETIC WAVE TRANSMISSION .SYSTEM Filed April l2, 1943 7 Sheets-Sheekl l TRA/vsh/rrf@ digg-1 #ECT/VER H. G. BuslGNn-:s 2,411,5l8-

ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM Filed April l2, 1945 7 Sheets-Sheet 2 vm 1 All m. w V V Y Y V11 l# L/ L @A f o a w m u w d .d w

Nov. 26, 1946.

NOV. 26, 1946. H G- BUSlGNlEs k2,411,518

ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM Filed April l2, 1943 7 Sheets-Sheet 3 OUTPUT Nov. 26, 1946.- H. G. USIG'NIES 2,411,518

ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM Filed April 12, 1945 7 sheets-sheet 4 Nw. 26, 1945." H Q BUSIGNES www ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM Filed April l2, 1945 7 Sheets-Sheet 5 I N V EN TOR. HfA/// G. 505/611055' Nov. 26, l1946. H. G. BuslGNlEs u 2,411,518

ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM Filed April 12, 1945 '7 shams-sheet e Dmmmnmm Fr-f INVENTOR. /ff/v/P/ G. sw/@M55 Nov. 26, 1946. H. G. BuslGNlEs 2,4l1,51

ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM Filed ApIil 12, 1945` 7 Sheets-Sheet '7 caMB//w/vs ,427

oEv/cE l OUTPUT IN V EN TOR.

WMNEY f Patented Nov. 26, 1946 mais ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM Henri G. Busignies, Forest Hills, N. Y., assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application April 12, 1943, Serial No. 482,677

In France May 27, 1942 19 Claims.

The present invention relates to electromagnetic wave transmission systems, and in particular to systems such as transmitter systems wherein a transmitted wave is characterized by having a spectrum of frequencies, the frequencies varying with different directions of propagation, and/or receiver systems wherein the frequency of a received wave may be translated to other frequencies depending upon the direction of wave propagation with respect to a receiving system.

In a general way, the wave transmission systems provided for in the present invention are characterized by the fact that they not only permit the radiation of waves having frequencies dierent from the frequency of the oscillations which produce the waves, but also permit in the case of reception, a frequency translation of received waves whereby the frequencies of currents in the receiver circuits are different from those f observable in the vicinity ef the receiving equipment,'and to which the receiving antennas are tuned.

The transmission systems provided for in the present invention also comprise means for making the frequency of a transmitted wave dependent upon the angle of radiation from a transmitter on the one hand, and for making the frequency of a received wave on the other hand dependent upon the angle of incidence which the wave makes with a receiving system.

The processes for establishing wave transmission systems such as those defined above are such that the frequencies of the radiated or the received waves are different from those frequencies which are created in the circuits of the transmitting or receiving apparatus as the case may be, and vary in a manner dependent upon the direction of the propagated wave with respect to a predetermined axis of either a transmitting or receiving antenna array.

- in accordance with one feature of my invention, means may be provided at a transmitter for modifying the radiation from a group of transmitting aerials in such a way that the radiation successively has as a center, a different aerial of the group. Similarly, in accordance with another feature of my invention, means may be provided at a receiver for successively intercepting energy from a different aerial of a group of receiving aerials. The angular variation of phase, and consequently the variation in frequency, as well as the directivity of the aerial systems depends on the rapidity at which the aerials of a group of aerials successively perform their radiating or receiving function.

The transmission and reception features of my invention may best'be explained by rst considering the Doppler-Fizeau principle. Consider, for example, a radiating antenna moving through space at high velocity. In accordance with the Doppler-Fizeau effect the result would be thatl a spectrum of waves-varying in frequency would exist in space. The wave of maximum frequency would be in the direction toward which the antenna was moving and the wave of minimum frequency in the opposite direction. The rate of angular frequency variation in azimuth would be dependent on the velocity of the moving antenna. If a receiver were suiciently selective, it could detect small frequency variations and therefore small angular variations.

If, in a unit of time, a transmitting antenna is moved toward a receiving antenna by a distance nl, the Wave frequency appearing at a receiving antenna will have been increased by n periods during the unit` of time. If the transmitting antenna had moved in the opposite dii rection or directly away from the receiving antenna, the wave frequency at the receiving antenna would have been decreased by n periods.

Similar phenomena would also take place if the transmitting antenna were stationary and the receiving antenna were moved to and from the transmitting antenna. However, in both of these cases the frequency would not have varied at all if one of the antennas had been moved on a circumference centered on the other antenna orin a direction perpendicular to the direction dened by the two antennas provided the displacement or total antenna motion was small with respect to the distance between the antennas. If the direction of motion of one of the antennas is at an angle to the direction defined by the antennas, there will be a change in frequency determined by the cosine of the angle determined by said two directions. Let 0 be the acute angle between the direction of the displacement and the direction in line with the two antennas. kIi' the displacement amounts to nl in a unit of time, one of the antennas will have moved with respect to the other by m cos 0, and the received or transmitted frequency will have varied by 1LT cos 0 where T is the period of one cycle. When the cos 0 is positive, the frequency will have increased; and when the cosine is negative the frequency will have decreased.

Obviously it is impossible to physically move an antenna at a velocity which would produce a neasuralble Doppler effect, but in accordance yith my invention, I produce by electrical means ihe effect of an antenna moving with great ve- Locity.

The equivalent of a rapidly moving antenna provides means for producing several novel communication systems, direction finding systems, beacons, etc. For example, in distinction to known forms of direction finding systems wherein direction determination is effected by direction finders which select radio waves of one constant frequency as the result of the orientation of a directive aerial system, the equivalent of a. rapidly moving antenna Provides a means for determining direction by a selection of frequency. In general, in transmission systems embodying an` an.. tenna having the above described characteristics, several transmissions that are made on the same frequency but which come from different directions, or portions of a single transmission that arrive over different spacial paths, will appear to the receiver as if they had different frequencies, thus permitting the picking up and the selecting of these various transmissions according to their directions of propagation.

In the following I have enumerated' several objects of my invention namely:

l. To provide a method of wave transmission or reception, as the case may be, which comprises electrically producing the effect of an antenna moving rapidly through space;

2. To provide an antenna array wherein the aerials thereof are energized successively from one end of the array to the other end thereof;

3. To provide a wave transmission system in which the frequency of the radiated wave in space varies with different directions of radiation;

4. To provide a wave transmission system by which a determination ofV direction may be made by frequency selection.

5. To provide a wave transmission system wherein the apparent frequency of a carrier Wave may be varied at the receiver;

6'. Toprovide a radio beacon system wherein various courses may be determined by the beats produced from a plurality of radiations of variable frequency.

7. rTo provide a radio direction finding system wherein the sense of direction is determined by frequency selection;

8. To provide for the elimination of polarization errors in radio. direction finders;

9. To provide. a communication system wherein by the transmission of waves of different frequencies at different angles in the vertical plane the quality of reception is greatly improved.

l0. To provide radio transmitters which are difficult to locate byl triangulation methodsY withY direction finders; and

ll. To provide a receiving system which is free from polarization errors.

Other objects, features, capabilities and advantages of my invention will appear from the following detailed description taken in connection with the accompanying drawings showing several illustrative embodiments and wherein:

Fig. 1 is a schematic representation of a wave transmission system for illustrating a principle of my invention;

Fig; Z'is av series of'vector diagrams illustrating the operation of'my Wave transmission system;

Fig. 3 is a schematic circuit diagram illustrating the operation and energization of a transmitting antenna array inaccordancevvvth .my invention;

Fig. 4 is a schematic circuit diagram of a portion of Fig. 3 modified for illustrating how the antenna system of my invention may be employed for the reception of radio waves;

Fig. 5 illustrates a series of electrical voltage waves for controlling and regulating the radiation from, orv in general the conditioning of, the various individual antennas of my antenna array;

Fig. 6 illustrates schematically a radio beacon system in accordance with my invention;

Fig. 7 illustrates schematically a direction finding system comprising the wave transmission system in accordance with my invention;

Fig. 8 is a block diagram illustrating a two course beacon comprising crossed antenna arrays:

Fig. 9rk is a block diagram illustrating a communication system for reducing the effects of fading in accordance with my invention; and

Fig. l() is a block diagram illustrating a second type of communication system for reducing the effects of fading in accordance with my invention.

Referring iirst to Fig. 1, the transmitter 'I' and the receiver R represent a communication system. The transmitter may be of any type and radiates a carrier wave represented by the reference character W. 'Ihe receiver R may be of any type suitable for receiving the type of wave W and is assumed to be capable of moving at high velocity in the direction of the arrow which is at an angle 0 with the direction joining the transmitter and the receiver. If the angle 0 were zero and the receiving aerial were moved directly toward the transmitter, in a unit of time it would have travelled a distance nk and the received frequency would have been increased by n periods per second. On the other hand', if the receiving aerial had moved directly away from the transmitter, the frequency would have been diminished by n periods in a unit of time. If the receiver were moved in the direction of the arrow 0 having a finite value, the received frequency would have been varied in a unit of time by the value 11T cos 0 Where T is the period of one oscillation. If the cosine of 0 were positive the frequency would have been increased and if the cosine of 0 were negative the frequency Would have been increased.

Remarks similar to the abovev could be made if it were assumed that the receiving aerial was fixed and the transmitting aerial was moving. The same formulas willhold true in either case wherein 0 represents the angle between the direction of the moving aerial and the direction represented by the line between the transmitter and the receiver.

It is obvious that neither a transmitting nor a receiving aerial can be moved rapidly through space .but in Fig. 2 I have diagrammatically illustrated how a transmitting antenna consisting of an array of aerials in accordance with my invention will produce the same result as if a transmittingv aerial were actually physically moved through space.

Referring now to Fig. 2, the numerals l, 2, 3, l and 5. represent individual fixed aerials of a five aerial array. A receivingy aerial 9 is located at a distance from the aerial array.. In order to illustrate the operation of the array the separation of the aerials thereof. have been given predetermined valuesand for simplicity of discus-r sion the separation has been chosen as a quarter wavelength at the operating frequency. All of the aerials are conditioned so that they will radiate in phase for a predetermined time period 5 which will be further explained hereafter. Let us further assume that the magnitude of the radiated wave as radiated from a single antenna varies in accordance with the positive half of a sine wave and that no more than two adjacent aerials are radiating simultaneously.

In accordance with my invention at zero time, as noted on the time scale at the left of Fig. 2, antenna I is radiating a, wave of maximum amplitude and is represented by the vector V1. At the remote receiving aerial 9 the Vector of the received Voltage is represented by V2. The phase relationship between V1 and V2 may be of any value whatsoever but I have illustrated them both as being in the same direction or phase which would correspond to the condition in which there were an even number of wavelength between the transmitting and receiving antennas. The vector f the received voltage would be a maximum at the same time that the transmitter was radiating at maximum amplitude at some subsequent period, this period being equal to the time required by the radiated wave to travel between the transmitter and the receiver. At zero time the radiation from antennas 2, 3, 4 and 5 is zero.

As above mentioned, the radiation from each antenna is modulated in accordance with the positive half of a sine wave, the modulating waves for each antenna being displaced in phase by 90 for adjacent antennas. In other words, when the radiated wave from one antenna is a maximum, the radiated wave from an adjacent antenna is zero. Again referring to Fig. 2, vectors Va and V4 represent the values of the radiated waves from antenna l and 2, respectively, as they would exist at a time equal to one-eighth of a cycle of the modulating wave following the time zero. This is equivalent to a 45 phase displacement of the modulating voltage. The vector V1 would have decreased to a value of 0.707 of its original value. Vector V4 would have increased from zero to a value of 0.707 of its maximum value.

Although there has been a phase rotation of 45 during this period, I have represented vectors V1 and V3 in the same direction for simplicity of disclosure and since the main object of this iigure is to illustrate the manner in which the voltage vector at the receiver is displaced in phase. At the time T/8 when V3 is equal to 0.707 of V1 the voltage vector V5 at the receiver has also been reduced to 0.707 of its maximum value. The voltage vector V6 at the receiver represents the magnitude and phase relation of the energy re` ceived from antenna 2. It will be recalled that all antennas, when radiating, are radiating in phase and since antenna 2 is closer to the receiver by a distance equal to one-fourth wavelength of its radiated wave, the energy from antenna 2 arrives at the receiver one-fourth cycle in advance of the energy received from antenna l. This accounts for the 90 advance phase relation of vector V6 with respect to vector V5. The result out of V5 and Vs is represented by V7. It

will be observed that V1 has advanced one-eighth` An eighth of a modulation cycle later, the current in antenna 2 has decreased to 0.707 of its maximum value as represented by vector V10 and at this time the radiation from antenna 3 represented by vector V11 has increased from zero to 0.707 of its maximum value. The current in antenna l remains zero since it will be recalled that the antennas are only radiating on the positive halves of the modulation cycle. The vectors V12 and V13 at the receiver correspond to the vectors V10 and V11 at the transmitter and their resultant vector V14 illustrates the fact that another advance of one-eighth cycle has taken place and that the maximum value has remained unchanged.

It is not believed necessary to continue with a detailed discussion of the vectors as they would occur during following time period-s. It will be seen, however, that for a complete cycle of the modulating wave the resultant vector at the receiver has rotated 360 or one revolution in a forward direction. 'Ihis is equivalent to increasing the frequency at the receiver by one cycle. If the time period of a single cycle of the modulating wave is taken very small, for example, twenty microseconds, there would be 50,000 rotations of the resultant voltage vector at the receiver every second.` This would correspond to an apparent increase in frequency at the receiver of 50 kilocycles or the frequency of the received wave would be 50 kilocycles greater than the carrier wave radiated by the antenna-s 1 to 5 individually.

Refer now to Fig. 3 wherein I have illustrated my invention as embodied in a transmitter consisting of eight antennas in a lineal array together with control apparatus for their energization. The antennas l, 2, 3, 4, 5, 6, l, and 8 are separated one from the other, a distance equal to one-quarter wave length of the frequency at which they are designed to radiate. The complete array therefore covers a distance of one and three-quarters wave lengths. This spacing is by way of example only and other spacings may be employed as explained more fully hereinafter.

Connected to antenna l is control device l0, which I have illustrated as a vacuum tube having a cathode, an anode, and three grid electrodes. Similar control devices Il to l1 are connected to antennas 2 to 8 respectively. Anode potential for the devices is derived from a source I8 illustrated as a battery. Choke coils 20 to 26 are connected between the antennas as illustrated in order to isolate the antennas for radio frequency currents. High impedance circuits could be employed in place of choke coils if desired. Choke coil 21 isolates the power supply from the antenna 8. A high frequency source is illustrated by the block 29. This source may be of any type suitable for delivering high frequency energy to the grids 30 to 31 of control devices i0 to I l respectively. The voltages applied to grids 30 to 37 are in-phase one with the other and this condition may be o-btained, for example, by making the 'lengths of the transmission lines 40 to 41 all equal. If transmission lines are not employed for connecting the high frequency source to the grids of the control devices, other known forms of obtaining in-phase voltages may be employed. In .accordance with my invention as illustrated in Fig. 3, the antennas l to 8 are caused to radiate lsuccessively in the following manner. A plurality of modulating sweep voltages operate on other grids associated with the control devices I0 to l'i in such a manner that the initiation of radiation in an antenna follows the initiation of radiation in an adjacent antenna by a time period equal to one-quarter cycle of the modulating sweep voltage. In Fig. 3 it is assumed that the initiation of radiation from antenna 2 follows the initiation of radiation from antenna l and that the initiation of energy in antenna 3 follows the initiation of energy in antenna 2 and so forth throughout the complete array. The term modulating sweep voltages is used since these voltages determine the rapidity with which the antennas are energized in sequence. The control circuits for controlling the initiation of radiation in the antennas are such that radiation takes place only during the positive halves of the modulating sweep voltage waves as will be more fully explained hereinafter.

In accordance with my invention as illustrated in Fig. 3 not more than two antennas should radiate at the same time. To prevent the simultaneous radiation of more than two antennas further blocking or conditioning control voltages are applied to an additional set of grids in control devices l to il. rlhe conditioning voltages are applied to grids 50 to 51, and the modulating sweep voltages are applied to the grids 110 to 41 of the control devices I0 to l1 respectively.

In order to more clearly illustrate the operation of my invention, the method of obtaining the modulating and the blocking o-r conditioning voltages and the manner in which they are generated and applied to the control devices will now be described.

Take, for example, the numerical illustration given in connection with Fig. 2 wherein the time period of the modulating sweep voltage was twenty microseconds. Since each antenna is energized every quarter period of the modulating sweep voltage cycle, the initiation of radiation from one antenna will follow that of the other by one-quarter of twenty microseconds or ve microseconds. This corresponds to a modulating frequency of fifty kilocycles per second. Conditioning voltages having a period twice that of the modulating voltages are also required. This is equivalent to a conditioning voltage frequency of 25 kilocycles per second. It is convenient to first generate the conditioning voltage and to then. obtain the modulating sweep voltage from the second harmonic of the conditioning voltage. Four modulating sweep voltages separated in phase by 90 are required in the present illustration. Likewise four blocking or conditioning voltages are required. Two of these conditioning voltages have a phase displacement of 90 and the other two voltages have a phase separation of 180 from the 90 phase related voltages. In Fig. I have illustrated the modulating sweep voltages by curves A, B, C, and D and the conditioning voltages by curves M, N, S, and T. The lower portion of Fig. 3 illustrates in block diagram the manner in which all of the various modulating sweep voltages and the conditioning voltages are obtained. This portion of the diagram and the voltage curves of Fig. 5 are to be considered together. First, a blocking voltage M of 25 kilocycles is generated in any convenient manner. In Fig. 3 the oscillator 6i! represents the generator of this voltage. A second blocking voltage N is obtained by passing the voltage M through phase shifter El wherein theY latter is retarded 90. A third blocking voltage S isolo-` tained by shifting the phase of the voltage M by 180. This phase shift is accomplished by means of the phase shifter 62. A fourth blocking voltage time sequence.

T is obtained by shifting the phase of voltage N 180 by the phase shifter 63. Many forms of phase Shifters are well known in the art and require no detailed explanation as to their operation. The output of the oscillator is also passed through a frequency doubler B4 to form the modulating sweep voltage A. The latter voltage is passed through a phase shifter 65 in which it is retarded to produce the voltage B and the voltage D is obtained by shifting the phase of B by the phase shifter 65. Voltage C is obtained from voltage A by shifting the phase of the latter 180 by phase shifter El. It will be noticed in passing that the voltages resulting from the 90 phase Shifters are retarded rather than advanced.

Rectiers lll, l5, '16, and 'Il have been included in the connections leading to various grids of the control devices. In the circuit arrangement for carrying out my invention illustrated in Fig. 3, these rectiers are not absolutely necessary a1- though they introduce no harmful results. They, however, are desirable in certain instances as will be explained hereinafter. The characteristics of the control devices of Fig. 3 are such that when the devices are conditioned for operation, the potential on the grids 40 to 4l are in effect biasingV the devices to cut-off, that is, current will flow in the various antennas only when the positive half cycles of the modulating voltages are applied. The grids and cathodes are in eiect functioning as rectiiiers and therefore the additional rectiers l-ll merely constitute other rectiers in series. However, there are types of control devices other than those illustrated in Fig. 3 which could be employed, for example, devices operating on the principle of balanced modulators. In control devices of this latter type the use of rectifiers in the position shown in Fig. 3 would usually be essential. The negative halves of curves A, B, C and D have been shown in dotted lines to illustrate that these voltages are rectified.

Limiters 90, 9|, 92, 93 are placed between the blocking voltage sources M, N, S, and T and the grids 50-5 l 52-53, 541-55, and 55l respectively of control devices. These limiters limit the output voltage of the blocking voltages M, N, S and T to a value L illustrated by the dotted lines K in Fig. 5. The purpose of the blocking voltages is to so condition the control devices that the latter will be free to operate and permit wave energy to radiate from the antennas at certain times, and to prevent radiation from the antennas at other times, all in accordance. with a predetermined The control devices have characteristics such that the limited blocking or conditioning voltages in themselves contribute substantially nothing to the radiated wave energy. The envelope of the modulated radiated wave is controlled substantially entirely by the modulating sweep voltages A, B, C, and D. The limiters are employed to reduce the large voltage peaks of the blocking voltages which otherwise might produce deleterious radiation.

The reason for originally giving the conditioning voltages a large amplitude and then for reducing their amplitude by limiting is to produce a voltage wave having relatively steep sides in order that they will act on the control devicesv for substantially the complete cycle of the modulating sweep voltages,

Other types of conditioning voltages could also be employed. For example, a substantially square voltage wave having the shape of the curve U as 9 shown in Fig. would be equally as eiective as the voltage M, N, S or T.

Considering now the time zero when antenna I is iirst conditioned to radiate. Voltage M is applied to grid 50 and voltage A is applied to grid 40. The voltage M unblocks or conditions the device IIJ and the voltage A modulates the antenna current, the frequency of which is controlled by the high frequency voltage applied to the grid 30.

IAt this time the voltage M also unblocks control device I I, but current is not radiated from the antenna 2 associated therewith since the modulating voltage B has not as yet been applied to the grid 4I of the control device. Similarly antennas 3 and 4 cannot radiate since the modulating voltages C and D have not as yet been applied to the grids 42 and 43 of the control devices I2 and I3 respectively.

At zero time it will be seen that modulating voltage A is also applied to the grid 44 of device I4 which is associated with antenna 5 one wavelength away from antenna I, and in the absence of preventive means undesired radiation from antenna 5 would take place. To prevent this radiation, the blocking voltage S is applied to the grid 54 of the device Ill.

A one-quarter cycle of the modulating voltage later, antenna 2 begins tc radiate since it is at this time that the modulating voltage B is rst applied to the grid 4I. At this time, an antenna I is radiating at maximum amplitude and antenna 2 is just beginning to radiate. None of the other antennas can radiate at this time since their associated control devices either blocked or the modulating waves have not as yet been applied to the grids of the control devices associated with these antennas. Another one-quarter cycle later antenna 3 just begins to radiate due to the fact that modulating voltage C is just becoming positive and the control device l2 has been unblocked by voltage N which is also becoming positive. At this moment antenna 2 is radiating alone at maximum output antenna l having discontinued to radiate. Another one-quarter cycle later antenna 4 begins to radiate and at this time antenna 3 is radiating at maximum output.

An analysis of all of the control devices as they are being controlled in accordance with the voltages of curves of Fig. 4 would lead to the observation that no more than two adjacent antennas of the antenna array are radiating at any one time, and also that the sum of the radio frequency currents radiated by the array remain constant. However, as each antenna of the array begins to radiate, the phase of the high frequency wave is advanced one-quarter of a cycle. It will be seen that the frequency of the radio wave in space has been increased one cycle for every sweep of a modulating sweep cycle voltage. As illustrated in Fig. 3 the frequency of the radiated waves has been increased for a receiver located to the right of the figure and has been decreased for a receiver located to the left.

I have also illustrated in Fig. 3 a source of voltage represented -by the block 80 for modulating the radiated current at, for example, a voice frequency. This modulating voltage is impressed on the anodes of the control devices through the transformer 8l. A frequency measuring device located at a distance to the right and in line with the antenna array of Figure 3 would respond not to the frequency ofthe high frequency source 29, but that frequency as modied by the frequency of the modulating sweep voltages. For example, in the numerical case previously taken, the frequency of the source 29 would be increased by 50 kilocycles per second. A receiver located at this distant point could therefore be made selective to this increased frequency and of course, with suitable detecting apparatus, would reproduce the modulation originally placed on the carrier wave by the source 80.

While in the above description of the wave propagating system shown in Fig. 3 I have assumed an antenna spacing of one-quarter wave length, this spacing was by way of example only.

With the one-quarter wave length spacing the required modulating sweep voltages are four in number and differ in phase by 90. Other antenna spacing could also be employed. For example, if the antenna spacing were made equal to one-third of a wave length, three modulating sweep voltages would be employed diiering in phase by 120. In general the number of sweep circuit voltages required in any system is equal to the wave length of the high frequency source divided by'the spacing between the antennas as measured in wave length.

In Fig. 4 I have illustrated a portion of a receiving antenna array similar in character to the transmitting array shown in Fig. 3. I have illustrated only two antennas and their associated apparatus in Fig. 4 in order to avoid unnecessarily complicating the gure. In Fig. 4, antenna Ia is connected to ground through an impedance |50 and antenna 2a is similarly connected to ground through an impedance I5I The grids 30a and 3Ia of the two conditioning devices IIla and IIa are connected across the impedances I50 and I5I respectively. Modulating sweep voltages are applied to grids 40a and IIa and blocking voltages are applied to grids 50a and 5Ia. These voltages may be of the same type as illustrated by the curves of Fig. 5 and are applied to various grids of the conditioning devices in accordance with the circuit arrangement shown inthe lower portion of Fig. 3. For example, the modulating sweep voltage A is applied to grid 40a, the modulating voltage B is applied to grid llla, and the blocking voltage M is applied to grids 50a and 5Ia. A system of this type is useful in providing the elect of a receiving antenna moving rapidly through space such as will be described later in connection with Fig. 10. v

The above described wave propagation system may be employed in combination with other equipment to produce several new and novel results. Fo-r example, in Fig. 6 I have illustrated a radio beacon formed by combining a wave propagation system such as shown in Fig. 3 with a non-directional antenna to form a composite radiating system. The wave propagating system comprises an antenna array composed of eight separate antennas, a conditioning or control device connected to each antenna, a modulating sweep voltage generator and a blocking voltage generator such as are illustrated in Fig. 3. The antennas and other associated conditioning and control means are illustrated in Fig. 6 by the blocks I to 8, When an antenna array of this type is operating the carrier wave is not of constant frequency for all directions from the array but varies from a maximum to a minimum value, the maximum value being in the direction in which the separate antennas are successively excited and the minimum value in the opposite direction.

A separate antenna is positioned near the antenna array and is separately excited at a frequency preferable between the maximum and l l minimumr frequencies of the carrier waves radi ated by the antenna array. In Fig. 6 this separate antenna is shown as the block |06, and for example it is excited at a frequency of cycles per second, the excitation frequency for each antenna of the array being F, and the frequency of the modulating sweep voltage being f.

At a distance from the array the carrier wave from the array and from the separate antenna combine or interfere to form beats. In the direction shown by the arrow the frequency of a space wave from the array is F-i-f and in the direction shown by the arrow |02, the frequency is F-f. When these frequencies are combined with f F-l- 2 the frequency of the separate antenna |00, the beat frequency in the direction of the arrow ll is and in the opposite direction it is 11/21. At right the resulting beat frequencies at right angles to the array is in both directions.

The frequency of the carrier wave radiated from the array at an angle of 60 from the direction shown by the arrow |0| is F+f cos 60 or lug This frequency, which is radiated in the direction shown by the arrows |63 and |04, would combine with the frequency the frequency of the wave radiated by the separate antenna |00, to form a resulting beat frequency equal to zero.

A direction along which the beat frequency is zero could be employed as a course of a radio beacon. For example, an airplane ying this course and having a receiver capable of receiving a band of frequencies F-i-f to F-f would indicate a zero beat while on the course, but a finite beat while off the course. Should the plane be off course, the pilot need only y in the direction of lower beat frequency to arrive on the course.

The course or courses of any beacon may easily be changed in accordance with my invention. All that is required is to vary the frequency the wave radiated by the yseparate antenna |00. For example, if this frequency is changed from the value Fig shown in Fig. 6 to a value F-i-f, the beacon will armere 12 determine only a single course `and this in the direction of the arrow Iil.

Principles, similar to those employed for defining the radio beacon illustrated in Fig. 6, may also be employed to provide a radio direction finder such, for example, as illustrated in Fig. '7. In this figure, the antenna array and its associated apparatus are also illustrated by the blocks to 8. A separate antenna system and its associated control equipment is illustrated by the block 0. All antennas are now to be considered as receiving antennas. The receiving antenna array is preferably mounted in a manner such that it may be rotated through 360 and is, therefore, capable of being orientated in any direction.

The problem now is to determine from what direction a signal wave is arriving. It may be arriving from any direction as illustrated in Fig. 7 by the several arrows marked F. Actually the received signal is arriving from only one direction and by rotating the receiving antenna array, this particular direction may be determined in the following manner. A voltage from a modulating sweep voltage source is employed to sweep across the antenna conditioning means associated with the antenna array. Let the frequency of the sweep voltage source be f. When the array is pointing toward the true source of signal having frequency F, the apparent frequency in the circuits of the receiver associated with the antenna array is F-l-f. This presupposes, of course, that the direction in which the antennas of the array are successively conditioned to receive is toward the origin of the signal wave.

If the antenna array is not pointing toward the incoming signal, the frequency developed in the circuits of the array receiver will be F--f cos 0, 0 being the angle between the direction of the incoming signal and the direction of the antenna array.

The non-directional receiver H0 also receives the wave having the frequency F. In the receiver, this frequency F is also modulated by the frequency f of the sweep voltage source with the result that a side band frequency F-i-f appears in the receiver output. The carrier frequency F and the other side band F-f are suppressed.

The two frequencies F-i-f cos 0 from the array and F-l-J from the separate receiving antenna are combined and detected in a detector ||2 the output of which is equal to f-J cos 0. This frequency may be employed to operate an indicator H3. It will be seen that when the direction of the incoming signal and the direction of the array coincide, the cosine of 0 is equal to one and the frequency for operating the indicator is equal to zero. Many forms of indication capable of indicating this condition of zero beat are known in the art.

From a study of Fig. it will be observed that there will be only one direction in which this condition of zero beat occurs and therefore I have devised a direction finding system in which the well-known 180 ambiguity of direction is not present.

In Fig. 8, I have illustrated a radio beacon system comprising two antenna arrays and their associated equipment positioned at right angles to each other. The antennas of each array are excited in phase at the frequency F and are conditioned to radiate by modulating sweep voltage f. An analysis, in accordance with methods dis- Y cussed in connection with Figs. 6 and 7, of the beat frequencies occuring at a distance from the antenna arrays will showthat there will be two directions,v 180 apart-in which the beati frequency will be zero. The Wave propagating system illustrated in Fig. 8 would therefore be suitable for a two course beacon. Changing the modulating sweep voltage frequency of one of the arrays with respect to the modulating sweep voltage frequency of the other, will provide a means for changing the direction in which zero beat will occur and therefore a means for changing the direction of the courses.

Referring now to Fig. 9 I have illustrated a communication system in accordance with my invention which provides a means for reducing the effects of fading at a receiver. In the examples discussed above, it has been tacitly assumed that the variation in carrier wave frequency radiated at various angles to the antenna array occurred in the horizontal plane.

Actually, of course, a wave of any given carrier frequency defines a cone of revolution with the axis of the cone coinciding with the direction of the array. This means, of course that the frequency radiated from the antenna array of my invention varies in a vertical plane in the same manner that it does in a horizontal plane.

Considering now the antenna transmitting array and its associated equipment shown by the block 300 in Fig. 9. Also assume thatthe direction in which the antennas of the array are successively energized is in the direction H. Carrier waves having different frequencies will be radiated in the vertical plane. If the frequency at which each antenna of the array is excited is F, and the frequency of the modulating sweep voltage is .'f, as in the other illustrations herein given, the frequencies of the various waves in the vertical plane will be F-l-f cos where 6 is the angle between the horizontal and the direction in the vertical plane in which the carrier wave is propagated.

Somewhere in the upper atmosphere the various carrier1 waves are reflected and eventually arrive at a receiving point illustrated in Fig. 9 as an antenna SID. The antenna is connected to a broad band receiver 3| l, the band width of the receiver being sufficient to cover substantially all of that portion of the frequency spectrum of the various carrier waves reaching the receiving antenna. A plurality of frequency selectors are connected to the wide band receiver for selecting those carrier frequencies which preferably contain the most energy. In the gure, I have illustrated two selectors only namely 3I2 and 3|3, it being understood that as many selectors as desirable could be employed. To each frequency selector is connected a detector shown as blocks 314 and SI5. The detected outputs are combined directly and may be amplified in the amplifier illustrated as block Slt. The output of SES represents the desired signal.

Referring now to Fig. 10, I have illustrated a second type of communication system employing the principle of an antenna moving rapidly through space. In contradistinction to the system illustrated in Fig. 2 wherein the transmitter employed the antenna array of my invention, the antenna array in Fig. 10 is employed at the receiver. In Fig. 10 a transmitting antenna 400 is assumed to be transmitting a voice modulated carrier wave to the receiving system All). The carrier wave may take a plurality of paths, the wave along each path being reflected in the upper atmosphere, and arriving at the receiving system at various vertical angles. The carrier waves are all of the same frequency in distinction to their having different frequencies as described in connection with Fig. 9.

As the carrier waves strike the receiver antennas at various angles, there is developed within the receiver a plurality of different frequencies depending upon the angle of reception and the periodicity of the modulating sweep voltage. The conditioning devices and control circuits therefore are illustrated by the block 4i l. All of the frequencies developed are passed to a wide band amplifier illustrated by the block 412. Fromthe wide band amplifier connections are made to a plurality of frequency selectors illustrated by the blocks M3, lllll, M5, and M6.

l. To each selector is connected a separate detector illustrated by the blocks 523, 624, 425, and Q25. The outputs from the detectors are directly combined in a combining device G21. The output from the combining device represents the signal.

It is preferable that the selecting devices 443 to M6 select those frequencies which contain the most energy and this may be accomplished by connecting to the wide band amplifier a scanning frequency receiver illustrated by block 428. The output of the scanning frequency receiver is connected to a cathode ray oscillograph 429 which will show all of the frequencies developed from the carrier wave by the receiving antenna,

and also the relative magnitudes at the variousV frequencies. Knowing the frequencies having the greater magnitudes it is possible to adjust the selectors M3 to M6 to select these frequencies for final detection thereby obtaining maximum output.

It will be appreciated from a study of Figs. 9 and 10 and the descriptions relating thereto that the communication systems illustrated depend upon the principles of frequency selection in order to avoid the effects of fading.

This method of overcoming fading is distinctly different from methods employed in the prior art which make use of either a plurality of antennas geographically spaced or of very sharp directive receiving systems.

It should be pointed out in passing that any transmitter employing the principles of my invention radiates waves the source of which is very difficult to locate by triangulation methods. For example, a direction finding system located at a distance from the source of waves will respond only to a particular frequency depending on the angle between the direction of propaga'- tion of the waves and the direction of the antenna array producing the waves. The direction finder can only determine the line of propagation of the received waves. To determine the exact location of the source of waves by triangulation methods, another direction finder must also determine the direction of wave propagation of the received waves with respect to its position. However, the two direction finders, although taking bearings on the same wave source, are actually receiving waves of different frequencies and unless some characteristic modulation is present in the waves, it will be difficult for said direction finders to be sure that they are triangulating on the same wave source.

While I have described above the principles of my invention in connection with specific apparatus and in several modifications thereof, it is to be clearly understood that this description is-given only by Way of example and not as a limitation on the scope of my invention as set forth in the objects of my invention and the accompanying claims.

I claim:

i. An antenna Vsystem comprising a plurality of antennas arranged in a predetermined array, each of said antennas having substantially the same radiation pattern, and antenna conditioning means connected to said antennas to condition the same for successive wave translation in a manner simulating the effect of a single antenna together with its radiation pattern moving through space.

2. A wave translating system comprising a plurality of antennas arranged in a predetermined array, each of said antennas having substantially the same radiation pattern, antenna conditioning means connected to each antenna for conditioning said antennas to operate successively for wave translating purposes, and control means for timing the operation of said conditioning means to initiate the conditioning of one of said antennas while discontinuing the conditioning of another of said antennas.

3. A directional wave propagating system for a predetermined wavelength, comprising a .plurality of antennas arranged in a predetermined array, a high frequency power source, said antennas being spaced apart a distance equal to a predetermined fraction of the wavelength corresponding to the frequency of said source, wave generating means including a power supply means connected to each of said antennas for energizing same at predetermined time intervals, means connecting said source to said generating means for conditioning said generating means to generate in-phase energy at said yfrequency, and control means connected to said generating means for timing the radiation of said in-phase energy whereby each antenna radiates successively at said predetermined time intervals to produce a wave in space having a length equal to said predetermined wavelength.

4. A directional wave propagating system in accordance with claim 3 wherein said control means comprises a second Wave generating means having a frequency equal to the difference in frequency between the frequency corresponding to said predetermined wavelength and the frequency of said power source.

5. A directional wave propagating system for a predetermined wavelength comprising a high frequency power source, a plurality of subordinate antenna arrays, each subordinate array comprising a plurality of antennas, the spacing Vof antennas in each subordinate array being the same, said subordinate arrays being arranged -in overlapping spaced relation -to form Aa lineal main antenna array, the antennas of the main array being spaced apart a distance equal to a predetermined fraction of the wavelength corresponding to the frequency of said Source, wave generating means connected to each of said antennas for energizing same at predetermined time intervals, means connecting said source to all of lsaid generating means for conditioning saidgenerating means to generate in-phase energy at said frequency, control means vconnected to said -generating means for timing the initiation of the radiation of said iii-phase energy and for determining said time interval, -said control means comprising a second wave generating means for generating a plurality -of out-of-phase voltages equal in number to the number of said subordinate antenna arrays, the time-phase between vtwo successive voltages of said out-ofphase voltages being substantially equa1 -to the total variation in space-phase of a wave radiated -by any antenna over a distance equal to the spacing `between two adjacent antennas, one of said out-of-phase voltages controlling only the wave generating means connected to the antennas of one subordinate antenna array whereby the initiation of radiation from one antenna follows the initiation of `radiation from an adjacent antenna by said time interval to produce a wave in space having a length equal to said predetermined wavelength.

6. A directional wave propagating system in accordance with claim 5, wherein said control means also comprises a wave blocking means, said blocking means comprising generating means for generating a second plurality of out-of-phase voltages, the phase relation between the firstnamed plurality of out-of-phase voltages and said second plurality of out-of-phase voltages being such that no more than a given number of said antennas are radiating simultaneously.

'7. A wave propagating system comprising a plurality of antennas arranged in lineal array in a fixed direction and means for energizing said antennas successively whereby the frequency of a space wave varies directly as the cosine of the angle between the direction of said array and the direction of propagation of said space wave.

8. A wave propagating system comprising a plurality of antennas arranged in lineal array, and means for energizing said antennas in phase with a voice modulated high frequency wave successively one after the other, said means comprising a modulating sweep voltage generator and a blocking voltage generator, the phasing of said sweep voltage and said blocking voltage being such that the time-phase at which any two adjacent antennas are energized is substantially equal to the total variation in space-phase of a wave radiated oy any one of said antennas over a distance equal to the spacing between said adjacent antennas whereby a plurality of space waves of different carrier frequencies but having the same modulation are radiated in a vertical plane passing through said array.

9. A radio direction finding system comprising a rotatable group of antennas arranged in a predetermined array, antenna conditioning means connected to said antennas to condition said antennas for successive wave translation, a non-directional wave translating means, control means for timing the operation of said conditioning means and for modulating said non-directional wave translating means, combining means for combining the output of the first-named wave translating means and of said non-directional wave translating means, and an indicator connected to said combining means for indicating the direction of a received signal.

10. A radio beacon comprising a plurality of antennas arranged in a predetermined array, antenna conditioning means connected to said antennas to condition said antennas for successive wave radiation, control means for timing the operation of said conditioning means whereby a plurality of waves lof different frequencies are radiated from said array, the frequencies of said radiated waves varying as a function of the angle between the direction of said Yarray and the directions of propagation of said radiated waves, a separate antenna, means for energizing said separate antenna at a frequency such that the resulting radiated wave therefrom is equal to the frequency of one of the waves radiated from said antenna array.

11. A radio beacon comprising a rst wave transmitting system comprising a plurality of lantennas in lineal array, antenna conditioning means connected to said antennas to condition said antennas for successive wave radiation, control means connected to said conditioning means for timing the operation of said conditioning means to initiate the conditioning of one of the antennas while discontinuing the conditioning of another of the antennas, a second wave transmitting system comprising a plurality of antennas in a second lineal array, a second conditioning means connected to said antennas of said second array to condition the antennas of said second array for successive wave radiation, a second control means connected to said second conditioning means for timing the operation of said second conditioning means to initiate the conditioning of one of the antennas of said second array while discontinuing the conditioning of another of the antenna thereof, and a high frequency power source connected to both of said conditioning means for producing radiation from the antennas thus conditioned to produce interference patterns in space, said patterns having at least one direction in which the resultant radiated energy is substantially zero.

12. A radio beacon in accordance with claim 11 wherein the first-named lineal antenna array and said second lineal array are positioned at right angles to each other.

13. A wave communication system comprising a plurality of antennas arranged in lineal array, means for energizing said antennas in phase with a voice modulated high frequency wave successively one after the other, said means comprising a modulating sweep voltage generator and a blocking voltage generator, the phasing of said sweep voltage and said blocking voltage being such that the time-phase at which any two adjacent antennas are energized is substantially equal to the total variation in space-phase of a wave radiated by any one of said antennas over a distance equal to the spacing between said adjacent antennas whereby a plurality of space waves of different carrier frequencies but having the same modulation are radiated in a vertical plane passing through said array, a receiving system located at a distance from said antenna array, said receiving system comprising a receiving antenna and a receiver, said receiver having a plurality of frequency selecting means, each of said selecting means being tuned to select a different one of said space waves of different carrier frequency, separate detecting means connected to each selecting means for detecting said voice modulation and means to combine the output of said detecting means.

14. A wave communication system comprising a transmitting antenna for transmitting a modulated wave having a single carrier frequency, a receiving system, said receiving system comprising a plurality of spaced antennas arranged in a predetermined array, antenna conditioning means connected to each antenna of said array for conditioning same to operate successively for wave translating purposes, control means for timing the operation of said conditioning means to initiate the conditioning of one of said antennas while discontinuing the conditioning of another of said antennas whereby said carrier Wave of single frequency is translated into a wave having a frequency spectrum, an amplifier connected to said antenna array for amplifying the energy in said frequency spectrum, a plurality of selector means connected to said amplifier for selecting from said wave having a frequency spectrum a plurality of Waves of different frequency, and detecting and combining means connected to each of said selector means for reproducing said modulation.

15. A Wave communication system in accordance with claim 14 further comprising a scanning frequency receiver and an oscillograph connected to said amplifier for determining the Waves having the maximum energy.

16. The method of producing in space a spectrum of frequencies varying from a maximum in one direction to a' minimum in another direction, comprising sequentially radiating from separate origins a plurality of in-phase electro-magnetic waves.

17. The method of producing the effect of a single antenna moving through space, comprising successively conditioning for translation of wave energy a plurality of similar antenna systems spaced inA a predetermined array,

18. In a communication system, the method of reducing the effects of fading, comprising transmitting wave energy in the form of a modulated carrier wave, said carrier Wave having a frequency which varies with the direction of wave transmission, making an energy collection of at least a portion of said Wave energy, selecting a portion of said collected energy, said selected portion having a plurality of predetermined frequen.. cies, and detecting and combining said selected portions to reproduce said modulation.

19. In a communication system, the method of reducing the effects of fading, comprising transmitting wave energy in the form of a modulated carrier wave of single frequency, making an energy collection of at least a portion of said wave energy While simultaneously translating the single frequency of said wave portion to a frequency spectrum, selecting from said spectrum energy portions each having a predetermined frequency and detecting and combining said selected energy portions to reproduce said modulation.

, HENRI G. BUSIGNIES.

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