US 3109174 A
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R. E. PLUMMER ANTENNA ARRAY Oct. 29, 1963- 2 Sheets-Sheet 1 Filed Nov. 2, 1959 ROBERT E. PLUMME INVENT ATTORNEY Oct. 29, 1963 R. E. PLUMMER 3, 7
ANTENNA ARRAY Filed NOV. 3, 1959 2 Sheets-Sheet 2 URRENT SUPPLY ROBERT E. PLUMMER.
INVENTOR g; I; ATTORNEY United States Patent poration of Delaware Filed Nov. 2, less, Ser. No. 851,212 6 Qlaims. ((Il. S ilt-1%) The present invention relates to antennas and more particularly to means for electronically controlling the disection and shape of a beam of electromagnetic energy radiated from an antenna array.
In the past, it has been customary for radar systems to employ antenna means wherein the shape of the radiated beam is determined by the physical shape of the structure while the direction of the beam is determined by the physical position of the antenna. In order to obtain the desired amount of beam shaping it has been necessary for the antenna array to be large and bulky. This results in the antenna array having large inertia which in turn imposes limits on the speed at which the array can be moved. In addition, the array is subject to large forces whenever it is exposed to a high wind.
These and other problems are particularly acute in airborne radar wherein the antenna array is mounted on an aircraft. A partial solution to these problems is to place the antenna array inside of a streamlined radome mounted on the aircraft. Although these radomes are more or less transparent to electromagnetic radiations, they may cause distortions of the beam and/ or they project from the surface of the aircraft and thereby produce an objectionable amount of aerodynamic drag.
More recently, numerous eiforts have been made to develop antenna means that may be mounted flush with the exterior surface of the aircraft. In one form of flush mounted antenna array a waveguide system is provided that has a plurality of radiating apertures disposed in the surface of the aircraft. This type of antenna eliminates the necessity for a radome and also decreases the aerodynamic drag. The control over the radiation patterns from these antennas heretofore has not been entirely satlisfactory and also it has been extremely difli cult, if not impossible, to vary the direction of the radiated electromagnetic beam throughout a sufiiciently wide area.
:It is therefore an object of the present invention to provide an antenna array having electronic means for controlling the shape of the radiation pattern.
It is also an object to provide an antenna in which the beam of electromagnetic energy may be electronically scanned throughout any desired angle at a high rate of speed.
It is also an object to provide means for readily controlling the shape of the radiation pattern of an antenna array.
These and other objects are to be accomplished by providing an antenna array which includes at least one waveguide having a plurality of radiation apertures in one wall thereof adapted to be excited by a traveling wave of electromagnetic energy within the waveguide. The degree of coupling of each aperture to the traveling wave is individually controllable by separate field rotating means for each aperture. The traveling wave is fed into the waveguide in a mode that will not excite the apertures but the field rotating means will be effective to convert at least a portion of the energy into a mode that will excite the apertures subsequent thereto. Thus it is possible to separately control the amount of coupling between each individual aperture and the traveling wave. This in turn allows the amounts of radiation from each of the apertures to be controlled whereby the shape of the radiation pattern may be controlled.
319E. i Patented Get. 29, 1963 In addition, separate phase shifting means may be provided, for each of the individual apertures whereby the phases of the individual radiations may be controlled. This in turn will permit the direction of the resultant beam of electromagnetic energy to be varied throughout any desired range.
-In the drawings:
FIGURE 1 is a perspective view, with portions thereof broken away, of an antenna array embodying one form of the present invention.
FIGURE 2 is a plan view of an antenna array embodying a modification of the present invention.
FIGURE 3 is a perspective view of control means for the antenna array in FIGURE 2.
Referring to the drawings in more detail, the present invention is embodied in an antenna array 10 for radiating a beam of electromagnetic energy into space. The array includes a plurality of waveguides that are adapted to be connected to one or more sources of electromagnetic energy. (not shown). In the present instance there are only two substantially identical waveguides l2 and 14 illustrated; however, it will become apparent that only a single waveguide or a large number of waveguides ma be employed, if desired The first waveguide 12 is of the so-called square type in which the corresponding dimensions of each of the side walls 24, 26, 28 and 30 are substantially identical. As a result, the waveguide 12 is capable of conducting a traveling wave of electromagnetic energy with equal facility in either of two fundamental modes. For example, a traveling wave of energy may be propagated along the waveguide 12 in the TE and/or the TE modes. The electric fields of these modes are indicated by the arrows E and E respectively in FIG. 1.
The input end 16 of the waveguide 12 is adapted to be coupled to a source of microwave energy of desired frequency whereby a traveling wave of electromagnetic energy will be propagated along the waveguide 12. This source which is not shown may be of any conventional design but is preferably interconnected with the Waveguide 12 for creating a traveling wave in the waveguide that will be propagated along the guide 12 entirely in the TE mode.
The opposite end 20 of the waveguide is terminated in a power absorbing load. Thus, any energy that reaches this end will be absorbed and will not be reflected backwardly along the waveguide.
A plurality of apertures are provided in one of the side walls 3% of the waveguide 12 for coupling the electromagnetic energy in the traveling wave from the inside of the waveguide 12 to the outside of the waveguide 12. Although the apertures may be any desired variety, in the present instance they comprise a series of substantially identical elongated slotsrsuch as slot 32D that are located in the center of the side wall 30.
The slots 32 are relatively narrow but of resonant length with the long dimension extending substantially parallel to the axis of the waveguide 12. It may be seen that the currents induced in the side wall 3% by the TE mode will not intersect any of the slots, and accordingly, these slots will be inefiective to couple any of the energy in the TE mode to the exterior of the waveguide 12.
However, energy being propagated along the waveguide in the TE mode will create currents in the side wall 30 that will excite the slots. As a consequence, it may be seen that at least a portion of the energy in the TE mode present at any given slot will be coupled to the exterior of the waveguide 12.
In order to separately control the individual amounts of coupling between each of the slots 32 and the traveling wave in waveguide 12, a field rotating means 34A to U 34G is provided anterior to each of the slots 32 for rotating the field of the traveling wave. In addition, field rotating means 34H may be provided posterior to the slot 32G.
In the present instance, these field rotating means utilize the so-called Faraday field rotating efiect wherein the presence of a ferrite and a magnetic field will cause the electric field to undergo angular rotation as it progresses therethrough. The field rotating means 34 are all substantially identical and include coils 36A to 366 wrapped around the exterior of the waveguide 12. Thus a direct current in one of these coils will create a DC. magnetic field inside of the waveguide. In addition, a ferrite core 38 is provided in the center of the waveguide 12 so as to be disposed in this field. The core 33 may be a single member that forms a continuous cylinder of ferrite mate rial that extends the entire length of the waveguide 12. However, if desired, the core may comprise separate sections of ferrite that have lengths corresponding to the lengths of the coils and are positioned in alignment with the coils 36. Thus the ferrite material will not extend into the vicinity of the slots and the slots will be isolated from the effects of the magnetic field. Nonferrite sections having the same dielectric constant as the ferrite sections may be provided between the ferrite sections and in alignment with the slots 32 to prevent undesirable reflections of energy within the waveguide.
It may be seen that the application of a direct current to any particular coil 36A to 36H will cause a D.C. flux field in the waveguide and in the ferrite core that will cause the field of the traveling wave to rotate as the energy in the wave passes through the coil. The direction and amount of this rotation will be a function of the direction and amount of the current in the coil, respectively. As the field of the wave rotates the mode of propagation of the wave will tend to change from the T E mode to the TE mode or vice versa. Ninety degrees of rotation will cause the waves propagation to be completely changed from one mode to another. However, a lesser amount of rotation will cause the traveling wave to have one component thereof propagated in the TE mode and another component thereof propagated in the TE mode.
If the energy is introduced into the waveguide 12 entirely in the TB mode, the field of the wave will be oriented as indicated by the arrow E and as the energy travels along the guide there will be no coupling between the traveling wave and the slots 32. However, if a direct current of some predetermined amount is circulating in one of the coils, for example 36D, the field of the traveling wave will rotate by some predetermined amount less than ninety degrees as it passes through the field of coil 36D. Thus, the traveling wave posterior to the energized coil 36D will include two separate components, one of which will be in the TE mode and the other of which will be in the TE mode. Thus at least the first .slot 32D subsequent to the energized coil 36D will be excited by the traveling wave inside of the waveguide and at least a portion of the energy in this mode will be coupled to the outside of the guide 12. The amount of energy passing through the slot 32D will be a function of the amplitude of the component in the TE mode which in turn will be a function of the current in the coil 36D.
If it is desired to excite one or more of the succeeding slots such as 32E, 32F, and/or 326 to the same or different extents, the coils 36E, 36F, and/or 36G immediately anterior to slots 32E, 32F, and/or 32G, respectively, may be energized by a direct current. The amplitude of this current may be chosen so as to rotate the field of the traveling wave just suificiently to produce a component in the TE mode with an amplitude requisite for producing the desired degree of excitation of the slots 32E, 32F and/ or 32G.
If it is desired to prevent one or more of the succeeding slots 32E, 32F and/ or 320 from being coupled to the traveling wave, a current of reversed polarity may be circulated through coil 36E, 36F, or 36G. This will cause the traveling wave field to be rotated back into the TE mode. Thus all of the energy in the traveling wave reaching the slots subsequent to the reversely energized coil 36E, 36F or 36G will be in a mode that will not excite the slots. Consequently, no electromagnetic energy will pass through any of these slots. It may thus be seen that the slots that are excited and the amount of excitation thereof may be individually and independently controlled by the current in the coils 36A to 36G. The coil 36H may be utilized to insure the energy arriving at the end 20 being entirely in the TE mode. Thus in the event any energy is reflected back along the waveguide, it will not excite the slots.
If the slots 32 were free to radiate the energy passing therethrough directly into space, the resultant radiations would combine with each other to form a beam of energy whereby the waveguide 12 would act as an antenna. The direction of the beam would be determined by various factors such as the size and spacing of the slots, the relative phases of the radiations, etc. Normally, the direction of the beam would be fixed relative to the waveguide and would be directed obliquely to the axis of the waveguide, i.e., the structure would act as something between an endfire array and a broadside array.
The shape of the radiation pattern will be determined by the number of slots that are excited and the relative amplitudes of the radiations from the slots 32. Accordingly, varying the amounts of the currents flowing through the various coils 36 will vary the radiation pattern. With a single waveguide such as 12 it would be possible to produce beam sharpening in planes containing the axis of the waveguide 12 and/ or the slots 32.
Although it would be possible to permit the slots to radiate directly into space and thereby act as an antenna array it has been found preferable to employ a separate auxiliary waveguide 33A to 38G for each slot 32A to 326 (only 32D shown). The auxiliary waveguides 38 are all substantially identical and have a rectangular cross section and are of relatively short length. Each guide 38 is rigidly secured to the main waveguide 12. whereby one end of the guide registers with a slot. The broad walls of the guides 38 are all parallel to the long dimensions of the slots 32 so that the open ends or apertures 42A to 42G of the guides 38 form a straight row. Thus, any energy passing. through a slot 32 will travel along one of the auxiliary waveguides 3S and be radiated into space from the open end 42 thereof.
Each auxiliary waveguide includes a phase shifter for controlling the phases of the radiations from the apertures 42. Each phase shifter includes a coil 44A to 446 that is wound around the exterior of the auxiliary guide and a ferrite core 46A to 46G (only 46D shown) that is inside of the auxiliary guide. The core 46 may be either ferrite strips on the top and bottom broad walls of the guide to produce a negative phase shift or a ferrite rod in the center of the guide to produce a positive phase shift.
The current in a particular coil 44 will produce a DC. magnetic field in the waveguide and in the core. Since the auxiliarywaveguides are of rectangular shape, this will be effective to control the phase of any energy that is traveling through the waveguide 40. Thus the individual radiations emanating from each of the open ends 42 of the auxiliary guides 38 may be readily controlled by means of the current flowing through the coils 44.
It may be seen that varying the current flowing through the coils 36 in the field rotating means will control the amount of coupling between the slots 32 and the energy in the traveling wave. Thus the current in the coils will therefore be effective to determine the amount of beam sharpening in planes containing the apertures 42. Also it is apparent that varying the currents flowing through the coils 44 in the phase shifting means will vary the relative phase of the radiations emanating from the apertures ergized with predetermined amounts of current.
42 and will therefore be eflective to determine the direction of the beam.
If it is desired to provide additional control over the shape and direction of the beam, additional waveguides such as waveguide 14 may be provided. In the present instance, only one additional guide is shown, but it will be apparent that if more complete control is required a greater number of waveguides may be employed.
The waveguide 14 is substantially identical to the first waveguide 12 in that it is also of square dimension and can carry electromagnetic energy in either the TB mode or in theTE mode. The input end 18 of the waveguide 14 may be connected to the same source of energy as the first waveguide 12. The energy is fed into the wave so that it will be propagated along the guide in the TE mode. One side wall of the waveguide 14 has a row of slots 48 therein that are substantially the same as in the first waveguide 14. The long dimensions of the slots extend parallel to the slots 32 in the first waveguide 12 and to the axis of the second waveguide 14. As a consequence, the slots will not be excited by any of the energy in the T E mode, but they will be excited by the energy in the TE mode.
A separate field rotating means 56 is provided for each of the slots 48A to 486 (only 48A shown) and one is provided posterior to all of the slots d8. These means may be substantially identical to those in the first waveguide and include a ferrite core 52 in the center of the waveguide 14 and coils 54 wound around the exterior of the waveguide 14. These coils 54 and core 52 will thus be efiective to control the amount of energy that is coupled out of the waveguide 14 at each slot 4-8.
In addition, separate auxiliary waveguides 56 are provided for each slot 48. These waveguides 56 are substantially identical to those in the first waveguide and the ends thereof form a second row of radiating apertures 58 that is parallel to the first row. Each auxiliary waveguide is provided with phase shifting means that includes a coil 6th on the outside of the waveguide 56A and a ferrite core 62A in the center. these coils 60 are effective to control the phase relations of the energies emanating from the apertures 58.
In order to employ the antenna array 10 for scanning an area with a beam of radiated electromagnetic energy, a source of microwave energy is energized to supply microwave energy to the input ends 16, 18 of the waveguides 12, 14. This energy will then be propagated along the waveguides l2 and 14 by means of traveling waves that are in the TE modes. The energy in this mode will be ineffective to excite any of the slots, and accordingly, there will be no coupling of such energy to the outside of either of the waveguides.
In order to cause radiations of a beam of electromagnetic energy from the antenna array, preselected combinations of the field rotating coils 35A to 36G are en- As the energy in the traveling waves passes through the coils and along the core the electric fields will be rotated. As a result, a component of energy in the TE mode will be present at each of the slots 32, 43 that it is desired to excite. The intensities of the excitations of the slots 32 in the first waveguide 12 relative to each other and the intensities of the excitations of the slots 48 in the second waveguide 14 relative to each other will be effective to control the amount of beam sharpening in planes containing the apertures'42, 58. The intensities of the excitations radiated from apertures 42 relative to those radiated from the apertures 58 will be effective to control the amount of beam sharpening in planes normal to the side wall 26. It may thus be seen that by controlling the current in the coils 36 and 54, the radiations from the apertures 42 and 58 may be collimated or focused into a pencil beam or into any other desired shape.
In addition, the control means may be effective to vary the current in the phase coils 44- and 60. Thus the phases of the radiations from the apertures 42A to 42G relative The currents flowing through 6 to each other may be varied so as to control the direction of the beam in planes containing the apertures 42. Also, the currents in the coils 66 may be varied relative to each other to control the direction of the beam in the same planes.
In addition, the currents in the coils 44 may be adjusted relative to the currents in the coils 64) so as to regulate the relative phase relationship between the radiations from the two rows of apertures so as to control the direction of the beam in planes normal tothe side Wall 26.
It will thus be seen that it is possible to focus the beam by controlling the currents in coils 36 and 54- and to control the direction of the. beam by varying the current in coils 44 and 60'. As a result, the beam may be scanned throughout an area. by electronic means, thus eliminating the necessity for any mechanical movement or" the ditierent. portions of the antenna array.
In order to provide a control for these coils a current supply may be connected to commutating means such as slip. rings and brushes. This will energize the field rotating coils in a certain sector so that the energy in the traveling wave will be coupled to the auxiliary guides in this sector and will be radiated from the open ends of these guides.
In order to collimate these radiations the commutating means may also energize the phase shifting means on the radiating auxiliary guides so as to produce a phase shifting of the radiated signals. Thus, the elevation of the beam may be controlled by means of the phase shifting coils. If it is desired to focus the beam more sharply, a plurality of the circular arrays may be provided.
If it is desired to sweep the electromagnetic beam throughout a greater volume, the array 16d in FIGURES 2 and 3 may be employed. In this embodiment the antenna array includes a plurality of waveguides that are formed into substantially complete circles and are stacked up on top of each other so as to be substantially normal to the axis of the array. The input ends 164 of the waveguides are disposed immediately adjacent the terminal ends 136 and are adapted to receive electromagnetic energy from a waveguide 168 that is connected to an energy source.
Each of the waveguides 162 has a substantially square cross section so that a traveling wave of electromagnetic energy may be propagated therealong in either of two fundamental modes, for example, the TE mode or the TE mode.
The waveguide 103- is connected to the input end 104 so that a traveling wave of energy will be launched into and propagated along the guide 192 entirely in the TE mode. The terminal end 196 of the guide 102 is provided with a nonreflecting load that will absorb any energy that may reach that end.
The outer cylindrical walls of the waveguides 102 include a plurality of apertures that are adapted to couple the energy in the traveling wave from the inside to the outside of the waveguide 10-2. In the present instance, these apertures comprise elongated slots having a resonant length with the long dimensions thereof extending in a circumferential direction.
Thus, any energy in the TE mode which is present in the waveguides will not set up any currents in the side walls 11d that will excite the slots. Consequently, energy in such a mode will not be coupled through the slots to the outside of the waveguide 102.
In order to separately control the individual degrees of coupling between the various slots and the energy in the traveling waves, a separate field rotating means is provided immediately anterior to each slot. These field rotating means are substantially identical to those in the first embodiment. Each field rotating means includes a coil 112 that is wound around the exterior of the waveguide 192 and a ferrite core 114 that is disposed in the center thereof. For the sake of clarity only one of these coils 7 112 is shown in the drawings, but it should be understood that there are separate coils for each slot.
The ferrite core 114 may be a substantially continuous ring of ferrite or a plurality of ferrite sections aligned with the coils and nonferrite sections aligned with the slots.
The currents in the coils 112 are regulated by a control means 116 which includes a current source that has a plurality of separate outputs 118, 120, 122, 124 and 126'. Each output is adapted to supply a predetermined amount of direct current that may be of the same amount or a diiferent amount than that in the other outputs. Each output is connected to a separate slip ring 128, 130, 132, 134 and 136. These rings are fixed, i.e., they remain in a stationary position.
A rotating commutator 138 is provided that has a plurality of separate segments 149 that correspond in number to the number of coils 112 on the waveguide 1 2. A preselected group of these segments 14% are grounded at 14-2 while another group are connected to brushes 144 that slide on the slip rings. Each of the coils 112 is connected to one or more brushes 145 that ride on the surface of the commutator 13S and successively contact the various segments 14%. It may thus be seen that as the commutator 13% rotates, the coils 112 will be energized in sequence and the currents in the coils 112 will be equal to predetermined amounts that are determined by currents from the outputs 118 to 126.
Since the currents in the coils 112 determine the amount of energy that is coupled out through the slots, there will be energy coupled out in sequence so as to produce a beam that will rotate about the axis of the array The number of slots in each waveguide 102 that are excited and the relative amplitudes of the excitation will be effective to determine the amount of collimation of the radiations and thus will provide a control over the focusing of the beam.
In addition, a separate auxiliary waveguide 146 is provided on the exterior of each circular waveguide 192 for each slot. The inner ends of the auxiliary waveguides 145 are secured to the waveguide 102 so as to register with the slots and so as to project radially outward. The waveguides 146 are preferably of rectangular cross sections with the wide dimensions running parallel to the lengths of the slot. Thus the outer or open ends of the auxiliary waveguides 146 for each of the waveguides 102 will form a circle of radiating apertures. It may thus be seen that any energy that is coupled through a slot will enter an auxiliary waveguide 146 and travel therealong until it is radiated from the open end of the guide 146. The amount of the energy that is coupled through any given slot and into an auxiliary waveguide is of course a function of the current in the coil 112 immediately preceding the slot.
Each of the auxiliary waveguides are provided with individual phase control means similar to those in the first embodiment. These phase control means include a ferrite core 148 and a coil 150. Although there is a separate coil 150 for each auxiliary Waveguide, only one is shown for the sake of clarity. These coils 150' are connected to a commutator 152 similar to or a part of the first commutator 138 by means of brushes 154. The segments of the commutator 152 are in turn connected to a current source so that the coils 150 will be energized to predetermined amounts. These coils will be excited in sequence at the same rateas the coils 112. Thus they will be effective to control the direction of the radiated beam in planes containing the axis of the array and planes normal thereto.
In order to employ the array 100, the energy is fed through the waveguide 108 so as to produce traveling waves of energy in the waveguides 1132. Simultaneously therewith the commutators will rotate at a speed corresponding to the rate at which the beam is to scan the area. This will cause the energy in the traveling wave to be coupled through the slots and into the auxiliary waveguides. The energy .will then be radiated into space from the ends of the auxiliary waveguides. This Will occur in a sequence that will cause the beam to rotate at the same speed as the commutators 133 and 152. At the same time, the coils 15%? will vary the relative phases of the various radiations so as to cause the beam to be scanned throughout a predetermined range of angles in planes containing the axis of the array 106.
It may thus be seen that the beam may be scanned entirely throughout any given area. The only moving parts are the small commutators 138 and 152 so that the scan rate may be extremely high.
What is claimed is:
1. In a device of the class described, the combination of waveguiding means for carrying electromagnetic energy therealong, a plurality of radiation means disposed along said waveguiding means and adapted to be coupled thereto, said waveguiding means having electromagnetic energy applied thereto in a mode that Will not excite said radiation means, a plurflity of mode shifting means spaced along said waveguiding means for transforming said energy from one mode to another mode at a plurality of preselected points along said waveguiding means, and control means operatively interconnected with said mode shifting means for energizing only preselected ones of said mode shifting means to transfer said electromagnetic energy from said first mode into said second mode so as to excite the radiation means subsequent thereto, said control means being effective to energize preselected ones of said mode shifting means for transforming said electromagnetic energy back into the other of said modes.
2. In a device of the class described, the combination of waveguiding means for carrying a traveling wave of electromagnetic energy therealong in either of two modes, a plurality of radiation means spaced along said Waveguiding means and adapted to be coupled to energy in a first mode, one end of said waveguiding means having electromagnetic energy applied thereto that axially traverses said waveguiding means in a second mode that will not excite said radiation means, a separate mode shifting means disposed anterior to each of said radiators, each of said mode shifting means being effective to change the mode of propagation of said energy in said waveguiding means posterior thereto into one of said modes, and control means associated with each of said mode shifting means for independently actuating said mode shifting means to control the mode of said energy posterior to its associated means, said control means being effective to independently cause only preselected ones of said mode shifting means to transform said energy into said first mode to thereby excite said radiation means posterior thereto, said control means being effective to independently cause other preselected ones of said mode shifting means to transform said energy into said second mode which will not excite said radiation means.
3. An antenna array comprising a waveguide for carrying electromagnetic energy therealong, a series of resonant apertures in one wall of said waveguide for radiating electromagnetic energy into space, "one end of said waveguide having electromagnetic energy applied thereto in a mode that will normally not excite said apertures, separate mode shifting means for each of said apertures disposed anterior thereto for changing the propagation of said energy from one mode to another mode, means for energizing one of said mode shifting means to cause said energy to be transformed into a mode that will excite the aperture immediately posterior thereto whereby it will radiate energy into space, and means for energizing another of said mode shifting means posterior to said first energized mode shifting means to cause said energy to be transformed back into said first mode whereby said apertures posterior thereto will not be excited by the energy in said waveguide.
4. An antenna array comprising a waveguide for carrying electromagnetic energy therealong, a plurality of radi ators disposed along said waveguide for radiating said energy into space, electromagnetic energy being coupled into said waveguide in a mode that will not excite said radiators, a ferrite element disposed in said waveguide whereby said energy will propagate therethrough, a separate inductive means disposed anterior to each of said radiators for creating a magnetic flux field within said ferrite element for causing the mode of said energy to change, means for individually energizing one of said inductive means whereby the electromagnetic energy posterior thereto will be in a mode that will excite said radiators and cause radiations into space therefrom, and means for exciting a subsequent one of said inductive means whereby the energy pos erior thereto will again be in said first mode whereby subsequent radiators will not be excited.
5. An antenna array comprising a plurality of parallel waveguides for carrying electromagnetic energy therealong, a plurality of apertures disposed in one wall of each or" said Waveguides for radiating electromagnetic energy into space, electromagnetic energy being coupled into each of said waveguides to form traveling Waves that are in modes that Will not excite said apertures, at least one ferrite means positioned inside of each of said waveguides and disposed within said electromagnetic energy, separate coils disposed around said waveguides anterior to each of said apertures, each of said coils being effective to create a magnetic field through said ferrite means for causing the mode of said traveling Wave to change at that point, means for individually energizing preselected ones of said coils whereby the traveling Waves posterior thereto will be in modes that will excite said apertures and cause electromagnetic radiations into space therefrom, and means for exciting subsequent ones of said coils for causing the modes of said traveling waves to be transformed hack into said first nrodes whereby subsequent apertures will not be excited.
6. An antenna array comprising a waveguide arranged into a circle to form a cylindrical outer wall, one end of said waveguide having electromagnetic energy applied thereto, a plurality of apertures in the outer wall of said waveguide for radiating electromagnetic energy radially outwardly into space therefrom, said apertures being arranged so that they are not normally coupled to a traveling wave propagating through said waveguide in a given mode, mode shifting means for each of said apertures disposed anterior to the aperture for changing the mode of said traveling wave to individually couple said apertures to said traveling wave whereby said energy will be radiated outwardly in a predetermined radial direction, a separate auxiliary waveguide section mounted on said Waveguide for each of said apertures, phase shifter means in each of said auxiliary waveguides, and means for individually actuating each of said phase shifter means in preselected combinations.
References Cited in the file of this patent UNITED STATES PATENTS