US2973516A

US2973516A - Scanning antenna using magneticallycontrolled internal ferrite wave refraction

Info

Publication number: US2973516A
Application number: US690761A
Authority: US
Inventors: David B Medved
Original assignee: General Dynamics Corp
Current assignee: General Dynamics Corp
Priority date: 1957-10-17
Filing date: 1957-10-17
Publication date: 1961-02-28
Anticipated expiration: 1978-02-28

Description

1.4 11L Q1] U U Feb. 28, 1961 D. B. MEDVED 2, 7

SCANNING ANTENNA USING MAGNETICALLY-CONTROLLED INTERNAL FERRITE WAVE REFRACTION Filed Oct. 17, 1957 s Sheets-Sheet 1 DECIBELS INVENTOR. DAVID B. MEDVED FIG. 3

ATTORNEY Feb. 28, 1961 Filed Oct. 17, 1957 D B. MEDVED 2,973,516

SCANNING ANTENNA U SING MAGNETICALLY-CONTROLLED INTERNAL FERRITE WAVE REFRACTION 3 Sheets-Sheet 3 FIG. 8

INVENTOR. DAVID B. MEDVED AT TORNE Y United States Patent SCANNING ANTENNA USING MAGNETICALLY- CONTROLLED INTERNAL FERRIIE WAVE RE- FRACTION David B. Medved, San Diego, Calif, assignor to General Dynamics Corporation, San Diego, Calif., a corporation of Delaware Filed Oct. 17, 1957, Ser. No. 690,761

7 Claims. (Cl. 343-783) This invention relates to directional antennae, and more particularly to a waveguide directional antenna which may be lobed or scanned electronically through selective application of fields to materials placed adjacent the aperture of the waveguide.

Means are frequently employed for providing a lobed radiation pattern in radar systems to enable increased angular accuracy. Lobing devices heretofore known to the art have been either electro-mechanical, including complex, troublesome motor driven switches in the radiofrequency lines, have required two receiving antennae, or have required critical phasing lines in connection with bedspring antenna arrays. Microwave radar systems have employed conical scan devices which are analogous to lobing devices in function, as is well known to those skilled in the art. Conical scan devices known to the art employ electric motors to rotate a dipole radiator oflset slightly from the focal point of a parabaloidal reflector. The scanning speed is limited to a relatively low figure due to the inherent unbalance of the off-center feed and resulting vibration.

In contrast to prior art lobing and scanning devices, the present invention does not employ any moving parts. A controllable phase front deflection material is inserted in a waveguide aperture. Means are provided adjacent to the controllable phase front deflection material to apply a field across the material. Variation of the intensity and direction of the field causes the controllable phase front deflection material to deflect the phase front of an electromagnetic radiation in varying directions and angles dependent upon the polarity and magnitude of the applied field. The applied field may be generated and controlled electronically, thereby dispensing with mechanical movements and enabling greatly increased lobing or conical scan frequencies. Various controllable phase front deflection materials may be employed. Ferrite materials inserted in the waveguide produce controlled phase front deflection in accordance with the amplitude and direction of application of a magnetic field, while silicon or germanium inserted in the waveguide produce controlled deflection in accordance with the amplitude and polarity of an applied electric field. Production and variation of the field may be accomplished by electronic circuits, thereby enabling employment of extremely rapid lobing and scanning frequencies.

It is, therefore, an object of this invention to provide means for extremely rapid lobing and scanning of an antenna pattern.

Another object of this invention is to provide electronic means for extremely rapid lobing and scanning of an antenna pattern.

Another object of this invention is to provide an electronically controllable phase front deflection device for controlling the pattern of an antenna.

Another object of this invention is to provide a controllable phase front deflection device in a waveguide which is responsive to the intensity and polarity of an applied field.

ice

Another object of this invention is to provide an electronic lobing and scanning waveguide antenna having a gerrite wave front steering device responsive to a magnetic eld.

Another object of this invention is to provide a ferrite wave front steering device in connection with a waveguide antenna and a magnetic field producing means for enabling the ferrite to control the pattern of the antenna.

Another object of this invention is to provide a lobing device including a ferrite inserted in the aperture of a waveguide and means for impressing a controllable magnetic field on the ferrite.

Another object of this invention is to provide an electrically lobed directional microwave antenna.

Another object of this invention is to provide an electrically lobed directional waveguide antenna which is light, compact, capable of high lobing frequencies, does not employ high speed rotating parts, and is simple and economical to build.

These and other objects and features of the present invention will become apparent upon careful consideration of the following detailed description taken with the accompanying drawings, wherein:

Figure 1 illustrates a cross-sectional view of one embodiment of this invention,

Figure 2 illustrates the phase front deflection control assembly of the embodiment of Figure 1,

Figure 3 is a graph illustrating the characteristic of the ferrite employed in the embodiment of Figure 1,

Figure 4 is a plot illustrating the relationship between the power in the radiation pattern at a given point and the angle relative to the axis of directivity in response to three conditions of magnetic field strength applied to the ferrite phase front controller illustrated by Figures 1 and 2,

Figure 5 illustrates the mode of lobing or scanning the antenna pattern produced by the embodiment illustrated by Figures 1 and 2,

Figure 6 illustrated in block diagram form a scanning circuit suitable for use in connection with the embodiment illustrated by Figures 1 and 2,

Figure 7 illustrates in block diagram form an alternative scanning circuit suitable for use in connection with the embodiment of Figures 1 and 2,

Figure 8 illustrates a plurality of waveforms explaining the operation of the circuits illustrated in Figures 6 and 7,

Figure 9 illustrates a second embodiment of this invention,

Figure 10 illustrates a third embodiment of this invention,

Figure 11 illustrates a modification of the embodiment of Figures 1 and 2, and

Figure 12 illustrates a third embodiment of this invention.

Referring now to Figures 1 and 2 of the drawings, a Waveguide assembly 11 includes a first square waveguide 12 and a second square waveguide 13 connected at right angles to first square waveguide 12. A wafer 14 of a suitable ferrite material is inserted in the open end of waveguide 12 with the flat surfaces of the wafer substantially perpendicular to the longitudinal axis of waveguide section 12. A first magnetic field substantially perpendicular to the longitudinal axis of waveguide section 12 and parallel to the flat surfaces or faces of ferrite wafer 14 is established by electromagnet assembly 15, comprising

coils

16 and 17,

pole pieces

21 and 22 adjacent the edges of ferrite wafer 14 and a U-shaped core 23. The closed end of the U-shaped core is split so as to pass on either side of waveguide section 12. Means for establishing a second magnetic field parallel to the faces of ferrite wafer 14, perpendicular to said first magnetic field and perpendicular to the longitudinal axis of waveguide section 12 include electromagnet assembly 24, oriented at right angles to electromagnet assembly 15, including two coils, not shown in Figures 1 and 2,

pole pieces

25 and 26 adjacent the edges of ferrite wafer 14, and a U-shaped core 27. Core 27 is split at the closed end of the U to enable the magnetic circuit to pass on either side of Waveguide section 12 in the manner of core 23.

As is well known to those skilled in the art, two distinct modes of electromagnetic waves may be propagated in a square wave-guide simultaneously. In the embodiment of Figures 1 and 2, the TE mode and the TE mode, having mutually perpendicular electric fields may be present in the waveguide. In order to separate the two modes for individual reception by elevation receiver 31 and azimuth receiver 32, a plurality of shorting rods such as 33 are placed across the waveguide and are connected to the side Walls of the waveguide. The shorting rods serve to reflect the TE mode upward into waveguide section 13, connected to elevation receiver 31 by means of coaxial cable 34. The TE mode signal passes through the shorting rods substantially unaffected, and is connected to azimuth receiver 32 through coaxial cable 35.

Length and width of wafer 14 are substantially idertical to the interior dimensions of square waveguide 12. Wafer 14 is positioned at substantially the aperture of the waveguide. Thickness of the ferrite wafer is not critical. However, at present, a thickness of one quarter guide wavelength is preferred. Ferrite materials suitable for fabrication of wafer 14 are ferrimagnetic, exhibiting the B-H characteristics of such common magnetic materials as iron and nickel. In contrast to metals, ferrite materials are substantially non-conductors and therefore do not have eddy current losses. As a result, ferrite materials are essentially transparent to microwave energy. A ferrite material suitable for use in this invention is a magnesium-manganese ferrite having the chemical composition (MgMn)Fe O with the mole ratio However, other ferrite materials known to those skilled in the art may be employed in practicing this invention.

Received signals are focused on the ferrite filled aperture by a spherical microwave Luneberg lens 36, providing a narrow, highly directional pattern. A complete discussion of the theory and construction of such lenses is included on pages 86 to 89, inclusive, of Microwave Lenses by I. Brown, published by Methuen. As will be apparent to those skilled in the art, other forms of microwave lenses or reflectors may be employed in connection with this invention.

A plot of the deflection angle versus magnetic field characteristics of ferrite wafer 14 is illustrated in Figure 3. A small variation of deflection angle with a large change in magnetic field may be had by operating the ferrite on either side of the zero magnetic field point. However, it is preferred at the present time to apply a steady, biasing magnetic field to bias the operating point of the ferrite about the point designated 37 in Figure 3. At point 37, a large deflection in either direction may be obtained with small variations in the biasing magnetic field. Permanent magnets, not visible in Figures 1 and 2, are included in

magnet assemblies

15 and 24 to provide the magnetic field bias for ferrite wafer 14, thereby enabling operation of ferrite wafer 14 at critical point 37. Alternatively, a biasing direct current of sufiicient magnitude to provide a magnetic field at point 37 may be passed through the coils such as 16 and 17. It has been discovered that a biasing field of about 700 gauss applied to the ferrite wafer enables operation at the critical point 37.

Application of current to the deflection coils generates an additional magnetic field which may buck or aid the biasing field. When the additional field bucks, and therefleets in the positive direction, as is apparent from Figure 3. Similarly, when the additional field applied by current in the deflection coils aids the biasing field, the antenna pattern deflects in the negative direction.

Typical antenna pattern measurements of the lobing antenna of Figures 1 and 2 are illustrated in Figure 4. The normal pattern of the antenna with only the biasing magnetic field applied to ferrite wafer 14 is illustrated by curve 41. The beam is approximately seven degrees wide. Upon application of an additional bucking magnetic field, the antenna pattern is shifted approximately four degrees to the right, as illustrated by curve 42. Similarly, application of an additional aiding magnetic field deflects the antenna pattern four degrees to the left, as illustrated by curve 43. Application of alternately aiding and bucking fields results in a lobed pattern having a notch at the zero deflection point about four decibels below the maximum point of undeflected beam pattern 41.

It has been discovered that conventional conical scan patterns cannot be obtained with the embodiment of this invention disclosed in Figures 1 and 2 due to inherent non-reciprocal properties of the ferrite material. However, scanning modes are illustrated by Figure 5 which provide an indication as accurate as that provided by conventional conical scan. Four overlapping

antenna patterns

37, 41, 42 and 43 are illustrated in Figure 5. Each of

patterns

37, 41, 42 and 43 represent one possible position of the actual pattern produced by waveguide 12 and ferrite wafer 14 upon application to the ferrite of a suitable magnetic field.- The field pattern is deflected to 37 when the magnetic field applied to the ferrite wafer by

pole pieces

25 and 26 is increased by an aiding current flow in the coils, and is deflected to 42 when the magnetic field is decreased by a bucking current flow in the coils. Similarly, the field pattern is deflected to 41 when the magnetic field applied to the ferrite

b-y pole pieces

21 and 22 is increased by an aiding current flow in the coils, and is deflected to 43 when the magnetic field is decreased by a bucking current flow in the coils. By selectively applying square current waves to the coils, the pattern may be sequentially deflected from position 37 to 41 to 42 to 43. The pattern may be substantially instantaneously switched from one position to the next at extremely high switching rates by electronic circuits. Alternatively to the square sequential lobing arrangement hereinabove disclosed, a cross pattern of lobe switching may be employed. Starting from pattern position 37, the beam may be switched to position 42, then to position 43 and finally to position 41. As will be apparent to those skilled in the art, other patterns and switching arrangements may be employed.

An electronic switching circuit suitable for applying lobing currents to the coils of the directional antenna of this invention is illustrated in Figure 6. A synchronizing oscillator 44 provides a sine wave signal at the desired switching frequency to a pair of

square wave generators

45 and 46.

Square wave generators

45 and 46 are preferably multivibrators synchronized by the signal from oscillator 44. Multivibrator 45 is adjusted to operated at half the frequency of multivibrator 46, in a manner well known to those skilled in the art. Multivibrator 45 is composed of two sections 45:: and 45b, and multivibrator 46 is composed of sections 46a and 46b. As is well known to the art, section 45a will be conducting while section 45b is nonconducting, and vice versa. Similarly. sections 46a and 46b are alternately conducting. Multivibrator section 45a is connected to one input terminal of two input and

gate circuits

47, 51, 52 and 53. Section 46a of multivibrator 46 is connected to the other input terminal of and

gates

47 and 53, and section 46b is: connected to the other input terminal of and

gates

51 and 52. The output terminals of and

gates

47 and 52 are connected to horizontalradiation pattern deflecting coils 54 and 55, positioned on V-shaped coil 24, and the by decreases, the biasing field, the antenna pattern de Output terminals of and

gates

51 and 53 are connected to vertical radiation pattern deflecting coils 16 and 17, positioned on V shaped coil 15.

As illustrated in Figure 8, the synchronizing oscillator 44 provides a synchronizing sine wave e to the

multivibrators

45 and 46. Multivibrator 45 is adjusted to produce square waves a and e from sections 45a and 45b respectively, at the same frequency as the synchronizing signal 2 Multivibrator 46 is adjusted to produce square waves a and e from sections 46a and 46b respectively, at twice the frequency of the synchronizing

signal e Gates

47 and 51 will conduct and produce a positive polarity output signal only when two positive polarity signals are applied to the two input terminals thereof.

Gates

52 and 53, on the other hand, conduct and produce a negative polarity output signal only when two negative polarity signals are applied to the two input terminals thereof.

Signal e from multivibrator section 45a and signal e from multivibrator section 46a are applied to the two input terminals of gate 47. An output signal from gate 47 is produced only at the time both input signals are positive. This occurs only at times 1 and i as illustrated in Figure 8. Gate 51 produces an output signal when e and e are both positive, occurring only at times t and t6- when e and e are negative, at times 1 and t and gate 53 produces an output signal at times t and t when 2 and e are negative. Signal i applied to horizontal deflection coils 54 and 55, is composed of the output signals from positive gate 47 and negative gate 52. Similarly, signal i applied to vertical deflection coils 16 and 17, is composed of the output signals from positive gate 51 and negative gate 53. It will be apparent, therefore, that the radiation pattern will be deflected to the right to position 37 in Figure 5 at times t and t up to position 41 at times t and i left to position 42 at times 1 and t and down to position 43 at times A; and 1 A circuit enabling another means of sequential lobing is illustrated in Figure 7. Here, synchronizing oscillator 44,

multivibrators

45 and 46 and

gates

47, 51, 52 and 53 are substantially identical to the like numbered elements in Figure 7. However,

gates

47 and 53 are connected to multivibrator sections 45a and 46a and gates 51 and 5-2 are connected to multivibrator sections 45b and 46a. Positive gate 47 produces a positive output signal when 2 and a are positive at times t and t while negative output signal when '2 and e; are negative at times 1 and Similarly, positive gate 51 produces a positive output signal when 2 and e; are positive at times t and t while negative gate 52 produces a negative output signal when and 2 are negative at times 1 and t Output signals from positive gate 47 and negative gate 52 are combined to produce i applied to horizontal pattern deflection coils 54 and 55, and output signals from positive gate 51 and negative gate 53 are combined to produce i applied to vertical

pattern deflection windings

16 and 17. Thus, the radiation pattern is first deflected to the right to position 37 at time t then at t to the left to position 42, then at 1 up to position 41, and at L down to position 43.

The ferrite phase front controlling material at the aperture of space waveguide 12 may be more efliciently employed if arranged in a lattice configuration as illustrated in Figure 9. Two horizontal ferrite strips, 56 and 57, and two vertical ferrite strips, 61 and 62, are arranged in interlocking relationship at the aperture of waveguide 12. The ferrite strips are placed at a distance from the sides of the square waveguide at the areas of maximum interaction between the H component of the signal, the magnetic field, and the ferrite whereby the wherein a=the diameter of the square waveguide and Similarly, gate 52 produces an output signal only k =the free space wavelength of the signal frequency of the guide. This distance is not critical as to frequency, however, and is effective over a wide band of frequencies.

The lattice ferrite structure illustrated in Figure 10 is substantially similar to that illustrated in Figure 9. A pair of horizontally disposed ferrite strips 56 and 57, and a pair of vertically disposed ferrite strips 61 and 62 are arranged in the manner disclosed hereinabove in connection with Figure 9. Instead of the vertical

deflection pole pieces

21 and 22 and horizontal

deflection pole pieces

25 and 26 extending across the entire width of the waveguide, each pole piece is split into two sections, each disposed adjacent to the edge of the corresponding ferrite strip. Thus, pole pieces 21a and 22a are adjacent ferrite strip 61, pole pieces 21:) and 22b apply a magnetic field to ferrite strip 62, pole pieces 25a and 26a are associated with ferrite strip 56, and

pole pieces

25b and 26b are adjacent ferrite strip 57. It will be apparent that a smaller magnet or other source of magnetic field may be employed for applying the magnetic field required by the ferrite phase front controlling device.

Another manner of reducing the amount of magnetizforce required is illustrated in Figure 11. Square waveguide section 12 is fitted with a tapered waveguide transition section 63 and a small square waveguide aperture section 64 filled with ferrite wafer 65 substantially similar to, but smaller than, ferrite wafer 14. A tapered dielectric post 66, shown in phantom view in Figure 11, aids the waveguide transition section 63 in matching the impedance of large square waveguide section 12 to that of small square waveguide section 64 in a manner well known to the art. The smaller ferrite wafer reduces the distance between the pole pieces, not shown in Figure 11, thereby reducing the energy required to supply the required magnetic field to the ferrite wafer.

The embodiments of this invention disclosed hereinabove all employ both the TE and TE modes in square Waveguide to enable sequential scan with mutually perpendicular magnetic fields applied to the ferrite. In the modification of this invention illustrated in Figure 12, true conical scan of the antenna pattern is produced employing only one mode of propagation in the wave guide. A radar transmitter 67 is connected to a square waveguide section 71 through rectangular waveguide section 72 and transition section 73. Square waveguide section 71 includes a ferrite magnetic rotator 74, comprising a ferrite cylinder '75 suitably suspended in waveguide section 71, and a solenoid 76 connected to a sawtooth generator 77. Rotators such as rotator 74 are Well known to those skilled in the art. A suitable rotator is disclosed in Electronics, vol. 25, No. 6; June 1952 on page 162. Other suitable microwave phase rotating devices known to the art may alternatively be employed. An ATR switch 81 and a TR switch 82, of a type well known to the art, are included to isolate the receiver 83 from transmitter 67. Receiver 33 is connected to square waveguide section 71 through a first rectangular waveguide section 84, a second rectangular waveguide section 85 connected to square waveguide section 71 at right angles to first rectangular waveguide section 34, and a hybrid junction 86, of a type well known to those skilled in the art. A TR switch 82 is inserted between junction 86 and receiver 83. Ferrite wafer 14, identical to those employed in the embodiments of Figures 1 and 2, is mounted in the aperture of waveguide section 71.

Instead of the four position magnet assembly disclosed hereinabove, the magnetic field parallel to the face of the wafer is caused to rotate by means of a magnet assembly substantially identical to those employed as polyphase induction rotor stator assemblies. Such a magnetic assembly is disclosed on page 705-708 of Stand ard Handbook for Electrical Engineers, Eighth edition, 0. E. Knowlton and R. M. Shoop, published in 1949 by McGraw-Hill Book Co., Inc. The rotating field magnetic assembly includes a three phase Y connected winding 87 wound on an iron stator assembly 91 similar to that disclosed in the above referenced Knowlton and Shoop publication. An electronic three phase generator 92 furnishes three phase current for winding 87. One phase of the three phase generator output is connected to sawtooth generator 77, providing a synchronizing signal enabling operation of ferrite rotator 74 in synchronizing with the rotating magnetic field applied to the ferrite wafer. An electronic switch 89, inserted between generator 92 and winding 87 and connected to transmitter 67, opens the circuit supplying current to winding 87 at the time a pulse is generated by transmitter 67.

Conical scan is obtained in the embodiment of this invention illustrated in Figure 12. A signal from transmitter 67 is launched into square waveguide 71 in the TE mode. Rotator '74 rotates the TE mode signal from the transmitter continuously under control of the output from three phase generator 92. A pulse from transmitter 67, synchronized with the transmitted R.-F. pulse, is applied to electronic switch 89, opening the switch for the duration of the pulse. Opening of switch 89 removes the rotating magnetic field from ferrite wafer 14. Due to the inherent non-reciprocal properties of ferrite, the transmitted antenna pattern would otherwise be deflected 180 degrees away from the received antenna pattern. It will be seen, therefore, that removal of the magnetic field from the ferrite enables transmission of a pencil beam with the direction of polarization rotating due to the rotator. Since the magnetic field applied to the ferrite when an R.-F. pulse is not being transmitted is rotated in synchronism with the polarization of the transmitted signal, the polarization of a received pulse reflected from a target will be in substantially correct alignment with respect to the direction of the magnetic field applied to ferrite wafer 14. As disclosed hereinabove, the received antenna pattern is deflected by the ferrite wafer upon application of the magnetic field, and rotates to provide conical scan in synchronism with the gyrator or rotator 74, since the control windings of both are connected to the three phase generator. The received signal in the waveguide is reflected by ATR switch 81, and passed to receiver 83 through rectangular waveguide section 84 or rectangular waveguide section 85, junction 86, and TR switch 82. Depending upon the direction of the vector defined by the rotating polarization of the received instant, the received signal divides between

rectangular waveguides

84 and 85. The horizontal component of the received signal vector is connected to the receiver by waveguide section $6, and the vertical component by waveguide section 85, in a manner obvious to those skilled in the art.

A suitable microwave lens, such as Luneberg lens 36 illustrated in Figure 1, may be employed in conjunction with the modifications of this invention illustrated by Figures 2, 9, 1G, 11 and 12 to provide a narrow pencil beam for greater accuracy. Semi-active missile homing systems, wherein the target is illuminated by a radar transmitter on the ground, require only a sequential lobing or conical scan receiving antenna disclosed hereinabove in Figures 1, 2, 9, l and 11. As will be apparent to those skilled in the art, radar search, wherein the radiation pattern may be swept through a hemisphere, requires means, not disclosed, for pointing the entire assembly including waveguide, ferrite, magnetic field means, and lens, through wide angles. However, such mechanical antenna positioning means are well known to the radar art and form no part of the present invention.

Hereinabove has been disclosed means for electronic lobing and scanning a radio beam at high speeds through electronic means. Ferrite at the aperture of a waveguide causes the phase front of a radio wave to be defiected in accordance with the strength of a magnetic field applied across the ferrite and parallel to the aperture in the Waveguide. While certain preferred embodiments of this invention are disclosed hereinabove, the invention is not intended to be limited thereto. Numerous changes in form and detail may be made, and this invention is to be limited only by the spirit and scope of the appended claims.

What I claim is:

1. A directive microwave antenna comprising a hollow waveguide having a square cross section and an aperture at one end perpendicular to the longitudinal axis of said waveguide, magnetic field responsive phase front deflecting means comprising a square ferrite wafer inserted in said aperture with a surface perpendicular to the interior surface of said waveguide, means for applying a first magnetic field to said ferrite wafer parallel to the surface of said wafer comprising a first electromagnet and a first pair of pole pieces adjacent said ferrite wafer, means for applying a second magnetic field to said ferrite wafer perpendicular to said first magnetic field comprising a second electromagnet and a second pair of pole pieces adjacent said ferrite wafer and perpendicular to said first pair of pole pieces, and means for varying the intensity and direction of said first and second magnetic fields for enabling selective phase front deflection of a wave at said aperture by said ferrite water.

2. A directive microwave antenna comprising a hollow elongated waveguide having a square cross section and an aperture at one end perpendicular to the longitudinal axis of said waveguide, magnetic field responsive phase front deflecting means comprising a square ferrite wafer inserted in said aperture with a surface perpendicular to the longitudinal axis of said waveguide, means for applying a first magnetic field across said ferrite wafer parallel to the surface of said wafer comprising a first electro magnet having first pole pieces adjacent each of two opposed edges of said ferrite wafer, means for applying a second magnetic field across said ferrite wafer parallel to the surface of said wafer and perpendicular to said first magnetic field comprising a second electromagnet having second pole pieces adjacent each of two opposed edges of said wafer perpendicular to said first pole pieces. means for applying current to said electromagnets, and means for controlling said currents for selectively varying the intensity and direction of said first and second magnetic fields for enabling selective phase front deflection by said ferrite wafer.

3. A directive microwave antenna comprising a hollow elongated waveguide having a square cross section and an aperture at one end perpendicular to the longitudinal axis of said waveguide, magnetic field responsive phase front deflecting means comprising a square ferrite wafer inserted in said aperture with a surface perpendicular to the longitudinal axis of said waveguide, a microwave lens adjacent said ferrite having a focal point at said ferrite wafer, means for applying a first magnetic field across said ferrite wafer parallel to the surface of said wafer comprising a first electromagnet having first po-le pieces adjacent each of two opposed edges of said ferrite wafer, means for applying a second magnetic field across said ferrite wafer parallel to the surface of said wafer and perpendicular to said first magnetic field comprising a second electromagnet having second pole pieces adjacent each of two opposed edges of said water perpendicular to said first po-le pieces, means for applying current to said electromagnets, and means for controlling said currents for selectively varying the intensity and direction of said first and second magnetic field for enabling selective phase front deflection by said ferrite Wafer.

4. A directive microwave antenna comprising a hollow waveguide having a square cross section and an aperture at one end perpendicular to the longitudinal axis of said waveguide, magnetic field responsive phase front deflecting means comprising a plurality of ferrite strips in a lattice array inserted in said aperture, an electromag net for applying a magnetic field to said ferrite strips perpendicular to said longitudinal axis of said waveguide, and means for varying the intensity and direction of said magnetic field for enabling selective phase front deflection by said lattice array of ferrite strips.

5. A directive microwave antenna comprising a hollow waveguide having a square cross section and an aperture at one end perpendicular to the longitudinal axis of said waveguide, magnetic field responsive phase front deflecting means comprising a lattice array of ferrite strips inserted in said aperture, said array comprising first and second ferrite strips parallel to and spaced from a first pair of opposed walls of said waveguide and one another, and third and fourth ferrite strips perpendicular to said first and second ferrite strips arranged parallel to and spaced from a second pair of opposed walls of said waveguide, means for applying a first magnetic field across said lattice array parallel to said first and second ferrite strips comprising a first electromagnet having first pole pieces adjacent each of two opposed edges of said first and second ferrite strips, means for applying a second magnetic field across said lattice array parallel to said third and fourth ferrite strips and perpendicular to said first magnetic field comprising a second electromagnet having second pole pieces adjacent each of two opposed edges of said third and fourth ferrite strips and perpendicular to said first pole pieces, means for applying current to said electromagnets, and means for controlling said currents for selectively varying the intensity and direction of said first and second magnetic fields for enabling selective phase front deflection by said ferrite strips.

6. A directive microwave antenna comprising a hollow waveguide having a square cross section and an aperture at one end perpendicular to the longitudinal axis of said waveguide, magnetic field responsive phase front deflecting means comprising a lattice array of ferrite strips inserted in said aperture, said array comprising first and second ferrite strips parallel to and spaced from a first pair of opposed walls of said waveguide and one another, and third and fourth ferrite strips perpendicular to said first and second ferrite strips arranged parallel to and spaced from a second pair of opposed walls of said waveguide, means for applying a first magnetic field across said lattice array parallel to said first and second ferrite strips comprising a first electromagnet having a first plurality of pole pieces, each adjacent an edge of said first and second ferrite strips, means for applying a second magnetic field across said lattice array parallel to said third and fourth ferrite strips and perpendicular to said first magnetic field comprising a second electromagnet having a second plurality of pole pieces, each adjacent an edge of said third and fourth ferrite strips and perpendicular to said first pole pieces, means for applying current to said electromagnets, and means for controlling said currents for selectively varying the intensity and direction of said first and second magnetic fields for enabling selective phase front deflection by said ferrite strips.

7. A directive microwave antenna comprising a hollow waveguide having an aperture at one end perpendicular to the longitudinal axis of said waveguide, magnetic field responsive phase front deflecting means comprising a ferrite wafer inserted in said aperture, means for applying a magnetic field rotating about an axis parallel to the longitudinal axis of said waveguide to said ferrite wafer, said means comprising an electromagnet with a core having a plurality of pole pieces adjacent the circumference of said ferrite wafer, 21 polyphase winding on said core, and means for applying a polyphase electric current to said polyphase winding, thereby producing a rotating magnetic field and enabling a rotating phase front deflection by said ferrite wafer.

References Cited in the file of this patent UNITED STATES PATENTS 2,787,765 Fox Apr. 2, 1957 2,808,584- Kock Oct. 1, 1957 2,863,144 Herscovici et al. Dec. 2, 1958 2,892,191 Hogg June 23, 1959 FOREIGN PATENTS 751,348 Great Britain June 27, 1956 OTHER REFERENCES Pub. I Radiation from Ferrite-Filled Apertures, Proceedings of the IRE, October 1956, pp. 1463-1468.

Pub. II The Bell System Technical Journal, vol. XXXIV, January 1955, No. 1, page 41.

Pub. III Journal of Applied Physics, article by Artman, vol. 28, No. 1, January 1957, pp. 92-98.

Pub. IV Microwave Lenses, J. Brown, published by John Wiley & Sons, Inc. 1953, pp. 86-89.