Phased array source of electromagnetic radiation

Information

  • Patent Grant
  • 6724146
  • Patent Number
    6,724,146
  • Date Filed
    Tuesday, November 27, 2001
    23 years ago
  • Date Issued
    Tuesday, April 20, 2004
    20 years ago
Abstract
An electromagnetic radiation source is provided which includes an anode and a cathode separated by an anode-cathode space. The source further includes electrical contacts for applying a dc voltage between the anode and the cathode and establishing an electric field across the anode-cathode space. At least one magnet is arranged to provide a dc magnetic field within the anode-cathode space generally normal to the electric field. A plurality of openings are formed along a surface of the anode which defines the anode-cathode space, whereby electrons emitted from the cathode are influenced by the electric and magnetic fields to follow a path through the anode-cathode space and pass in close proximity to the openings. A common resonator receives electromagnetic radiation induced in the openings as a result of the electrons passing in close proximity to the openings, and reflects the electromagnetic radiation back towards the openings to produce oscillating electric fields across each of the openings at a desired operating frequency.
Description




TECHNICAL FIELD




The present invention relates generally to electromagnetic radiation sources, and more particularly to a phased array source of electromagnetic radiation.




BACKGROUND OF THE INVENTION




Magnetrons are well known in the art. Magnetrons have long served as highly efficient sources of microwave energy. For example, magnetrons are commonly employed in microwave ovens to generate sufficient microwave energy for heating and cooking various foods. The use of magnetrons is desirable in that they operate with high efficiency, thus avoiding high costs associated with excess power consumption, heat dissipation, etc.




Microwave magnetrons employ a constant magnetic field to produce a rotating electron space charge. The space charge interacts with a plurality of microwave resonant cavities to generate microwave radiation. Heretofore, magnetrons have been generally limited to maximum operating frequencies below about 100 Gigahertz (Ghz). Higher frequency operation previously has not been considered practical for perhaps a variety of reasons. For example, extremely high magnetic fields would be required in order to scale a magnetron to very small dimensions. In addition, there would be considerable difficulty in fabricating very small microwave resonators. Such problems previously have made higher frequency magnetrons improbable and impractical.




Recently, the applicant has developed a magnetron that is suitable for operating at frequencies heretofore not possible with conventional magnetrons. This high frequency magnetron is capable of producing high efficiency, high power electromagnetic energy at frequencies within the infrared and visible light bands, and which may extend beyond into higher frequency bands such as ultraviolet, x-ray, etc. As a result, the magnetron may serve as a light source in a variety of applications such as long distance optical communications, commercial and industrial lighting, manufacturing, etc. Such magnetron is described in detail in commonly assigned, copending U.S. patent application Ser. No. 09/584,887, filed on Jun. 1, 2000, now U.S. Pat. No. 6,373,194, and Ser. No. 09/798,623, filed on Mar. 1, 2001, now U.S. Pat. No. 6,504,303, the entire disclosures of which are both incorporated herein by reference.




This high frequency magnetron is advantageous as it does not require extremely high magnetic fields. Rather, the magnetron preferably uses a magnetic field of more reasonable strength, and more preferably a magnetic field obtained from permanent magnets. The magnetic field strength determines the radius of rotation and angular velocity of the electron space charge within the interaction region between the cathode and the anode (also referred to herein as the anode-cathode space). The anode includes a plurality of small resonant cavities which are sized according to the desired operating wavelength. A mechanism is provided for constraining the plurality of resonant cavities to operate in what is known as a pi-mode. Specifically, each resonant cavity is constrained to oscillate pi-radians out of phase with the resonant cavities immediately adjacent thereto. An output coupler or coupler array is provided to couple optical radiation away from the resonant cavities in order to deliver useful output power.




Nevertheless, there remains a strong need in the art for even further advances in the development of high frequency electromagnetic radiation sources. For example, there remains a strong need for a device with fewer loss mechanisms and hence even further improved efficiency. More particularly, there is a strong need for a device which does not utilize a plurality of small resonant cavities. Such a device would offer greater design flexibility. Moreover, such a device would be particularly well suited for producing electromagnetic radiation at very short wavelengths.




SUMMARY OF THE INVENTION




A phased array source of electromagnetic radiation (referred to herein as a “phaser”) is provided in accordance with the present invention. The phaser converts direct current (dc) electricity into single-frequency electromagnetic radiation. Its wavelength of operation may be in the microwave bands or infrared light or visible light bands, or even shorter wavelengths.




In the exemplary embodiments, the phaser includes an array of phasing lines and/or interdigital electrodes which are disposed around the outer circumference of an electron interaction space. During operation, oscillating electric fields appear in gaps between adjacent phasing lines/interdigital electrodes in the array. The electric fields are constrained to point in opposite directions in adjacent gaps, thus providing so-called “pi-mode” fields that are necessary for efficient magnetron operation.




An electron cloud rotates about an axis of symmetry within the interaction space. As the cloud rotates, the electron distribution becomes bunched on its outer surface forming spokes of electronic charge which resemble the teeth on a gear. The operating frequency of the phaser is determined by how rapidly the spokes pass from one gap to the next in one half of the oscillation period. The electron rotational velocity is determined primarily by the strength of a permanent magnetic field and the electric field which are applied to the interaction region. For very high frequency operation, the phasing lines/interdigital electrodes are spaced very closely to permit a large number of gap passings per second.




According to one particular aspect of the invention, an electromagnetic radiation source is provided. The source includes an anode and a cathode separated by an anode-cathode space. Electrical contacts are provided for applying a dc voltage between the anode and the cathode and establishing an electric field across the anode-cathode space. At least one magnet is arranged to provide a dc magnetic field within the anode-cathode space generally normal to the electric field. A plurality of openings are formed along a surface of the anode which defines the anode-cathode space, whereby electrons emitted from the cathode are influenced by the electric and magnetic fields to follow a path through the anode-cathode space and pass in close proximity to the openings. The source further includes a common resonator which receives electromagnetic radiation induced in the openings as a result of the electrons passing in close proximity to the openings, and which reflects the electromagnetic radiation back towards the openings and produces oscillating electric fields across each of the openings at a desired operating frequency.




According to another aspect of the invention, an electromagnetic radiation source is provided which includes an anode and a cathode separated by an anode-cathode space. The source further includes electrical contacts for applying a dc voltage between the anode and the cathode and establishing an electric field across the anode-cathode space. In addition, the source includes at least one magnet arranged to provide a dc magnetic field within the anode-cathode space generally normal to the electric field, and an array comprising N pin-like electrodes forming at least a part of the anode and arranged in a pattern to define the anode-cathode space. Furthermore, the source includes at least one common resonant cavity in proximity to the electrodes. The electrodes are spaced apart with openings therebetween, and electrons emitted from the cathode are influenced by the electric and magnetic fields to follow a path through the anode-cathode space and pass in close proximity to the openings to establish a resonant electromagnetic field within the common resonant cavity.




To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is an environmental view of a phased array source of electromagnetic radiation (phaser) in accordance with the present invention as part of an optical communication system;





FIG. 2

is a cross-sectional view of a phaser including phasing lines in accordance with one embodiment of the present invention;





FIG. 3

is a cross-sectional top view of the phaser of

FIG. 2

in accordance with the present invention, taken along line


3





3


;





FIGS. 4



a


and


4




b


are perspective views of even-numbered wedges and odd-numbered wedges, respectively, which are suitable for forming an anode structure for the phaser of

FIG. 2

in accordance with the present invention;





FIG. 5

is a cross-sectional view of a phaser with interdigital electrodes and a wide anode construction in accordance with another embodiment of the present invention;





FIG. 6

is a cross-sectional top view of the interaction region of the phaser of

FIG. 5

in accordance with the present invention, taken along line


6





6


;





FIG. 7

is a schematic view of the interaction region of the phaser of

FIG. 5

in accordance with the present invention;





FIG. 8

is a cross-sectional view of a phaser with interdigital electrodes and a narrow anode construction in accordance with still another embodiment of the present invention;





FIG. 9

is a cross-sectional top view of the interaction region of the phaser of

FIG. 8

in accordance with the present invention, taken along line


9





9


;





FIG. 10

is a schematic front view of the interaction region of the phaser of

FIG. 8

in accordance with the present invention;





FIG. 11

is a schematic front view of an alternative embodiment of the anode configuration in accordance with the present invention; and





FIG. 12

is a cross-sectional view of a phaser with floating interdigital electrodes in accordance with another embodiment of the present invention.











DETAILED DESCRIPTION OF THE INVENTION




Referring initially to

FIG. 1

, a high frequency communication system


20


is shown. In accordance with the present invention, the communication system


20


includes a phased array source of electromagnetic radiation (phaser)


22


. The phaser


22


serves as a high-efficiency source of high frequency electromagnetic radiation. Such radiation may be, for example, in the microwave bands or infrared light or visible light bands, or even shorter wavelengths. The output of the phaser


22


may be light used to communicate information optically from point-to-point. Although the phaser


22


is described herein in the context of its use in an optical band communication system


20


, it will be appreciated that the phaser


22


has utility in a variety of other applications. The present invention contemplates any and all such applications.




As is shown in

FIG. 1

, the phaser


22


serves to output optical radiation


24


such as coherent light in the infrared, ultraviolet or visible light region, for example. The optical radiation is preferably radiation which has a wavelength λ corresponding to a frequency of 100 Ghz or more. In a more particular embodiment, the phaser


22


outputs optical radiation having a wavelength in the range of about 10 microns to about 0.5 micron. According to an even more particular embodiment, the phaser


22


outputs optical radiation having a wavelength in the range of about 3.5 microns to about 1.5 microns. However, it will be appreciated that the phaser


22


has application even at frequencies substantially less 100 Ghz.




The optical radiation


24


produced by the phaser


22


passes through a modulator


26


which serves to modulate the radiation


24


using known techniques. For example, the modulator


26


may be an optical shutter which is computer controlled based on data to be communicated. The radiation


24


is selectively transmitted by the modulator


26


as modulated radiation


28


. A receiving device


30


receives and subsequently demodulates the modulated radiation


28


in order to obtain the transmitted data.




The communication system


20


further includes a power supply


32


for providing an operating dc voltage to the phaser


22


. As will be explained in more detail below, the phaser


22


operates on a dc voltage provided between the cathode and anode. In an exemplary embodiment, the operating voltage is on the order of 1 kilovolt (kV) to 4 kV. However, it will be appreciated that other operating voltages are also possible.




Referring now to

FIGS. 2 and 3

, a first embodiment of the phaser


22


is shown. The phaser


22


includes a cylindrically shaped cathode


40


having a radius rc (see, FIG.


3


). Included at the respective ends of the cathode


40


are endcaps


41


. The cathode


40


is enclosed within a hollow-cylindrical shaped anode


42


which is aligned coaxially with the cathode


40


relative to axis A. The anode


42


has an inner radius ra (see.

FIG. 3

) which is greater than rc so as to define an electron interaction region or anode-cathode space


44


between an outer surface


48


of the cathode


40


and an inner surface


50


of the anode


42


.




Terminals


52


and


54


respectively pass through an insulator


55


and are electrically connected to the cathode


40


to supply power to heat the cathode


40


and also to supply a negative (−) high voltage to the cathode


40


as seen in FIG.


2


. The anode


42


is electrically connected to the positive (+) or ground terminal of the high voltage supply via terminal


56


(see, FIG.


2


). During operation, the power supply


32


(

FIG. 1

) applies heater current to and from the cathode


40


via terminals


52


and


54


. Simultaneously, the power supply


32


applies a dc voltage to the cathode


40


and anode


42


via terminals


54


and


56


. The dc voltage produces a dc electric field E which extends radially between the cathode


40


and anode


42


throughout the anode-cathode space


44


.




The phaser


22


further includes a pair of magnets


58


and


60


located at the respective ends of the anode


42


as seen in FIG.


2


. The magnets


58


and


60


are configured to provide a dc magnetic field B (see,

FIG. 2

) in an axial direction which is normal to the electric field E throughout the anode-cathode space


44


. As is shown in

FIG. 3

, the magnetic field B is into the page within the anode-cathode space


44


. The magnets


58


and


60


in the exemplary embodiment are permanent magnets which produce a magnetic field B on the order of 2 kilogauss, for example. Other means for producing a magnetic field may be used instead (e.g., an electromagnet) as will be appreciated. However, one or more permanent magnets


58


and


60


are preferred particularly in the case where it is desirable that the phaser


22


provide some degree of portability, for example.




The crossed magnetic field B and electric field E influence electrons emitted from the cathode


40


to move in curved paths through the anode-cathode space


44


. With a sufficient dc magnetic field B, the electrons will not arrive at the anode


42


, but return instead to the cathode


40


.




The anode


42


has formed therein an even-numbered array of straight single-mode waveguides


59




a


and


59




b


(represented in phantom in FIG.


3


). The waveguides


59




a


and


59




b


function as respective phasing lines and have dimensions which are selected using conventional techniques such that the waveguides operate in single-mode at the desired operating wavelength λ. The waveguides


59




a


and


59




b


extend radially (relative to the axis A) from the anode-cathode space


44


, thru the body of the anode


42


, to a common resonant cavity


66


. In particular, each of the waveguides


59




a


and


59




b


include an opening at the inner surface


50


of the anode


42


into the anode-cathode space


44


. At the outer surface


68


of the anode


42


, the waveguides


59




a


and


59




b


open into the common resonant cavity


66


. The openings of the waveguides


59




a


and


59




b


are evenly and alternately spaced circumferentially along the inner and outer surfaces of the anode


42


. The gap between openings along the inner surface


50


is represented by Gp as seem on FIG.


2


.




As is represented in

FIGS. 2 and 3

, the waveguides


59




a


(nominally referred to herein as even-numbered waveguides) are relatively narrow waveguides compared to the waveguides


59




b


(nominally referred to herein as odd-numbered waveguides). The widths of the waveguides are selected such that the odd numbered waveguides


59




b


have a width Wb (see,

FIG. 2

) which is greater than the width Wa (also,

FIG. 2

) of the even numbered waveguides


59




a


so as to provide an additional ½-λ phase delay compared to the even-numbered waveguides


59




a


at the operating wavelength λ. In the exemplary embodiment, four even-numbered waveguides


59




a


are arranged side-by-side in the axial direction along axis A, and three of the wider odd-numbered waveguides


59




b


are similarly arranged. It will be appreciated, however, that the particular number of waveguides arranged in the axial direction is a matter of choice and may be different depending on desired output power, etc.




The common resonant cavity


66


is formed around the outer circumference of the anode


42


, and is defined by the outer surface


68


of the anode


42


and a cavity defining wall


70


formed within a resonant cavity structure


72


. The wall


70


is curved and forms a toroidal shaped resonant cavity


66


. The radius of curvature of the wall


70


is on the order of 2.0 cm to 2.0 m, depending on the operating frequency.




As is shown in

FIGS. 2 and 3

, the resonant cavity structure


72


forms a cylindrical sleeve which fits around the anode


42


. The resonant cavity


66


is positioned so as to be aligned with the outer openings of the respective waveguides


59




a


and


59




b


. The resonant cavity


66


serves to constrain the oscillations thru the respective waveguides


59




a


and


59




b


so as to operate in the pi-mode as is discussed more fully below.




In addition, the cavity structure


72


may serve to provide structural support and/or function as a main housing of the device


22


. The cavity structure


72


also facilitates cooling the anode


42


in the event of high temperature operation.




The common resonant cavity


66


includes at least one or more output ports


74


(see,

FIG. 2

) which serve to couple energy from the resonant cavity


66


out through a transparent output window


76


as output optical radiation


24


(see, FIG.


2


). The output port(s)


74


are formed by holes or slots provided through the wall of the resonant cavity structure


72


.




The structure shown in

FIGS. 2 and 3

, together with the other embodiments described herein, is preferably constructed such that the anode-cathode space


44


and resonant cavity


66


are maintained within a vacuum. This prevents dust or debris from entering into the device and otherwise disturbing the operation thereof.




The resonant cavity


66


is designed using conventional techniques to have an allowed mode at the desired operating frequency (i.e., at the desired operating wavelength λ). Such techniques are known, for example, in connection with optical resonators conventionally used with laser devices. In the exemplary embodiment, the waveguides


59




a


and


59




b


are tapered waveguides. The waveguides


59




a


and


59




b


are designed to cut off frequencies which correspond to all possible resonant modes of the resonant cavity


66


below the desired operating frequency. In addition, the waveguides


59




a


and


59




b


are dimensioned to provide the aforementioned relative ½ wavelength phase difference at the operating frequency and only at that frequency.




The spacing Gp between openings of adjacent waveguides at the inner anode surface


50


is selected to optimize gain at the desired operating wavelength λ and to suppress oscillations at higher frequencies. The result is that a rotating electron cloud that is formed within the anode-cathode space


44


interacts with pi-mode electric fields at the inner anode surface


50


, and pi-mode oscillation occurs.




More particularly, during operation power is supplied to the cathode


40


and anode


42


. Electrons are emitted from the cathode


40


and follow the aforementioned curved paths through the anode-cathode space


44


and pass in close proximity to the openings of the waveguides


59




a


and


59




b


. As a result, an electromagnetic field is induced within the waveguides


59




a


and


59




b


. Electromagnetic radiation in turn travels through the waveguides


59




a


and


59




b


and enters the common resonant cavity


66


. Electromagnetic radiation within the cavity


66


begins to resonate and is in turn coupled back through the waveguides


59




a


and


59




b


toward the anode-cathode space


44


.




As a result, the electrons emitted from the cathode


40


tend to form a rotating electron cloud within the anode-cathode space


44


. Oscillating electric fields appear in the gaps between the openings of the waveguides


59




a


and


59




b


at the inner surface


50


of the anode


42


. Because the waveguides


59




a


and


59




b


are ½λ out-of-phase, the electric fields between the gaps are constrained to point in opposite directions with respect to adjacent gaps. Thus, the so-called “pi-mode” fields necessary for efficient magnetron-like operation are provided.




The electron cloud rotates about the axis A within the anode-cathode space


44


. As the cloud rotates, the electron distribution becomes bunched on its outer surface forming spokes of electronic charge which resemble the teeth on a gear. The operating wavelength (equal to λ) of the phaser


22


is determined by how rapidly the spokes pass from one gap to the next in one half of the oscillation period. The electron rotational velocity is determined primarily by the strength of a permanent magnetic field and the electric field which are applied to the anode-cathode region


44


. For very high frequency operation, the phasing lines formed by the waveguides


59




a


and


59




b


are spaced very closely to permit a large number of gap passings per second.




The total number N of waveguides


59




a


and


59




b


in the anode


42


is selected such that the electrons moving through the anode-cathode space


44


preferably are moving substantially slower than the speed of light c (e.g., approximately on the order of 0.1 c to 0.3 c). Preferably, the circumference 2 πra of the inner surface


50


of the anode is greater than λ, where λ represents the wavelength of the operating frequency As previously noted, the waveguides


59




a


and


59




b


are evenly spaced around the inner circumference of the anode


42


, and the total number N is selected so as to be an even number in order to permit pi-mode operation.




In the above discussed embodiment of

FIGS. 2 and 3

, the waveguides


59




a


and


59




b


are oriented with their respective E-planes perpendicular to the axis A. The waveguides


59




a


and


59




b


are straight tapered waveguides, although it will be appreciated that the waveguides may instead be non-tapered. Moreover, differences in phase length between the respective waveguides may be carried out via other techniques such as providing curved waveguides


59




b


within the anode


42


versus forming the wider waveguides.




Exemplary dimensions for the anode


42


in an embodiment having non-tapered waveguides


59




a


and


59




b


are as follows:


















operating frequency:




36.4 Ghz (λ = 8.24 mm = 0.324″)






inner radius ra:




4.5 mm = 0.177″






outer radius:




24.04 mm = 0.9465″






waveguide 59a:




0.254 mm × 5.32 mm (0.010″ × 0.209″)






waveguide 59b:




0.254 mm × 7.67 mm (0.010″ × 0.302″)






number of waveguides along




148






given circumference:














As far as manufacture, the cathode


40


of the phaser


22


may be formed of any of a variety of electrically conductive metals as will be appreciated. The cathode


40


may be solid or simply plated with an electrically conductive and emissive material such as nickel, barium oxide or strontium oxide, or may be fabricated from a spiral wound thoriated tungsten filament, for example. Alternatively, a cold field emission cathode


40


which is constructed from micro structures such as carbon nanotubes may also be used.




The anode


42


is made of an electrically conductive metal and/or of a non-conductive material plated with a conductive layer such as copper, gold, aluminum or silver. The resonant cavity structure


72


may or may not be electrically conductive, with the exception of the walls of the resonant cavity


66


and output port(s)


74


which are either plated or formed with an electrically conductive material such as copper, gold or silver. The anode


42


and resonant cavity structure


72


may be formed separately or as a single integral piece as will be appreciated.





FIGS. 4



a


and


4




b


illustrate wedges that may be used to form the anode


42


in one embodiment of the invention. As is explained in the aforementioned U.S. Pat. No. 6,504,303, an anode similar to the anode


42


may be formed by a plurality of pie-shaped wedges. Likewise, the anode


42


may be formed by a combination of wedges


80




a


and


80




b


as shown in

FIGS. 4



a


and


4




b


, respectively.




For example, the inner surface


50


of the anode


42


may include a plurality N of waveguide openings spaced circumferentially about a given axial point along the axis A. The number N and dimensions of the openings depends on the desired operating wavelength λ as discussed above. The anode


42


is formed by a plurality N of the pie-shaped wedge elements


80




a


and


80




b


, referred to herein generally as wedges


80


. When stacked side by side, the wedges


80


form the structure of the anode


42


.





FIGS. 4



a


and


4




b


represent perspective views of the wedge elements


80




a


and


80




b


. Each wedge


80


has an angular width φ equal to (2π/N) radians, and an inner radius of ra equal to the inner radius ra of the anode


42


. The outer radius ro of the wedge


80


corresponds to the outer radius ro of the anode


42


(i.e., the radial distance to the outer surface


68


. The front face of each wedge


80




a


has formed therein the bottom and side surfaces of the even-numbered waveguides


59




a


. Likewise, the front face of each wedge


80




b


has formed therein the bottom and side surfaces of the odd-numbered waveguides


59




b.






A total of N/2 wedges


80




a


and N/2 wedges


80




b


are assembled together side-by-side in alternating fashion to form a complete anode


42


as represented in FIG.


3


. The back face of each wedge


80


thus serves as the top surface of the waveguide formed in the adjacent wedge


80


.




The wedges


80


may be made from various types of electrically conductive materials such as copper, aluminum, brass, etc., with plating (e.g., gold) if desired. Alternatively, the wedges


80


may be made of some non-conductive material which is plated with an electrically conductive material at least in the regions in which the waveguides


59




a


and


59




b


are formed.




The wedges


80


may be formed using any of a variety of known manufacturing or fabrication techniques. For example, the wedges


80


may be machined using a precision milling machine. Alternatively, laser cutting and/or milling devices may be used to form the wedges. As another alternative, lithographic techniques may be used to form the desired wedges. The use of such wedges allows precision control of the respective dimensions as desired.




After the wedges


80


have been formed, they are arranged in proper order (i.e., even-odd-even-odd . . . , etc.) to form the anode


42


. The wedges


80


may be held in place by a corresponding jig, and the wedges soldered, brazed or otherwise bonded together to form an integral unit.





FIGS. 5 and 6

illustrate another embodiment of the phaser


22


having a different anode structure. More particularly, the phasing lines formed by the waveguides


59




a


and


59




b


in the previous embodiment are replaced by interdigital electrodes. The interdigital electrodes permit very fine electrode spacing independent of the operating wavelength λ. As there are many similarities between the respective embodiments described herein like reference numerals referring to like elements throughout), only the relevant differences will be discussed below for sake of brevity.




As is shown in

FIGS. 5 and 6

, the phaser


22


includes permanent magnets


58


and


60


for providing the cross magnetic field B as seen in FIG.


5


. Mounted concentrically about the axis A on each of the magnets


58


and


60


is a corresponding cylindrical pole piece


90


made of iron or the like. Each of the pole pieces


90


includes a smooth, highly electrically conductive cladding


92


made of silver or the like. The pole pieces


90


are generally symmetric and face each other as shown in

FIGS. 5 and 6

. The width W of the pole pieces


90


and corresponding cladding


92


(see.

FIG. 5

) defines a relatively wide anode-cathode space


44


therebetween.




In the exemplary embodiment, each pole piece


90


includes a plurality of electrodes


96


equally spaced about the circumference of a circle with a radius rcb from the axis A. The electrodes


96


in the exemplary embodiment are each formed by an electrically conductive pin made of silver, copper, or the like. The electrodes


96


may have a circular or square cross section, for example. The electrodes


96


have a length of ¼λ, where λ is again the wavelength at the desired operating frequency. The electrodes


96


are mechanically coupled to and extend from the base of the corresponding pole pieces


90


parallel with the axis A. In addition, the electrodes


96


from each pole piece


90


are electrically coupled to the pole piece


90


in this embodiment so as to remain electrically at the same electrical potential as the corresponding pole piece


90


. Moreover, the electrodes


96


from the upper pole piece


90


are interdigitated with the electrodes


96


of the lower pole piece


90


as shown in FIG.


5


. As a result, a cylindrical “cage” is formed about the cathode


40


in the anode-cathode space


44


defined between the respective pole pieces


90


. Adjacent electrodes


96


from the different pole pieces are thus spaced from one another by a gap represented by Gp as shown in FIG.


7


. It will be appreciated that the number of electrodes


96


shown in the figures is reduced for ease of illustration.




According to the embodiment of

FIGS. 5-7

, the radial distance from the electrodes


96


to the outer edge of the pole pieces


90


(inclusive of the cladding


92


) is λ/2, for example (FIG.


7


). The spacing S (see,

FIG. 7

) between the opposing faces


98


of the pole pieces


90


is slightly greater than λ/4 (to avoid electrode contact with the oppositely facing pole piece


90


). As a result, the opposing faces


98


of the pole pieces


90


form a waveguide or parallel plate transmission line having a length along the radial direction of λ/2 which begins at the edge of the cylindrical cage formed by the electrodes


96


and opens into the common resonant cavity


66


.




The cathode


40


extends along the axis A (e.g., through the lower magnet


60


and the pole piece


90


) so as to be centered within the cage formed by the interdigital electrodes


96


. As in the previous embodiment, terminals


52


and


54


respectively pass through an insulator


55


and are electrically connected to the cathode


40


to supply power to heat the cathode


40


and also to supply a negative (−) high voltage to the cathode


40


. The respective pole pieces


90


in this embodiment are electrically connected to the positive (+) or ground terminal of the high voltage supply via terminal


56


. During operation, the power supply


32


(

FIG. 1

) applies heater current to and from the cathode


40


via terminals


52


and


54


. Simultaneously, the power supply


32


applies a dc voltage to the cathode


40


and anode


42


via terminals


54


and


56


. The dc voltage produces a dc electric field E which extends radially between the cathode


40


and the electrodes


96


throughout the anode-cathode space


44


.




Electrons are emitted from the cathode


40


and again follow the aforementioned curved paths through the orthogonal E field and B field in the anode-cathode space


44


. The electrons in turn pass in close proximity to the electrodes


96


and induce opposite charges on adjacent electrodes


96


as represented in FIG.


7


. The induced charges further induce an electromagnetic signal which radiates outward between the opposing faces


98


of the pole pieces


90


into the resonant cavity


66


. The radiated electromagnetic signal is reflected by the resonant cavity


66


back towards the anode-cathode space


44


so as to reinforce the alternating charge which is induced on the adjacent electrodes


96


.




In this manner, the energy within the phaser


22


begins to oscillate at the desired operating frequency in conjunction with the electron cloud which forms and rotates within the anode-cathode space


44


. Standing-wave electromagnetic fields are established between the straight and curved surfaces of the toroidal resonant cavity


66


. A portion of those fields are conducted inward between the opposing faces


98


of the pole pieces


90


toward the interdigital electrodes


96


. At a specific instant of time during a cycle of oscillation, the standing-wave fields will cause the face


98


and electrodes


96


of the upper pole piece


90


to be charged negatively while the face


98


and electrodes


96


of the lower pole piece


90


are charged positively.




The resultant alternating positively and negatively charged interdigital electrodes


96


cause horizontal electric fields Eh to exist in the gaps between the electrodes


96


as represented in FIG.


7


. As the standing-wave field reverses in time during the cycle of oscillation, the face


98


and electrodes


96


of the upper pole piece


90


become positively charged while the face


98


and electrodes


96


of the lower pole piece


90


become negatively charged. The horizontal electric fields Eh between the electrodes


96


thus reverse in direction during each cycle. These horizontal electric fields Eh thus become the pi-mode fields which interact with the rotating electron cloud within the anode-cathode space to produce oscillations within the phaser


22


.





FIGS. 8-10

illustrate another embodiment of the phaser


22


(FIG.


8


). As was shown in the previous embodiment of

FIGS. 5-8

, the phaser


22


illustrated in

FIG. 8

includes a cathode


40


(FIG.


9


), an anode


42


, an anode-cathode space


44


(FIG.


9


), terminals


52


,


54


,


56


, permanent magnets


58


,


60


, a common resonant cavity


66


, a cavity defining wall


70


formed within a resonant cavity structure


72


, one or more output ports


74


, a transparent output window


76


. As shown in

FIGS. 8-10

, a cylindrical pole piece


90


, a highly electrically conductive cladding


92


(FIG.


8


), plurality of electrodes


96


, and opposing faces


98


(

FIGS. 8 and 9

) of the pole pieces


90


(FIGS.


8


and


9


).




In an embodiment according to

FIGS. 5-7

, exemplary dimensions and characteristics of the phaser


22


are as follows:




desired operating frequency: 10 Ghz




diameter of pole pieces


90


(including cladding


92


): 3.9 cm




length Lc of resonant cavity


66


: 8.86 cm




width Wc of resonant cavity


66


: 10.6 cm




electrode


96


(pin) length: ¼λ




number of electrodes


96


: 40 (20 on upper pole piece; 20 on lower pole piece)




diameter of electrodes


96


: 0.020 inch




spacing between electrodes


96


(gap Gp): 0.010 inch.




The embodiment illustrated in

FIGS. 8-10

is similar to the embodiment of

FIGS. 5-7

, with the exception that the wide anode structure


42


has been replaced with a narrow anode structure


42


(FIG.


8


). Specifically, the diameter of the pole pieces


90


(including the cladding


92


of

FIG. 8

) is only slightly larger than the diameter (2×rcb) of the circle formed by the electrodes


96


as best shown in FIG.


9


. Operation is similar to that described above with respect to the embodiment of

FIGS. 5-7

. However, in this embodiment the standing-wave fields in the resonant cavity


66


are applied directly to the interdigital electrodes


96


as shown in FIG.


8


. There is no effective λ/2 waveguide or parallel plate transmission line between the “cage” formed by the electrodes


96


and the opening to the resonant cavity


66


.




The narrow anode embodiment of

FIGS. 8-10

is particularly useful for constructing a phaser


22


designed to operate at very short wavelengths. This narrow anode design facilitates forming multiple “cages” of interdigital electrodes


96


stacked atop one another along the axis A. Thus, even when the length of the cage pin electrodes


96


become very short at infrared and optical wavelengths, for example, the stacked cages provide a larger interaction surface area within the anode-cathode space


44


.




Referring briefly to

FIG. 11

, an alternate embodiment of the anode


42


is shown in accordance with the present invention. The anode


42


includes a hollow cylindrical tube


110


made of glass or other type of dielectric material. The interdigital electrodes


96


are fabricated as metalized patterns on the inner surface of the tube


110


. Thus, simple lithography techniques commonly used with the fabrication of semiconductor devices can be used to form fine, precision interdigital electrodes


96


. The tube


110


is then place along the axis A of the phaser


22


so as to surround the cathode


40


and is located between the magnets


58


and


60


as represented in the other embodiments. The interdigital electrodes


96


each are coupled to ground or a positive dc voltage via respective upper and lower conductive rings


112


and


114


which also are patterned on the surface of the tube


110


along with the interdigital electrodes


96


. The tube


110


serves as a support substrate for the electrodes


96


formed thereon, particularly at shorter wavelengths when the electrodes


96


become quite small.




In addition, the tube


110


can serve as an outer vacuum envelope. Outside the tube


110


, the phaser


22


(e.g., resonant cavity


66


) may be filled with air. Meanwhile, the interdigital electrodes


96


formed on the inner surface of the tube


110


are exposed to the vacuum and the rotating electrons emitted from the cathode


40


. Air cooling against the outer wall of the tube


110


can be used to cool the interdigital electrodes


96


on the inner surface.




Thus, the tube


110


is convenient as it surrounds the cathode


40


and can be the only portion of the device


22


which contains a vacuum. The portions of the tube


110


which do not include the interdigital electrodes


96


may include a metalized film on the inner surface so as to be electromagnetically reflective as desired. The tube


110


with electrodes


96


and the anode


40


may be formed as a composite structure in much the same manner as linear light bulbs with electrical connections at the ends and a vacuum inside.





FIG. 12

illustrates yet another embodiment of the phaser


22


in accordance with the present invention. The embodiment is similar to the embodiment of

FIGS. 5-7

with the following exceptions. In this embodiment, the interdigital electrodes


96


are held at a positive high dc voltage and are isolated from the pole pieces


90


. As is shown in

FIG. 12

, the interdigital electrodes


96


associated with each pole piece


90


are respectively formed on and extend from an electrically conductive ring


120


. Each ring


120


is electrically isolated from its corresponding pole piece


90


by an insulating spacer


122


.




Consequently, the interdigital electrodes


96


float electrically relative to the pole pieces


90


. In operation, the electrodes


96


are connected electrically to a positive (+) high voltage supply via terminal


56


and the conductive rings


120


. The pole pieces


90


are themselves coupled to the cathode ground via terminal


54


. Again, the voltage difference between the cathode


40


and the interdigital electrodes


96


results in an E field which extends radially therebetween. Operation is again similar to the previous embodiments.




Although the floating interdigital electrode


96


embodiment of

FIG. 12

is shown in accordance with a wide anode embodiment, it will be appreciated that the floating interdigital electrodes


96


could similarly be applied to the narrow anode embodiment of

FIGS. 8-10

without departing from the scope of the invention. Moreover, another embodiment of the phaser


22


may utilize interdigital electrodes


96


with pole pieces


90


that are flared such that their surface


98


tapers away from the cage formed by the interdigital electrodes


96


in the radial direction.




Furthermore, the various embodiments of the anode


42


using interdigital electrodes


96


may include some electrodes


96


which extend completely between the respective pole pieces


90


so as to be in direct electrical contact with both pole pieces and/or conductive rings. Such connections provide increased DC continuity if desired.




It will be appreciated that the phaser


22


is described herein in the context of an anode structure which surrounds the cathode. In an alternate embodiment, the structure may be inverted. The anode may be surrounded by a cylindrical cathode. The present invention includes both inverted and non-inverted forms.




Although the invention has been shown and described with respect to certain preferred embodiments, it is obvious that equivalents and modifications will occur to others skilled in the art upon the reading and understanding of the specification. The present invention includes all such equivalents and modifications, and is limited only by the scope of the following claims.



Claims
  • 1. An electromagnetic radiation source, comprising:an anode and a cathode separated by an anode-cathode space; electrical contacts for applying a dc voltage between the anode and the cathode and establishing an electric field across the anode-cathode space; at least one magnet arranged to provide a dc magnetic field within the anode-cathode space generally normal to the electric field; a plurality of waveguides within the anode respectively having anode-cathode space openings formed along a surface of the anode which defines the anode-cathode space, whereby electrons emitted from the cathode are influenced by the electric and magnetic fields to follow a path through the anode-cathode space and pass in close proximity to the anode-cathode space openings, and wherein the surface of the anode does not include openings to any resonant cavities other than a common resonator: and wherein the common resonator receives electromagnetic radiation induced in each of the anode-cathode space openings as a result of the electrons passing in close proximity to the anode-cathode space openings, and traveling through the respective waveguides into the common resonator via corresponding common resonator and openings of the waveguides, and wherein the common resonator reflects the electromagnetic radiation back towards the anode-cathode space openings and produces oscillating electric fields across each of the anode-cathode space openings at a desired operating frequency, and wherein the plurality of waveguides comprises waveguides having different electrical lengths to provide different phasing to the electromagnetic radiation passing therethrough.
  • 2. The source of claim 1, wherein the oscillating electric fields of a particular opening are 180 degrees out of phase with respect to adjacent anode-cathode space openings.
  • 3. The source of claim 1, wherein:the cathode is cylindrical having a radius rc; the anode is annular-shaped having a radius ra and is coaxially aligned with the cathode to define the anode-cathode space with a width wa=ra−rc; and a circumference 2 π ra of the surface of the anode is greater than λ, where λ represents the wavelength of the operating frequency.
  • 4. The source of claim 1, wherein the anode comprises a plurality of wedges arranged side by side to provide a hollow-shaped cylinder having the anode-cathode space located therein, and each of the wedges comprises a first recess which defines at least in part a waveguide among the plurality of waveguides with an anode-cathode opening exposed to the anode-cathode space.
  • 5. The source of claim 1, wherein the waveguides having different electrical lengths are comprised of waveguides having different dimensions.
  • 6. The source of claim 5, wherein the different dimensions are in the H-plane.
  • 7. The source of claim 5, wherein the different dimensions are a result of the waveguides having different lengths.
  • 8. The source of claim 1, wherein the difference in electrical length between the plurality of wave guides is equal to about one-half λ, where λ represents the wavelength of the operating frequency.
  • 9. An electromagnetic radiation source, comprising:an anode and a cathode separated by an anode-cathode space; electrical contacts respectively attached to the anode and cathode for applying a dc voltage between the anode and the cathode and establishing an electric field across the anode-cathode space; at least one magnet arranged to provide a dc magnetic field within the anode-cathode space generally normal to the electric field; an array comprising N pin-like electrodes providing at least a part of the anode and arranged in a pattern to define the anode-cathode space; and at least one common resonant cavity in proximity to the N electrodes, wherein the N electrodes are spaced apart with openings therebetween, and electrons emitted from the cathode are influenced by the electric and magnetic fields to follow a path through the anode-cathode space and pass in close proximity to the openings to establish a resonant electromagnetic field within the at least one common resonant cavity, and a circumference of the pattern of N electrodes defining the anode-cathode space being greater than λ, where λ represents the wavelength of the operating frequency of the electromagnetic radiation source.
  • 10. The source of claim 9, wherein the cathode is generally cylindrically shaped about an axis, and the N electrodes provide at least one cylindrical cage coaxially around the cathode.
  • 11. The source of claim 10, wherein the N electrodes are aligned parallel with the axis.
  • 12. The source of claim 10, wherein N/2 of the electrodes originate from a lower part of the anode-cathode space and the remaining N/2 of the electrodes originate from an upper part of the anode-cathode space.
  • 13. The source of claim 12, wherein the N/2 electrodes originating from the lower part of the anode-cathode space are interdigitated with the N/2 electrodes originating from the upper part of the anode-cathode space.
  • 14. The source of claim 13, wherein the N electrodes are tied to a fixed dc potential to establish the electric field, and ac potentials are induced on the N electrodes by the resonant electromagnetic field.
  • 15. The source of claim 14, wherein the ac potentials induced on adjacent interdigitated electrodes are respectively 180 degrees out-of-phase.
  • 16. The source of claim 13, wherein the N electrodes are patterned from a conductive layer formed on a tube.
  • 17. The source of claim 13, wherein the upper and lower parts of the anode-cathode space are respectively defined by upper and lower magnetic pole pieces.
  • 18. The source of claim 17, wherein the N electrodes are electrically and mechanically coupled to a corresponding pole piece.
  • 19. The source of claim 17, wherein the N electrodes are electrically isilated from a corresponding pole piece.
  • 20. The source of claim 17, wherein the pole pieces define a waveguide between the N electrodes and the at least one common resonant cavity.
  • 21. The source of claim 20, wherein the waveguide is approximately an integer multiple of λ/2 in length, where λ is the wavelength of the frequency of the resonant magnetic field.
  • 22. The source of claim 10, wherein the at least one cylindrical cage includes a plurality of cylindrical cages, and the N electrodes provide the plurality of cylindrical cages coaxially around the cathode, the plurality of cylindrical cages being stacked one upon another.
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Number Date Country
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Entry
Partial International Search Report Re: PCT/US01/16622 mailed on Nov. 13, 2001 with Invitation to Pay Additional Fees.
International Search Report, Application No. PCT/US02/26689, Filing Date: Aug. 22, 2002.
International Search Report regarding International Application No. PCT/US02/26689 mailed Feb. 21, 2003.