Patent Application
20140265826
Backward-wave oscillation in traveling wave-tube amplifiers has been a problem since the development of traveling wave tubes in the 1940s. Traveling wave-tube amplifiers are configured to affect interaction between an input radio frequency (RF) wave and an input electron beam. Backward wave oscillation occurs when a reflected RF wave traveling towards the input interacts with the electron beam. The backward wave is amplified and causes oscillation of the traveling wave-tube amplifier. Backward-wave oscillation limits the operational bandwidth of traveling wave-tube amplifiers to a fraction of the theoretical bandwidth as well as its output power.
Various solutions have been attempted to limit the backward-wave oscillation of traveling wave amplifiers. For example, attenuation sections may be added to the traveling wave-tube amplifier to cause attenuation of the backward wave. However, this attenuation also affects the forward wave, and therefore the length of the traveling wave-tube amplifier circuit must be increased to compensate. The lengthening of the traveling wave-tube amplifier creates further backward wave oscillation. Also, from thermal considerations, the attenuations are limited to the traveling wave-tube gain sections and not to the power output section. The existing techniques for limiting backward-wave oscillation still result in loss of bandwidth and provide less efficiency as the power of the input wave is increased.
In various embodiments, a traveling wave amplifier circuit is disclosed. The traveling wave amplifier circuit is configured to receive an RF wave and an electron beam. The traveling wave amplifier effects synchronized interaction between the RF wave and the electron beam. The traveling wave amplifier circuit comprises a waveguide. The waveguide comprises a plurality of asymmetric cells arranged periodically. The waveguide is configured to receive an electron beam. The waveguide affects interaction between the RF input way and the electron beam. Each of the asymmetric cells comprises at least one asymmetrical structure within the asymmetric cell to modify the dispersion relation of the waveguide.
In various embodiments, a traveling wave tube amplifier is disclosed. The traveling wave tube amplifier comprises a waveguide. The waveguide comprises a plurality of asymmetric cells arranged periodically. The waveguide is configured to receive an electron beam. Each asymmetric cell comprises at least one asymmetrical structure within the asymmetric cell to modify the dispersion relation of the waveguide. The modified dispersion relation prevents backward-wave oscillation in the waveguide. The traveling wave tube amplifier further comprises an electron beam input device configured to generate the electron beam in the waveguide. The waveguide is configured to slow a wave velocity of an input radiofrequency beam to match an input velocity of the electron beam.
The features of the various embodiments are set forth with particularity in the appended claims. The various embodiments, however, both as to organization and methods of operation, together with advantages thereof, may best be understood by reference to the following description, taken in conjunction with the accompanying drawings as follows:
In various embodiments, a traveling wave amplifier circuit is disclosed. The traveling wave amplifier circuit is configured to receive an RF wave and an electron beam. The traveling wave amplifier effects synchronized interaction between the RF wave and the electron beam. The traveling wave amplifier circuit comprises a waveguide. The waveguide comprises a plurality of asymmetric cells arranged periodically. The waveguide is configured to receive an electron beam. The waveguide affects interaction between the RF input way and the electron beam. Each of the asymmetric cells comprises at least one asymmetrical structure within the asymmetric cell to modify the dispersion relation of the waveguide.
In various embodiments, a traveling wave tube amplifier is disclosed. The traveling wave tube amplifier comprises a waveguide. The waveguide comprises a plurality of asymmetric cells arranged periodically. The waveguide is configured to receive an electron beam. Each asymmetric cell comprises at least one asymmetrical structure within the asymmetric cell to modify the dispersion relation of the waveguide. The modified dispersion relation prevents backward-wave oscillation in the waveguide. The traveling wave tube amplifier further comprises an electron beam input device configured to generate the electron beam in the waveguide. The waveguide is configured to slow a wave velocity of an input radiofrequency beam to match an input velocity of the electron beam.
Reference will now be made in detail to several embodiments, including embodiments showing example implementations of asymmetrical slow wave structures. Wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. The figures depict example embodiments of the disclosed systems and/or methods of use for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative example embodiments of the structures and methods illustrated herein may be employed without departing from the principles described herein.
The symmetric waveguide 100 may comprise multiple modes, such as a first, or fundamental, mode and a second mode. Each mode may comprise one or more forward-wave segments and one or more backward-wave segments. During a forward-wave segment, an input RF wave travels along the axis of propagation in the direction shown by arrow 120 and is complimentary to the electron beam 102. During a backward-wave segment, a reflected RF wave is traveling in the opposite direction of arrow 120. In a symmetrical waveguide structure, such as waveguide 100, the backward-wave segment of higher modes, for example, the backward-wave segment of the second mode, may intersect the electron beam 102. The second made may be referred to as a backward-wave mode due to the interaction between the second mode's backward-wave segment and the electron beam 102. The interaction between a backward wave and the electron beam 102 causes backward-wave oscillation in the symmetrical waveguide 100. The backward-wave oscillation effectively limits the usable amplification and the usable bandwidth of the waveguide 100.
In some embodiments, by breaking the symmetry of each individual cell 310 in the asymmetric waveguide 300, an RF reflection may be generated by each asymmetric cell 310. As a result of the large number of asymmetric cells 310 in an asymmetric slow wave structure, such as the asymmetric waveguide 300, for example, a high reflectance may be achieved over a given frequency band, even where the signal reflection from an individual asymmetric cell 310 may be very small. In some embodiments, the high reflectance generated in the asymmetric waveguide 300 creates a forbidden propagation frequency gap, or band-gap, in the asymmetric waveguide's 300 dispersion relation. In a symmetric slow wave structure, such as, for example, the symmetric waveguide 100 shown in
In some embodiments, an asymmetric slow wave structure, such as, for example, the asymmetric waveguide 300, may comprise a plurality of asymmetric cells comprising two asymmetric substructures comprising different phase velocities Vp1 and Vp2, such as, for example, a plurality of asymmetrical cells 310. The asymmetric cells may receive an input RF wave, such as, for example, a transverse-magnetic field input RF wave. The radial frequency to circuit wave number curve (ω−β) of the slow wave structure may be given by the equation:
wherein Lp is the period length of the slow wave structure, aj (j=1, 2) is the substructure length of the asymmetric structure such that a1+a2=Lp, β is the circuit wave number, and Vpj (j=1, 2) is the phase velocity of the electromagnetic frequency, f, in each sub-cell such that:
A band-gap in the dispersion relation of equation (1) will occur wherever the right-hand side of the equation (1) exceeds 1. The first band-gap will therefore exist at:
β*Lp=π±i*x i=√{square root over (−1)} (4)
The maximum band-gap frequency will be achieved at:
In this case:
Where ω0 is the center frequency of the band-gap, the band-gap frequencies may be express as the equation:
which for small variations in phase velocities, ΔVp, the frequency gap can be approximated by:
As can be seen in equation (8), even a small asymmetry in the individual cells of the slow wave structure creating two sub-cells with different phase velocities may generate a band-gap of forbidden frequencies for the asymmetric slow wave structure. The first order of the forbidden frequency gap is linear with the difference between the two phase velocities. Although the band-gap has been discussed with reference to the asymmetric waveguide 300, a transverse-magnetic field RF wave input and a two-substructure asymmetric cell, those skilled in the art will recognize that a band-gap may be similarly created in any slow wave structure comprising a periodic plurality of asymmetric cells. The asymmetric cells may comprise two or more asymmetric substructures. The asymmetric slow wave structure may be configured to receive a transverse magnetic field and/or a combination transverse magnetic field and transverse-electric field RF wave inputs For example, a band-gap may be created in asymmetric slow wave structures configured to receive an input electron beam, such as, for example, an electron beam.
In some embodiments, the use of an asymmetric slow wave structure, such as the asymmetric waveguide 300, for example, may allow the size of the slow wave structure to be reduced as compared to a symmetric slow wave structure, such as the symmetric waveguide 100, configured for use in comparable frequency ranges. In symmetric slow wave structures it may be necessary to add attenuation sections to the slow wave structure to cause attenuation of the backward wave in an attempt to limit backward-wave oscillation. However, the attenuation sections also affect forward wave amplification, and therefore additional symmetric cells must be added to compensate for the loss of power in the forward wave. The additional symmetric cells may necessitate additional attenuation sections. The feedback loop created between adding attenuation sections and compensating amplification sections may result in extremely large slow wave structures. In contrast, attenuation sections are not required in asymmetric slow wave structures, as backward wave oscillation does not occur in the asymmetric slow wave structures. Therefore, a smaller asymmetric slow wave structure may provide equivalent, or better, amplification than a larger symmetrical slow wave structure comprising multiple attenuation sections.
In some embodiments, the input electron beam, for example the electron beam 802, may comprise, for example, an elliptical electron beam, a circular electron beam, and/or a hollow electron beam. The electron beam may comprise a plurality of electron beams. The plurality of electron beams may be generated by a plurality of electron guns. The plurality of electron beams may comprise a plurality of elliptical electron beams, circular electron beams, hollow electron beams, sheet electron beams, or any combination thereof.
In one embodiment, the asymmetrical helical waveguide 700 may comprise a discontinuous helical structure. For example, the asymmetrical helical waveguide 700 may comprise a periodic plurality of cells comprising a first pitch at a first angle and a second pitch at a second angle. The first and second pitches may be discontinuous. A discontinuous helix may be generated by any suitable manufacturing technique, such as, for example, electro-discharge machining (EMD). The discontinuous pitches may modify the dispersion relation of the discontinuous helical waveguide.
It is worthy to note that any reference to “one aspect,” “an aspect,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the aspect is included in at least one aspect. Thus, appearances of the phrases “in one aspect,” “in an aspect,” “in one embodiment,” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more aspects.
Some aspects may be described using the expression “coupled” and “connected” along with their derivatives. It should be understood that these terms are not intended as synonyms for each other. For example, some aspects may be described using the term “connected” to indicate that two or more elements are in direct physical or electrical contact with each other. In another example, some aspects may be described using the term “coupled” to indicate that two or more elements are in direct physical or electrical contact. The term “coupled,” however, also may mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other.
Although various embodiments have been described herein, many modifications, variations, substitutions, changes, and equivalents to those embodiments may be implemented and will occur to those skilled in the art. Also, where materials are disclosed for certain components, other materials may be used. It is therefore to be understood that the foregoing description and the appended claims are intended to cover all such modifications and variations as falling within the scope of the disclosed embodiments. The following claims are intended to cover all such modification and variations.
All of the above-mentioned U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications, non-patent publications referred to in this specification and/or listed in any Application Data Sheet, or any other disclosure material are incorporated herein by reference, to the extent not inconsistent herewith. As such, and to the extent necessary, the disclosure as explicitly set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein will only be incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material.
One skilled in the art will recognize that the herein described components (e.g., operations), devices, objects, and the discussion accompanying them are used as examples for the sake of conceptual clarity and that various configuration modifications are contemplated. Consequently, as used herein, the specific exemplars set forth and the accompanying discussion are intended to be representative of their more general classes. In general, use of any specific exemplar is intended to be representative of its class, and the non-inclusion of specific components (e.g., operations), devices, and objects should not be taken limiting.
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations are not expressly set forth herein for sake of clarity.
The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable,” to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components, and/or wirelessly interactable, and/or wirelessly interacting components, and/or logically interacting, and/or logically interactable components.
In some instances, one or more components may be referred to herein as “configured to,” “configurable to,” “operable/operative to,” “adapted/adaptable,” “able to,” “conformable/conformed to,” etc. Those skilled in the art will recognize that “configured to” can generally encompass active-state components and/or inactive-state components and/or standby-state components, unless context requires otherwise.
While particular aspects of the present subject matter described herein have been shown and described, it will be apparent to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from the subject matter described herein and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of the subject matter described herein. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to claims containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations.
In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that typically a disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms unless context dictates otherwise. For example, the phrase “A or B” will be typically understood to include the possibilities of “A” or “B” or “A and B.”
With respect to the appended claims, those skilled in the art will appreciate that recited operations therein may generally be performed in any order. Also, although various operational flows are presented in a sequence(s), it should be understood that the various operations may be performed in other orders than those which are illustrated, or may be performed concurrently. Examples of such alternate orderings may include overlapping, interleaved, interrupted, reordered, incremental, preparatory, supplemental, simultaneous, reverse, or other variant orderings, unless context dictates otherwise. Furthermore, terms like “responsive to,” “related to,” or other past-tense adjectives are generally not intended to exclude such variants, unless context dictates otherwise.
Although various embodiments have been described herein, many modifications, variations, substitutions, changes, and equivalents to those embodiments may be implemented and will occur to those skilled in the art. Also, where materials are disclosed for certain components, other materials may be used. It is therefore to be understood that the foregoing description and the appended claims are intended to cover all such modifications and variations as falling within the scope of the disclosed embodiments. The following claims are intended to cover all such modification and variations.
In summary, numerous benefits have been described which result from employing the concepts described herein. The foregoing description of the one or more embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or limiting to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The one or more embodiments were chosen and described in order to illustrate principles and practical application to thereby enable one of ordinary skill in the art to utilize the various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the claims submitted herewith define the overall scope.
