RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 62/913,774 filed October 11 , 2019, which is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] The invention relates to microwave or radio-frequency (RF) pulse generation systems.

DESCRIPTION OF THE RELATED ART

[0003] Various applications use directed energy. For example, high-power radio frequency (RF) or microwave directed energy weapons may be implemented in suitable platforms for military applications, such as in land vehicles, space vehicles, aircraft, and sea vessels used to execute a particular mission. Some of the advantages of using high-power RF directed energy weapons include the ability of the weapons to have instant effect, provide precise targeting, produce scalable effects, counter electronic weapons, and have an unlimited or nearly unlimited number of RF pulses. Other exemplary directed energy applications include weapon platforms, targeting devices, position detecting systems, and communications systems.

[0004] Some directed energy applications benefit from using high peak power and short length RF pulses. The pulse power may be provided by high-power devices such as solid-state amplifiers or vacuum electron devices. However, the peak power capability of solid-state amplifiers is typically much less than the power produced by vacuum electron devices.

SUMMARY OF THE INVENTION

[0005] A radio-frequency (RF) pulse generation system for generating a short high-power RF pulse may be used in a directed energy application. The RF pulse generation system includes an RF signal source that generates an input RF signal and/or amplifies the input RF signal to generate an amplified signal of a power higher than the input RF signal, and a pulse compression circuit connected to the RF signal source for receiving the amplified signal and outputting a short high-power RF pulse. The pulse compression circuit includes at least one RF cavity composed of a three- dimensional photonic crystal arrangement of dielectric structures arranged in such a manner to form at least one RF cavity. The arrangement of the dielectric structures may be selected based on the desired power output for a particular application. [0006] The dielectric structures are formed of high permittivity, low-loss dielectric materials that have dielectric constants of around ten or more and loss tangents that are on the order of or less than 0.0005. Using the high permittivity, low-loss dielectric materials enables the RF cavities to have smaller diameters that are at least three times smaller as compared with the diameters of conventional RF cavities with the actual size determined by the frequency of operation. The low loss dielectrics also enable a substantially higher quality factor to be achieved. The RF pulse generation system can be configured to cover any frequency within the RF spectrum, up to and including millimeter waves.

[0007] The pulse compression circuit may be connected to a solid-state amplifier. Using the pulse compression circuit and the solid-state amplifier, or an array of amplifiers, enables a smaller system with improved power densities and minimal energy losses as compared to the power produced by conventional RF systems. In exemplary applications, the peak power output may be increased by a factor of ten or more as compared with conventional RF systems that do not include a pulse compression circuit. In a directed energy application or a directed energy weapon, the pulse compression circuit is small enough to be integrated between the solid- state amplifier and an RF radiating structure, such as an antenna. Thus, the entire system is advantageously compact as compared with conventional pulse compression schemes that are too large and unsuitable for smaller applications such as in directed energy weapons.

[0008] According to an aspect of the invention, an RF pulse generation system includes an RF signal source and a pulse compression circuit.

[0009] According to an aspect of the invention, an RF pulse generation system includes a pulse compression circuit that includes at least one RF cavity having dielectric structures. [0010] According to an aspect of the invention, a directed energy system includes a solid-state amplifier, an RF radiating structure, and a pulse compression circuit connected between the RF radiating structure and the solid-state amplifier.

[0011] According to an aspect of the invention, an RF pulse generation system for generating an ultrashort high-power RF pulse includes an RF signal source that generates an input RF signal and/or amplifies the input RF signal to generate an amplified signal of a power higher than the input RF signal, and a pulse compression circuit connected to the RF signal source for receiving the amplified signal. The pulse compression circuit includes at least one RF cavity that includes a three- dimensional photonic crystal arrangement of a dielectric structure or structures to form the RF cavity.

[0012] According to an embodiment of any paragraph(s) of this summary, the dielectric structures are formed of a dielectric material having a dielectric constant that is greater than four.

[0013] According to an embodiment of any paragraph(s) of this summary, the dielectric structures are formed of a sapphire material.

[0014] According to an embodiment of any paragraph(s) of this summary, the dielectric structures are formed of a combination of a sapphire material and a material with a dielectric constant that is greater than four.

[0015] According to an embodiment of any paragraph(s) of this summary, the at least one RF cavity is cylindrical in shape and the dielectric structures are solid or hollow rod-shaped structures.

[0016] According to an embodiment of any paragraph(s) of this summary, the three-dimensional photonic crystal arrangement includes an ordered pattern.

[0017] According to an embodiment of any paragraph(s) of this summary, the at least one RF cavity includes a plurality of RF cavities that each contain a corresponding three-dimensional photonic crystal arrangement.

[0018] According to an embodiment of any paragraph(s) of this summary, the RF signal source includes a microwave tube or a solid-state amplifier.

[0019] According to an embodiment of any paragraph(s) of this summary, the solid-state amplifier includes an array of solid-state amplifiers.

[0020] According to an embodiment of any paragraph(s) of this summary, each of the solid-state amplifiers in the array has a corresponding pulse compression circuit. [0021 ] According to another aspect of the invention, a directed energy system includes at least one solid-state amplifier that receives an input RF signal and generates an amplified signal of a power higher than the input RF signal, an RF radiating structure, and a pulse compression circuit connected between the RF radiating structure and the solid-state amplifier. The pulse compression circuit includes at least one RF cavity having a three-dimensional photonic crystal arrangement of dielectric structures.

[0022] According to an embodiment of any paragraph(s) of this summary, the dielectric structures are formed of a dielectric material having a dielectric constant that is greater than four.

[0023] According to an embodiment of any paragraph(s) of this summary, the dielectric structures are formed of a sapphire material.

[0024] According to an embodiment of any paragraph(s) of this summary, the dielectric structures are formed of a combination of a sapphire material and a material with a dielectric constant that is higher than four.

[0025] According to an embodiment of any paragraph(s) of this summary, the RF radiating structure is an antenna.

[0026] According to an embodiment of any paragraph(s) of this summary, the dielectric structures are hollow rod-shaped structures.

[0027] According to an embodiment of any paragraph(s) of this summary, the dielectric structures are solid rod-shaped structures.

[0028] According to an embodiment of any paragraph(s) of this summary, the photonic crystal arrangement of dielectric structures includes an ordered pattern. [0029] According to an embodiment of any paragraph(s) of this summary, the directed energy system is a weapon.

[0030] According to still another aspect of the invention, a method of increasing a peak power output is used in an RF pulse generation system. The method includes generating an input RF signal, amplifying the input RF signal to generate an amplified signal of a power higher than the input RF signal, receiving the amplified signal in a pulse compression circuit, forming the pulse compression circuit to have at least one RF cavity having a photonic crystal arrangement of dielectric structures, and outputting an ultrashort high-power RF pulse. [0031 ] To the accomplishment of the foregoing and related ends, the invention 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 DRAWINGS

[0032] The annexed drawings, which are not necessarily to scale, show various aspects of the invention.

[0033] Fig. 1 shows a radio-frequency (RF) pulse generation system arranged as part of a directed energy system in accordance with an exemplary embodiment of the present application.

[0034] Fig. 2 shows a front view of an RF cavity in a pulse compression circuit of the RF pulse generation system of Fig. 1 in accordance with an exemplary embodiment of the present application.

[0035] Fig. 3 shows a side view of an RF cavity in a pulse compression circuit of the RF pulse generation system of Fig. 1 in accordance with another exemplary embodiment of the present application.

[0036] Fig. 4 shows a front view of an RF cavity in a pulse compression circuit of the RF pulse generation system of Fig. 1 in accordance with another exemplary embodiment of the present application.

[0037] Fig. 5 shows a front view of an RF cavity in a pulse compression circuit of the RF pulse generation system of Fig. 1 in accordance with another exemplary embodiment of the present application.

[0038] Fig. 6 shows a side view of an RF cavity in a pulse compression circuit of the RF pulse generation system of Fig. 1 in accordance with another exemplary embodiment of the present application.

[0039] Fig. 7 shows a directed energy weapon including the RF pulse generation system of Fig. 1. [0040] Fig. 8 shows an RF pulse generation system in accordance with another exemplary embodiment of the present application.

[0041 ] Fig. 9 shows a flowchart for a method of increasing a peak power output in a RF pulse generation system.

DETAILED DESCRIPTION

[0042] The principles described herein have application in directed energy used for military applications including weapons, weapon platforms, targeting devices, position detecting systems, and communications systems. Any suitable platforms may use directed energy such as land vehicles, space vehicles, aircraft, and sea vessels. Other military or non-military applications in which radio-frequency (RF) or microwave generation systems are used may also be suitable. For example, radar, power transfer, and biomedical applications may be suitable.

[0043] Referring first to Fig. 1 , a schematic drawing of a microwave or radio frequency (RF) pulse generation system 20 is shown. The RF pulse generation system 20 includes a prime power source 22, a pulse power device 24, an RF source/transmitter 26, and a pulse compression circuit 28 that is connected to the RF source/transmitter 26. In an exemplary embodiment, the prime power source 22 may be a motor generator, battery or any other suitable power supply. The pulse power device 24 may include a storage device for storing electrical power from the power supply until the power is released for use. The storage device may include at least one of a battery, capacitor, inductive device such as a coil, chemical explosives, flywheels, or combinations thereof. More than one energy storing stage may be used. The pulse power device 24 may further include any suitable high- power switch for releasing the energy. Exemplary high-power switches include tubes and solid-state.

[0044] After the switch is activated to release the energy for use, the RF source/transmitter 26 is used to provide a pulsed RF waveform than can be a single pulse or a continuous series of pulses. The RF source/transmitter 26 may include an electron beam-based source, a solid-state amplifier, or any other suitable source of pulsed RF. In an exemplary embodiment in which the RF source/transmitter 26 includes a solid-state amplifier, the solid-state amplifier may be a gallium nitride (GaN) monolithic microwave integrated circuit (MMIC) amplifier. In an exemplary embodiment in which the RF source/transmitter 26 includes a microwave tube, the microwave tube may be a magnetron tube, traveling wave tube, or klystron tube. [0045] The RF source/transmitter 26 is used to generate an RF signal if an oscillator or amplify a lower level RF signal using voltage and current from the pulse power device 24. The pulse compression circuit 28 is configured to receive the RF signal and produce a compressed ultrashort high peak power version of the original pulse. The peak power output may be greater than 10 times the peak power of the RF source/transmitter 26 and in exemplary applications using the pulse compression circuit 28 with a solid-state amplifier enables unprecedented peak power output of the RF pulse generation system 20. The RF pulse generation system 20 may be used with any RF frequency spanning MFIz to millimeter wave frequencies. In a typical application, the pulse compression circuit 28 is narrowband operating at essentially a single frequency. In some applications the pulse compression circuit 28 may be tunable to allow wider bandwidth operation of the RF pulse generation system 20.

[0046] Using the pulse compression circuit is advantageous in increasing the peak power output for the system with minimal energy loss as compared with conventional solid-state systems that have limited power outputs. The energy loss is determined by comparing the output pulse to the initial pulse. As compared with conventional systems, the power output using the RF pulse generation system 20 may be boosted by a factor of ten or more.

[0047] Referring in addition to Figs. 2 and 3, the pulse compression circuit 28 includes at least one microwave or RF cavity 30 composed of a photonic crystal arrangement of dielectric structures 32 that are arranged to form the RF cavity 30 to confine or trap an RF field 34. Each dielectric structure 32 is formed of a high- permittivity, ultra-low loss dielectric material. A suitable material includes sapphire or engineered dielectric materials. Glass or other ceramics may be suitable. Suitable dielectric materials for use in the RF cavity 30 include materials having a dielectric constant that is greater than six and has a loss tangent that is 0.0005 or less such that the pulse compression circuit 28 provides a low energy loss relative to the initial pulse in a compact configuration. In an exemplary embodiment, the dielectric material may have a dielectric constant that is approximately ten. [0048] The dielectric structures 32 may have any suitable shape that leads to confinement of the RF in the cavity 30. For example, each dielectric structure 32 may have a hollow cylindrical or rod-shaped structure as shown in Fig. 3. The cylindrical features may be holes in a solid dielectric material or solid dielectric rods surrounded by air or one solid dielectric embedded in another dielectric of differing dielectric constant. Each dielectric structure 32 may have the same shape and size. In other exemplary embodiments, the dielectric structures 32 may have different shapes and/or sizes. The dielectric structures 32 may have a large length relative to the RF cavity 30. The RF cavity 30 is cylindrical in shape and extends along a longitudinal axis L. The RF is primarily confined to a defect in the dielectric structure with the rest of the structure forming the RF cavity 30 serving to keep the RF confined in the defect. In an exemplary embodiment, each dielectric structure 32 may extend along an axis that is parallel to the longitudinal axis L. The RF cavity 30 may be surrounded by a closed metal structure 36 to define the cavity 30 and ensure complete confinement of the RF fields and is configured to have quality factors (Q factors) of up to 10 ⁶ . Suitable metal materials for surrounding the RF cavity 30 include silver, copper, and gold. Other metal materials may be suitable. In exemplary applications, more than one RF cavity 30 may be used and the multiple RF cavities 30 may be coupled to each other to further increase the power output for the pulse compression circuit 28.

[0049] Using the photonic crystal arrangement of low-loss, high permittivity dielectric structures 32 can enable the RF cavity 30 to have dimensions substantially smaller than one half of the RF wavelength, as compared with conventional RF cavities that dimensions comparable to or greater than one half of the RF wavelength. In an exemplary embodiment, the RF cavity 30 may have a diameter that is around 2.5 centimeters for an operating frequency around 2.9 GFIz. Advantageously, the smaller size enables the pulse compression circuit 28 to be integrated in smaller applications, such as between a MMIC solid-state amplifier output and an RF radiating element.

[0050] Referring in addition to Figs. 4-6, the arrangement of dielectric structures 32 is a three-dimensional photonic crystal structure that is formed of periodic dielectric structures that have a band gap. The dielectric structures 32 may be arranged in any suitable pattern to form a desired structure and achieve a desired mode confinement for the RF field 34 to produce a certain pulse compressed power output. Accordingly, the arrangement of the dielectric structures 32 may be dependent on the application.

[0051] As shown in Figs. 2 and 3, the dielectric structures 32 are formed as part of an ordered array 36 in which each dielectric structure 32 extends along an axis that is parallel to the axes along which the other dielectric structures 32 extend. Fig. 2 shows a front view of the cavity 30 and Fig. 3 shows a side view of the cavity 30. The ordered array 36 is formed by the dielectric structures 32 being uniformly sized and spaced relative to each other. The array may be formed to have a polygonal shape such as the hexagonal array 36 of Fig. 2. Fig. 4 shows a rectangular or square array 36’ of the dielectric structure 32 to form the RF cavity 30. Other polygonal shapes may be suitable for the array, including circular, triangular, pentagonal, octagonal, etc. The spacing between the dielectric structures 32 is in general less than the diameter of the dielectric structures 32.

[0052] Many other arrangements of the dielectric structures 32 may be suitable and the pattern may be ordered or disordered. Fig. 5 shows a disordered array 36” in which the spacing between the dielectric structures 32 is non-uniform. For example, the spacing may be greater between some of the dielectric structures 32 as compared with other structures. Fig. 6 shows an exemplary arrangement in which the dielectric structures 32 cross over each other such that the dielectric structures 30 extend transversely to the longitudinal axis L of the RF cavity 30.

[0053] Referring in addition to Fig. 7, in an exemplary application, the RF pulse generation system 20 may be used in a directed energy system 40 as also shown in Fig. 1. The directed energy system 40 may be a directed energy weapon having any suitable prime power source 22 and an RF radiating structure 42 which may be mounted to a platform 44 on which the RF pulse generation system 20 is also arranged. The platform 44 is shown as a land vehicle, but the platform 44 may be any suitable air, sea, or space vehicle. The directed energy system 40 may be a high-power RF/microwave directed energy weapon, which is also referred to as an electromagnetic weapon, RF weapon, non-nuclear, EM pulse, or electronic-bomb. The directed energy system 40 may include a target 46 having a critical component 48, an RF point of entry 50, and a coupling path 52 from the point of entry 50 to the critical component 48 of the target 46, as shown in Fig. 1. [0054] The RF radiating structure 42 is configured to generate RF propagation 54 toward the target 46. In an exemplary embodiment, the RF radiating structure 42 may be an antenna that is configured to reach the electronics of the target 46. The RF pulse generation system 20 may be suitable for use with different antennas including narrow band and wide band antennas. Many other RF outputs other than antennas may also be suitable with the RF pulse generation system 20. For example, the pulse compression circuit 28 may be used in test equipment for generating ultrashort high-power RF pulses.

[0055] The directed energy weapon may include other suitable components such as transformers, diodes, capacitors, and magnetrons, and the components used may be dependent on the application. The weapon may be suitable for many different lethal and non-lethal applications including targeting unmanned aerial vehicles such as drones and drone swarms. Exemplary applications include the directed energy system 40 being implemented in a Tactical Fligh-Power Microwave Operational Responder (THOR), and a small-truck-mounted narrow band high-power microwave source.

[0056] Referring in addition to Fig. 8, an exemplary embodiment of the RF pulse generation system 20’ is shown. The RF pulse generation system 20’ includes an array of solid-state amplifiers 26’ that are arranged between the power supply 22/pulse power device 24 and the pulse compression circuit 28. Using more than one solid-state amplifier or the array of solid-state amplifiers 26’ is further advantageous in enabling higher power densities being produced by the RF pulse generation system 20’. The RF pulse generation system 20’ may also be used with the RF radiating structure 42 that is connected to the pulse compression circuit 28 in the directed energy system 40 shown in Fig. 7.

[0057] Fig. 9 shows a flowchart for a method 60 of increasing a peak power output in a radio-frequency (RF) pulse generation system 20 as shown in Figs. 1-5. The method 60 includes a step 62 of generating an input RF signal and a step 64 of amplifying the input RF signal to generate an amplified signal. The RF signal may be amplified using a solid-state amplifier or an array of solid-state amplifiers as shown in Figs. 1, 4, and 5. In other exemplary embodiments, a microwave tube could be used instead of a solid-state amplifier. Step 66 of the method 60 includes receiving the amplified signal in the pulse compression circuit 28 having the RF cavity 30 and the dielectric structures 32 as shown in Figs. 1 -5. Step 68 of the method 60 includes outputting an ultrashort high-power RF pulse. The pulse compression circuit 28 may be arranged between a solid-state amplifier output and a feed to an antenna, such as the RF radiating element 42 shown as an antenna in Fig. 7.

[0058] Using the pulse compression circuit and the solid-state module enables the RF pulse generation system to boost a power output for the system by at least a factor of ten as compared with conventional solid-state modules. Accordingly, using the RF pulse generation system described herein enables a solid-state module having higher power outputs as compared with conventional solid-state modules that were not able to output as much power as systems using electron tubes. In addition to directed energy applications, the pulse compression circuit described herein may also be used in particle accelerator applications, particularly in particle accelerator applications that may use solid-state modules instead of the conventional tube- based modules. Medical applications such as cancer therapy may also implement the pulse compression circuit. Still other suitable applications include detectors and microwave telescopes.

[0059] Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (external components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e. , that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.