Patent Description:
This invention relates to a resonant cavity combined solid state amplifier system.

High-power transistor, such as microwave transistors, are available with power levels up to about <NUM> watts at radio frequencies, decreasing to less than about <NUM> watts at higher microwave frequencies. For applications requiring a much greater power level than the power level of a single high-power transistor, the outputs of a number of high-power transistors needs to be coherently combined.

One conventional system to combine the outputs of a number of high-power transistors relies on building many individual amplifier modules, each with a single transistor, and then combining the outputs of the amplifier modules using a microwave power combiner. Such a conventional system typically requires a set of microwave cables, electrical power cables and cooling lines for each module. For a high-power solid-state amplifier with many modules this may represent a significant complexity which may increase costs and potentially decreases reliability. Moreover, in the event of a failure of one or more of the modules or transistors, the conventional system is typically turned off and the defective high-power transistor or amplifier module must be replaced.

<CIT> for a Solid State Microwave Oven Power Source discloses a solid state power source which combines the power of a plurality of negative resistance transistor packages in a circular cavity to form an oscillator producing a resonant source of microwave energy for radar or microwave energy oven applications. <CIT> for a High-Power Adjustable RF Coupling Loop discloses a high power adjustable RF coupling loop which may be used to interface a transmission line to a resonant cavity. The '<NUM> Publication teaches a coupling loop is made entirely of metallic parts and is therefore ideal for high power RF applications. <NPL>, discloses an example of resonant power combiners.

In one aspect there is provided a resonant cavity combined solid-state amplifier system as claimed in claim <NUM>.

Further features and aspects of the invention are disclosed in the claims, description and drawings.

In accordance with the invention, each output impedance matching network includes at least one transmission line. The output impedance matching network includes a coupling loop coupled to the transmission line to electromagnetically couple power. The output impedance matching network includes an electric element coupled to the transmission line to electromagnetically couple power. The plurality of transistors may include a predetermined number N of high-power transistors. A combined power of the N high-power transistors may be combined in the resonant cavity to provide single combined high-power output. The system may include a plurality of input matching impedance networks each coupled to one of the high-power transistors configured to match an impedance of RF signals to an input impedance of one of the high-power transistors. The system may include an RF cavity splitter coupled to each of the plurality of input impedance matching networks configured to simultaneously divide an RF signal from an RF signal source into identical separate RF drive signals for each of the plurality of input impedance matching networks each coupled to one of the plurality of high-power transistors. The transmission line may include one or more stubs configured to resonate power from each of the plurality of transistors into the cavity. The one or more stubs may be located proximate an end of the transmission line. Each output impedance matching network may be configured to operate the plurality of transistors in one or more amplification classes. The amplification classes may include one or more of amplification classes: A, B, AB, C, D, E, and F. The plurality of high-power transistors may be configured such that a failure of one or more of the plurality of high-power transistors does not substantially impede operation of the resonant cavity. Each output impedance matching network may include at least one transmission line having a length configured such that a failure of one or more of the plurality of transistors does not substantially impede operation of the resonant cavity. Each output impedance matching network may include at least one transmission line having a length configured to provide approximately a <NUM>/<NUM> wavelength transmission line impedance transformation at the fundamental frequency of the resonant cavity. A failure of one or more of the high-power transistors may include a soft failure. The soft failure may include at least one shorted high-power transistor or a fused DC choke. The system may include a DC power choke coupled between a DC bus and each of the plurality of output impedance networks configured to isolate a failed transistor from the DC bus. The system may include a frequency tuning device coupled to the resonant cavity configured to adjust a resonant frequency of the resonant cavity to adjust and/or improve operation of a resonant cavity. The system may include a variable output power coupling device coupled to the resonant cavity configured to extract a desired power to the combined high-power output or compensate for a failure of one or more of the plurality of high-power transistors. The system may include a variable output power coupling device configured to extract a desired power. A cooling line embedded in one or more plates of the resonant cavity may be configured to cool one or more plates of the resonant cavity and each of the plurality of high-power transistors directly thermally coupled to one or more plates. The transmission line includes a plurality of asymmetrically trimmed connection points between one of the high-power transistors and the transmission line.

In another aspect, a modular resonant cavity system is featured in accordance to claim <NUM>.

Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:.

Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways within the scope of the claims.

Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.

As discussed in the Background section above, one conventional system to combine the outputs of a number of high-power transistors relies on building many individual amplifier modules, each with a single transistor, and then combining the outputs of the amplifier modules using a conventional microwave power combiner. <FIG> shows an example of conventional system <NUM> used to combine the outputs of N high-power inputs, e.g., plurality amplifier modules each having a transistor, in this example eight amplifier modules, exemplarily indicated at <NUM>, each having high-power transistor <NUM>. Conventional system <NUM> then combines the output power of each transistors <NUM> of each amplifier module <NUM> using microwave binary combiners <NUM> as shown to provide a combined high-power output <NUM>. Typically, there is log<NUM>N stages and 2N-<NUM> total connections for combing N transistors <NUM>. Each amplifier module <NUM> typically requires a set of microwave cables, electrical power cables, cooling lines, and the like. The complex design of conventional system <NUM> may increase costs and decrease reliability. Moreover, in the event of a failure of one or more of amplifier modules <NUM> or high-power transistors <NUM>, conventional system <NUM> is typically turned off and the module must be replaced.

There is shown in <FIG> one embodiment of resonant cavity combined solid-state amplifier system <NUM> of this invention. System <NUM> includes resonant cavity <NUM> including at least one output port <NUM> coupled to high-power transmission line <NUM>. System <NUM> also includes a plurality of high-power transistors, exemplarily indicated at <NUM>, shown in greater detail in <FIG> and <FIG>, each configured to generate a variable amount of power directly into resonant cavity <NUM>. In one example, each of high-power transistors <NUM> may be configured to provide up to about <NUM> watts at radio frequencies or up to about <NUM> watts at higher frequencies, e.g., frequencies in the range of about <NUM> to about <NUM>. In one example, system <NUM> may include eight high-power transistors <NUM>, e.g., as shown in <FIG>. In other examples, system <NUM> may include any number of high-power transistors <NUM> needed for a combined high-power output which is output to at least one output port <NUM> coupled to high-power transmission line <NUM>.

In one design, system <NUM>, <FIG> and <FIG>, may include a plurality of input impedance matching networks <NUM>, <FIG>, shown in further detail in <FIG> and <FIG>, each coupled to one of the plurality of high-power transistor <NUM>. Each input impedance matching network <NUM> preferably matches the impedance of radio frequency (RF) signals to the input impedance of high-power transistors <NUM>. <FIG> shows a schematic front-view showing in further detail the primary components of one example of one input impedance matching network <NUM>. In this example, input impedance matching network <NUM> includes inductors <NUM>, <NUM>, and <NUM>, radio frequency (RF) balun <NUM>, and exponential taper impedance matching line <NUM>. In other designs system <NUM> need not necessarily include input impedance matching network <NUM> when the impedance of input RF signals matches the impedance of high-power transistors <NUM>.

System <NUM> also includes a plurality of output impedance matching networks <NUM>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>, each coupled to one of high-power transistors <NUM> which extend into resonant cavity <NUM> as shown and discussed in detail below.

Each output impedance matching network <NUM> coupled to one of high-power transistor <NUM> matches the impedance of its high-power transistor <NUM> to an impedance of resonant cavity <NUM> and electromagnetically couples power from its high-power transistor <NUM> into resonant cavity <NUM> to provide a combined high-power output to output port <NUM>, <FIG> and <FIG>, coupled to high-power transmission line <NUM>. In one example, the combined high-power output by system <NUM> may be about <NUM> kW provided by four combined output impedance networks <NUM> and their associated high power transistors <NUM> or may be about <NUM> kW for eight output impedance networks <NUM> and their associated high power transistors <NUM>, e.g., as shown in <FIG>.

The result is resonant cavity combined solid-state amplifier system <NUM> directly, efficiently and effectively combines the power from each of the plurality of high-power transistors <NUM> in one stage to a combined high-power output of the high-power transistors <NUM> in a less complex and cumbersome design than conventional system <NUM>, <FIG> discussed above, or similar type systems. Thus, system <NUM> is more reliable than conventional system <NUM>, or similar type systems, and as will be discussed below, can remain operational if one or more of output impedance networks <NUM> and/or their associated high power transistors <NUM> fails.

In one embodiment, each of the plurality of output impedance networks <NUM>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG> includes at least one transmission line, e.g., transmission line <NUM>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>, which extends into resonant cavity <NUM> as shown. Transmission line <NUM> of each of output impedance matching networks <NUM> preferably matches the impedance of its high-power transistor <NUM> to the impedance of resonant cavity <NUM>. Transmission line <NUM> of each output impedance matching network <NUM> preferably includes coupling loop <NUM>, <FIG>, shown in greater detail in <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG> configured to electromagnetically couple power from high-power transistor <NUM> to resonant cavity <NUM>.

<FIG> shows a circuit diagram of showing in further detail one example of one output impedance matching network <NUM> coupled to high-power transistor <NUM>, and transmission line <NUM>. Transmission line <NUM> preferably includes top surface <NUM> made of a conducting material, e.g., copper or similar type conducting material, and bottom surface <NUM> made of a conducting material, e.g., copper or similar type conducting material. Between top surface <NUM> and bottom surface <NUM>, transmission line <NUM> preferably includes insulating dielectic material <NUM>, <FIG>, shows in further detail one example transmission line <NUM> with top surface <NUM>, bottom surface <NUM> with insulating material <NUM> sandwiched therebetween.

In one design, transmission line <NUM> of each output impedance matching networks <NUM>, <FIG>, <FIG>, <FIG>, <FIG>, 5D, <FIG>, <FIG>, and <FIG>, preferably includes one or more stubs, e.g., stub <NUM>, <FIG>, <FIG>, and <FIG>, configured to resonant power from high-power transistor <NUM> into resonant cavity <NUM>. In one design, stub <NUM> is preferably an open stub and located proximate the end of transmission line <NUM> as shown. Preferably, the function of stub <NUM> is to present to transistor <NUM> an impedance which efficiently resonates power from transistor <NUM> to resonant cavity <NUM>. In one design, inserting stub <NUM> at the end of transmission line <NUM> as shown compensates the coupling loop inductance and, via the quarter-wavelength transmission line impedance transformation, presents to transistor <NUM> a desirable slightly inductive load.

In one design, output impedance matching network <NUM>, <FIG> preferably includes transmission line <NUM> with connection points <NUM> and <NUM> and removed conductor sections <NUM> and <NUM>. Similar as discussed above with reference to <FIG>, transmission line <NUM>, <FIG>, preferably includes top surface <NUM> made of a conducting material, e.g., copper or similar type conducting material, and bottom surface <NUM> made of a conducting material, such as copper or similar type conducting material. Between top surface <NUM> and bottom surface <NUM>, transmission line <NUM> preferably includes insulating dialectic material. <FIG>, <FIG> shows in further detail one example transmission line <NUM> with top surface <NUM>, bottom surface <NUM> with insulating material <NUM> sandwiched there between. Connection points <NUM> and <NUM>, <FIG>, between the transmission line <NUM> and the two push-pull transistor tabs, preferably have a designed width to give a desired inductance in the output impedance matching network. In this example, connection point <NUM> is between the top surface <NUM> of transmission line <NUM> and one of the transistor tabs, e.g., transistor tab <NUM>, <FIG>, (shown covered with soldering material) and connection point <NUM>, <FIG>, between the bottom surface <NUM> and the other transistor tab, e.g., transistor tab <NUM>, <FIG>. In one design, connection point <NUM>, <FIG>, is preferably less wide than connection point <NUM>, e.g., as shown. The asymmetry of connection points <NUM> and <NUM> compensates for a different asymmetric part of the output impedance matching network <NUM>. In this example, section <NUM> is removed from top surface <NUM> of transmission line <NUM> and section <NUM> is removed from bottom surface <NUM> of the transmission line <NUM>. <FIG> shows an example of trimmed connection point <NUM> and removed section <NUM> for bottom surface <NUM> of transmission line <NUM>. Preferably, an amount of conducting material may be removed to provide a desired connection width between the transistor tabs and the two surfaces of the transmission line <NUM>.

Preferably, each of output impedance matching networks <NUM>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>, is configured to operate each of high-power transistors <NUM> in one or more amplification classes including classes A, B, AB, C, D, E, and F. <FIG> shows an example of output impedance matching network <NUM> configured for classes A, B, AB, C, and D. <FIG> shows an example of output impedance matching network <NUM> configured for class, D, E and F.

Each of output impedance matching networks <NUM> may include an electrical element coupled to transmission line <NUM> to electrically couple power, e.g., electrical element <NUM>, <FIG> and <FIG>, preferably coupled between top surface <NUM> and bottom surface <NUM> of transmission line <NUM> as shown. In one example, electrical element <NUM> may be configured such that an antenna, monopole, dipole, plate, and the like, such that energy is controlled by transistors <NUM> and transmitted by transmission lines <NUM> and coupled to resonant cavity <NUM> thru electrical element <NUM> operating via the radiated electric field inducing cavity resonance.

In one example, resonant cavity combined solid-state amplifier system <NUM> is preferably configured such that failure of one of the plurality of high-power transistors <NUM>, e.g., as shown in one or more of <FIG>, does not substantially impede operation of resonant cavity <NUM>. In one design, length <NUM>, <FIG> and <FIG>, of transmission line <NUM> of one or more of output impedance matching networks <NUM>, <FIG>, <FIG>, <FIG>, <FIG>, 5D, <FIG>, <FIG>, and <FIG>, is configured such that failure of one the plurality of high-power transistors <NUM> does not substantially impede the operation of resonant cavity <NUM>.

Preferably, the failure of one or more of the high-power transistors <NUM> includes a soft failure, e.g., a failure that does not substantially impede the operation of system <NUM>. This may be accomplished through a combination of the short-circuit failure mode characteristic of the selected high-power transistors <NUM>, fusible DC choke <NUM>, <FIG> and <FIG>, and the characteristics of transmission line <NUM>. In one example, to accommodate for a soft failure, the plurality of high-power transistors <NUM> preferably includes one or more redundant high-power transistors <NUM>. In one design, system <NUM> may include frequency tuning device <NUM>, <FIG> and <FIG>, configured to tune resonant cavity <NUM> to compensate for a failure of one or more of plurality of high-power transistors <NUM>. In one design, frequency tuning device <NUM> preferably includes cavity tuning plunger <NUM> coupled to tuning rod <NUM> which extends into resonant cavity <NUM> as shown and may be positioned in the direction indicated by arrows <NUM>, <NUM>, <FIG>. Moving cavity tuning plunger <NUM> in the direction into resonant cavity <NUM> shown by arrow <NUM> decreases the resonant frequency. Moving cavity tuning plunger <NUM> in the direction out of resonant cavity <NUM> in the direction shown by arrow <NUM> increases the resonant frequency of resonant cavity.

System <NUM>, <FIG>, <FIG>, and <FIG>, also preferably includes variable output coupling device <NUM> coupled to resonant cavity <NUM> configured to extract the desired power to the combined high-power output port <NUM> coupled to high-power transmission line <NUM> or to compensate for a failure of one or more of the plurality of high-power transistors <NUM>. In one example, variable output coupling device <NUM> includes variable coupling capacitor plate <NUM>, <FIG>, coupled to tuning rod <NUM>. Moving variable coupling capacitor plate <NUM> in the direction into resonant cavity <NUM>, e.g., as shown by arrow <NUM>, <FIG>, increases electric coupling in resonant cavity <NUM> which increases the combined high-power output to output port <NUM> coupled to high-power transmission line <NUM>. Moving variable coupling capacitor plate <NUM> in the direction out of resonant cavity <NUM>, e.g., as shown by arrow <NUM> decreases the electric coupling in resonant cavity <NUM> which decreases the combined high-power output to output port <NUM>, <FIG>, coupled to high-power transmission line <NUM>.

In one design, length <NUM>, <FIG> and <FIG>, of transmission line <NUM> of output impedance matching network <NUM> may be configured to provide approximately <NUM>/<NUM> wavelength transmission line impedance transformation at the fundamental frequency of resonant cavity <NUM>. In another design, length <NUM>, <FIG>, of transmission line <NUM> of output impedance matching network <NUM> may be configured to provide approximately <NUM>/<NUM> wavelength transmission line impedance transformation at the fundamental frequency of resonant cavity <NUM>.

In one design, each of the plurality of output impedance matching networks <NUM>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG> and <FIG> preferably, includes DC power choke and fuse <NUM>, <FIG> and <FIG>, coupled between DC bus capacitor <NUM> and output impedance network <NUM> as shown which are fused in the event high-power transistor <NUM> fails.

In one example, the plurality of high-power transistors <NUM>, shown in one or more of <FIG> preferably includes a predetermined number N of high-power transistors. In the example shown in <FIG> and <FIG>, the predetermined number N of high-power transistors <NUM>, <FIG>, is eight high-power transistors <NUM>. In other examples, the predetermined number N of high-power transistors <NUM> may any number of high-power transistors <NUM> needed to provide a desired combined high-power output which is output to at least one output port <NUM>, <FIG>, <FIG>, and <FIG>, coupled to high-power transmission line <NUM>. As shown in <FIG>, there may be up to <NUM> or more high-power transistors <NUM> directly coupled to upper plate <NUM> and/or to lower plate <NUM>, where high-power transistors <NUM> cannot be seen but coupling loops <NUM> attached to transmission line <NUM> can be seen extending into resonant cavity <NUM>. Preferably, the combined power of the predetermined number N of high-power transistors is combined in the resonant cavity as combined high-power output which is output to at least one output port <NUM>, <FIG>, <FIG>, and <FIG>.

In one design, system <NUM> preferably includes RF cavity splitter <NUM>, <FIG> and <FIG>, coupled to RF signal source <NUM>. RF cavity splitter <NUM> is configured to simultaneously divide an RF signal from RF signal source <NUM> by line <NUM>, <FIG>, into identical separate RF drive signals for each of the plurality input impedance matching networks <NUM> coupled to one of the plurality of high-power transistors <NUM>, e.g., by lines <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

In one example, system <NUM> may include cooling line <NUM>, <FIG>, in this example, embedded in plate <NUM> of resonant cavity <NUM>, <FIG> and <FIG>, configured to cool plate <NUM> and each of the plurality of high-power transistors <NUM> directly thermally coupled to plate <NUM> of resonant cavity <NUM>. In a similar manner, system <NUM> may include cooling line <NUM>, <FIG>, embedded in plate <NUM>, <FIG> and <FIG>, of resonant cavity <NUM> configured to cool plate <NUM> and each of the plurality of high-power transistors <NUM> directly thermally coupled to plate <NUM>. In one design, system <NUM> may include coolant inlet lines <NUM> and <NUM>, <FIG>, which receive a flow a coolant liquid, e.g., water, glycol, mineral oil, or similar type coolant fluid and provided the coolant to a cooling line embedded in upper plate <NUM>, <FIG> and <FIG>, and lower plate <NUM>, respectively. <FIG> shows an example of cooling line <NUM> embedded in lower plate <NUM>. System <NUM> also preferably includes coolant outlet lines <NUM> and <NUM>, <FIG>, which output a flow of heated coolant liquid. In one design, system <NUM> may include low current bias input <NUM>, high current drain port <NUM> and RF shield <NUM>.

Modular resonant cavity system <NUM>, <FIG>, includes a plurality of resonant cavity combined solid-state amplifier systems <NUM> as discussed above with reference to one or more of <FIG>, which each output a combined high-power output to output port <NUM>, <FIG> and <FIG>, coupled to high-power transmission line <NUM>. The combined high-power from each of resonant cavity <NUM>, <FIG>, is combined by combiner resonant cavity <NUM> to provide a combined high-power output to high-power transmission line <NUM>. Combiner resonant cavity <NUM> may include tuning rod <NUM> coupled to a variable coupling capacitor plate similar to tuning rod <NUM>, as discussed above with reference to <FIG>, <FIG>, and <FIG>. In the example shown in <FIG>, four resonant cavity combined solid-state amplifier systems <NUM> are combined using combiner resonant cavity <NUM>. In other examples, system <NUM> may include more or less than four resonant-cavity combined solid-state amplifier systems <NUM> as needed to provide a desired combined high-power output to high-power transmission line <NUM>. In the example shown in <FIG>, the combined high-power output may be in the range of about <NUM> kW to about <NUM> kW.

Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words "including", "comprising", "having", and "with" as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments.

Claim 1:
A resonant cavity combined solid-state amplifier system (<NUM>) comprising:
a resonant cavity (<NUM>) including at least one output port (<NUM>) coupled to a high-power transmission line (<NUM>);
a plurality of high-power transistors (<NUM>) each configured to generate a variable amount of power input directly into the resonant cavity (<NUM>); and
a plurality of output impedance matching networks (<NUM>) each including at least one transmission line (<NUM>) and a coupling loop (<NUM>) coupled to the transmission line (<NUM>), each transmission line coupled to a corresponding one of the plurality of high-power transistors (<NUM>) and extending into the resonant cavity (<NUM>) and configured to match an impedance of each said transistor (<NUM>) to an impedance of said resonant cavity (<NUM>) and configured to electromagnetically couple power from each of said plurality of high-power transistors (<NUM>) into the resonant cavity (<NUM>) to provide a combined high-power output to the high- power transmission line (<NUM>); whereineach output impedance matching network (<NUM>) includes a stub (<NUM>) coupled to the transmission line (<NUM>) to electromagnetically couple power from a transistor to the resonant cavity.