Adaptive impedance matching apparatus, system and method with improved dynamic range

[0001] This application is a divisional of U.S. patent application Ser. No. 11/594,309, filed Nov. 8, 2006 now U.S. Pat. No. 7,535,312, entitled, ADAPTIVE IMPEDANCE MATCHING APPARATUS, SYSTEM AND METHOD WITH IMPROVED DYNAMIC RANGE, by William E. McKinzie.

[0002] The function of an adaptive impedance matching module is to adaptively maximize the RF power transfer from its input port to an arbitrary load impedance ZL that changes as a function of time.

[0003] One of the important engineering specifications of an impedance matching control system is the dynamic range of input power over which it will operate. The lowest cost RF voltage detector is a simple diode detector, but it has a limited dynamic range of about 25 dB. Logarithmic amplifiers (that detect the signal envelope) have a much higher dynamic range of 50 dB to 60 dB, but their cost, complexity, chip area, and current drain is also much higher. Thus, a strong need exists for an improved adaptive impedance matching apparatus, system and method.

[0004] An embodiment of the present invention provides an apparatus, comprising an RF matching network connected to at least one RF input port and at least one RF output port and including one or more voltage or current controlled variable reactive elements, a voltage detector connected to the at least one RF output port via a variable voltage divider to determine the voltage at the at least one RF output port and provide voltage information to a controller that controls a bias driving circuit which provides bias voltage or bias current to the RF matching network, and wherein the RF matching network is adapted to maximize RF power transferred from the at least one RF input port to the at least one RF output port by varying the voltage or current to the voltage or current controlled variable reactive elements to maximize the RF voltage at the at least one RF output port.

[0005] In an embodiment of the present invention, the voltage detector may be a diode detector and wherein the variable voltage divider connected to the voltage detector may be adapted to improve the dynamic range of the apparatus. Further, a loop controller may be associated with the variable voltage divider to make the variable voltage divider programmable and the variable voltage divider may be implemented using a multi-pole RF switch to select one of a plurality of different resistances. In an embodiment of the present invention, the variable voltage divider may be operable to allow a detector coupled to the output port to be more isolated at higher power levels and improve linearity of the module for high signal levels. Further, the RF output node may be connected to a shunt RF branch comprising a series string of capacitors and by selectively tapping into various circuit nodes along the string, a variable output voltage divider is obtained. In an embodiment of the present invention and not limited in this respect, tapping into various circuit nodes may be accomplished using a digitally controlled RF switch and the RF switch may be selected from the group consisting of: FETs, MEMS or PIN diodes.

[0006] In yet another embodiment of the present invention is provided a method of adaptive impedance matching, comprising connecting an RF matching network to at least one RF input port and at least one RF output port and including one or more voltage or current controlled variable reactive elements, using a voltage detector connected to the at least one RF output port via a variable voltage divider to determine the voltage at the at least one RF output port and providing the voltage information to a controller that controls a bias driving circuit which provides bias voltage or bias current to the RF matching network, and adapting the RF matching network to maximize RF power transferred from the at least one RF input port to the at least one RF output port by varying the voltage or current to the voltage or current controlled variable reactive elements to maximize the RF voltage at the at least one RF output port.

[0007] In still another embodiment of the present invention is provided a machine-accessible medium that provides instructions, which when accessed, cause a machine to perform operations comprising connecting an RF matching network to at least one RF input port and at least one RF output port and including one or more voltage or current controlled variable reactive elements, using a voltage detector connected to the at least one RF output port via a variable voltage divider to determine the voltage at the at least one RF output port and providing the voltage information to a controller that controls a bias driving circuit which provides voltage or current bias to the RF matching network, and adapting the RF matching network to maximize RF power transferred from the at least one RF input port to the at least one RF output port by varying the voltage or current to the voltage or current controlled variable reactive elements to maximize the RF voltage at the at least one RF output port.

[0015] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.

[0016] Some portions of the detailed description that follows are presented in terms of algorithms and symbolic representations of operations on data bits or binary digital signals within a computer memory. These algorithmic descriptions and representations may be the techniques used by those skilled in the data processing arts to convey the substance of their work to others skilled in the art.

[0017] An algorithm is here, and generally, considered to be a self-consistent sequence of acts or operations leading to a desired result. These include physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers or the like. It should be understood, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities.

[0018] Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as “processing,” “computing,” “calculating,” “determining,” or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities within the computing system's registers and/or memories into other data similarly represented as physical quantities within the computing system's memories, registers or other such information storage, transmission or display devices.

[0019] Embodiments of the present invention may include apparatuses for performing the operations herein. An apparatus may be specially constructed for the desired purposes, or it may comprise a general purpose computing device selectively activated or reconfigured by a program stored in the device. Such a program may be stored on a storage medium, such as, but not limited to, any type of disk including floppy disks, optical disks, compact disc read only memories (CD-ROMs), magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), electrically programmable read-only memories (EPROMs), electrically erasable and programmable read only memories (EEPROMs), magnetic or optical cards, or any other type of media suitable for storing electronic instructions, and capable of being coupled to a system bus for a computing device.

[0020] The processes and displays presented herein are not inherently related to any particular computing device or other apparatus. Various general purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct a more specialized apparatus to perform the desired method. The desired structure for a variety of these systems will appear from the description below. In addition, embodiments of the present invention are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the invention as described herein. In addition, it should be understood that operations, capabilities, and features described herein may be implemented with any combination of hardware (discrete or integrated circuits) and software.

[0021] Use of the terms “coupled” and “connected”, along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular embodiments, “connected” may be used to indicate that two or more elements are in direct physical or electrical contact with each other. “Coupled” my be used to indicated that two or more elements are in either direct or indirect (with other intervening elements between them) physical or electrical contact with each other, and/or that the two or more elements co-operate or interact with each other (e.g. as in a cause an effect relationship).

[0022] An embodiment of the present invention provides closed-loop control of an adaptive impedance matching module (AIMM). The RF output node voltage of the AIMM tuner circuit may be monitored and maximized to insure the best available impedance match to arbitrary load impedance. In addition, improvement in dynamic range may be achieved by adaptively changing the RF coupling level between the voltage sensed at the output port (antenna side) of the matching network and the voltage provided to the detector. This coupling level may be controlled by a processor which also does the closed loop tuning. A simple voltage divider comprised of resistors and a digitally controlled RF switch may be used to realize variable coupling levels, although the present invention is not limited in this respect. Another means of realizing variable coupling levels is to digitally switch between different tap points in a series string of variables capacitors which form a shunt voltage tunable dielectric capacitor at the output node of the AIMM tuner.

[0023] The function of an adaptive impedance matching module (AIMM) is to adaptively maximize the RF power transfer from its input port to an arbitrary load impedance Z_L where the load changes as a function of time. Turning now to the figures, FIG. 1, shown generally as 100, is an AIMM block diagram.

[0024] The RF matching network 110 may contain inductors and capacitors required to transform the arbitrary load impedance Z_L 135 to an impedance equal to or close to a defined system impedance, such as 50 ohms. The net benefit of this transformation is an improvement in the level of power transferred to the load Z_L 135, and a reduction in the level of reflected power from the RF input port 105. This second benefit is also known as an improvement in the input mismatch loss where mismatch loss is defined as (1−|S₁₁|²).

[0025] The RF matching network 110 may contain one or more variable reactive elements which are voltage controlled. The variable reactive elements may be, although are not required to be, variable capacitances, variable inductances, or both. In general, the variable capacitors may be semiconductor varactors, MEMS varactors, MEMS switched capacitors, ferroelectric capacitors, or any other technology that implements a variable capacitance. The variable inductors may be switched inductors using various types of RF switches including MEMS-based switches. The reactive elements may be current controlled rather than voltage controlled without departing from the spirit and scope of the present invention.

[0026] In an embodiment of the present invention, the variable capacitors of the RF matching network may be tunable integrated circuits, such as voltage tunable dielectric capacitors or Parascan Tunable Capacitors (PTCs). Each tunable capacitor may be realized as a series network of capacitors which are all tuned using a common tuning voltage.

[0027] The RF voltage detector 130 of FIG. 1 may be used to monitor the magnitude of the output nodal voltage. The fundamental concept used in this control system is that the RF power transferred to the arbitrary load impedance 135 is maximized when the RF voltage magnitude at the output port 115 is maximized. It is the understanding of this concept that allows one to remove the directional coupler conventionally located in series with the input port and to thus simplifying the architecture of the control system. A directional coupler is undesirable for numerous reasons:

• • [0028] (1) The cost of the coupler,
  • [0029] (2) The physical size of the directional coupler may be prohibitive: Broadband couplers are typically ¼ of a guide wavelength in total transmission line length at their mid-band frequency. For a 900 MHz band and an effective dielectric constant of 4, the total line length needs to be about 1.64 inches.
  • [0030] (3) The directivity of the directional coupler sets the lower limit on the achievable input return loss of the RF matching network. For instance, a directional coupler with 20 db of coupling will limit the input return loss for the AIMM to about −20 dB.
  • [0031] (4) Directional couplers have limited operational bandwidth, where the directivity meets a certain specification. In some applications, the AIMM may need to work at different frequency bands separated by an octave or more, such as at 900 MHz and 1900 MHz in a commercial mobile phone.

[0032] The RF voltage detector 130 may be comprised of a diode detector, a temperature compensated diode detector, a logarithmic amplifier, or any other means to detect an RF voltage magnitude. The phase of the RF voltage is not required. The controller 125 accepts as an input the information associated with the detected RF output 115 voltage. The controller 125 provides one or more outputs that control the bias voltage driver circuits. The controller 125 may be digitally-based such as a microprocessor, a digital signal processor, or an ASIC, or any other digital state machine. The controller may also be an analog-based system.

[0033] The bias voltage driver circuit 120 is a means of mapping control signals that are output from the controller 125 to a voltage range that is compatible with the tunable reactive elements in the RF matching network 110. The driver circuit may be an application specific integrated circuit (ASIC) whose function is to accept digital signals from the controller 125 and then output one or more analog voltages for one or more tunable reactive elements in the RF matching circuit 110. The driver circuit 120 may provide a wider range of analog tuning voltages than what is used as a power supply voltage by the controller 125. Hence the driver circuit 120 may perform the functions of voltage translation and voltage scaling.

[0034] The purpose of the control system shown in FIG. 1 is to monitor the output RF voltage magnitude and to use this information as an input to an algorithm that adjusts the tuning voltages provided to the tunable reactive elements in the RF matching network 110. The algorithm adjusts the reactances to maximize the RF output 115 voltage. Various options exist for control algorithms. In general, the algorithm may be a scalar multi-dimensional maximization algorithm where the independent variables are the tuning voltages for the reactive elements. Some embodiments of the operation of the tuning algorithm of the present invention, may increase performance of a network and/or enable it to perform in systems that might otherwise make it difficult for the system to make all the required system specifications. GSM, EDGE and WCDMA systems have specification limiting the allowable phase shifts within a transmit burst. Additionally, all cellular handsets have SAR (specific absorption rate) limits dictating how much RF energy may be absorbed by human bodies in close proximity. There are soon to be specifications that will dictate TRP (total radiated power) to be transmitted by cellular handsets, and handset suppliers will need to meet these specifications within a small number of transmit bursts (in a TDMA system) or in a very short period of time (in a continuous transmission system).

[0035] In order to achieve the above objectives, the AIMM tuning algorithm can contain the following attributes: 1—Limit the number of tuning “steps” that are taken within a transmit burst, or limit the steps to only be allowed between bursts (when the transmitter is disabled). This can be accomplished easily by putting time delays in the algorithm, or to only allow tuning when a Tx Enable line in the transmitter is low.

• [0036] 2—Limit the allowed tuning to avoid certain matching impedances, or put the tuner in a “default” position when the cellular handset transmitter is at the full power step. By doing so at the highest power level, we can avoid having the handset antenna couple higher power into the human tissue near the phone's antenna. It is only at the highest power level where the SAR limit typically becomes an issue, and by limiting the effectiveness of the AIMM tuner at this power level, we can avoid the possibility of causing the handset to exceed the SAR limits.
• [0037] 3—In order to allow the AIMM tuner to achieve the optimal match as quickly as possible, a memory system could be engaged in which the optimal match is stored for each frequency band, or perhaps even for each group of channels, and this memorized optimal match is used as the starting position any time the phone is directed to that particular band or channel. This memory could also remember operating positions such as flip-open or flip-closed in order to better “guess” the best starting position for the matching network.

[0038] The simplified control system shown in FIG. 1 is illustrated using a 2 port RF matching network. However, this control system is extensible to multi-port RF matching networks as shown in FIG. 2, generally as 200. Consider a RF multiplexing filter with N input ports where each port is designed for a specific band of frequencies. Assume that N transmitters drive the N input ports 205, 210, 215 and 220, and that each input port is coupled to the single RF output port 240 using RF circuits that contain variable reactive elements. The objective of the control system remains the same, to maximize the RF output voltage magnitude, and thus to optimize the power transfer from the nth input port to the arbitrary load impedance. Further, the RF voltage detector 245, controller 235 and bias voltage driver circuit 230 functions as described above with reference to FIG. 1 and in the embodiment of FIG. 2, the RF matching networks is a multi-port RF matching network 225.

[0039] Although the present invention is not limited in this respect, the arbitrary load impedance Z_L 250 may be a multi-band antenna in a mobile wireless device and the multi-port matching network 225 may be a diplexer whose function is to route the signal between two or more paths by virtue of the signal frequency.

[0040] Looking now at FIG. 3, the variable capacitors (such as, but not limited to, PTCs) 320, 325 and 330 and inductors 305 and 310 may be built into a multichip module 300 containing a detector 360, an ADC 365, a processor 355, DACs 370, voltage buffers, and charge pump 335. This multichip module 300 may be designed with a closed loop feedback system to maximize the RF voltage across the output node by adjusting all the PTC 320, 325 and 330 bias voltages, and doing so independently.

[0041] In an embodiment of the present invention as provided in FIG. 3, the RF matching network may be comprised of inductors L₁ 310, L₂ 305 and variable capacitors PTC₁ 320, PTC₂ 325 and PTC₃ 330. Note that each variable capacitor may itself be a complex network. The RF voltage detector 360 in this AIMM may be comprised of a resistive voltage divider (5KΩ/50Ω) and the simple diode detector. In an embodiment of the present invention, the controller may be comprised of the analog-to-digital converter or ADC₁ 355, the microprocessor 355, plus the digital-to-analog converters DAC₁ 370, DAC₂ 375 and DAC₃ 380. The controller may use external signals such as knowledge of frequency, Tx or Rx mode, or other available signals in the operation of its control algorithm. The bias voltage driver circuit may be comprised of a DC-to-DC converter such as the charge pump 335, in addition to the three analog buffers whose output voltage is labeled V_bias1, 385, V_bias 390, and V_bias3 395. The DC-to-DC voltage converter may be needed to supply a higher bias voltage from the analog buffers than what is normally required to power the processor 355. The charge pump may supply a voltage in the range of 10 volts to 50 volts, and in some embodiments, both positive and negative supply voltages may be used.

[0042] It should be noted that the RF matching network shown in FIG. 2 is representative of many possible circuit topologies. Shown in FIG. 2 is a ladder network, but other topologies such as a T or Pi network may be used. The variable reactive elements (capacitors) are shown in shunt connections but that is not a restriction, as they may be used in series in other applications. Furthermore, three independent variable capacitances are shown in this RF matching network. However, fewer or more variable reactive elements may be used depending on the complexity needed to meet RF specifications.

[0043] In FIG. 3, the inductors for the RF matching network are shown to be included in the AIMM multichip module. In practice, this may not always be the case. If the module is extremely small, it may be more convenient to use external inductors for the matching network. External inductors may have a higher Q factor than smaller inductors that are able to be integrated on the module.

[0044] One of the important engineering specifications of the simplified AIMM control system is the dynamic range of input power over which it will operate. The lowest cost RF voltage detector is a simple diode detector, but it has a limited dynamic range of about 25 dB. Logarithmic amplifiers (that detect the signal envelope) have a much higher dynamic range of 50 dB to 60 dB, but their cost, complexity, chip area, and current drain is also much higher. In an embodiment of the present invention, as illustrated in FIG. 4 at 400, one may use a variable voltage divider to improve the dynamic range of a simple diode detector. The variable voltage divider 430 may be added between the RF output port 435 and the RF voltage detector 425. It is controlled by the loop controller 420 (microprocessor, ASIC, etc), and therefore it is a programmable voltage divider. Bias voltage driver circuit 415 and RF matching network 410 operate as described above with respect to FIG. 1.

[0045] As shown in FIG. 5, an embodiment of the present invention provides a simple resistive voltage divider 550 which is implemented using a three-pole RF switch 560 to select one of three different resistances: R1 530, R2 535, or R3 540. Although not limited in this respect, typical values may be 100Ω, 1KΩ, and 10 KΩ. A typical value for R4 565 may be 50Ω which would be a desirable value for most RF detector designs. Assuming a high input impedance for the detector 555, the voltage coupling levels would then be ⅓, 1/21, and 1/201.

[0046] This corresponds to voltage coupling levels of −9.5 dB, −26.4 dB, and −46 dB. At high power levels the lowest coupling is desired. At low power levels, the highest coupling level is desired. The dynamic range of the control loop is equal to that of the detector plus the difference in dB between the highest and lowest coupling levels. As an example, assume a simple diode detector is used which has about 25 dB of dynamic range. The loop dynamic range will then be 25+[−9.5−(−46)]=61.6 dB. The improvement over using no variable voltage divider is more than 36 dB.

[0047] Equally important as enhancing the dynamic range is improving the output harmonics and IP3 of the module. The variable voltage divider 550 will allow the detector input port 505 to be more isolated at the higher power levels. This will improve linearity of the module for high signal levels.

[0048] Turning now to FIG. 6, generally at 600 are the functional blocks of a variable voltage divider 640, and the RF matching network 610 may be combined in hardware to some degree by understanding that the output node 625 of the matching network 610 may be connected to a shunt RF branch comprised of a series string of capacitors 660 and to impedance 635. An input node for RF_in 605 may also be connected to the RF matching network 610. This series string 660 may be a RF voltage divider 640, and by selectively tapping into various circuit nodes along the string, one may obtain a variable output voltage divider 640. In an embodiment of the present invention, this is done with a digitally controlled RF switch 630. The switch 630 may be realized with FETs, MEMS, PIN diodes, or any other RF switch technology. Associated with variable voltage divider 640 is RF voltage detector 655 and controller 620, which is further connected to RF matching network 610 via bias voltage driver circuit 615.

[0049] As a practical matter, the resistance of R1 645 will need to be much higher (>10×) than the reactance of the string of series capacitors 660 between the tap point and ground. An alternative circuit to FIG. 6 would have the resistor R₁ 645 moved to the capacitor side of the switch SW₁ 630 and placed in each of the three lines going to the tap points. This will allow the resistors to be built on-chip with the tunable IC used in the matching network. Resister R4 may also be utilized at 650.

[0050] Some embodiments of the invention may be implemented, for example, using a machine-readable medium or article which may store an instruction or a set of instructions that, if executed by a machine, for example, by the system of FIG. 1 or FIG. 2, by controller 125 and 235 in communication with bias voltage driver circuit 120 and 230, by processor 355 of FIG. 3, or by other suitable machines, cause the machine to perform a method and/or operations in accordance with embodiments of the invention. Such machine may include, for example, any suitable processing platform, computing platform, computing device, processing device, computing system, processing system, computer, processor, or the like, and may be implemented using any suitable combination of hardware and/or software. The machine-readable medium or article may include, for example, any suitable type of memory unit, memory device, memory article, memory medium, storage device, storage article, storage medium and/or storage unit, for example, memory, removable or non-removable media, erasable or non-erasable media, writeable or re-writeable media, digital or analog media, hard disk, floppy disk, Compact Disk Read Only Memory (CD-ROM), Compact Disk Recordable (CD-R), Compact Disk Re-Writeable (CD-RW), optical disk, magnetic media, various types of Digital Versatile Disks (DVDs), a tape, a cassette, or the like. The instructions may include any suitable type of code, for example, source code, compiled code, interpreted code, executable code, static code, dynamic code, or the like, and may be implemented using any suitable high-level, low-level, object-oriented, visual, compiled and/or interpreted programming language, e.g., C, C++, Java, BASIC, Pascal, Fortran, Cobol, assembly language, machine code, or the like.

[0051] An embodiment of the present invention provides a machine-accessible medium that provides instructions, which when accessed, cause a machine to perform operations comprising adapting an RF matching network to maximize RF power transferred from at least one RF input port to at least one RF output port by controlling the variation of the voltage or current to voltage or current controlled variable reactive elements in said RF matching network to maximize the RF voltage at said at least one RF output port. The machine-accessible medium of the present invention may further comprise said instructions causing said machine to perform operations further comprising receiving information from a voltage detector connected to said at least one RF output port which determines the voltage at said at least one RF output port and providing voltage information to a controller that controls a bias driving circuit which provides voltage or current bias to said RF matching network.

[0052] Some embodiments of the present invention may be implemented by software, by hardware, or by any combination of software and/or hardware as may be suitable for specific applications or in accordance with specific design requirements. Embodiments of the invention may include units and/or sub-units, which may be separate of each other or combined together, in whole or in part, and may be implemented using specific, multi-purpose or general processors or controllers, or devices as are known in the art. Some embodiments of the invention may include buffers, registers, stacks, storage units and/or memory units, for temporary or long-term storage of data or in order to facilitate the operation of a specific embodiment.

[0053] Throughout the aforementioned description, BST may be used as a tunable dielectric material that may be used in a tunable dielectric capacitor of the present invention. However, the assignee of the present invention, Paratek Microwave, Inc. has developed and continues to develop tunable dielectric materials that may be utilized in embodiments of the present invention and thus the present invention is not limited to using BST material. This family of tunable dielectric materials may be referred to as Parascan®.

[0054] The term Parascan® as used herein is a trademarked term indicating a tunable dielectric material developed by the assignee of the present invention. Parascan® tunable dielectric materials have been described in several patents. Barium strontium titanate (BaTiO3-SrTiO3), also referred to as BSTO, is used for its high dielectric constant (200-6,000) and large change in dielectric constant with applied voltage (25-75 percent with a field of 2 Volts/micron). Tunable dielectric materials including barium strontium titanate are disclosed in U.S. Pat. No. 5,312,790 to Sengupta, et al. entitled “Ceramic Ferroelectric Material”; U.S. Pat. No. 5,427,988 by Sengupta, et al. entitled “Ceramic Ferroelectric Composite Material-BSTO-MgO”; U.S. Pat. No. 5,486,491 to Sengupta, et al. entitled “Ceramic Ferroelectric Composite Material-BSTO-ZrO2”; U.S. Pat. No. 5,635,434 by Sengupta, et al. entitled “Ceramic Ferroelectric Composite Material-BSTO-Magnesium Based Compound”; U.S. Pat. No. 5,830,591 by Sengupta, et al. entitled “Multilayered Ferroelectric Composite Waveguides”; U.S. Pat. No. 5,846,893 by Sengupta, et al. entitled “Thin Film Ferroelectric Composites and Method of Making”; U.S. Pat. No. 5,766,697 by Sengupta, et al. entitled “Method of Making Thin Film Composites”; U.S. Pat. No. 5,693,429 by Sengupta, et al. entitled “Electronically Graded Multilayer Ferroelectric Composites”; U.S. Pat. No. 5,635,433 by Sengupta entitled “Ceramic Ferroelectric Composite Material BSTO-ZnO”; U.S. Pat. No. 6,074,971 by Chiu et al. entitled “Ceramic Ferroelectric Composite Materials with Enhanced Electronic Properties BSTO Mg Based Compound-Rare Earth Oxide”. These patents are incorporated herein by reference. The materials shown in these patents, especially BSTO-MgO composites, show low dielectric loss and high tunability. Tunability is defined as the fractional change in the dielectric constant with applied voltage.

[0055] Barium strontium titanate of the formula Ba_xSr_1-xTiO₃ is a preferred electronically tunable dielectric material due to its favorable tuning characteristics, low Curie temperatures and low microwave loss properties. In the formula Ba_xSr_1-xTiO₃, x can be any value from 0 to 1, preferably from about 0.15 to about 0.6. More preferably, x is from 0.3 to 0.6.

[0056] Other electronically tunable dielectric materials may be used partially or entirely in place of barium strontium titanate. An example is Ba_xCa_1-xTiO₃, where x is in a range from about 0.2 to about 0.8, preferably from about 0.4 to about 0.6. Additional electronically tunable ferroelectrics include Pb_xZr_1-xTiO₃ (PZT) where x ranges from about 0.0 to about 1.0, Pb_xZr_1-xSrTiO₃ where x ranges from about 0.05 to about 0.4, KTa_xNb_1-xO₃ where x ranges from about 0.0 to about 1.0, lead lanthanum zirconium titanate (PLZT), PbTiO₃, BaCaZrTiO₃, NaNO₃, KNbO₃, LiNbO₃, LiTaO₃, PbNb₂O₆, PbTa₂O₆, KSr(NbO₃) and NaBa₂(NbO₃)5KH₂PO₄, and mixtures and compositions thereof. Also, these materials can be combined with low loss dielectric materials, such as magnesium oxide (MgO), aluminum oxide (Al₂O₃), and zirconium oxide (ZrO₂), and/or with additional doping elements, such as manganese (MN), iron (Fe), and tungsten (W), or with other alkali earth metal oxides (i.e. calcium oxide, etc.), transition metal oxides, silicates, niobates, tantalates, aluminates, zirconnates, and titanates to further reduce the dielectric loss.

[0057] In addition, the following U.S. patents and patent Applications, assigned to the assignee of this application, disclose additional examples of tunable dielectric materials: U.S. Pat. No. 6,514,895, entitled “Electronically Tunable Ceramic Materials Including Tunable Dielectric and Metal Silicate Phases”; U.S. Pat. No. 6,774,077, entitled “Electronically Tunable, Low-Loss Ceramic Materials Including a Tunable Dielectric Phase and Multiple Metal Oxide Phases”; U.S. Pat. No. 6,737,179 filed Jun. 15, 2001, entitled “Electronically Tunable Dielectric Composite Thick Films And Methods Of Making Same; U.S. Pat. No. 6,617,062 entitled “Strain-Relieved Tunable Dielectric Thin Films”; U.S. Pat. No. 6,905,989, filed May 31, 2002, entitled “Tunable Dielectric Compositions Including Low Loss Glass”; U.S. patent application Ser. No. 10/991,924, filed Nov. 18, 2004, entitled “Tunable Low Loss Material Compositions and Methods of Manufacture and Use Therefore” These patents and patent applications are incorporated herein by reference.

[0058] The tunable dielectric materials can also be combined with one or more non-tunable dielectric materials. The non-tunable phase(s) may include MgO, MgAl₂O₄, MgTiO₃, Mg₂SiO₄, CaSiO₃, MgSrZrTiO₆, CaTiO₃, Al₂O₃, Sio₂ and/or other metal silicates such as BaSiO₃ and SrSiO₃. The non-tunable dielectric phases may be any combination of the above, e.g., MgO combined with MgTiO₃, MgO combined with MgSrZrTiO₆, MgO combined with Mg₂SiO₄, MgO combined with Mg₂SiO₄, Mg₂SiO₄ combined with CaTiO₃ and the like.

[0059] Additional minor additives in amounts of from about 0.1 to about 5 weight percent can be added to the composites to additionally improve the electronic properties of the films. These minor additives include oxides such as zirconnates, tannates, rare earths, niobates and tantalates. For example, the minor additives may include CaZrO₃, BaZrO₃, SrZrO₃, BaSnO₃, CaSnO₃, MgSnO₃, Bi2O₃/2SnO₂, Nd₂O₃, Pr₇O₁₁, Yb₂O₃, H_o2O₃, La₂O₃, MgNb₂O₆, SrNb₂O₆, BaNb₂O₆, MgTa₂O₆, BaTa₂O₆ and Ta₂O₃.

[0060] Films of tunable dielectric composites may comprise Ba1-xSrxTiO3, where x is from 0.3 to 0.7 in combination with at least one non-tunable dielectric phase selected from MgO, MgTiO₃, MgZrO₃, MgSrZrTiO₆, Mg₂SiO₄, CaSiO₃, MgAl₂O₄, CaTiO₃, Al₂O₃, SiO₂, BaSiO₃ and SrSiO₃. These compositions can be BSTO and one of these components, or two or more of these components in quantities from 0.25 weight percent to 80 weight percent with BSTO weight ratios of 99.75 weight percent to 20 weight percent.

[0061] The electronically tunable materials may also include at least one metal silicate phase. The metal silicates may include metals from Group 2A of the Periodic Table, i.e., Be, Mg, Ca, Sr, Ba and Ra, preferably Mg, Ca, Sr and Ba. Preferred metal silicates include Mg₂SiO₄, CaSiO₃, BaSiO₃ and SrSiO₃. In addition to Group 2A metals, the present metal silicates may include metals from Group 1A, i.e., Li, Na, K, Rb, Cs and Fr, preferably Li, Na and K. For example, such metal silicates may include sodium silicates such as Na₂SiO₃ and NaSiO₃-5H₂O, and lithium-containing silicates such as LiAlSiO₄, Li2SiO₃ and Li₄SiO₄. Metals from Groups 3A, 4A and some transition metals of the Periodic Table may also be suitable constituents of the metal silicate phase. Additional metal silicates may include Al₂Si₂O₇, ZrSiO₄, KalSi₃O₈, NaAlSi₃O₈, CaAl₂Si₂O₈, CaMgSi₂O₆, BaTiSi₃O₉ and Zn₂SiO₄. The above tunable materials can be tuned at room temperature by controlling an electric field that is applied across the materials.

[0062] In addition to the electronically tunable dielectric phase, the electronically tunable materials can include at least two additional metal oxide phases. The additional metal oxides may include metals from Group 2A of the Periodic Table, i.e., Mg, Ca, Sr, Ba, Be and Ra, preferably Mg, Ca, Sr and Ba. The additional metal oxides may also include metals from Group 1A, i.e., Li, Na, K, Rb, Cs and Fr, preferably Li, Na and K. Metals from other Groups of the Periodic Table may also be suitable constituents of the metal oxide phases. For example, refractory metals such as Ti, V, Cr, Mn, Zr, Nb, Mo, Hf, Ta and W may be used. Furthermore, metals such as Al, Si, Sn, Pb and Bi may be used. In addition, the metal oxide phases may comprise rare earth metals such as Sc, Y, La, Ce, Pr, Nd and the like.

[0063] The additional metal oxides may include, for example, zirconnates, silicates, titanates, aluminates, stannates, niobates, tantalates and rare earth oxides. Preferred additional metal oxides include Mg₂SiO₄, MgO, CaTiO₃, MgZrSrTiO₆, MgTiO₃, MgA₁₂O₄, WO3, SnTiO₄, ZrTiO₄, CaSiO₃, CaSnO₃, CaWO₄, CaZrO₃, MgTa₂O₆, MgZrO₃, MnO₂, PbO, Bi₂O₃ and La₂O₃. Particularly preferred additional metal oxides include Mg₂SiO₄, MgO, CaTiO₃, MgZrSrTiO₆, MgTiO₃, MgAl₂O₄, MgTa₂O₆ and MgZrO₃.

[0064] The additional metal oxide phases are typically present in total amounts of from about 1 to about 80 weight percent of the material, preferably from about 3 to about 65 weight percent, and more preferably from about 5 to about 60 weight percent. In one preferred embodiment, the additional metal oxides comprise from about 10 to about 50 total weight percent of the material. The individual amount of each additional metal oxide may be adjusted to provide the desired properties. Where two additional metal oxides are used, their weight ratios may vary, for example, from about 1:100 to about 100:1, typically from about 1:10 to about 10:1 or from about 1:5 to about 5:1. Although metal oxides in total amounts of from 1 to 80 weight percent are typically used, smaller additive amounts of from 0.01 to 1 weight percent may be used for some applications.

[0065] The additional metal oxide phases can include at least two Mg-containing compounds. In addition to the multiple Mg-containing compounds, the material may optionally include Mg-free compounds, for example, oxides of metals selected from Si, Ca, Zr, Ti, Al and/or rare earths.

[0066] While the present invention has been described in terms of what are at present believed to be its preferred embodiments, those skilled in the art will recognize that various modifications to the disclose embodiments can be made without departing from the scope of the invention as defined by the following claims.