US20020186099A1 - Electrically tunable filters with dielectric varactors - Google Patents
Electrically tunable filters with dielectric varactors Download PDFInfo
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- US20020186099A1 US20020186099A1 US09/457,943 US45794399A US2002186099A1 US 20020186099 A1 US20020186099 A1 US 20020186099A1 US 45794399 A US45794399 A US 45794399A US 2002186099 A1 US2002186099 A1 US 2002186099A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P1/00—Auxiliary devices
- H01P1/20—Frequency-selective devices, e.g. filters
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P1/00—Auxiliary devices
- H01P1/20—Frequency-selective devices, e.g. filters
- H01P1/207—Hollow waveguide filters
- H01P1/208—Cascaded cavities; Cascaded resonators inside a hollow waveguide structure
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H11/00—Networks using active elements
- H03H11/02—Multiple-port networks
- H03H11/04—Frequency selective two-port networks
- H03H11/12—Frequency selective two-port networks using amplifiers with feedback
- H03H11/1217—Frequency selective two-port networks using amplifiers with feedback using a plurality of operational amplifiers
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H11/00—Networks using active elements
- H03H11/02—Multiple-port networks
- H03H11/04—Frequency selective two-port networks
- H03H11/12—Frequency selective two-port networks using amplifiers with feedback
- H03H11/126—Frequency selective two-port networks using amplifiers with feedback using a single operational amplifier
Definitions
- the present invention relates generally to electronic filters and more particularly to filters that include tunable varactors.
- Tunable filters are widely used in radio frequency (RF) and microwave circuits. Tunable filters may significantly improve the performance of the circuits, and simplify the circuits.
- RF radio frequency
- diode varactor diode varactor
- Mechanically tunable filters have the disadvantages of large size, low speed, and heavy weight.
- Diode-tuned filters that include conventional semiconductor varactor diodes suffer from low power handling capacity, that is limited by intermodulation of the varactor, which causes signals to be generated at frequencies other than those desired. This intermodulation is caused by the highly non-linear response of conventional semiconductor varactors to voltage control.
- Tunable filters for use in radio frequency circuits are well known. Examples of such filters can be found in U.S. Pat. Nos. 5,917,387, 5,908,811, 5,877,123, 5,869,429, 5,752,179, 5,496,795 and 5,376,907.
- Varactors can be used as tunable capacitors in tunable filters.
- Common varactors used today are Silicon and GaAs based diodes. The performance of these varactors is defined by the capacitance ratio, C max /C min , frequency range and figure of merit, or Q factor (1/tan ⁇ ) at the specified frequency range.
- the Q factors for these semiconductor varactors for frequencies up to 2 GHz are usually very good. However, at frequencies above 2 GHz, the Q factors of these varactors degrade rapidly. At 10 GHz the Q factors for these varactors are usually only about 30.
- Varactors that utilize a thin film ferroelectric ceramic as a voltage tunable element in combination with a superconducting element have been described.
- U.S. Pat. No. 5,640,042 discloses a thin film ferroelectric varactor having a carrier substrate layer, a high temperature superconducting layer deposited on the substrate, a thin film dielectric deposited on the metallic layer, and a plurality of metallic conductive means disposed on the thin film dielectric, which are placed in electrical contact with RF transmission lines in tuning devices.
- Another tunable capacitor using a ferroelectric element in combination with a superconducting element is disclosed in U.S. Pat. No. 5,721,194.
- This invention provides a voltage tunable filter comprising an input connection, an output connection, and a circuit branch electrically coupled to the input connection and the output connection and including a voltage tunable dielectric varactor electrically connected to an inductor.
- the voltage tunable filter can be one of a low-pass, high-pass, band-pass, or band-stop filter.
- the varactor can include built-in DC blocking capacitors.
- the voltage tunable dielectric varactor includes a substrate having a first dielectric constant and having a generally planar surface, a tunable dielectric layer positioned on the generally planar surface of the substrate, with the tunable dielectric layer having a second dielectric constant greater than the first dielectric constant, and first and second electrodes positioned on a surface of the tunable dielectric layer opposite the generally planar surface of the substrate.
- the first and second electrodes are separated to form a gap therebetween.
- a bias voltage applied to the electrodes changes the capacitance of the varactor between an input and an output thereof.
- the present invention provides radio frequency (RF) electrically tunable filters, tuned by dielectric voltage-variable capacitors.
- RF radio frequency
- FIG. 1 is a top plan view of a planar voltage tunable varactor as described in U.S. patent application Ser. No. 09/149,126 that can be used in the preferred embodiment of the present invention
- FIG. 2 is a cross-sectional view of the varactor of FIG. 1, taken along line 2 - 2 ;
- FIGS. 3 a , 3 b and 3 c are graphs illustrating the capacitance and loss tangent of voltage tunable varactors constructed in accordance with this invention at various operating frequencies and gap widths;
- FIG. 4 is a top view of a planar varactor assembly with built-in DC blocking capacitors as described in U.S. patent application Ser. No. 09/434,433;
- FIG. 5 is a cross sectional view of the varactor assembly of FIG. 4, taken along line 5 - 5 ;
- FIG. 6 is a schematic diagram of the varactor of FIGS. 4 and 5;
- FIG. 7 is a schematic diagram of an example Chebyshev bass-pass filter constructed in accordance with this invention.
- FIG. 8 is a graph of the attenuation of the filter shown in FIG. 7 operated at various bias voltages on the varactors;
- FIG. 9 is a schematic diagram of a low pass filter constructed in accordance with this invention.
- FIG. 10 is a graph of the losses of the filter shown in FIG. 9 operated at various bias voltages on the varactor;
- FIG. 11 is a schematic diagram of a high pass filter constructed in accordance with this invention.
- FIG. 12 is a graph of the losses of the filter shown in FIG. 11 operated at various bias voltages on the varactors;
- FIG. 13 is a schematic diagram of a band stop filter constructed in accordance with this invention.
- FIG. 14 is a graph of the losses of the filter shown in FIG. 13 operated at various bias voltages on the varactors.
- FIGS. 1 and 2 are top and cross sectional views of a varactor 10 as described in the above-mentioned U.S. patent application Ser. No. 09/149,126.
- the varactor 10 includes a substrate 12 having a generally planar top surface 14 .
- a tunable dielectric layer 16 is positioned adjacent to the top surface of the substrate.
- a pair of metal electrodes 18 and 20 is positioned on top of the dielectric layer.
- the substrate 12 is comprised of a material having a relatively low permittivity such as MgO, Alumina, LaAlO 3 , Sapphire, or a ceramic.
- a low permittivity is a permittivity of less than about 30.
- the tunable dielectric layer 16 is comprised of a material having a permittivity in a range from about 20 to about 2000, and having a tunability in the range from about 10% to about 80% at a bias voltage of about 10 V/ ⁇ m.
- this layer is preferably comprised of Barium-Strontium Titanate, Ba x Sr 1-x TiO 3 (BSTO), where x can range from zero to one, or BSTO-composite ceramics.
- BSTO composites include, but are not limited to: BSTO-MgO, BSTO-MgAl 2 O 4 , BSTO-CaTiO 3 , BSTO-MgTiO 3 , BSTO-MgSrZrTiO 6 , and combinations thereof.
- the tunable layer in one preferred embodiment has a dielectric permittivity greater than 100 when subjected to typical DC bias voltages, for example, voltages ranging from about 5 volts to about 300 volts.
- a gap 22 of width g is formed between the electrodes 18 and 20 .
- the gap width must be optimized to increase ratio of the maximum capacitance C max to the minimum capacitance C min (C max /C min ) and increase the quality facto (Q) of the device.
- the width of this gap has the most influence on the varactor parameters.
- the optimal width, g will be determined by the width at which the device has maximum C max /C min and minimal loss tangent.
- a controllable voltage source 24 is connected by lines 26 and 28 to electrodes 18 and 20 . This voltage source is used to supply a DC bias voltage to the dielectric layer, thereby controlling the permittivity of the layer.
- the varactor also includes an RF input 30 and an RF output 32 . The RF input and output are connected to electrodes 18 and 20 , respectively, by soldered or bonded connections.
- the varactors may use gap widths of less than 5-50 ⁇ m.
- the thickness of the dielectric layer ranges from about 0.1 ⁇ m to about 20 ⁇ m.
- a sealant 34 is positioned within the gap and can be any non-conducting material with a high dielectric breakdown strength to allow the application of high voltage without arcing across the gap.
- the sealant can be epoxy or polyurethane.
- the length of the gap L can be adjusted by changing the length of the ends 36 and 38 of the electrodes. Variations in the length have a strong effect on the capacitance of the varactor. The gap length will optimized for this parameter. Once the gap width has been selected, the capacitance becomes a linear function of the length L. For a desired capacitance, the length L can be determined experimentally, or through computer simulation.
- the thickness of the tunable dielectric layer also has a strong effect on the C max /C min .
- the optimum thickness of the ferroelectric layers will be determined by the thickness at which the maximum C max /C min occurs.
- the ferroelectric layer of the varactor of FIGS. 1 and 2 can be comprised of a thin film, thick film, or bulk dielectric material such as Barium-Strontium Titanate, Ba x Sr 1-x TiO 3 (BSTO), BSTO and various oxides, or a BSTO composite with various dopant materials added. All of these materials exhibit a low loss tangent.
- the loss tangent would range from about 0.0001 to about 0.001.
- the loss tangent would range from about 0.001 to about 0.01.
- the loss tangent would range from about 0.005 to about 0.02.
- the electrodes may be fabricated in any geometry or shape containing a gap of predetermined width.
- the required current for manipulation of the capacitance of the varactors disclosed in this invention is typically less than 1 ⁇ A.
- the electrode material is gold.
- other conductors such as copper, silver or aluminum, may also be used.
- Gold is resistant to corrosion and can be readily bonded to the RF input and output. Copper provides high conductivity, and would typically be coated with gold for bonding or nickel for soldering.
- the varactors of FIGS. 1 and 2 can be fabricated using bulk, thick film, and thin film techniques.
- FIGS. 1 and 2 show a voltage tunable planar varactor having a planar electrode with a predetermined gap distance on a single layer tunable bulk, thick film or thin film dielectric.
- the applied voltage produces an electric field across the gap of the tunable dielectric that produces an overall change in the capacitance of the varactor.
- the width of the gap can range from 5 to 50 ⁇ m depending on the performance requirements.
- Such varactors operate at room temperature and can have Q factors ranging from about 50 to about 10,000 when operated at frequencies ranging from about 1 GHz to about 40 GHz.
- the capacitance (in pF) and the loss factor (tan ⁇ ) of the varactors measured at 3, 10 and 20 GHz for gap distances of 10 and 20 ⁇ m are shown in FIGS. 3 a , 3 b and 3 c .
- the Q's for the varactors are approximately the following: 200 at 3 GHz, 80 at 10 GHz, 45-55 at 20 GHz.
- typical Q's for GaAs semiconductor diode varactors are as follows: 175 at 2 GHz, 35 at 10 GHz and much less at even higher frequency. Therefore at frequencies greater than or equal to 10 GHz the varactors of this invention have much better Q factors.
- FIGS. 4 and 5 are top and cross sectional views of a varactor assembly 40 having built in DC blocking capacitors as described in U.S. patent application Ser. No. 09/434,433.
- the varactor assembly 40 includes a substrate 42 having a generally planar top surface 44 .
- a tunable dielectric layer 46 is positioned adjacent to the top surface of the substrate.
- Metal electrodes 48 and 50 are positioned on top of the dielectric layer.
- the electrodes 48 and 50 are shaped to have projections 52 and 54 . The ends of these projections form a gap 56 on the surface of the tunable dielectric layer.
- the combination of electrodes 48 and 50 , and tunable dielectric layer 46 form a tunable capacitor 84 .
- the capacitance of the tunable capacitor can be changed by applying a bias voltage to the electrodes 48 and 50 .
- the substrate 42 is comprised of a material having a relatively low permittivity such as MgO, Alumina, LaAlO 3 , Sapphire, or a ceramic.
- a low permittivity is a permittivity of less than about 30.
- the tunable dielectric layer 16 is comprised of a material having a permittivity in a range from about 20 to about 2000, and having a tunability in the range from about 10% to about 80% at a bias voltage of about 10 V/ ⁇ m.
- the tunable dielectric layer can be comprised of Barium-Strontium Titanate, Ba x Sr 1-x TiO 3 (BSTO), where x can range from zero to one, or BSTO-composite ceramics.
- BSTO composites include, but are not limited to: BSTO-MgO, BSTO-MgAl 2 O 4 , BSTO-CaTiO 3 , BSTO-MgTiO 3 , BSTO-MgSrZrTiO 6 , and combinations thereof.
- the dielectric film of the dielectric capacitor may be deposited by screen printer, laser ablation, metal-organic solution deposition, sputtering, or chemical vapor deposition techniques.
- the tunable layer in one preferred embodiment has a dielectric permittivity greater than 100 when subjected to typical DC bias voltages, for example, voltages ranging from about 5 volts to about 300 volts.
- the gap width must be optimized to increase ratio of the maximum capacitance C max to the minimum capacitance C min (C max /C min ) and increase the quality factor (Q) of the device.
- the width of this gap has the most influence on the varactor parameters.
- the optimal width, g will be determined by the width at which the device has maximum C max /C min and minimal loss tangent.
- a controllable voltage source 58 is connected by lines 60 and 62 to electrodes 48 and 50 . This voltage source is used to supply a DC bias voltage to the dielectric layer, thereby controlling the permittivity of the layer.
- the varactor assembly further includes first and second non-tunable dielectric layers 64 and 66 positioned adjacent to the generally planar surface of the substrate 42 and on opposite sides of the tunable dielectric layer 46 . Electrode 48 extends over a portion of the top surface of non-tunable material 64 . Electrode 68 is positioned adjacent a top surface of non-tunable layer 64 such that a gap 70 is formed between electrodes 48 and 68 . The combination of electrodes 48 and 68 and non-tunable layer 64 forms a first DC blocking capacitor 72 .
- the varactor assembly also includes an RF input 80 and an RF output 82 .
- Electrode 74 is positioned adjacent a top surface of non-tunable layer 66 such that a gap 76 is formed between electrodes 50 and 74 .
- the combination of electrodes 50 and 74 and non-tunable layer 66 forms a second DC blocking capacitor 78 .
- the dielectric films of the DC blocking capacitors may be deposited by screen printer, laser ablation, metal-organic solution deposition, sputtering, or chemical vapor deposition techniques.
- An RF input 80 is connected to electrode 68 .
- An RF output 82 is connected to electrode 74 .
- the RF input and output are connected to electrodes 68 and 74 , respectively, by soldered or bonded connections.
- the non-tunable dielectric layers 64 and 66 , in the DC blocking capacitors 72 and 78 are comprised of a high dielectric constant material, such as a BSTO composite.
- the DC blocking capacitors 72 and 78 are electrically connected in series with the tunable capacitor 84 to isolate the DC bias from the outside of the varactor assembly 40 .
- the electrodes have an interdigital arrangement as shown in FIG. 4.
- FIG. 6 is a schematic diagram of the varactor of FIGS. 4 and 5 showing the three capacitors formed by the structure.
- the varactors may use gap widths of 5-50 ⁇ m.
- the thickness of the tunable dielectric layer ranges from about 0.1 ⁇ m to about 20 ⁇ m.
- a sealant can be inserted into the gaps to increase breakdown voltage.
- the sealant can be any non-conducting material with a high dielectric breakdown strength to allow the application of high voltage without arcing across the gap, for example, epoxy or polyurethane.
- This invention utilizes room temperature tunable dielectric the varactors such as those shown in FIGS. 1, 2, 4 and 5 in an electronically tunable RF filter.
- the lump element filter in the present invention may be low-pass, high-pass, band-pass, or band-stop designed by Bessel, Butterworth, Chebyshev, Elliptical or other methods.
- FIG. 7 is a schematic diagram of a band pass filter 100 constructed in accordance with this invention.
- This capacitor coupled LC filter circuit which is commonly referred to as a capacitively coupled tank circuit, includes a plurality of resonators 102 , 104 and 106 with capacitive coupling between those resonators, input connection points 108 and 110 , and output connection points 112 and 114 .
- resonator 102 comprising the parallel connection of capacitor C 2 and inductor L 1 , is connected to node 116 and input connection point 110 and output connection point 114 , and is coupled to input connection point 108 through capacitor C 1 .
- resonator 104 comprising the parallel connection of capacitor C 4 and inductor L 2
- resonator 106 is connected to node 120 and input connection point 110 and output connection point 114 , and is coupled to node 118 through capacitor C 5 .
- resonator 106 is coupled to output connection point 112 through capacitor C 7 .
- the filter is tuned by varactors C 2 , C 4 and C 6 , which in the preferred embodiment are constructed in accordance with either FIGS. and 1 and 2 or FIGS. 4 and 5.
- Common connection points 110 and 114 may be connected to ground.
- capacitors C 1 and C 7 are 5.6 pF
- capacitors C 3 and C 5 are 0.48 pF
- capacitors C 2 and C 6 are 8.0 pF
- capacitor C 4 is 13.1 pF
- inductors L 1 , L 2 and L 3 are 500 nH.
- the input and output of the filter are matched to 50 ⁇ .
- FIG. 8 is a graph 122 of the attenuation of the filter shown in FIG. 7 wherein capacitors C 2 , C 4 and C 6 are voltage tunable varactors operated at various bias voltages.
- Curves 124 , 126 , 128 , 130 and 132 shown the filter attenuation at the bias voltages shown in Table I. TABLE I Varactor bias voltages. Curve C2 Bias C4 Bias C6 Bias 124 0 0 0 126 180 80 180 128 400 160 400 130 600 210 600 132 700 500 700
- FIG. 9 is a schematic diagram of a low pass filter constructed in accordance with this invention.
- low pass filter 140 includes an input connection point 142 , and output connection point 144 and a common connection point 146 .
- An RF source 148 supplies an RF signal to the filter.
- Resistor RS represents the filter input impedance.
- a load as represented by resistor RL is connected between the output connection point 144 and the common connection point 146 .
- Inductors L 4 and L 5 are electrically connected in series between input connection point 142 and output connection point 144 .
- a tunable varactor as represented by capacitor C 8 is connected between the common connection point 146 and a node 150 between inductors L 4 and L 5 .
- FIG. 10 is a graph of the losses of the filter shown in FIG. 9 operated at various bias voltages on the varactor.
- C 8 133.8 pF at zero bias.
- Curves 156 and 152 represent the insertion loss and return loss at zero bias voltage, respectively.
- Curves 158 and 154 represent the insertion loss and return loss at 500 volts bias, respectively.
- FIG. 11 is a schematic diagram of a high pass filter constructed in accordance with this invention.
- high pass filter 160 includes an input connection point 162 , and output connection point 164 and a common connection point 166 .
- An RF source 168 supplies an RF signal to the filter.
- Resistor RS represents the input impedance of the filter.
- a load as represented by resistor RL is connected between the output connection point 164 and the common connection point 166 .
- Tunable varactors as represented by capacitors C 9 and C 10 are electrically connected in series between input connection point 162 and output connection point 164 .
- Inductor L 6 is connected between the common connection point 166 and a node 170 between capacitors C 9 and C 10 .
- FIG. 12 is a graph of the losses of the filter shown in FIG. 11 operated at various bias voltages on the varactor.
- RS RL 50 ⁇
- L 6 52.6 nh
- Curves 172 and 176 represent the insertion loss and return loss at zero bias voltage, respectively.
- Curves 174 and 178 represent the insertion loss and return loss at 600 volts bias, respectively.
- FIG. 13 is a schematic diagram of a band stop filter 180 constructed in accordance with this invention.
- band stop filter 180 includes an input connection point 182 , and output connection point 184 and a common connection point 186 .
- An RF source 188 supplies and RF signal to the filter.
- Resistor RS represents the input impedance of the filter.
- a load as represented by resistor RL is connected between the output connection point 184 and the common connection point 186 .
- a first circuit branch 192 comprising the parallel connection of inductor L 7 and a varactor represented by capacitor C 11 is electrically connected between input connection point 182 and node 190 .
- a second circuit branch 194 comprising the parallel connection of inductor L 8 and a varactor represented by capacitor C 12 is electrically connected between output connection point 184 and node 190 .
- a third circuit branch 196 comprising the series connection of inductor L 9 and a varactor represented by capacitor C 13 is electrically connected between common connection point 186 and node 190 .
- FIG. 14 is a graph of the losses of the filter shown in FIG. 13 operated at various bias voltages on the varactors.
- L 9 1457 nH
- C 13 4.83 pF at zero bias.
- Curves 198 and 202 represent the insertion loss and return loss at zero bias voltage, respectively.
- Curves 200 and 204 represent the insertion loss and return loss at 500 volts bias, respectively.
- the lumped element filter in the present invention may be designed by Bessel, Butterworth, Chebyshev, Elliptical or other methods. Examples of band-pass, low pass, high pass and band stop filters have been presented. Dielectric varactors with built-in DC blocks can be used in the filter as the tunable elements. By utilizing low loss (tan ⁇ 0.02) dielectrics of predetermined dimensions, the varactors of FIGS. 1, 2, 4 and 5 can operate at high levels at high frequencies, for example, greater than 3 GHz.
- the dielectric varactors of FIGS. 1, 2, 4 and 5 operate at high speeds, with high Quality Factor (Q), high power handling, and more importantly low intermodulation distortion products. Filters using dielectric varactors have better performance than semiconductor diode-tuned filters, especially in the properties of high power handling, low intermodulation distortion, and the ability to cover capacitance ranges that are not possible with conventional varactors.
- Q Quality Factor
- varactors using dielectric materials can work at much higher capacitance values than conventional diode varactors. This allows the construction of compact electronically tunable filters using lumped element capacitors with performances that are not possible with conventional varactors.
- a low loss, highly tunable dielectric varactor with or without built-in DC blocks may be used in the present invention, the built-in DC block dielectric varactor may reduce DC block insertion loss, and make it easier to use in the filter design.
- the tunable dielectric varactors of this invention have increased RF power handling capability and reduced power consumption and cost.
- the present invention by utilizing dielectric varactors, provides high performance electrically tunable filters that operate in the RF frequency range.
- This invention has many practical applications and many other modifications of the disclosed devices may be obvious to those skilled in the art without departing from the spirit and scope of this invention. While the present invention has been described in terms of what are at present its preferred embodiments, various modifications of such embodiments can be made without departing from the scope of the invention, which is defined by the claims.
Abstract
Description
- This application claims the benefit of U.S. Provisional Patent Application No. 60/111,888, filed Dec. 11, 1998.
- The present invention relates generally to electronic filters and more particularly to filters that include tunable varactors.
- Electronic filters are widely used in radio frequency (RF) and microwave circuits. Tunable filters may significantly improve the performance of the circuits, and simplify the circuits. There are two well-known kinds of analog tunable filters used in RF applications, one is electrically tuned, usually by diode varactor, and the other is mechanically tuned. Mechanically tunable filters have the disadvantages of large size, low speed, and heavy weight. Diode-tuned filters that include conventional semiconductor varactor diodes suffer from low power handling capacity, that is limited by intermodulation of the varactor, which causes signals to be generated at frequencies other than those desired. This intermodulation is caused by the highly non-linear response of conventional semiconductor varactors to voltage control.
- Tunable filters for use in radio frequency circuits are well known. Examples of such filters can be found in U.S. Pat. Nos. 5,917,387, 5,908,811, 5,877,123, 5,869,429, 5,752,179, 5,496,795 and 5,376,907.
- Varactors can be used as tunable capacitors in tunable filters. Common varactors used today are Silicon and GaAs based diodes. The performance of these varactors is defined by the capacitance ratio, Cmax/Cmin, frequency range and figure of merit, or Q factor (1/tan δ) at the specified frequency range. The Q factors for these semiconductor varactors for frequencies up to 2 GHz are usually very good. However, at frequencies above 2 GHz, the Q factors of these varactors degrade rapidly. At 10 GHz the Q factors for these varactors are usually only about 30.
- Varactors that utilize a thin film ferroelectric ceramic as a voltage tunable element in combination with a superconducting element have been described. For example, U.S. Pat. No. 5,640,042 discloses a thin film ferroelectric varactor having a carrier substrate layer, a high temperature superconducting layer deposited on the substrate, a thin film dielectric deposited on the metallic layer, and a plurality of metallic conductive means disposed on the thin film dielectric, which are placed in electrical contact with RF transmission lines in tuning devices. Another tunable capacitor using a ferroelectric element in combination with a superconducting element is disclosed in U.S. Pat. No. 5,721,194.
- Commonly owned U.S. patent application Ser. No. 09/149,126, filed Oct. 15, 1999, and titled “Voltage Tunable Varactors And Tunable Devices Including Such Varactors”, discloses voltage tunable varactors that operate at room temperature and various devices that include such varactors. Commonly owned U.S. patent application Ser. No. 09/434,433, filed Nov. 4, 1999, and titled “Ferroelectric Varactor With Built-In DC Blocks” discloses voltage tunable varactors that include built-in DC blocking capacitors. These varactors operate at room temperatures to provide a tunable capacitance.
- There is a need for tunable filters that can operate at radio frequencies with reduced intermodulation products and at temperatures above those necessary for superconduction.
- This invention provides a voltage tunable filter comprising an input connection, an output connection, and a circuit branch electrically coupled to the input connection and the output connection and including a voltage tunable dielectric varactor electrically connected to an inductor. The voltage tunable filter can be one of a low-pass, high-pass, band-pass, or band-stop filter. The varactor can include built-in DC blocking capacitors.
- In the preferred embodiment, the voltage tunable dielectric varactor includes a substrate having a first dielectric constant and having a generally planar surface, a tunable dielectric layer positioned on the generally planar surface of the substrate, with the tunable dielectric layer having a second dielectric constant greater than the first dielectric constant, and first and second electrodes positioned on a surface of the tunable dielectric layer opposite the generally planar surface of the substrate. The first and second electrodes are separated to form a gap therebetween. A bias voltage applied to the electrodes changes the capacitance of the varactor between an input and an output thereof.
- The present invention provides radio frequency (RF) electrically tunable filters, tuned by dielectric voltage-variable capacitors. The filters can handle high power with lower intermodulation distortion.
- A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
- FIG. 1 is a top plan view of a planar voltage tunable varactor as described in U.S. patent application Ser. No. 09/149,126 that can be used in the preferred embodiment of the present invention;
- FIG. 2 is a cross-sectional view of the varactor of FIG. 1, taken along line2-2;
- FIGS. 3a, 3 b and 3 c are graphs illustrating the capacitance and loss tangent of voltage tunable varactors constructed in accordance with this invention at various operating frequencies and gap widths;
- FIG. 4 is a top view of a planar varactor assembly with built-in DC blocking capacitors as described in U.S. patent application Ser. No. 09/434,433;
- FIG. 5 is a cross sectional view of the varactor assembly of FIG. 4, taken along line5-5;
- FIG. 6 is a schematic diagram of the varactor of FIGS. 4 and 5;
- FIG. 7 is a schematic diagram of an example Chebyshev bass-pass filter constructed in accordance with this invention;
- FIG. 8 is a graph of the attenuation of the filter shown in FIG. 7 operated at various bias voltages on the varactors;
- FIG. 9 is a schematic diagram of a low pass filter constructed in accordance with this invention;
- FIG. 10 is a graph of the losses of the filter shown in FIG. 9 operated at various bias voltages on the varactor;
- FIG. 11 is a schematic diagram of a high pass filter constructed in accordance with this invention;
- FIG. 12 is a graph of the losses of the filter shown in FIG. 11 operated at various bias voltages on the varactors;
- FIG. 13 is a schematic diagram of a band stop filter constructed in accordance with this invention; and
- FIG. 14 is a graph of the losses of the filter shown in FIG. 13 operated at various bias voltages on the varactors.
- Referring to the drawings, FIGS. 1 and 2 are top and cross sectional views of a
varactor 10 as described in the above-mentioned U.S. patent application Ser. No. 09/149,126. Thevaractor 10 includes asubstrate 12 having a generally planartop surface 14. A tunabledielectric layer 16 is positioned adjacent to the top surface of the substrate. A pair ofmetal electrodes substrate 12 is comprised of a material having a relatively low permittivity such as MgO, Alumina, LaAlO3, Sapphire, or a ceramic. For the purposes of this invention, a low permittivity is a permittivity of less than about 30. Thetunable dielectric layer 16 is comprised of a material having a permittivity in a range from about 20 to about 2000, and having a tunability in the range from about 10% to about 80% at a bias voltage of about 10 V/μm. In the preferred embodiment this layer is preferably comprised of Barium-Strontium Titanate, BaxSr1-xTiO3 (BSTO), where x can range from zero to one, or BSTO-composite ceramics. Examples of such BSTO composites include, but are not limited to: BSTO-MgO, BSTO-MgAl2O4, BSTO-CaTiO3, BSTO-MgTiO3, BSTO-MgSrZrTiO6, and combinations thereof. The tunable layer in one preferred embodiment has a dielectric permittivity greater than 100 when subjected to typical DC bias voltages, for example, voltages ranging from about 5 volts to about 300 volts. Agap 22 of width g, is formed between theelectrodes - A
controllable voltage source 24 is connected bylines electrodes RF input 30 and anRF output 32. The RF input and output are connected toelectrodes - The varactors may use gap widths of less than 5-50 μm. The thickness of the dielectric layer ranges from about 0.1 μm to about 20 μm. A
sealant 34 is positioned within the gap and can be any non-conducting material with a high dielectric breakdown strength to allow the application of high voltage without arcing across the gap. In the preferred embodiment, the sealant can be epoxy or polyurethane. - The length of the gap L can be adjusted by changing the length of the
ends - The thickness of the tunable dielectric layer also has a strong effect on the Cmax/Cmin. The optimum thickness of the ferroelectric layers will be determined by the thickness at which the maximum Cmax/Cmin occurs. The ferroelectric layer of the varactor of FIGS. 1 and 2 can be comprised of a thin film, thick film, or bulk dielectric material such as Barium-Strontium Titanate, BaxSr1-xTiO3 (BSTO), BSTO and various oxides, or a BSTO composite with various dopant materials added. All of these materials exhibit a low loss tangent. For the purposes of this description, for operation at frequencies ranging from about 1.0 GHz to about 10 GHz, the loss tangent would range from about 0.0001 to about 0.001. For operation at frequencies ranging from about 10 GHz to about 20 GHz, the loss tangent would range from about 0.001 to about 0.01. For operation at frequencies ranging from about 20 GHz to about 30 GHz, the loss tangent would range from about 0.005 to about 0.02.
- The electrodes may be fabricated in any geometry or shape containing a gap of predetermined width. The required current for manipulation of the capacitance of the varactors disclosed in this invention is typically less than 1 μA. In the preferred embodiment, the electrode material is gold. However, other conductors such as copper, silver or aluminum, may also be used. Gold is resistant to corrosion and can be readily bonded to the RF input and output. Copper provides high conductivity, and would typically be coated with gold for bonding or nickel for soldering. The varactors of FIGS. 1 and 2 can be fabricated using bulk, thick film, and thin film techniques.
- FIGS. 1 and 2 show a voltage tunable planar varactor having a planar electrode with a predetermined gap distance on a single layer tunable bulk, thick film or thin film dielectric. The applied voltage produces an electric field across the gap of the tunable dielectric that produces an overall change in the capacitance of the varactor. The width of the gap can range from 5 to 50 μm depending on the performance requirements.
- Such varactors operate at room temperature and can have Q factors ranging from about 50 to about 10,000 when operated at frequencies ranging from about 1 GHz to about 40 GHz. The capacitance (in pF) and the loss factor (tan δ) of the varactors measured at 3, 10 and 20 GHz for gap distances of 10 and 20 μm are shown in FIGS. 3a, 3 b and 3 c. Based on the data shown in FIGS. 3a, 3 b and 3 c, the Q's for the varactors are approximately the following: 200 at 3 GHz, 80 at 10 GHz, 45-55 at 20 GHz. In comparison, typical Q's for GaAs semiconductor diode varactors are as follows: 175 at 2 GHz, 35 at 10 GHz and much less at even higher frequency. Therefore at frequencies greater than or equal to 10 GHz the varactors of this invention have much better Q factors.
- Referring to the drawings, FIGS. 4 and 5 are top and cross sectional views of a
varactor assembly 40 having built in DC blocking capacitors as described in U.S. patent application Ser. No. 09/434,433. Thevaractor assembly 40 includes asubstrate 42 having a generally planartop surface 44. Atunable dielectric layer 46 is positioned adjacent to the top surface of the substrate.Metal electrodes electrodes projections gap 56 on the surface of the tunable dielectric layer. The combination ofelectrodes dielectric layer 46 form atunable capacitor 84. The capacitance of the tunable capacitor can be changed by applying a bias voltage to theelectrodes - In the preferred embodiment, the
substrate 42 is comprised of a material having a relatively low permittivity such as MgO, Alumina, LaAlO3, Sapphire, or a ceramic. For the purposes of this description, a low permittivity is a permittivity of less than about 30. In the preferred embodiment, thetunable dielectric layer 16 is comprised of a material having a permittivity in a range from about 20 to about 2000, and having a tunability in the range from about 10% to about 80% at a bias voltage of about 10 V/μm. The tunable dielectric layer can be comprised of Barium-Strontium Titanate, BaxSr1-xTiO3 (BSTO), where x can range from zero to one, or BSTO-composite ceramics. Examples of such BSTO composites include, but are not limited to: BSTO-MgO, BSTO-MgAl2O4, BSTO-CaTiO3, BSTO-MgTiO3, BSTO-MgSrZrTiO6, and combinations thereof. The dielectric film of the dielectric capacitor may be deposited by screen printer, laser ablation, metal-organic solution deposition, sputtering, or chemical vapor deposition techniques. The tunable layer in one preferred embodiment has a dielectric permittivity greater than 100 when subjected to typical DC bias voltages, for example, voltages ranging from about 5 volts to about 300 volts. The gap width must be optimized to increase ratio of the maximum capacitance Cmax to the minimum capacitance Cmin (Cmax/Cmin) and increase the quality factor (Q) of the device. The width of this gap has the most influence on the varactor parameters. The optimal width, g, will be determined by the width at which the device has maximum Cmax/Cmin and minimal loss tangent. - A
controllable voltage source 58 is connected bylines electrodes substrate 42 and on opposite sides of thetunable dielectric layer 46.Electrode 48 extends over a portion of the top surface ofnon-tunable material 64.Electrode 68 is positioned adjacent a top surface ofnon-tunable layer 64 such that agap 70 is formed betweenelectrodes electrodes non-tunable layer 64 forms a first DC blocking capacitor 72. The varactor assembly also includes anRF input 80 and anRF output 82. - Electrode74 is positioned adjacent a top surface of
non-tunable layer 66 such that agap 76 is formed betweenelectrodes 50 and 74. The combination ofelectrodes 50 and 74 andnon-tunable layer 66 forms a secondDC blocking capacitor 78. The dielectric films of the DC blocking capacitors may be deposited by screen printer, laser ablation, metal-organic solution deposition, sputtering, or chemical vapor deposition techniques. - An
RF input 80 is connected toelectrode 68. AnRF output 82 is connected to electrode 74. The RF input and output are connected toelectrodes 68 and 74, respectively, by soldered or bonded connections. The non-tunabledielectric layers DC blocking capacitors 72 and 78, are comprised of a high dielectric constant material, such as a BSTO composite. TheDC blocking capacitors 72 and 78 are electrically connected in series with thetunable capacitor 84 to isolate the DC bias from the outside of thevaractor assembly 40. To increase the capacitance of the twoDC blocking capacitors 72 and 78 the electrodes have an interdigital arrangement as shown in FIG. 4. FIG. 6 is a schematic diagram of the varactor of FIGS. 4 and 5 showing the three capacitors formed by the structure. - In the preferred embodiments, the varactors may use gap widths of 5-50 μm. The thickness of the tunable dielectric layer ranges from about 0.1 μm to about 20 μm. A sealant can be inserted into the gaps to increase breakdown voltage. The sealant can be any non-conducting material with a high dielectric breakdown strength to allow the application of high voltage without arcing across the gap, for example, epoxy or polyurethane.
- This invention utilizes room temperature tunable dielectric the varactors such as those shown in FIGS. 1, 2,4 and 5 in an electronically tunable RF filter. The lump element filter in the present invention may be low-pass, high-pass, band-pass, or band-stop designed by Bessel, Butterworth, Chebyshev, Elliptical or other methods.
- FIG. 7 is a schematic diagram of a
band pass filter 100 constructed in accordance with this invention. This capacitor coupled LC filter circuit, which is commonly referred to as a capacitively coupled tank circuit, includes a plurality ofresonators resonator 102, comprising the parallel connection of capacitor C2 and inductor L1, is connected tonode 116 andinput connection point 110 andoutput connection point 114, and is coupled to inputconnection point 108 through capacitor C1. Similarly,resonator 104, comprising the parallel connection of capacitor C4 and inductor L2, is connected tonode 118 andinput connection point 110 andoutput connection point 114, and is coupled tonode 116 through capacitor C3.Resonator 106, comprising the parallel connection of capacitor C6 and inductor L3, is connected tonode 120 andinput connection point 110 andoutput connection point 114, and is coupled tonode 118 through capacitor C5. In addition,resonator 106 is coupled tooutput connection point 112 through capacitor C7. The filter is tuned by varactors C2, C4 and C6, which in the preferred embodiment are constructed in accordance with either FIGS. and 1 and 2 or FIGS. 4 and 5. Common connection points 110 and 114 may be connected to ground. - In the preferred embodiment, with zero bias voltage on the tunable capacitors, capacitors C1 and C7 are 5.6 pF, capacitors C3 and C5 are 0.48 pF, capacitors C2 and C6 are 8.0 pF, capacitor C4 is 13.1 pF, and inductors L1, L2 and L3 are 500 nH. The input and output of the filter are matched to 50 Ω. FIG. 8 is a
graph 122 of the attenuation of the filter shown in FIG. 7 wherein capacitors C2, C4 and C6 are voltage tunable varactors operated at various bias voltages.Curves TABLE I Varactor bias voltages. Curve C2 Bias C4 Bias C6 Bias 124 0 0 0 126 180 80 180 128 400 160 400 130 600 210 600 132 700 500 700 - FIG. 9 is a schematic diagram of a low pass filter constructed in accordance with this invention. In FIG. 9,
low pass filter 140 includes aninput connection point 142, andoutput connection point 144 and acommon connection point 146. AnRF source 148 supplies an RF signal to the filter. Resistor RS represents the filter input impedance. A load as represented by resistor RL is connected between theoutput connection point 144 and thecommon connection point 146. Inductors L4 and L5 are electrically connected in series betweeninput connection point 142 andoutput connection point 144. A tunable varactor as represented by capacitor C8 is connected between thecommon connection point 146 and anode 150 between inductors L4 and L5. - FIG. 10 is a graph of the losses of the filter shown in FIG. 9 operated at various bias voltages on the varactor. In the embodiment used to construct the graph of FIG. 10, RS=RL=50 Ω, L4=L5=217 nH, and C8=133.8 pF at zero bias.
Curves Curves - FIG. 11 is a schematic diagram of a high pass filter constructed in accordance with this invention. In FIG. 11,
high pass filter 160 includes an input connection point 162, andoutput connection point 164 and acommon connection point 166. AnRF source 168 supplies an RF signal to the filter. Resistor RS represents the input impedance of the filter. A load as represented by resistor RL is connected between theoutput connection point 164 and thecommon connection point 166. Tunable varactors as represented by capacitors C9 and C10 are electrically connected in series between input connection point 162 andoutput connection point 164. Inductor L6 is connected between thecommon connection point 166 and anode 170 between capacitors C9 and C10. - FIG. 12 is a graph of the losses of the filter shown in FIG. 11 operated at various bias voltages on the varactor. In the embodiment used to construct the graph of FIG. 10, RS RL=50 Ω, L6=52.6 nh, and C9=C=32.4 pF at zero bias.
Curves Curves - FIG. 13 is a schematic diagram of a
band stop filter 180 constructed in accordance with this invention. In FIG. 13,band stop filter 180 includes aninput connection point 182, andoutput connection point 184 and acommon connection point 186. AnRF source 188 supplies and RF signal to the filter. Resistor RS represents the input impedance of the filter. A load as represented by resistor RL is connected between theoutput connection point 184 and thecommon connection point 186. Afirst circuit branch 192 comprising the parallel connection of inductor L7 and a varactor represented by capacitor C11 is electrically connected betweeninput connection point 182 andnode 190. Asecond circuit branch 194 comprising the parallel connection of inductor L8 and a varactor represented by capacitor C12 is electrically connected betweenoutput connection point 184 andnode 190. Athird circuit branch 196 comprising the series connection of inductor L9 and a varactor represented by capacitor C13 is electrically connected betweencommon connection point 186 andnode 190. - FIG. 14 is a graph of the losses of the filter shown in FIG. 13 operated at various bias voltages on the varactors. In the embodiment used to construct the graph of FIG. 13, RS=RL=50 Ω, L7=L8=7.83 nH, L9=1457 nH, C11=C12=899 pF at zero bias voltage, and C13=4.83 pF at zero bias.
Curves Curves - The lumped element filter in the present invention may be designed by Bessel, Butterworth, Chebyshev, Elliptical or other methods. Examples of band-pass, low pass, high pass and band stop filters have been presented. Dielectric varactors with built-in DC blocks can be used in the filter as the tunable elements. By utilizing low loss (tan δ<0.02) dielectrics of predetermined dimensions, the varactors of FIGS. 1, 2,4 and 5 can operate at high levels at high frequencies, for example, greater than 3 GHz.
- The dielectric varactors of FIGS. 1, 2,4 and 5 operate at high speeds, with high Quality Factor (Q), high power handling, and more importantly low intermodulation distortion products. Filters using dielectric varactors have better performance than semiconductor diode-tuned filters, especially in the properties of high power handling, low intermodulation distortion, and the ability to cover capacitance ranges that are not possible with conventional varactors.
- In the preferred embodiment, varactors using dielectric materials can work at much higher capacitance values than conventional diode varactors. This allows the construction of compact electronically tunable filters using lumped element capacitors with performances that are not possible with conventional varactors. A low loss, highly tunable dielectric varactor with or without built-in DC blocks may be used in the present invention, the built-in DC block dielectric varactor may reduce DC block insertion loss, and make it easier to use in the filter design. In addition, the tunable dielectric varactors of this invention have increased RF power handling capability and reduced power consumption and cost.
- Accordingly the present invention, by utilizing dielectric varactors, provides high performance electrically tunable filters that operate in the RF frequency range. This invention has many practical applications and many other modifications of the disclosed devices may be obvious to those skilled in the art without departing from the spirit and scope of this invention. While the present invention has been described in terms of what are at present its preferred embodiments, various modifications of such embodiments can be made without departing from the scope of the invention, which is defined by the claims.
Claims (12)
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US09/457,943 US20020186099A1 (en) | 1998-12-11 | 1999-12-09 | Electrically tunable filters with dielectric varactors |
US10/979,001 US7145415B2 (en) | 1998-12-11 | 2004-11-01 | Electrically tunable filters with dielectric varactors |
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US11188898P | 1998-12-11 | 1998-12-11 | |
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- 1999-12-09 DE DE69916660T patent/DE69916660T2/en not_active Expired - Fee Related
- 1999-12-09 EA EA200100654A patent/EA200100654A1/en unknown
- 1999-12-09 AT AT99961959T patent/ATE265093T1/en not_active IP Right Cessation
- 1999-12-09 EP EP99961959A patent/EP1145362B1/en not_active Expired - Lifetime
- 1999-12-09 WO PCT/US1999/029230 patent/WO2000035042A1/en not_active Application Discontinuation
- 1999-12-09 JP JP2000587403A patent/JP2002532889A/en active Pending
- 1999-12-09 US US09/457,943 patent/US20020186099A1/en not_active Abandoned
- 1999-12-09 CN CN99814262A patent/CN1329762A/en active Pending
- 1999-12-09 AU AU18434/00A patent/AU1843400A/en not_active Abandoned
- 1999-12-09 CA CA002352166A patent/CA2352166A1/en not_active Abandoned
- 1999-12-09 KR KR1020017007172A patent/KR20010080727A/en not_active Application Discontinuation
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2004
- 2004-11-01 US US10/979,001 patent/US7145415B2/en not_active Expired - Lifetime
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US20070229716A1 (en) * | 2001-10-16 | 2007-10-04 | Kimitake Utsunomiya | Methods and apparatus for implementing a receiver on a monolithic integrated circuit |
US20070126937A1 (en) * | 2001-10-16 | 2007-06-07 | Kimitake Utsunomiya | Methods and apparatus for implementing a receiver on a monolithic integrated circuit |
US20070165143A1 (en) * | 2001-10-16 | 2007-07-19 | Kimitake Utsunomiya | Methods and apparatus for implementing a receiver on a monolithic integrated circuit |
US7333155B2 (en) | 2002-06-05 | 2008-02-19 | Rfstream Corporation | Quadratic video demodulation with baseband nyquist filter |
US20040095513A1 (en) * | 2002-06-05 | 2004-05-20 | Takatsugu Kamata | Quadratic video demodulation with baseband nyquist filter |
US20040224649A1 (en) * | 2003-02-05 | 2004-11-11 | Khosro Shamsaifar | Electronically tunable power amplifier tuner |
US7183880B2 (en) | 2003-07-18 | 2007-02-27 | Rfstream Corporation | Discrete inductor bank and LC filter |
US7719392B2 (en) | 2003-10-20 | 2010-05-18 | University Of Dayton | Ferroelectric varactors suitable for capacitive shunt switching |
US7692270B2 (en) | 2003-10-20 | 2010-04-06 | University Of Dayton | Ferroelectric varactors suitable for capacitive shunt switching |
US20070024400A1 (en) * | 2003-10-20 | 2007-02-01 | Guru Subramanyam | Ferroelectric varactors suitable for capacitive shunt switching |
US20070069264A1 (en) * | 2003-10-20 | 2007-03-29 | Guru Subramanyam | Ferroelectric varactors suitable for capacitive shunt switching and wireless sensing |
US20070176217A1 (en) * | 2003-10-20 | 2007-08-02 | University Of Dayton | Ferroelectric varactors suitable for capacitive shunt switching |
WO2006020542A3 (en) * | 2004-08-13 | 2007-05-18 | Paratek Microwave Inc | Method and apparatus with improved varactor quality factor |
WO2006020542A2 (en) * | 2004-08-13 | 2006-02-23 | Paratek Microwave Inc. | Method and apparatus with improved varactor quality factor |
US20060033593A1 (en) * | 2004-08-13 | 2006-02-16 | Qinghua Kang | Method and apparatus with improved varactor quality factor |
US20060208832A1 (en) * | 2005-03-11 | 2006-09-21 | Takatsuga Kamata | Radio frequency inductive-capacitive filter circuit topology |
WO2008042998A2 (en) * | 2006-10-05 | 2008-04-10 | University Of Dayton | Ferroelectric varactors suitable for capacitive shunt switching |
WO2008042998A3 (en) * | 2006-10-05 | 2008-06-19 | Univ Dayton | Ferroelectric varactors suitable for capacitive shunt switching |
US20100096678A1 (en) * | 2008-10-20 | 2010-04-22 | University Of Dayton | Nanostructured barium strontium titanate (bst) thin-film varactors on sapphire |
WO2010139562A1 (en) * | 2009-05-20 | 2010-12-09 | Unitron | Tv signal distribution filter having planar inductors |
US9000866B2 (en) | 2012-06-26 | 2015-04-07 | University Of Dayton | Varactor shunt switches with parallel capacitor architecture |
CN105210291A (en) * | 2013-03-15 | 2015-12-30 | 维斯普瑞公司 | Tunable filter systems, devices and method |
US20140285286A1 (en) * | 2013-03-15 | 2014-09-25 | Wispry, Inc. | Tunable filter systems, devices, and methods |
WO2014145662A2 (en) | 2013-03-15 | 2014-09-18 | Wispry, Inc. | Tunable filter systems, devices and method |
EP2974011A4 (en) * | 2013-03-15 | 2016-12-21 | Wispry Inc | Tunable filter systems, devices and methods |
US9559659B2 (en) * | 2013-03-15 | 2017-01-31 | Wispry, Inc. | Tunable filter systems, devices, and methods |
US20170244376A1 (en) * | 2013-03-15 | 2017-08-24 | Wispry, Inc. | Tunable filter systems, devices, and methods |
US10320357B2 (en) * | 2013-03-15 | 2019-06-11 | Wispry, Inc. | Electromagnetic tunable filter systems, devices, and methods in a wireless communication network for supporting multiple frequency bands |
US20190363691A1 (en) * | 2013-03-15 | 2019-11-28 | Wispry, Inc. | Electromagnetic tunable filter systems, devices, and methods in a wireless communication network for supporting multiple frequency bands |
US10911015B2 (en) * | 2013-03-15 | 2021-02-02 | Wispry, Inc. | Electromagnetic tunable filter systems, devices, and methods in a wireless communication network for supporting multiple frequency bands |
US9748916B2 (en) | 2013-07-29 | 2017-08-29 | Wispry, Inc. | Adaptive filter response systems and methods |
CN109643978A (en) * | 2016-08-19 | 2019-04-16 | 诺韦尔达公司 | Filter |
US20190356303A1 (en) * | 2016-08-19 | 2019-11-21 | Novelda As | Filter |
US10855253B2 (en) * | 2016-08-19 | 2020-12-01 | Novelda As | Filter |
Also Published As
Publication number | Publication date |
---|---|
DE69916660D1 (en) | 2004-05-27 |
US7145415B2 (en) | 2006-12-05 |
CN1329762A (en) | 2002-01-02 |
DE69916660T2 (en) | 2005-04-21 |
US20050088255A1 (en) | 2005-04-28 |
EP1145362B1 (en) | 2004-04-21 |
ATE265093T1 (en) | 2004-05-15 |
KR20010080727A (en) | 2001-08-22 |
EA200100654A1 (en) | 2001-12-24 |
EP1145362A1 (en) | 2001-10-17 |
WO2000035042A1 (en) | 2000-06-15 |
CA2352166A1 (en) | 2000-06-15 |
AU1843400A (en) | 2000-06-26 |
JP2002532889A (en) | 2002-10-02 |
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