Quasi-elliptic Microstrip Filters in K-Band Allen Chang Cornell University Advisor: Dr. Pearson SURE...
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Transcript of Quasi-elliptic Microstrip Filters in K-Band Allen Chang Cornell University Advisor: Dr. Pearson SURE...
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Quasi-elliptic Microstrip Filters in K-BandAllen ChangCornell UniversityAdvisor: Dr. PearsonSURE 2003
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OverviewNASA sponsored project: noise measurements in a specific frequency bandFront end filter needed for receiverFilter goals:
Low loss
High selectivity
Low complexity
Preliminary filter constructed by grad student Joel Simoneau
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BackgroundThree Common Types of Filters
Butterworth Chebychev Elliptical
None are particularly adequate
Proposed alternative: Quasi-elliptical filters
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Quasi-elliptic FiltersCombines features of elliptical and chebychev filtersAdvantages in selectivity over Butterworth and ChebychevDisadvantages in loss, and attenuation in comparison to Butterworth/ChebychevEasier to synthesize than elliptic
Ralph Levy proposed idea in 1976 , but wasnt fleshed out In recent years, Hong and Lancaster have explored this design at low microwave frequencies
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Filter TheoryModification of standard filter design
Transfer function realized through cross coupling
Middle and cross J-inverters interdependent
Generalized filter parameters Qe and Mxy can then be found
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Physical ImplementationMicrostrip formatDielectric sandwiched between conducting surfacesDesign etched or milled on top surfaceSupports quasi-TEM modeWhy microstrip?Compact, low cost, high volumeDrawbacks: lossy at high frequencies, low resonator Q factor
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Physical Implementation Our specifications:Conductor: Copper high conductivity, low lossDielectric: RT/Duroid 5880Note: 1 mil = 25 um
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Filter DesignOpen loop resonator design chosenDemonstration filter (N=6) fabricated:
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Demonstration Results
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Filter DesignSpacing between resonators dependent upon coupling configuration and open loop dimensionsThree primary coupling configurations:
Simulation software (Agilent-ADS) used to achieve desired coupling coefficient
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Filter DesignMiddle and cross coupling need to have opposite signs
Input/output tapping position also determined using simulation
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Open Loop LayoutFinal open loop filter layout at 24 Ghz
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Simulation Results:
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Alternative DesignFabrication problems with open loopHairpin design is a viable alternativeOperates on similar principlesHairpin Layout:
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Layout Comparison Standard chebychev parallel coupled filterUtilizes coupled input/output instead of tapOnly 2 half-wave resonators
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Performance Comparison
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Future WorkWays to decrease loss?Majority of losses stem from ohmic(metal) loss, which cant be helpedFocus on decreasing dielectric lossOne possibility: air dielectric filterSuspended on thin polyimide sheetWet etch process, gold conductor
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ConclusionsQuasi-elliptic filters can improve selectivity with minimal increase in fabrication complexityMetallic losses may dominate at high frequenciesApplications must be loss-tolerant
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AcknowledgementsDr. PearsonSURE coordinators Dr. Noneaker & Dr. XuJoel SimoneauVenkatesh SeetharamChris Tompkins