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CST STUDIO SUITE™ 2006Application and Feature Tutorial

Filter SimulationF. Hirtenfelder

Filter TerminologySolver SelectionMeshing TechniquesAccuracyTuning HintsExamplesConclusions

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Filter TerminologyClassification of Filters

LP-Prototype

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Solver Selection

Time Domain (TD)

Eigenmode (E)Modal (Resonant Fields)Lossy/Lossless

Frequency Domain (FD)

General Purpose

Resonant: Fast S-parameter (MOR)

Resonant: S-Parameter, Fields (Modal Analysis)

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Solver Selection: TimeDomain

Extremly small variations of tuning elements: require small mesh steps and thus long run timesPBA helps greatly to keep number of mesh cells low,Resonances requires long run times, AR Filter settings critical

1h 52 min (2.7 GHz PC)

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Solver Selection: Resonant Fast S-Param. Robust and fast solver

for filters andhighly resonant structures

12 min (2.7 GHz PC)

Resonant Fast S-Parameter Solver Advantages: • supports PBA• lossy dielectrics• insensible to high mesh ratios, small mesh steps• handle S-parameters for port modes under cutoff (required for submodeling in CST DS)

1234

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Solver Selection: Eigenmode

f3f2f1fof4f5f6

K34= (f4-f1)(f6-f3)/K12= =(1767-1735)(1791-1708)/66= 40.24MHz

Terminology: Coupling Bandwidth

Even/Odd Mode Multi Eigenmode

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Accuracy: PBA

2. Tuning Step30 Lines/Lambda = 51000 cells TD (AR) Solver time: 256 sResonant (MOR) Solver 91 s

slight readjustedment of only one parameterby 0.0125mm!!

1. Adaptive mesh refinementof untuned filter

3. Increased mesh density to 50 Lines/lambda

Resonant (MOR) Solver 414 s

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Accuracy: Staircase

89.000 Cells. 2.5 min(1.7 GHz Laptop)

Mesh density was increased:Results did not converge to the PBA-results

384.000 Cells. 27 min

600.000 Cells. 46 min1.050.000 Cells. 1h 15 min

(all MOR Solver, 1.7 GHz Laptop) 5Mio , 2.5 h

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Convergence using different Mesh types and Solvers

Accuracy: Hexa vs. Tetra

1)

2)

1)1) TD -FD Show same curve

Refined mesh (convergend solution) 2)

3) Tetra

1) TD vs FD must showsame results

2) PBA (Hexa) showsconvergence very early.(Refinement doesn‘t changesolution anymore).3)Tetra converges towardshigher frequencies.

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Convergence check using Tetra Mesh3 adaptive points togenerate a refined meshaccording to the appearanceof the various modes!

Inital and final mesh after 5 passes

Accuracy: Hexa vs. Tetra

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Accuracy: Hexa vs. Tetra

Check of Groupdelay Hexa vs. Tetra Mesh

Shape of groupdelay practically identical between Hexa and Tetra mesh.Deviation of Tetra results due to facetting: the resonators appearsmaller in size and thus shifts groupdelay towards higher frequencies

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Filter Tuning: SubmodelsTuning of a Combline Filter (Cross coupling)

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Approximation equations used as initial values for an optimizationperformed in CST DESIGN STUDIO

Theory

Filter Tuning: Equiv. Circuits

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Filter Tuning: Group delayCoupling Bandwidth, Group delay

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Filter Tuning: Groupdelay, ExamplesTuning of a Dual Mode Filter Iris Coupled Cavity Filter

Hairpin Filter

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The Inverse Chirp-Z TransformationFilter Tuning: Inverse Chirp-Z

Mistuned Coupling K12 (between Resonator 1 and 2)

Mistuned 2nd Resonator

1st Resonator OK3rd Resonator

K12 increased

1

2

4 x x

2nd Resonator mistuned

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Filter: Conclusions

• CAD Modeler easy to use with respect to parameterization

• Various solver technologies available: TD, FD, E• Optimization and parameterization control via

complex post processing templates• Various meshing techniques available• Flexible link to circuit simulator CST-

DESIGN STUDIO including CST-MICRO WAVE STUDIO submodels

• Various tuning procedures available