The use of CAD tools in filter design for ...web.ift.uib.no/~jankoc/publ/nera/ims2002_2.pdf · The...

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The use of CAD tools in filterdesign for telecommunication

applicationsJ. Kocbach & K. Folgerø

June 3rd 2002

CAD tools in filter design - June 2002

Outline

• Nera Filter applications

• Why do we need CAD tools?

• Use of CAD tools in a typical filter design cycle– Combination with circuit models

– Important requirements for CAD tools

• Application Examples

• Summary

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Nera Filter applications

• Tunable filters:

– Trunk (2 - 15 GHz)

• Tuningless filters & diplexers

– Mobile Infrastructure (15 - 40 GHz)

– Broadband Wireless Access (~40 GHz)

– DVB-RCS (~14 GHz)


Why do we need CAD-tools?

• Generally: Predictable & cost-efficient design– reduce costly prototyping & total development time

• design cycles, time to market– remove uncertainties & risks in development projects

• need predictable design procedures– semi/full automatic design procedures

• directly from specifications -> physical dimensions– optimal integration with radio/antenna

• short filters, folded/cross coupled filters, etc.

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• Tuneable filters– decide filter tuning range => easier system planning– good initial design gives larger tuning range and/or

less loss

NL 290 Post Filter



• Tuningfree filters– fast & efficient design of frequency variants– Tolerance analysis using CAD tools:

• Can the filter be made tuningless?• Determine possible production methods

CityLink Iris filters

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Typical Filter Design Cycle

Filterspecifications

Realization of filterdimensions

Buildprototype(s)

Prototypemeasurements

Final product

Circuit modelcalculations

Tolerance analysis orTuning range analysis

CAD tool

CAD tool

Few iterations if:- reliable circuit models- good design methodology- reliable CAD tools

CAD tool





Buildprototype(s)


Final product



• Example case:– CityLink Filter @ 23 GHz– 560 MHz bandwidth– Tuningfree design - account for prod. tol.

• To be realized as machined Al iris filter– rounded corners, r = 1 mm.

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Buildprototype(s)


Final product



22.4 22.6 22.8 23 23.2 23.4 23.6 23.8 24 24.2-60

-50

-40

-30

-20

-10

0

f [GHz]

S-pa

ram

eter

s [d

B]

Insertion loss < 0.8 dB

Return loss > 20 dB

Rejection > 30 dB


22.4 22.6 22.8 23 23.2 23.4 23.6 23.8 24 24.2-60

-50

-40

-30

-20

-10

0

f [GHz]

S-pa

ram

eter

s [d

B]




Buildprototype(s)


Final product



Insertion loss < 0.8 dB

Return loss > 20 dB

Rejection > 30 dB

Temperature variations

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Buildprototype(s)


Final product



22.4 22.6 22.8 23 23.2 23.4 23.6 23.8 24 24.2-60

-50

-40

-30

-20

-10

0

f [GHz]

S-pa

ram

eter

s [d

B]

Production tolerances Insertion loss < 0.8 dB

Return loss > 20 dB

Rejection > 30 dB





Buildprototype(s)


Final product



Rin

Rout

M23

M13 M3,n

M12

• Use circuit model to determine– filter topology/filter order– filter bandwidth

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Buildprototype(s)


Final product



Rin

Rout

M23

M13 M3,n

M12

22.4 22.6 22.8 23 23.2 23.4 23.6 23.8 24 24.2-60

-50

-40

-30

-20

-10

0

f [GHz]

S-pa

ram

eter

s [d

B]

7th order

6th order

5th order





Buildprototype(s)


Final product



Rin

Rout

M23

M13 M3,n

M12

22.4 22.6 22.8 23 23.2 23.4 23.6 23.8 24 24.2-60

-50

-40

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-20

-10

0

f [GHz]

S-pa

ram

eter

s [d

B]

6th order

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Buildprototype(s)


Final product



Rin

Rout

M23

M13 M3,n

M12

• Apply CAD-tool• Our choice:

– Step-by-step method– Treat each coupling and resonator separately

• Alternatively: Optimization


Rin

Rout

M23

M13 M3,n

M12




Buildprototype(s)


Final product



1 2 3 4 5 6

-18

-16

-14

-12

-10

-8

-6

-4

SimulationCircuit model

Iteration number

S21

[dB

]

Coupling 1

S21 = -5.1 dB

6 full-wavesingle-frequencysimulations at f0with varying irisopening.

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Rin

Rout

M23

M13 M3,n

M12




Buildprototype(s)


Final product



6 7 8 9

-16

-14

-12

-10

-8

-6

-4 S imulationCircuit model

Iteration number

S21

[dB

]

Coupling 2

S21 = -16.4 dB


Rin

Rout

M23

M13 M3,n

M12




Buildprototype(s)


Final product



9 10 11-20.5

-20

-19.5

-19

-18.5

-18

-17.5

-17

-16.5

-16S imulationCircuit model

Iteration number

S21

[dB

]

Coupling 3

S21 = -19.9 dB

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Rin

Rout

M23

M13 M3,n

M12




Buildprototype(s)


Final product



• Apply this procedure to each coupling– This case: Total of 12 single-frequency simulations– Call EM simulator 12 times

• Calculate resonator lengths based onphase of reflection ( )( )

πλ

φφπ2

0212

1 grl −−=


22.4 22.6 22.8 23 23.2 23.4 23.6 23.8 24 24.2-60

-50

-40

-30

-20

-10

0

f [GHz]

S-pa

ram

eter

s [d

B]




Buildprototype(s)


Final product



Rin

Rout

M23

M13 M3,n

M12

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Buildprototype(s)


Final product



22.4 22.6 22.8 23 23.2 23.4 23.6 23.8 24 24.2-60

-50

-40

-30

-20

-10

0

f [GHz]

S-pa

ram

eter

s [d

B]

• Tolerance analysis:– All dimensions varied– Gaussian distribution (σ = 4 µ m) - based on experience





Buildprototype(s)


Final product



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Buildprototype(s)


Final product



Electrical and mechanicalmeasurements

22.4 22.6 22.8 23 23.2 23.4 23.6 23.8 24 24.2-60

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-40

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-20

-10

0

f [GHz]

S-pa

ram

eter

s [d

B]





Buildprototype(s)


Final product



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Important CAD tool requirements



Buildprototype(s)


Final product



CA

D tool

• Different types of tools required– Full 3D solvers

• required for complex structures– Mode matching / segmentation approach

• MoM / BIE / FE / FD etc.• required for fast solutions• combine with full 3D solver if possible

• General requirements:– reliable, accurate, fast


• Valued features– combine CAD tool with circuit models– perform tolerance analysis– parametric sweeps– possible to combine different tools– built-in design methodology– use ascii input files for automatic design cycles

• Tools applied at Nera:– WASP-NET, HFSS, WIND, FEST



Buildprototype(s)


Final product



CA

D tool

Important CAD tool requirements

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Realization procedure (typical)

• Step-by-step procedure. Each step:

Example: Cross coupled filter Substructure 1Substructure 2

Substructure 4

Substructure 3

tune

tune

tune

tune

• Global optimization only if necessary -often not required

• See Th-1C-4: Thursday 09.00

– Simple substructures of complete structure– Tune one or a few variables in each step– Calculate for one or a few frequency points– Automatic/semiautomatic if possible– Use circuit model as tuning goal if applicable


Cross coupled filter

• Fast and predictable design (1-2 hours)– step-by-step procedure– Matlab & Wasp-Net

• No global optimization necessary

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Large radii iris filter• Low cost

– tuningfree– 3.0 mm milling radius– 4.0 mm iris length

• Fast & predictable design; minutes– Step-by-step procedure applied– Matlab & Wasp-Net

• No global optimization necessary• Application: DVB/RCS satellite terminal


15.24 15.26 15.28 15.3 15.32 15.34 15.36 15.38 15.4 15.42-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

frequency (GHz)

S (d

B)

Tunable Post filter

• Flexible & reliable design procedure– Step-by-step procedure applied– Calling HFSS from Matlab

• No global optimization necessary• Filter tunable from 14.9 to 15.35 GHz• Application: Trunk product (NL290)

Designed at 15.35 GHzTuned to 15.32 GHz

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Metal Insert Diplexer

• Flexible & reliable design; ~ 12-24 hours– Step-by-step procedure applied; automatic– Matlab & Wasp-Net– Successive optimization runs

• few propagating modes included• Optimization goals for poles of individual filters


Metal Insert Diplexer

• Application: Broadband access product• Tuningfree

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Summary

• Design methods:– required to be reliable & predictable– possibly automatic or semi-automatic

• CAD tools:– reliable, predictable & flexible– different tools necessary:

• Mode matching / segmentation for speed• Full 3D for complex structures

– possible to combine with external programs– closely related to reliable circuit models

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