FilterDesign and HFSS HO[1]

Filter Design and Ansoft Tools

1-1ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved.

Anders EdquistField Application Engineer

Introduction

Courtesy of Microdata Telecom Innovation

1-2ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved.ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved.

Courtesy of Powerwave Technologies

Courtesy of Powerwave Technologies

Introduction - Traditional Filter Synthesis

…The majority of modern microwave filters are designed by using the insertion-loss method, whereby the amplitude response of the filter is approximated by using network synthesis techniques that have been extended to accommodate microwave distributed circuit elements. A general four-step procedure is followed: determination of filter specifications, design of a low-pass prototype filter, scaling and transforming the filter , and implementation (conversion of lumped elements to distributed elements)…

LP


A group of traditional filter designers…

BP

Introduction - Prototype Filter Networks

- M - M

M


⋅=⋅=

12

21

iMjv

iMjv

ωω

v1

-L0-L0

L0 L0 v2i1 i2

M

MK ω=

kLMK 0ωω ==

M M M M

R1 R2

M01M12

M13

M23 M34

C2 C3C1 L0L0 L0

v1 v2i0 i1 i2 i3 i4

⋅= 1011 iMjv ω

Introduction - Prototype Filter Networks


iKu ⋅⋅= 0Ljω

( )( )

( )

⋅

−−

−=

−

−

−

4

3

2

1

0

34

341

0032313

231

00212

13121

00101

01

0

2

1

0000

0

00

0

0000

0

0

0

i

i

i

i

i

k

kjQkk

kjQk

kkjQk

k

Lj

v

v

ωδωδ

ωδω

( )( )( )( )( )( )

⋅=⋅+⋅−+⋅=

⋅+⋅−+⋅=

⋅+⋅−+⋅=

⋅=

−

−

−

4342

43431

0030223

32321

0020112

21211

0010001

1011

0

0

0

iMjv

iMjijQLjiMj

iMjijQLjiMj

iMjijQLjiMj

iMjv

ωωωδωωωωδωωωωδωω

ω

2

20

0 1ωωδ i

i −=

Introduction – The Coupling Matrix

R1 R2

M01M12

M13

M23 M34

C2 C3C1 L0L0 L0

v1 v2i0 i1 i2 i3 i4

iKu ⋅⋅= Ljω

2

20

0 1ωωδ i

i −=


( )( )

( )

−

= −

00000

01000

00100

00010

00000

0000

0

00

0

0000

10

34

34032313

230212

13120101

01

jQ

k

kkk

kk

kkk

k

ωδωδ

ωδK

Resonant frequency

Coupling coefficients

Q-values

Coupling Matrix

iKu ⋅⋅= 0Ljω

Introduction – Modern Filter Synthesis (example)

Output from synthesis tool

Is the Coupling Matrix


Courtesy of Guided Wave Technology

[1] R.J. Cameron, "Advanced coupling matrix synthesis techniques for microwave filters", IEEE Trans. Microwave Theory Tech., vol 51, pp. 1-10, Jan 2003.

[2] R.J. Cameron, "General coupling matrix synthesis methods for Chebyshev filtering functions", IEEE Trans. Microwave Theory Tech., vol 47, pp. 433-442, Apr 1999.

[3] A.E Atia and A.E. Williams, "New types of bandpass filters for satellite transponders", "COMSAT Tech. Rev., vol 1, no. 1, pp. 21-43, Fall 1971.

[4] Cameron, Kudsia, Mansour, "Microwave Filters for Communication Systems", Wiley-Interscience, 2007

[5] G. Macchiarella, S.C.D'Oro, "Design of Generalized Comb Filters With Asymmetric Transmission Zeroes Using Arbitrary Cascaded Triplet and Quadruplet Sections",

28th EUMC, Amsterdam 1998, pp. 179-183.

System Analysis

A prototype filter network based on the synthesised coupling matrix is easy to build

for use as a building block in a system simulation


The filters can be optimised based on the cascaded system performance.

System Analysis – Optimisation


Filter Realisation – Coupling Extraction

The key to the realisation of a synthesised prototype network:

– How to extract the mutual couplings between resonators of an arbitrary 3D geometry?


Design variables

v.s

Coupling coefficients?

Generalized bandpass filter circuit with admittance inverters

J01 J12 J23 Jn,n+1

GA GB

B1(ω)

Coupling coefficients can be calculated from (MYJ) External Q-values can be calculated from (Ness)

B2(ω) Bn(ω)

Coupling Extraction – Theory


[1] G.L. Matthaei, L. Young and E.M.T. Jones, Microwave Filters, Impedance-Matching Networks and Coupling Structures. New York: McGraw-Hill, 1964

[2] John B. Ness, A Unified Approach to the Design, Measurement, and Tuning of Coupled-Resonator Filters. IEEE Transactions on Microwave Theory and Techniques, vol 46, No 4, April 1998

( )

( )ω

ω

ωω

∂∂∠−=Γ

⋅Γ=

11

00

4

S

Q

d

de

020

1

11

1,1,

ff

jj

n

jjj

jjjj

df

dBfb

bb

Jk

=

−

=+

++

⋅=

=

Place lumped ports at every resonator1

Coupling Extraction – Implementation


Y11+Y12 Y22+Y12

J = -Y12-Y12

Y11 Y22

020

1

11

1,1,

ff

jj

n

jjj

jjjj

df

dBfb

bb

Jk

=

−

=+

++

⋅=

=

))((

)(

,

,,

jjj

jiji

Yimderivb

YimJ

=

=

Coupling Extraction – Port Re-normalisation

Port 1

(Zp = 50 Ω)

Port 2

(Zp = 50 Ω)

Port 3

(Zp = 50 Ω)Example:

Q = R / ω L

f0=1GHz

L = 1 nH

Q = 3000

R 3000 *2pi

R = 50 ohm

Q 50/2pi


Znorm = 1010 Ω(open)

Znorm = 10-10 Ω(short)

Port 1

(Zp = 50 Ω)

(open)

S11

Q 50/2pi

(HFSS > Results > Output Variables)

dBdB

Create Output Variables2

Coupling Extraction – Implementation


df

dB

df

dBBk jjii

jijiBW,,

,,, 2 ⋅⋅=

( )2

00 fQ d

e

⋅⋅Γ= πω

Coupling Extraction

Extracted couplings

Design variables

Extract Couplings for a given set of

Design variables3

(Analytical derivatives*)


*) The estimated aperture heights from a single extraction using Analytical Derivatives and

“Report Tuning” resulted in couplings within approx 5% from synthesis

Coupling Optimisation

Optimise all couplings simultaneously4


If making variants of the filter, getting the “designs curves” it’s

probably more preferable to run a parametric sweep rather than

multiple optimisations.

+

Verification – Virtual Tuning


oDynamic Link between Ansoft Designer and HFSS

oPlace capacitors at resonator ports

oInterpolate or Solve missing solutions

Good correspondence with synthesis

apart from at the transmission zeros.

WHY ???

HFSS

synthesis

Coupling Extraction – Parasitic Couplings


Main couplings Parasitic couplings

How large impact does the parasitic

couplings have on the ideal synthesised

response?

Port Tuning

Modify the prototype network built from synthesis and include the spurious coupling


Modify the prototype network built from synthesis and include the spurious coupling

Port Tuning


HFSS

(synthesis)

Synthesis

with parasitics

Summary

• A prototype filter network was built in Ansoft Designer based on a

synthesised coupling matrix and used in a system simulation.

• Based on the system simulations, a modified coupling matrix was retrieved.

• An efficient method of coupling extraction was implemented in HFSS for the

realisation of the coupling matrix.


realisation of the coupling matrix.

• The results from HFSS was dynamically linked into Ansoft Designer and the

filter was ”virtually tuned”.

• It was shown that parasitic couplings can have huge impact on the filter

performance.– The method for coupling extraction makes it possible to calculate these parasitics. Therefore, it is possible to

account for parasitics in an early stage of the design.

Thank You!


Thank You!

FilterDesign and HFSS HO[1]

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