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Design of Multilayer Balun for Balanced Mixers

using HFSS and Ansoft DesignerNikolay Ilkov – Synergy Microwave Research

Ansoft „Partners in Design“ WorkshopMunich, 8/11/2004



Synergy Microwave Research GmbHFounded in 2003 by Prof. Ulrich L. RohdeOffers R&D services in microwave and RF technology• RFIC and MMIC design in Si, SiGe and GaAs

• Modules on PCB, ceramic, LTCC• RF and Microwave measurements• Component development and modeling

Contact:Synergy Microwave Research GmbHPotsdamer Str. 18A, 14513 TeltowTel. 03328 351 771E-mail : [email protected]

Internet: www.synergymwavegmbh.com



B a

l u n

RF

Balun

LO

Balun

IF

There are two major challenges when designing a balanced mixer:

2. Designing the balun and passive matching circuit

1. Selection/design of the nonlinear elements



Balun Design Considerations

Technical Economic

Bandwidth

Matching

Loss

Symmetry

Size

Cost

Yield



The major design challenge for the balun is to minimizecoupling to the common mode.

BALUN+ +

-

In Differential Out

common mode

Odd (Differential) Mode Even (Common) Mode



0

0

IZ=0Ohm

PNUM=1RZ=50Ohm Port1

IZ=0Ohm


IZ=0Ohm

PNUM=3RZ=50OhmPort3

P=length

W=width

P=length

W=width

Differential

+-

Single Ended

The performance of the Marchand balun is less sensitive to low even modeimpedance than many other balun configurations.



0

0

IZ=0Ohm


IZ=0Ohm


IZ=0Ohm

PNUM=3RZ=50OhmPort3

P=length

W=width

P=length

W=width

λ /4 λ /4

Zoe2=Zse *Zd /2

Even, Zin = 8Even, Zin = 8 Odd, Zin ˜ 50?



• A practical implementation requires bent coupled lines inorder to reduce size.

• Microstrip to stripline transitions may cause non-idealbehavior

• Finite ground size and via connections between striplinegrounds may be critical to performance.

Analytic estimates are useful for theinitial design. However….

Integration of circuit and full-wave models must be efficientlycombined for design and verification.



1. Copper thickness is comparable to the gap between coupled lines.

Other issues that are not easilyhandled by the circuit simulator

2. Lack of circuit models for inhomogeneous stripline.

copperε r1

εr2

εr1



Designer circuit model

Comparison of Circuit model and transmission line model based on 2-Dfull-wave port solution

I n s e r t i o n L o s s

R e t ur nL o s s

Freq (GHz)

Transmission linemodel from HFSS



Using the dynamic link the exact trace width and length can be

easily optimized

00

0

IZ=0Ohm

PNUM=1RZ=50Ohm

IZ=0Ohm

PNUM=2RZ=50Ohm

IZ=0Ohm

PNUM=3RZ=50Ohm

WavePort1:T1

WavePort1:T2

WavePort2:T1

WavePort2:T2

WavePort1:T1

WavePort1:T2

WavePort2:T1

WavePort2:T2

WavePort1 WavePort2



Optimisation result. The ground and the feeds are ideal.



HFSS model of the module edge. The antipad size and the

stripline width are optimized for good return loss



Optimized HFSS model of the module edge together with

the solder pad

MS return loss

SL return loss



HFSS model of the differential port transition



HFSS model of the single-ended port transition



More realistic Designer simulation including the feeds and the via

IZ=0Ohm

PNUM=2RZ=50Ohm

IZ=0Ohm

PNUM=3RZ=50Ohm

IZ=0Ohm

PNUM=1RZ=50Ohm

Port3

Port4 Port5

Port6

M S

S L

M S

S L

WavePort1:T1

WavePort1:T2

WavePort2:T1

WavePort2:T2

WavePort1:T1

WavePort1:T2

WavePort2:T1

WavePort2:T2

M

S

S L

Coup1:T1

Coup1:T2

Coup2:T1

Coup2:T2

SingleLine

Coup1:T1

Coup1:T2

Coup2:T1

Coup2:T2

U n c o u p: T 1

U n c o u p: T 2

1

2

3



More realistic Designer simulation including the feeds and the viabut the coupler is not folded.

Full 3D

Designer

(no bends)

Diff to commonmodeconversion



HFSS broadside-coupled bend modelDifferential S-parameters

R e t ur nL o s s

I n s e r t i o n

L o s s



Complete balun model in Designer

IZ=0Ohm

PNUM=2RZ=50Ohm

IZ=0Ohm

PNUM=3RZ=50Ohm

IZ=0Ohm

PNUM=1RZ=50Ohm

Port3

Port4 Port5

Port6

WavePort1:T1

WavePort1:T2

WavePort2:T1

WavePort2:T2

WavePort1:T1

WavePort1:T2

WavePort2:T1

WavePort2:T2

C o u p 1 : T 1

C o u p 1 : T 2

C o u p 2 : T 1

C o u p 2 : T 2

S i n g l e L i n e

Coup1:T1

Coup1:T2

Coup2:T1

Coup2:T2

U n

c o u p: T 1

U n

c o u p: T 2

123

Port1:T1

Port1:T2P

o r t 2 : T

1

P o r t 2 : T

2P or t 1 : T 1

P or t 1 : T 2

Port2:T1

Port2:T2

W a v e

P o r t 1 : T

1

W a v e

P o r t 1 : T

2

W a v e

P o r t 2 : T

1

W a v e

P o r t 2 : T

2

W a v e

P o r t 1 : T

1

W a v e

P o r t 1 : T

2

W a v e

P o r t 2 : T

1

W a v e

P o r t 2 : T

2 P o r t 1 : T

1

P o r t 1 : T

2

P o r t 2 : T 1

P o r t 2 : T 2

P o r t 1 : T 1

P o r t 1 : T 2P

or t 2 : T 1

P or t 2 : T 2

WavePort1:T1

WavePort1:T2

WavePort2:T1

WavePort2:T2

WavePort1:T1

WavePort1:T2

WavePort2:T1

WavePort2:T2

P or t 1 : T 1

P or t 1 : T 2

Port2:T1

Port2:T2

Port1:T1

Port1:T2P

o r t 2 : T 1

P o r t 2 : T 2

W av eP

or t 1 : T 1

W av eP

or t 1 : T 2

W av eP

or t 2 : T 1

W av eP

or t 2 : T 2

W a v e P o r t 1 : T

1

W a v e

P o r t 1 : T

2

W a v e

P o r t 2 : T

1


2

P o r t 1 : T

1

P o r t 1 : T

2

P o r t 2 : T 1

P o r t 2 : T 2

P o r t 1 : T 1

P o r t 1 : T 2P

or t 2 : T 1

P or t 2 : T 2

WavePort1:T1

WavePort1:T2

WavePort2:T1

WavePort2:T2

Port1:T1

Port1:T2P

o r t 2 : T

1

P o r t 2 : T

2 W a v e

P o r t 1 : T

1

W a v e

P o r t 1 : T

2

W a v e

P o r t 2 : T

1


2 P o r t 1 : T

1

P o r t 1 : T

2

P o r t 2 : T 1

P o r t 2 : T 2

W a v e P o r t 1 : T 1

W a v e P o r t 1 : T 2

W a v e P o r t 2 : T 1

W a v e P o r t 2 : T 2

WavePort1:T1

WavePort1:T2

WavePort2:T1

WavePort2:T2

P or t 1 : T 1

P or t 1 : T 2

Port2:T1

Port2:T2

W a v e

P o r t 1 : T

1

W a v e

P o r t 1 : T

2

W a v e

P o r t 2 : T

1


2

P o r t 1 : T 1

P o r t 1 : T 2P

or t 2 : T 1

P or t 2 : T 2

W a v e P o r t 1 : T 1

W a v e P o r t 1 : T 2

W a v e P o r t 2 : T 1

W a v e P o r t 2 : T 2

M S

S L

M S

S L

M S

S L

The same HFSS Modes are reusedwithin the dynamic link



Designer model performance vs. HFSS simulation (full)

Designer



Complete Marchand balun in HFSS



Possible explanation for the matching discrepancy



Complete Marchand balun in HFSSStraightforward solution of the problem

The HFSS editor is very slow for complicated drawings

2h 20min to solve on 2.8GHz Xeon

Marchand balun in Designer using direct link to HFSS

Need 3 to 15min to solve depending on the parameter

No „debugging“ possibilities – easy to make mistakes

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