Using HFSS successfully at 77GHz Kate Moore Communications Sensors - - PowerPoint PPT Presentation

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using hfss successfully at 77ghz
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Using HFSS successfully at 77GHz Kate Moore Communications Sensors - - PowerPoint PPT Presentation

Aug 13, 2023 204 likes •449 views

Using HFSS successfully at 77GHz Kate Moore Communications Sensors Information Systems Contract R&D | Consultancy Specialist Products ROKE Presentation Title Using HFSS successfully at 77GHz Data sheets give you the dielectric

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Contract R&D | Consultancy Communications Sensors Information Systems Specialist Products

Kate Moore

Using HFSS successfully at 77GHz

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ROKE Presentation Title

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Using HFSS successfully at 77GHz

  • Data sheets give you the dielectric constant and

the loss tangent Or do they?

  • The materials properties are rarely measured at

high frequencies so the user must measure it themselves.

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ROKE Presentation Title

Material Properties

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Design

a resonant structure…

Ø outer Ø inner Track width Gap1 Gap2

Manufacture

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ROKE Presentation Title

Material Properties

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Measure

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ROKE Presentation Title

Material Properties

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Compare

with HFSS predictions: vary εr and tanδ until the measured results overlay the predictions

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75 76 77 78 79 80 81 82 83 84 85 S21 (dB) Frequency (GHz)

Resonant Rings: HFSS comparison 2

Ring 4 HFSS: Er=3.11 tand=0.009 straight sides

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ROKE Presentation Title

Track shape and profile

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Using HFSS successfully at 77GHz

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ROKE Presentation Title

Track shaping and cross section

  • The tracks are not perfect shapes
  • At these frequencies it makes a difference

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ROKE Presentation Title

Track shaping and cross section

  • HFSS allows you to change the profile of

the tracks easily

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ROKE Presentation Title

Track shaping and cross section

  • This shaping makes a difference

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ROKE Presentation Title

Bond Wires

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Using HFSS successfully at 77GHz

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ROKE Presentation Title

Bond Wires

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HFSS models of bondwires Real bondwires

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ROKE Presentation Title

Bond Wires

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  • HFSS predictions for an identical circuit with different bondwires

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0.00 Y1

Ansoft LLC LO Match1

Return Loss plot loss for different bondwire

ANSOFT

Curve Info Bondw ire 3 Bondw ire 2 Bondw ire 1

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ROKE Presentation Title

Ports, complex and otherwise

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Using HFSS successfully at 77GHz

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ROKE Presentation Title

Matching to ports

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  • Bondwire

Typical port measurement of a 77GHz device Matching to the port needs to include

  • Port impedance
  • Matching network (stub)
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ROKE Presentation Title

Complex ports – a bit quirky

  • Positive S parameters!
  • Positive S-parameters are possible if using

complex ports. The fields in the model are all correct but the return loss looks scary. It is due to the maths involved in normalising the ports.

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Smith Plot 1

What are you matching to? Port impedance from datasheet = 29 -75j Tune the stub to give a good match. What is the impedance of the circuit with the stub? 29-75j Which will not give a good match in real life. You must manually set the port to 29 + 75j

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ROKE Presentation Title

Matching to ports

To get around the positive s parameters: Divide the port into two parts:

  • 1. A resistive port corresponding to the

real part of the port impedance. i.e. 29 2.A reactive section in series corresponding to the port reactance i.e. 0.0273pF

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Lumped ports vs waveports

Lumped ports easy and small Can fit nicely on the end of a bond wire.

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Lumped ports

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Simple port at the end

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dielectric is 0.1mm thick A simple port should be

  • fine. Shouldn’t it?
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ROKE Presentation Title

Lumped ports

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The port may need to be

  • thinner. Comparing the

input impedance shows a significant difference. Which is correct? Lumped ports are not invisible they have dimensions and therefore parasitic L and C

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ROKE Presentation Title

Lumped ports

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L can be reduced by moving the ground plane up towards the track, shortening the port. Or use a wave port

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ROKE Presentation Title

Tolerance analysis

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Optimetrics

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ROKE Presentation Title

Optimetrics

  • PCB manufacturing accuracy is critical. Optimetrics can be used effectively

with parametric sweeps show the effects of over and under etching.

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Curve Info Ideal w ith C Under 10 Under 10 C Under 20 Under 20 C

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ROKE Presentation Title

Conclusions

  • HFSS can be used at every step when designing at

77GHz.

  • Initial designs
  • Validation of measured material properties
  • Further iteration with optimised material values
  • Analysis of manufacturing tolerances
  • However, you must be careful because effects which can

happily be ignored at lower frequencies are critical at mm waves

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ANSOFT Curve Info Ideal w ith C Under 10 Under 10 C Under 20 Under 20 C
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Contract R&D | Consultancy Communications Sensors Information Systems Specialist Products

Kate Moore

Using HFSS successfully at 77GHz