Hackers' Pub

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Andrew Zonenberg @azonenberg@ioc.exchange

6/20/2025, 2:46:28 AM

Public

I'm pretty happy with the top side Samtec ARF6 launch simulations now.

S11:
* Red: No cutout, -12 dB at 10 GHz, -7 at 20 GHz, -4.8 at 30 GHz
* Blue: Rectangular ground cutout the size of the pad, -22.5 at 10 GHz, -16.4 at 20 GHz, -11.7 at 30 GHz
* Green: 30um larger than the pad on all sides (1.06 x 0.41 mm), -30.5 at 10 GHz, -22 at 20, -15 at 30.

With the oversized cutout it's more than good enough for QSGMII and 25Gbase-R.

TDR:
* Red: No cutout, 64Ω Zdiff at the launch
* Yellow: Pad-sized cutout, 86Ω
* Orange: Oversized cutout, 94Ω

Sonnet EM solver S11 plot (see post text for discussion of data)

ngscopeclient TDR transform of the EM simulations

2D geometry view showing the oversized cutout under to the connector launch

3D current density view showing return currents in the ground plane flowing around the cutouts

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