I don't know what HP's original layout looks like, but here's one possibility for the doubled-up diode clamps: Note that they're not directly in parallel -- they're separated by other stuff. If that other stuff is intentionally made to look like a segment of slightly higher impedance line (and therefore inductive), then the diode capacitance gets more or less absorbed into the T-line, rather than looking like a lumped capacitive load. That way, you can get substantially better protection without killing bandwidth or SWR.
Don't know if that was HP's reason, but I've used similar protection strategies in a lot of designs. It's hard to get good ESD withstand at mm-wave freqs without doing something like this.
-- Cheers
Tom
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On 11/1/2023 9:03 AM, Jared Cabot via groups.io wrote:
The diodes are there because that's what HP did. I would also like to know the exact reason they did that too. :) It seems to work, so I'm sure there's a good reason for that layout.
