Products > Test Equipment
Agilent 8753ES A24 Microwave transfer switch substitute
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Joel_Dunsmore:
1: DC feed likely with 50 pF discoidal bypass capacitor
2: Bonding island to ground (just a gold brick).  Ground the resistor to the left that is connected to the main transmission line
3: Single layer capacitor, maybe 100 pf, used to bypass the bias-control lines to avoid leakage in them.
4: Pin Diode mounted ont top of a very large single-layer capacitor; the top of the capacitor is biased negative to turn on the pin diode. Bonding island 2 is biased positive to provide bias and voltages are set so the top of the Pin diode is 0 volts, that way no blocking capacitors are needed.
5: bonding island to the top of the cap, as the plating on the cap doesn't bond well
6&7: A little tuning stub, but it was not in the orginal design.  I guess the production engineer added them in case then needed to use them.  We used to use tuning ribbons but no one likes to have them in production.
inaxeon:
Brilliant. Thanks for typing that up.

I forgot to ask, either side of the GaAs switch, are those two blocks bypass capacitors?
Joel_Dunsmore:
yes, there's a total of something like 5 bypass on each line. In fact I think later other versions added a couple more as we found some leakage still occurred along the bias lines.
inaxeon:
I've plucked that diode and the results are... better...

Using the power-on default S11 measurement into an open connector on the front panel, the "before" was pretty ugly.

The "after" looks a lot better but still not like S22 which shows a flat 100% reflected, so perhaps the GaAs switch is damaged too.

I'll press on and make my switch and see how that goes...
inaxeon:
I pulled the switch out again and hooked up to my spectrum analyser/TG. I now can't see any measurable difference between port1/2 on either through or blocking states. Maybe pulling that diode did fix it. Maybe something else on port 1 is faulty. Argh!

More investigation needed...
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