Ok. I can describe what I use at 2-3GHz (not 35GHz, but maybe it still appies):
1>--------------------------<2
| Coupler |
3| ---------------- |4
| |
VarC<-- VarC<-------
| | | |
GND | GND |
| |
| |
Choke Choke
| |
--------------------------------------< DC Control Voltage
The coupler (with ports 1, 2, 3, 4) is a bi-directional coupler.
If the diode is a varacator (VarC as above), then this is a phase shifter where RF signal comes in from port 1 and output is port 2.
If diode is PIN (instead of VarC), then this is a VVA (Voltage Variable Attenuator).
It is called in general a reflective VVA (or phase shifter if used VarC), because signal comes in port 1, couples to port 4, then it will see the VarC with different C value according to the DC control, then the wave refelcts back to port 2.
Hence, the output signal is actually a reflected signal from port 4 and 3, but not a direct through signal from port 1. That is why it is called reflective. There are other type called absorptive, based on FET devices, and do not use a coupler.
The Choke is an inductor to isolate the DC control signal from the RF waves. usually a cap to ground is added to the choke for increased isolation.
You can go to SkyWorks Inc website (Alhpa industries):
**broken link removed**
and in the technical library->Application Notes, you will find tons of App Notes about PIN diods, Varactors, Phase shifters, VVAs, relfective, absorptive...etc. It is a nice read.
Now, I am not sure how much of this is relevant at 35GHz? I have no idea, but I guess the same (or similar) techniques apply...
Hope that helps...
Cheers...