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If I can understand correct what you say, although the information you provide is not clear. The diodes must be the Varicaps ( I hope), then for any Phase shifter configuration you will use , u need to apply a reverse bias voltage across the diode from a high impedance (at your frequency of operation) path and most people use a bias Tee for that.
The 2nd thing that comes to my mind is : If you want a certain phase shift at a certain voltage and because of the parasitics of the circuits you are not sure you can obtain the exact value, you can put in parallel with your diode an open stub (that is a Capacitor) and when you test your circuit by reducing the length of the stub (decrease the capacitance) you can adjust it to your specs.
If you become more specific with your problem maybe I can have some more information for you.
Hi, The issue are these>.. I used a PIN diode tomake a phase shifter obtaining a 90 degrees phase shift.Now I have been told by my supervisor to tune using stubs. I have read in Pozar and Fooks how to do it.But I am thinking about it in this way. Since Double stubs tuning is used when the load (PIN diode)changes impedance how will i be able to implement this?