Electrical – How to setup a simulation on QUCS for a RF differential source

Concerning the fact that Q dropped when you used an impedance matching network:

You used a simple L matching network consisting of just two components (a capacitor and an inductance) which both are completely determined by the input and output impedance of your situation.
This leaves you no parameter to control Q. You get whatever Q is a result of the component values you need for matching.

So I suppose what you need is a more sophisticated matching network containing at least three components (e.g. a T- or a Pi-network) that has another degree of freedom which allows you to control not only input and output impedance but also Q.

Since you are also asking for references I recommend very much the chapter about impedance matching and Smith charts in Chris Bowick, "RF Circuit Design". It explains and contains an example problem for impedance matching while also caring about Q.

The circuit simulator is solving for the steady-state initial condition before running the transient sim.

To get your desired behaviour you have to explicitly tell the simulator you want zero volts across the cap at t=0. To do this, double click on the part and set the initial voltage to zero - I've highlighted the line you need to change in the dialog below.