  Time-varying networks, consisting of lumped elements, such as resistors,
capacitors, and inductors, actively modulated in time, have introduced a host
of novel wave phenomena and witnessed a remarkable development during recent
years. This paper investigates the scattering from a time varying capacitor and
how such a load can be fully reflectionless when the capacitance is suitably
modulated in time. We analytically derive the required temporal dependence of
the capacitance and show how in contrast to other techniques it avoids extreme
and negative values and, as a result, can be implemented in a feasible way,
when the capacitor is charged with a DC voltage source. We also derive from
first principles the energy balance of such a time-varying capacitor, proving
that the energy of an incoming pulse is transferred to the modulation source.
Our findings clarify scattering of waves from time-varying capacitors and open
up a new way to matching of broadband pulses.
