Questions about RF ground plane and low frequency reflections
Microstrip and striplines were studied and characterized after solving Maxwell's equations in an infinite coaxial cable.
In that domain, if you treat frequency f as a fixed parameter, Maxwell's equations, provided voltage and current sources are purely sinusoidal, are solved in a closed form quite easy.
In a coaxial cable, the outer cylindrical conductor wraps the inner linear conductor.
Often, the outer conductor is called Reference Conductor or Ground conductor.

A stripline is derived from a coaxial cable where the outer conductor is opened and flattened to become a plane.
Often, the outer conductor is called Reference Plane or Ground Plane.

Reflections happen even when voltage or current sources are sine functions at a frequency 0.1 Hz.
To measure those reflections though you need conductors 10^9 km long.