What impedance does a 1/4-wavelength transmission line present to an RF generator when the line is open at the far end?
Why A quarter-wavelength line acts as an impedance inverter: Zin = Z0 squared divided by ZL. With the far end open, ZL is essentially infinite, so Zin goes to nearly zero and the generator sees a very low impedance, like a short. In physical terms the open end forces a voltage maximum and current zero, and a quarter wave back along the line those conditions reverse to a current maximum and voltage minimum.
Watch out Very high impedance is what a quarter-wave line shows when the far end is shorted, and it is also what an open half-wave line (or any multiple of a half wave) repeats back to the input.
Quarter wave flips it: open far end looks shorted, shorted far end looks open. Half wave repeats what it sees.