We present fast tunable superconducting microwave resonators fabricated from
planar NbN on a sapphire substrate. The 3λ/4 wavelength resonators are
tuning fork shaped and tuned by passing a dc current which controls the kinetic
inductance of the tuning fork prongs. The λ/4 section from the open end
operates as an integrated impedance converter which creates a nearly perfect
short for microwave currents at the dc terminal coupling points, thus
preventing microwave energy leakage through the dc lines. We measure an
internal quality factor Qint​>105 over the entire tuning range. We
demonstrate a tuning range of >3% and tuning response times as short as 20
ns for the maximum achievable detuning. Due to the quasi-fractal design, the
resonators are resilient to magnetic fields of up to 0.5 T