A method and a system are described for controlling and stabilizing in time, as temperature changes, the frequency of a signal generated by a controllable oscillator (3), the method includes the steps of: measuring the frequency of the signal generated by the controllable oscillator (3) by using a first signal, whose duration is proportional to the length of a delay line (5) includes at least a first (7) and a second (9) delay line portions arranged in series and having a first (L1) and a second (L2) lengths, respectively; applying a frequency correction to the signal generated by the controllable oscillator (3) if the difference in frequency between the signal and the desired frequency value exceeds a predetermined threshold; providing the first portion of the delay line (5) by coupling a conductive material to a first dielectric material having a first negative gradient of its dielectric constant as a function of temperature; providing the second portion (9) of the delay line (5) by coupling or another conductive material to a second dielectric material having a second negative gradient of its dielectric constant as a function of temperature, the absolute value of the second gradient being greater than that of the first gradient; selecting the second length (L2) of the second delay line portion (9) in a manner such that the relation L2=(L1·ΔR1)/abs(ΔR2) is true, wherein ΔR1 and ΔR2 represent, respectively, a first and a second delay variations introduced by the first (7) and the second (9) line portions, and wherein said first delay variation (ΔR1) is smaller, for each Kelvin degree, than the thermal expansion coefficient of or another conductive material.