A method for controlling and stabilizing in time, as temperature changes, the frequency of a signal generated by a controllable oscillator, said method comprising the steps of: - measuring the frequency of said signal generated by said controllable oscillator by using a first signal, whose duration is proportional to the length of a delay line comprising at least a first and a second delay line portions arranged in series and having a first and a second lengths, respectively; - applying a frequency correction to said signal generated by said controllable oscillator if the difference in frequency between said signal and the desired frequency value exceeds a predetermined threshold, said method being characterized by: - providing said first portion of said delay line 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 said second portion of said delay line by coupling said 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 said second gradient being greater than that of said first gradient; - selecting said second length of said second delay line portion in a manner such that the relation L 2 = (L 1 · ΔR 1) / abs (ΔR 2) is true, wherein ΔR 1 and ΔR 2 represent, respectively, a first and a second delay variations per Kelvin degree introduced by said first and said second line portions, and wherein said first delay variation (ΔR 1) is smaller, for each Kelvin degree, than the thermal expansion coefficient of said or another conductive material. - measuring the frequency of said signal generated by said controllable oscillator by using a first signal, whose duration is proportional to the length of a delay line comprising at least a first and a second delay line portions arranged in series and having a first and a second lengths, respectively; - applying a frequency correction to said signal generated by said controllable oscillator if the difference in frequency between said signal and the desired frequency value exceeds a predetermined threshold, said method being characterized by: - providing said first portion of said delay line 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 said second portion of said delay line by coupling said 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 said second gradient being greater than that of said first gradient; - selecting said second length of said second delay line portion in a manner such that the relation L 2 = (L 1 · ΔR 1) / abs (ΔR 2) is true, wherein ΔR 1 and ΔR 2 represent, respectively, a first and a second delay variations per Kelvin degree introduced by said first and said second line portions, and wherein said first delay variation (ΔR 1) is smaller, for each Kelvin degree, than the thermal expansion coefficient of said or another conductive material.