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Subject and Purpose. Designers of the research radars intended for detecting manifestations of biological activity of living organisms may be interested in the noise characteristics shown by their oscillators at offsets about 10–2 Hz or even 10–3Hz from the carrier frequency. Unfortunately, the producing companies do not practice regular information on noise performance of their products at frequencies below 1 Hz. The present authors have set the goal of deriving an analytical expression for the spectral density of flicker noise which should allow radar engineers estimating the probable noise performance of low-noise oscillators over any frequency range. Methods and Methodology. A great number of writers considering spectral properties of flicker noise tend to support the assertion that its spectral density increases continuously with a decrease in frequency, following the power law 1/f. Meanwhile, the present authors assume availability of a certain frequencyfmbelow which the spectral density should most likely remain unchanged, even to as low as zero frequency. Also, there is a range of frequencies above which the spectral density of flicker noise remains constant and the total spectral density is determined solely by thermal noise. Results.The spectral density of noise follows the power law 1/f throughout the range fromfm and up to the point where thermal noise starts to overbalance the flicker noise. The authors have proposed an approximating function to describe the behavior of the averaged spectral density of noise from the oscillator within the entire frequency range. Conclusions. The results obtained shall allow radio system designers to make estimates of the probable noise performance of low-noise oscillators in any frequency range, using only known reference data provided by the manufacturer.