Transformation of the phase structure of nanosecond radio signals while stroboscopic processing
The report considers the method of transforming the time scale of coherent microwave radio signals in the radio-impulse strobing circuit. The additional possibilities of the converter are investigated, which make it possible to expand the field of its application during phase measurements of short radio signals. We consider a linear mathematical model of a stroboscopic converter consisting of a multiplier of input and gating radio signals and a narrowband filter tuned to the difference frequency of the carriers. An asymptotic approach is used to the analysis of stroboscopic transformation systems of a time scale developed in the works of the authors. It is shown that the shift of the carrier frequency of the strobing radio pulse by the value of the first subharmonic of the repetition frequency makes it possible to transform the phase structure of the radio signal into modulation of the envelope without the use of additional phase-sensitive elements. This makes it possible to perform phase measurements at a low intermediate frequency by amplitude methods. Obtained asymptotic expressions show that the intrapulse phase modulation of a nanosecond signal can be measured by a compensation method not only by changing the phase of the carrier in the gate of the strobing radio pulse, but also by delaying the envelopes with respect to the high-frequency filling. It is noted that while switching of the radio pulse strobing circuit to the operation in the phase-sensitive mode, the harmonic of the intermediate frequency needs to synchronize not the clock speed of the system, but the frequency of the strobing radio pulse repetition. It is proposed to use the auto-shear scheme with the falling “slow” sawtooth voltage when forming the strobing moments to eliminate parasitic linear phase modulation, which distorts the envelope of the output signal of the converter in the phase-sensitive mode.
Estimate of sizes of small asteroids (cosmic bodies) by the method of stroboscopic radiolocation
Abstract Radiolocation methods of probing minor celestial bodies (asteroids) by the nanosecond pulses can be used for monitoring of near-Earth space with the purpose of identification of hazardous cosmic objects able to impact the Earth. Development of the methods that allow us to improve the accuracy of determining the asteroids size (i.e. whether it measures tens or hundreds meters in diameter) is important for correctly estimating the degree of damage which they can cause (either regional or global catastrophes, respectively). In this paper we suggest a novel method of estimating the sizes of the passive cosmic objects using the radiolocation probing by ultra-high-resolution nanosecond signals to obtain radar signatures. The modulation envelope of the reflected signal, which is a radar portrait of the cosmic object, is subjected to time scale transformation to carrier Doppler frequency by means of radioimpulse strobing. The shift of a strobe within the probing period will be performed by radial motion of the object which will allow us to forgo the special autoshift circuit used in the oscillographic technical equipment. The measured values of duration of radiolocation portrait can be used to estimate the mean radius of the object by using the average spatial length of the portrait. The method makes it possible to appraise the sizes of cosmic objects through their radiolocation portrait duration, with accuracy that is independent of the objects range.
Radar Observations of Earth-Approaching Asteroids
Long the province of supermarket tabloids, killer asteroids are actually worthy of serious study. A group at JPL finds them to be quite a remarkable rock collection.