The thesis describes studies of continuum, sporadic and pulsed radio emissions of objects of the Universe in decameter and meter wave ranges using a small-sized low-frequency radio telescope of the new generation. As an example of such radio telescope, a 25-element GURT radio telescope subarray was chosen.
At first, the parameters of the phased antenna array element and the entire subarray were carefully modelled and analyzed. Mathematical models of the GURT active antenna element and the GURT subarray were developed. Using these models allowed obtaining antennas noise and power performances which are impossible to measure or such measurements require unreasonably expensive resources. The models, unlike existing ones, take into account all sources of external and internal noise, the effect of the near ground surface, and the mutual coupling of the array elements. The models are based on the matrix theory of antenna arrays, the theory of noisy multiports and use the results of antenna computer simulations with software based on the method of moments. The results of modelling include frequency dependences of effective area, system sensitivity in terms of system equivalent flux density and sky noise dominance, the contribution of noise temperatures from various noise sources to the output signal in a wide frequency range, and for various main beam directions of the subarray. The adequacy of the developed mathematical models is confirmed with a comparison of modelling results and results of real active antenna and GURT subarray noise parameters measurements. The results of modelling prove that the developed subarray ensures the sky noise dominance of 6-10 dB for all beams, that completely satisfies the requirements for its application for radio astronomy observations and astrophysical studies. On the basis of sensitivity modelling results, there were estimated possibilities of radio astronomy observations of various types of emissions from cosmic radio sources. Many various observations with the GURT subarray and the single active antenna were carried out, which allowed registering active Sun (types II, III, IIIb, IV, U, drifting pairs), Jupiter (L- and S-bursts), galactic background and pulsar radio emissions in ultra-wide frequency range. Long-term observations of sky background noise have shown the high stability of the GURT subarray parameters. The observations of the active Sun made it possible to find features of sporadic solar radio emission that allow estimating parameters of the solar corona, acquiring statistics of solar drift pair bursts occurrence, as well as proving a good perspective of small-sized radio telescopes of new generation using for various studies. Such small instruments show their potential for long-term monitoring and gathering statistics of emission types occurrence. Jupiter’s decameter radio emission observations with GURT subarray were carried out in the frame of Juno space mission ground support. The S- and L-bursts were registered with the time resolution down to 10 ms. The observations of strongly polarized Jovian radio emission have shown the possibilities of polarized cosmic radio emission studies using the GURT active antenna subarray of two orthogonal linear polarizations. A survey of the strongest and nearest to the Earth pulsars was carried out with the GURT subarray. For the first time, the radio emission of 16 pulsars in the frequency range 30-70 MHz was registered using an antenna array of only 25 active antennas with integration time from 1 to 4 hours. A series of joint simultaneous pulsar observations in ultra-wide frequency range using UTR-2 radio telescope and GURT subarrays was carried out. Pulsar radio emission power flux densities and dispersion measures were determined for each pulsar. An observation technique for detecting the impact of ionospheric refraction on the pulsar flux density estimation was suggested and tested. The technique uses high flexibility of UTR-2 radio telescope and location of UTR-2 and GURT radio telescopes on the same observatory site. Two weekly observation sessions for pulsars B1133+16, B1508+55, and B1919+21 were carried out in order to register the variability of their flux densities and dispersion measures. The results have shown high variability of average visible pulsar flux density from day to day and stability of dispersion measure value during two weeks of observations with the accuracy of 0.006 pc/cm3. Continuum, sporadic, and pulsed radio emissions of objects of the Universe were studied using small low-frequency radio telescope of new generation.
