Synthesis of Symmetric Sounding Sequences for Ekaterinburg Coherent Decameter Radar
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Radiophysics and Quantum Electronics, Vol. 62, No. 11, April, 2020 (Russian Original Vol. 62, No. 11, November, 2019)
SYNTHESIS OF SYMMETRIC SOUNDING SEQUENCES FOR EKATERINBURG COHERENT DECAMETER RADAR O. I. Berngardt,∗ K. V. Grkovich, and R. R. Fedorov
UDC 551.501.81
Optimal sounding sequences described by a pair of mutually symmetric Golomb rulers lasting from 12 to 18 pulses were synthesized within the generalization of the previously developed 13pulse sounding sequence of SuperDARN radars. These sequences are pairs of identical sequences that are mutually symmetric in time, are separated by a lag, and do not contain an additional pulse used earlier to measure the power profile of the scattered signal. The optimal subsequences are sought by exhaustive search over the class of optimal and nearly optimal Golomb rulers. The optimality criterion is provision of the maximum information content of the received signal in the sense of a high spectral resolution with minimum accumulation time, as well as the requirement of its efficiency for measuring the power profile of the scattered signal. The work demonstrated the potential efficiency of one of the constructed signals (16-element one) for spectral measurements using the Ekaterinburg coherent decameter radar.
1.
INTRODUCTION
Radio sounding is one of the main methods for the Earth’s ionosphere research. Short radio waves experience significant refraction in the ionosphere, due to which they have a high sensitivity to changes in ionospheric characteristics and to ionospheric irregularities with different scales and dynamics. Various tools are employed to study different-scale irregularities in this frequency range, including vertical and oblique sounding ionosondes (pulsed and chirped), radiosonde — direction finder systems, etc. The structure, dynamics, and velocities of small-scale irregularities are mainly studied by using pulsed backscatter radars, namely, partial reflection radars, coherent radars, and incoherent scatter radars. Currently, the largest network of backscatter radars of the same type is apparently the network of SuperDARN (Super Dual Auroral Radar Network) coherent radars or similar ones [1, 2]. Study of the dynamics, and especially velocities, of ionospheric irregularities in the short-wave range encounters certain difficulties. Typical ionospheric velocities are much lower than the speed of sound at the ionospheric altitudes and are of the order of tens or hundreds of meters per second. This makes it necessary to measure Doppler shifts with accuracy no worse than a few hertz. The use of simple radio pulses in such radars results in that spatial resolution becomes comparable with characteristic ionosphere scales. Therefore, most often the problem of increasing spatial resolution without loss of spectral resolution is solved by using complex signals with specially selected properties and respective methods for the receivedsignal processing to provide simultaneously a high spatial and a high spectral resolution. Among such complex signals, we mention multipu
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