Aleksander Łabudziński’s scientific contributions

A method of and a circuit for radar signal compression according to the invention can be applied in radar systems, especially those generating and processing broadband radar pulses with constant amplitude and linear or nonlinear frequency modulation. In a composite radiolocation pulse composed of a definite number of subpulses with different carrier frequencies, signal compression can be accomplished with the use of analytical properties of signals matched to subpulses of the composite radar signal and storing them in a non-volatile memory block. Further, determination of an optimum low-pass representation of radar subpulses includes a stage of analog-digital conversion and a matched filtering stage in a bank of matched filters. Operation of each matched filter consists in calculation of two convolutions of the composite radar signal with analytic signals matched to subpulses.

The present invention relates to a method and an apparatus for reduction of the subpulses reciprocal intermodulation in a complex electromagnetic pulse and finds application in radar systems, in particular those generating and processing broadband radar pulses of constant amplitude with linear and nonlinear frequency modulation.

The mostly applicable radar signal is pulse signal with linear frequency modulation (LFM). The main feature such signal is time-bandwidth product (so called base) which is calculated as product of pulse duration and signal bandwidth. Theoretical peak to sidelobe level is achievable with time-bandwidth product value grater than 100. For time-bandwidth product smaller then 100 (i.e. short pulse duration or narrow deviation of FM modulation) peak-to-sidelobe level (PSL) and pulse compression coefficient are significantly reduced. Non-linear frequency modulated (NLFM) radar signal for small time-bandwidth product features better PSL and pulse compression coefficient. The NLFM signal synthesis algorithm and simulation results are presented in the paper. LFM and NLFM signals with small time-bandwidth product are compared and results are discussed in aspect of radar resolution improvement.

Przedmiotem wynalazku jest sposób i układ syntezy sygnału radiolokacyjnego z nieliniową modulacją częstotliwości znajdujący zastosowanie w systemach radiolokacyjnych. System formowania strefy wykrywania radaru trójwspółrzędnego wykorzystuje impulsy sondujące złożone z subimpulsów z liniową modulacją częstotliwości LFM+, LFM- oraz z nieliniową modulacją częstotliwości NLFM+, NLFM-. Liczba subimpulsów zależy od rodzaju i typu pracy radaru i może wynosić na przykład dla konkretnego radaru od 1 do 4. Z radarem emitującym sygnał złożony związana jest trudność separacji częstotliwości widm poszczególnych subimpulsów. Wzajemne przenikanie sąsiadujących widm może prowadzić do detekcji sygnału zakłócającego w sygnale użytecznym, co bezpośrednio przekłada się na otrzymanie fałszywych wykryć.

To meet the requirement of modern radar, a kind of NLFM signal is designed in this paper based on the stationary-phase concept and Kaiser window function. The algorithm to synthesize NLFM signal is presented. To achieve low autocorrelation sidelobe level without applying weighting function, Non-Linear Frequency Modulation (NLFM) signal has been investigated. Discussed algorithm cause Signal-to-Noise Reduction (SNR) gain, typically by 1 to 2 dB, in comparison with LFM signal with window tapering. (Radar signal synthesis with time sidelobes reduction).