Coding and sounding: extremely low power sounder

Coding techniques permitted the development of low power ionospheric sounders and radar systems. The used waveforms are characterized, in general, by their autocorrelation functions with low level of secondary lobes. Sequences with linear frequency modulation have been used for a long time in bistatic sounders. PN sequences used in bistatic systems have been applied in monostatic systems for backscattering and vertical sounding. Complementary sequences such as Golay sequences and Barker sequences are currently used in impulse systems. These sequences present interesting characteristics but not ideal, either their correlation functions are not null outside the main peak, or these sequences need impulsive emissions, or both simultaneously. Sequences used in systems have to obey general rules that can be represented by algebraic approaches. These representations give new sequence definitions whose experimental results are given.