High Freedom Parameterized FM (HFPFM) Code: Model, Correlation Function, and Advantages

The design of radar waveform represents a key factor to rule radar performance and has received considerable attention for several decades. The ideal phase-coded waveforms have the advantages of a parameterized coding structure. However, they suffer from the high spectral sidelobes due to the instantaneous phase change, and this issue has precluded their widespread use in high-power systems. To this end, recently developed polyphase-coded FM (PCFM) waveforms can promise a continuous phase function, whereas the spectral range is controlled by the frequency template error metric, which will increase the design complexity. Compared to the ideal phase code and PCFM waveforms, nonlinear-frequency-modulated waveforms can precisely define aggregate spectral content by easily setting the range of instantaneous frequency function and have shown great potential in the real synthetic aperture radars. However, they do not have a parameterized coding structure, which impedes their further development. To this end, this article introduces a high-freedom-parameterized-FM-coded waveform with a constant envelope, which has many advantages compared with the previous waveforms, e.g., parameterized coding structure, high design freedom, precise control for spectral range, lower range straddling loss, and sidelobe levels. Moreover, detailed comparative simulation and real system experiment results verify the practicability and advantages of the proposed FM coding scheme.