Research On The Signal Designing And Processing Of Multi-carrier Phase Coded Radar

It is of pressing military demands and practical signality to research utilizing single form of signal to realize new type wideband radar with multiple functions. The dissertation focuses on the research of signal designing and processing of multi-carrier phase coded (MCPC) radar. Three main subjects are addressed in this dissertation, which are designing of multi-carrier radar signal, pulse compression and target detection as well as parameter estimation and imaging of moving target.The derivation and category of multi-carrier radar signal is firstly addressed whose envelope and ambiguity function (AF) are two main characteristics. Based on the flexibility feature of MCPC, the impact of different sub-carrier weighting on signal envelope is analyzed. And the full expression of AF is deduced to research the relationship between auto cross function and signal parameters, which provides theoretical basis for signal designing.For the parameter designing and optimization of multi-carrier radar signal, based on the rule of AF, the OFDM signal with relatively less parameters is firstly designed to achieve very low sidelobes in ACF, which is suitable to target detection. Secondly, considering the high sidelobes in AF of MCPC and the drawback of current designing method, a random shifted phase-coded MCPC is proposed. Its envelope is efficiently lowered by time-frequency clipping iteration which leads to satisfied ambiguity diagram and envelope fluctuation at the same time. This method is able to expediently produce waveform-diverse pulse train with ideal AF and low recurrent sidelobes in ACF. Finally the multi-carrier radar system performance is analyzed to instruct the designing of transmitting waveform and designing samples towards specific mission are given.For the computational efficiency and full usage of multi-carrier structure in pulse compression (PC) of MCPC radar echo signal, based on sub-carrier separation, signal chips are firstly divided in time domain. Two-level PC process is deduced to efficiently compress a special kind of MCPC without sub-carrier weighting. And improved wide band synthetic filtering is proposed to lower the calculation amount when compressing MCPC with sub-carrier weighting. Afterward PC methods in frequency domain are addressed to avoid improper chip dividing problems. By changing the computing order of FFT, piecewise matching method in frequency domain is brought forward to realize separation and synthesis of sub bands without growing computational complexity. It is able to obtain integrated coarse resolution range profile (CRRP) and HRRP simultaneity. Finally the PC of pulse train is given. Also the performance and calculation amount are compared among different methods.For the target detection in MCPC radar, on the basis of two-level PC, wideband detection method is addressed upon HRRP. And a detection strategy based on narrow band frame is proposed upon integrated CRRP. For pulse train signal, this method guarantees SNR gain through coherent integration among pulses and obtains favorable energy gathering of scattering points through non-coherent integration among sub-carriers. Simulations indicate the advantage of detection method based on narrow band frame when detecting moving target at high velocity.For the parameter estimation of moving target in MCPC radar, based on random shifted phase-coded MCPC pulse train, its low AF sidelobes is utilized to eliminate recurrent range ambiguity. Distance measurement principle with simulations is then provided. While nowadays wideband radar faces the range walk of HRRP cells and velocity ambiguity problems, LSE method based on Doppler processing of sub-carriers is proposed to solve velocity ambiguity. This method promotes the suitable scope of velocity measurement to one CRRP cell that target walking through in integration interval. Experiments are given toward target moving at low, medium and high velocity respectively. Velocity resolution based on Radon -CLEAN is then brought forward and proved to distinguish targets with diverse speed against low SNR.For the ISAR imaging of fast moving target in MCPC radar, using the real-time estimated velocity and range as motion compensation and reference distance, an ISAR imaging method based on multiple pulse trains and multi-functional wideband radar in integrative frame are proposed. The phase error and scatter migration through resolution cell problem when imaging the fast moving target is discussed and the ISAR result is compared with LFM radar. Simulations present the advantage of MCPC radar in ISAR imaging after motion compensation by provided velocity.