| The complex battlefield environment of modern informationalized war requires radar to have wideband and high-resolution detection, tracking, imaging and target recognition ability, so as to adapt to the rapidly changing form of war and satisfy the urgent demand to improve the battlefield perception of both sides at war. Synthetic wideband PD radar has many outstanding characteristics, such as the two-dimensional high-resolution of range and velocity, no ambiguous in range and velocity measurement, strong suppression ability of ground and sea clutter as well as anti-interference ability, easy to project implementation etc. Thus it is one of the important developing directions of the future radar system. This paper studies the stepped frequency signal processing technology; deduces the one-dimensional high-resolution range measurement algorithm from frequency-time and time-frequency transformation; and introduces the target extraction algorithm and the range-velocity coupling characteristic. Then, this paper studies two-dimensional range-velocity joint high-resolution processing method. Besides, the working principle of DDS, the output spectrum structure, and the spurs distribution are discussed. Then, this paper analyses the parameters of PLL, including the loop lock time, steady-state error, stability, loop noise and spurs. On this basis, the output frequency of DDS is planned; the loop filter and the DDS frequency synthesizer board are designed; furthermore, the DDS+PLL stepped frequency synthesizer is developed. It is verified that the frequency synthesizer is featured with low spurs and very rapidly locked characteristics with less than sub-microsecond phase locking time through elaborate tests. In addition, the S-band stepped frequency radar system is designed according to the above research. In this work, this paper mainly emphasizing its frequency synthesizer and RF receiver design, where the stepped frequency synthesizer developed above is used as the second local oscillator of the radar frequency synthesizer and the DDS frequency synthesizer board is used to generate the narrowband modulated signal without spurs in intermediate frequency, and finally implement it in engineering. The closed-loop test of the radar proves the feasibility and validity of the system design. In the end, this paper carries out the ISAR imaging experiment of civil aircraft in the open environment. In the experiment, the active antennas are used to conduct the amplitude-phase consistency correction of radar system, and then this paper precedes the one-dimensional high-resolution range measurement and two-dimensional high-resolution imaging of the civil aircraft, getting its dynamic high-resolution range profiles(HRRPs) continuously changing along with time and its clear ISAR images. The experimental results prove the reliability, stability and advancement of the radar system, and also verify the high precision range and velocity measurement ability together with the high resolution imaging capability of the wideband PD radar system. |
