Study And Implementation Of Full Coherent Digital Monopulse Receiving System

Digital receiving technique is intended to being applied to communication system firstly, whereas it is penetrated to radar system in recent years based on the following three reasons: Firstly, the new technique can be used to replace the analog scheme, so that the system performance and parameters can be improved. Secondly, by means of the digitalized processing method and software-defined function, the flexibility of system configuration is promoted. Finally, the reliability, coherence, and producibility of the product are assured, and the new product development period and cost reduced accordingly.In this thesis, beginning with the performance improving of a PD radar seeker as the engine, the theory and methods about digital receiving technique are investigated in-depth; one PD radar seeker system is analyzed; and a prototype of full coherent digital monopulse receiving system is designed and implemented. The highlight contents including:1. A digitalized method of angle error extraction is provided. Taking advantage of this method, not only the amplitude and phase imbalance between analog I and Q channels is avoided, but also the measuring error due to Null-Depth effect of antenna is eliminated. In addition, little operation is needed, Namely, four addition, two multiplication, and one division.2. A calibration method of amplitude-phase imbalance among the three receiving channels of sum and difference is presented. Combined with the angle error extraction method mentioned above, the amplitude-phase imbalance is calibrated effectively. Thus, the measuring precision of angle error is higher.3. A digital velocity-tracking loop scheme is given, which is made up of digital frequency discriminator, numerical controlled oscillator, digital mixer and filter, instead of analog frequency discriminator, voltage controlled oscillator, analog mixer and filter. By means of this scheme, the measuring accuracy of Doppler frequency is improved evidently.4. A prototype of full coherent digital monopulse receiving system is designed and implemented. The measuring accuracy of Doppler frequency is hundred times higher than traditional system as well as the angle error precision is ten times higher than traditional scheme. Thereby, the performance of the modified proportional navigation is much more improved consequently. In addition, without any change, the system prototype can be used to realizing full digital receiving at either 1st IF or 2nd IF according to system demand. By reloading different software, the parameters of receiving channels can be re-configured conveniently without hardware change, which makes it possible for the seeker to deal with the problems of clutter suppress, anti-jamming, fake target intercepting, etc. Furthermore, the prototype has the basic characteristics of the "software defined seeker".