DDS Based Radar Signal Generator for Microwave Remote Sensing

A system design of a Direct Digital Synthesis (DDS) based radar signal generator is presented. The DDS technique has its inherent disadvantage in noise and spurious suppression, due to the all-digital structure. To overcome these disadvantages, we apply two efiective methods of a 3-order low-pass Butterworth fllter and the pre-distortion technique to greatly enhance the system performance. Microwave Remote Sensing (MRS) has become a targeted area of intensive research for its great application in diverse situations. Early MRS radar signal generators are analog devices with high- cost, short life, low reliability and low precision. At present, due to the advance of high-speed Very Large Scale Integrated Circuit (VLSI), the technique of Direct Digital Synthesis (DDS) is being widely used to synthesize complex waveforms for applications in MRS. DDS makes it easy to precisely control and adjust the frequency, amplitude and phase of the required Chirp signals that are widely used in MRS. However, DDS technique has its inherent disadvantages in noise and spurious suppression, due to its all-digital structure. This paper presents a system design of a DDS signal generator for MRS. Besides, we put forward two methods to improve the spectrum purity. The flrst one is to design a low-pass fllter to improve the SNR, and the second one is to employ the pre-distortion method to make spectrum within band much ∞atter.