Design And Realization Of A High Performance DDWS Radar Signal Generator

Radar is one of the most important electronic equipment used to detect and orientate radio signals. As it has been well developed, Radar technique has been extensively applied. The key technique of radar is to choose a suitable waveform for the specific application. The great success of high speed Very Large Scale Integration (VLSI) changes people's mind and habit from the analog world to a digital one. The same thing happened in radar signal production. A recent developed technique of Direct Digital Synthesis (DDS) promotes the digital radar signal generatior. DDS technic generates complex signal in two methods: Direct Digital Frequency Synthesis (DDFS) and Direct Digital Waveform Synthesis (DDWS). DDWS provides precise signal phase and powerful frequency resolving capability, meanwhile produces sorts of complex wave in a more convenient way and improves the spectrum purity. What the most important is that DDWS can Pre-distort the amplitude and phase in FM band, which makes the output signal more closely approaches the idea one.The work in this paper contrives a new broadband radar signal generator with DDWS technique. It is built up with a dual-channel based signal generator on DDWS and a quadrature modulator. The baseband part of DDWS signal generator generates two channel 50MHz-bandwidth signals. Their frequency, amplitude, phase and the pulse form can be controled precisly by setting the parameters in specific desgined software. The quadrature modulator then modulates them into a high intermediate frequency. Other parts of the circuit multipies the frequency, which result in a wideband or ultra wideband signal.The disadvantage of DDWS is the high spurious signal power. This work points that the origin of the noise in DDWS system is spurios from DAC, PCB design, and amplitude quantitative errors, which have been explained by illustrating the principle of high-speed circuit design. A suitable filter used to reduce high frequency spurios signal and high frequency resonance wave is designed. The pre-distortion principle is also illustrated.