Rf / Microwave Receiver Components And Their Dds Local Oscillator

The discovery of The Direct Digital Frequency Synthesizer is a revolution in the development of frequency synthesis technique, which consists of the phase accumulator, the sine look-up table, the digital to analog converter and the low band filter. DDS is of fast frequency switching speed, high frequency resolution, the function to switch frequencies while maintaining constant phase. It is very convenient to achieve many kinds of modulations and to be controlled by micro-processor. The DDS technique has gained its rapid development in recent years, which will be applied more and more extensively in such fields as radar, communications, electronic warfare and electronic measurement instruments.Broadband and high speed sweep source (579.3~1061.3MHz and 4070~6070MHz) have been designed by DDS technology in this paper, which will be used local source of receiver module (30~512MHz and 4~6GHz). Firstly, this paper firstly analyzes the essential configuration and the working mechanism of DDS from the two aspects of operational flow and mathematics, and probes into the spectrum characteristic of DDS output in ideal cases. Since the inherent spur performance of DDS is not in perfect condition, so, in order to make DDS work effectually, it is very necessary to understand the spur performance of DDS fully. So, Based on the thoughtfulness of frequency layout, this paper analyzes the spectrum characteristic of DDS output in practical cases and introduces the location and amplitude of spurs caused by various spur sources.Under the knowledge of above, by selecting proper frequency band of AD9858 and using amplify-filter/mixer-filter/multiplier-filter technology, two frequency sources 579.3~1061.3MHz and 4070~6070MHz are designed and machined, and the dimension of two frequency sources is 118*118*29mm3 and 180*158*28mm3. At end, the test result proved that the multiplier circuit gets good performance.The super heterodyne structure have testified well for two receiver module (30~51MHz and 4~6GHz), which be selected once and twice mixer technology. In first module, I/Q mixer and quadrature Hybrid are used for the target of achieve good image frequency rejection. But in the second module, high Q filter is used for this target. The test result showed that two receiver modules have 40dB image frequency rejection. The IF circuits of two modules, achieve 50dB dynamic range by AD8309, are the same. At end, the dimension of two receiver modules is 54*53*14mm3and 61*31*18mm3, and the test result prove that two receiver modules accomplish the engineering demand.