Design And Implementation Of C Band Continuous Wave Transponder

The C band continuous wave (CBCW) transponder is one of the high frequency band transponders that are developed for the first time by Micro-satellite Research Center of Zhejiang University. With the constant improvement technology, the low frequency transponder can’t fully meet the requirements of deep space exploration and the low earth orbit detection missions, so the development of high frequency band transponder is becoming more and more important. As one part of the payload system of the Zhejiang University XX satellite, the CBCW transponder is focused on miniaturization, high stability and fast locking according to the user’s requirements.Firstly, this thesis introduces the structure, the design process, and the implementation of the CBCW transponder, and conducts some problems encountered. Then, the parameters of the nested loop are redesigned and the locking time is analyzed; the interference the interference problem is also analyzed and methods are presented to avoid it. In the end, test results are given as well as the deficiencies in the design, which provides the improvement direction for future.The CBCW transponder is inherited from the S-band TT&C transponder of Zhejiang University and some C band components in the RF front end. According to the proportion relationship of the coherent model, we redesign the frequency distribution scheme and adopt a new nested loop with a new carrier tracking loop, which can lock fast with large range and can achieve better performance without any auxiliary circuit. By applying the integrated frequency synthesizer instead of discrete frequency multipliers, the transponder is made smaller. Due to the use of new carrier frequencies, the performance of the CBCW transponder changes a lot and some problems appear, so we need to redesign its nested loop’s parameters and analyze its locking time. Because the CBCW transponder is made up of two similar circuit structures with two close frequencies, how to reduce the mutual interference between them is every important. This thesis illustrates how to ensure normal operation of the transponder through careful signal configuration and PCB layout. Finally, test results show that the CBCW transponder achieves a sensitivity of-93dBm for both two pathways, a transmission power19.5dBm for one way and15dBm for the other, a frequency locking range of±200kHz and a locking time of640μs. It weights120g and consumes4.5W. These meet well with the design requirements.