The Design Of Ka Band High-dynamic Weak Signal Receiver

The capture and the tracking of the weak signals in Ka band under the super-high dynamic environment have been studied. With the development of the aerospace TT&C systems, the spread spectrum TT&C in Ka band have become one of the promising development directions in the future. The spread spectrum receiver in Ka band has been designed, in which the weak signals can be captured and tracked under the super-high dynamic environment.The thesis has come from the aerospace TT&C systems. It has concerned some question as following:1. The necessary of the spread spectrum TT&C of Ka band has been analyzed, and the development direction of the spread spectrum TT&C in Ka band has been presented. For there is more wider frequency band in Ka band, it may provide more capacity compared to S band. For the reason of itself, the capture time of the receiver in Ka band must be reduced greatly. The range of Doppler and the requirement of tracking dynamic performance have been enlarged ten multiples. These require more for spread spectrum receiver in Ka band. Considering the capture of LEO and MEO, the spread spectrum receiver in Ka band must work well under low SNR.2. The basic theory and character of the direct sequence spread spectrum communication has been studied. The m sequence and the Gold sequence which used frequently in spread spectrum TT&C have been introduced. And some concerned technology has been studied such as the two-order phase-locked loop, the three-order phase-locked loop, the frequency-locked loop and the capture and tracking of pseudorandom code. These support the design in theory.3. The project for capture and tracking of the pseudorandom code and the carry based on FFT has been designed. The capture of spread spectrum has been simulated under the high dynamic and low signal-noise ratio, so the quick capture project has been decided according this. This project may work well when the Doppler value is from the-1MHz to 1MHz, and the SNR is-27 dB. A algorithm combined the two order frequency-locked loop with three order phase-locked loop has been designed to meeting the requirement of super-high dynamic and weak signal. The algorithm has been simulated too, and the project of tracking the carry has been designed according it.4. The integrated baseband platform has been designed according the soft radio, so the spread spectrum receiver of Ka band has been realized in it. The hardware has been realized in the integrated baseband platform, and the detail design in FPGA has been presented. The test for capture, tracking and demodulate of spread spectrum receiver has been performed, and the result of test verified the rationality and the feasibility of the project, and it can be applied in the future. At last, it presents some targets about improving the capture and tracking performance and reducing the hardware resource of the spread spectrum receiver of Ka band in the future.