Research Of Narrow Band High-order Phase-Locked Loop

In deep space TT&C system, because of the limited aircraft transponder sending-power and the very long transmission distance, the received signals are weak. As a result, the carrier-to-noise (CNR) of intermediate frequency (IF) signals is too low to track. At the same time, the down-signals which are sent by transponder are mixed with highly-dynamic Doppler-frequency, when aircraft moves rapidly. These factors make carrier signals difficult to capture and track, and it's also bad to telemetry signals. As we know, all that signal demodulation, distance measure, speed measure and angle tracking would be destroyed. Therefore, improving filter performance of receiver is needed, it is a key technology. Especially, this paper researches for high-order PLL to solve the problem.Due to nonzero steady-state phase error, low-order PLLs would be lost when they are used to track Doppler signals. It is a big problem. As a new method, this paper introduces two models loop-filter to design three-order PLL. The type of PLL does well in tracking Doppler signals. It is true that the three-order PLL is a steady and dependable system by Nyquist principle. Loop-filter is an important part for PLL, so this paper pays more attention to build whole loop-parameter expressions, likewise compute loop-noise-band. Contrasting some experiments, we know loop-noise-band how to affect relative stability for PLL. Close analysis and simulations show that the type of PLL is preferable to track carrier signals including Doppler-frequency shift.There is a contradiction between loop-noise-band and PLL's dynamic tracking-ability. A narrow bandwidth could make dynamic tracking-ability weak, but wider loop-noise-band increases more noise to PLL adversely. This paper introduces a method to solve the problem. Instead of only FFT arithmetic, in this paper it adopts a new technique to estimate PLL center-frequency using FFT and Kalman filter. As a result, the precision of PLL's center-frequency will be reformed and tracking-ability is also advanced, so that PLL could track highly-dynamic signals through narrow loop-noise-band.At last, three-order PLL is tested in the hardware using FPGA+DSP. Carrier signals acquisition process is simulated on experiment board. The results show that the project and its implement are right.