A feedforward tracking filter. Part 1: Principle and tracking behaviour

Conventional tracking filters using feedback control encounter a hang-up problem when fast acquisition is required in high-speed TDMA systems. This paper introduces a feedforward tracking filter (FTF) which solves the hang-up problem. Using two identical bandpass filters (BPF5) and feedforward control to compensate both phase and frequency variations, this FTF provides fast acquisition and unconditional stability. Different BPF configurations used in the FTF scheme are evaluated and it is found that, for the same noise bandwidth of the BPF, the FTF using two identical double-tuned BPFs provides the best performance. The fast acquisition of the FTF is not degraded by the inter-burst-interference encountered in TDMA applications. The effects of misaligned BPFs on the tracking performance are studied analytically and experimentally.