Theoretical and experimental implementation of microwave active filters using automatic frequency control techniques

This paper discusses phase-locked loop (PLL) and magnitude-locked loop (MLL ) techniques based on a voltage-controlled filter (VCF) for the automatic f requency control (AFC) of active filters. Applications to a microwave plana r filter are considered. Theoretical analysis and simulated and measured re sults are presented for both phase and magnitude control circuits, enabling the filter to accurately track a reference signal. (C) 2000 John Wiley & S ons, Inc.