Theoretical and Experimental Analysis of Automatic Frequency Control Techniques for Microwave Active Filters

The paper discusses Phase Locked Loop (PLL) and Magnitude Locked Loop (MLL) techniques based on Voltage Controlled Filter (VCF), for the Automatic Frequency Control (AFC) of active filters. Applications to a microwave planar filter are considered. Theoretical analysis, simulated and measured results are presented for both phase and magnitude control circuits enabling the filter to accurately track a reference signal.