Microwave Active Filters Based on Coupled Negative Resistance Method

摘要

Microwave active filters based on the coupled negative resistance method areinvestigated. The filter tank circuit unloaded Q value is increased to a value close to infinity using this design method. Therefore, filter passband performance improves significantly. A one-pole and a 2-pole narrowband active filter based on end-coupled filter structure are designed and fabricated. Based on the same structure, a one-pole and a 2-pole varactor tunable active filter are also built. A modified end-coupled filter is developed to broaden the bandwidth with a factor from 5 to 20 times. Based on this new structure, three 2-pole active filters with bandwidth from 1.75 percent to 7.5 percent are built. To broaden the filter bandwidth further, a modified parallel-coupled filter structure is introduced. Compared to the traditional parallel-coupled filter, this new structure has better upper stopband performance. The new structure is suitable for broadband active filters with a bandwidth up to 40 percent. All of the active filters described previously are suitable for microwave monolithic integrated circuit (MMIC) due to their planar structures. A one-pole MMIC fixed frequency active filter is designed. (cp)