SEVERAL METHODOLOGIES FOR ACTIVE-FILTER DESIGN AT MICROWAVES

This article presents several directions for the development of active filter structures in both hybrid and monolithic technology. The first direction generally used consists in compensating intrinsic losses of classical passive structures due to active components. We apply this methodology to the design of a three-pole dielectric resonator structu re (DR), a dual HEM(11)delta DR mode two-pole filter, and a planar mic rostrip resonator. For all these filters, an active loop, composed of an amplifier and a phase shifter, performs the appropriate gain and ph ase values to tune the response and to compensate for the intrinsic lo sses of the different resonators. Using the same approach, a microstri p active resonator is developed with losses compensated for by the hel p of a negative resistance MMIC circuit. With the increasing developme nt of MMIC technology, a second direction, which appears to be quite p romising, focuses on new original structures fully integrable in MMIC technology. Following this, we present the design of recursive and tra nsversal filters which well meet the requirements for realization as M MICs for broadband and narrowband applications. (C) 1997 John Wiley & Sons, Inc.