Recent advances in microwave active filter design. Part 1: Low-frequency techniques and noise optimization

Abstract

This two-part article presents a representative sample of recent advances in microwave active filter design. In part one, we discuss design techniques based on both analog and digital low-frequency methods that have been adapted to microwaves. From circuits with analog origins, we present simulated results, with some experimental verification, for a frequency-dependent negative resistance (FDNR) and active-inductance MMIC bandpass filters. From circuits with digital origins, we present experimental results for recursive filters, including MMIC bandpass and bandstop structures as well as higher-order cascaded sections. Part one concludes with a discussion of the noise-wave formalism and experimental results for active-recursive and tunable ring-resonator filters with minimum noise figure.

Varactor-tuned hairpin bandpass filter with enhanced stopband performance

“…These trends have required the tunable BPF which has compact size and enables us to control the center frequency directed at these application [3]- [4]. The tunable BPF has been widely designed using microstrip line resonators which offer a very compact realization [5]- [6].…”