Tunable Dual-Frequency Interference Suppression Circuit with GaN MMIC Delay Lines

This paper presents a broadband interference suppression circuit covering the 2-4 GHz octave. The circuit is capable of placing simultaneously two notches within the band with tunable center frequencies. A hybrid four-branch interferometer topology with gain incorporates GaN MMIC loaded tunable transmission-line delays. The circuit reduces the power of interfering signals by at least 10 dB, while amplifying the desired signal by as much as 18 dB. The overall circuit had a NF of 5-8.5dB across the band. This technique lends itself to produce sharp notches without the requirement of high-Q resonators, so implementations on low complexity PCBs is feasible.