A nonreciprocal, frequency-tunable notch amplifier based on Distributedly Modulated Capacitors (DMC)

The tuning range of a high-Q resonator or a bandpass filter in conventional technology is very limited and often with high insertion loss in the passband. Recently, the directional parametric conversion effect in time-varying transmission lines (TVTLs) has been utilized to develop nonmagnetic nonreciprocal components operating like circulators [1, 2]. In a TVTL, the two frequencies, the original RF and the up-converted RF, are cross-coupled through a single-tone carrier. Such property can be used for a frequency-tunable high-gain narrowband amplifier through the creation of the sharp resonance at the up-converted frequency. In this work, the concept of the frequency-tunable notch amplifier based on the TVTL is validated and demonstrated with analysis and experiments. We propose to form a feedback loop of a TVTL in one of its practical implementations called Distributedly Modulated Capacitors (DMC). The narrowband gain of the notch amplifier can be tuned over a wide frequency range by just tuning the carrier frequency that modulates the TVTL. An experiment prototype on a Rogers board demonstrated larger than 17 dB gain with a less than 10 MHz bandwidth at a center frequency tunable from 1.48 to 1.65 GHz.