High purity signal sources are essential for the optimal use of the allowed bandwidth. Currently, the trade-offs between Q and size are well-known for microwave sources. Recently, the use of non-linearities in acoustic resonators allowed significant improvement in phase noise of RF oscillators. Indeed, the use of the non-linear response results in sharp phase slope of transmission response of the resonators and improvement in phase noise. So far, the first demonstrations have been made on acoustic resonators and are therefore limited up to VHF frequencies. Recently, the observation of such effects in conventional distributed microwave resonators at Purdue University and XLIM opens the way for higher frequencies implementations. The goal of this work package will be to explore possible implementations of such non-linear resonators using MEMS varactors. The progress steps include the realization of first prototypes based on previous works on non-linear MEMS power limiters, and their characterization under various bias and signal levels. The final part will include the fabrication of a prototype oscillator.
This work package will be focused on the development of frequency agile transmission systems. The goal is to develop high Q, low loss filters that can be inserted into intermediate amplification stages, that could be directly driven by digital signals. MEMS, and ferroelectric material based variable capacitors can handle signal levels up to several tens of watts, when included into microwave cavities . Such power levels were previously limited in the milliwatt range and low Q with semi-conductor diodes.
The ability to handle power permits post amplification filtering and signal cleaning of noisy digital-based data transmission. In such configuration, digital signals can be directly broadcasted, with all the flexibility, in frequency and modulation of digital approach. The power amplifier architecture can be very close to a power Digital to Analog Converter, making the RF architecture very close to being fully digital.
Progress steps include accurate modeling of tunable filters and the effects of signal transmission across high Q filters. Optimal topologies will be studied with different tuning technologies, and practical components will be fabricated. The final part will include the combination of digital driven power amplifier and a high power digital filter.