SBIR-STTR Award

This proposal will explore the design and fabrication of tunable nonreciprocal devices for isolation, full-duplex operation, and incorporation in topological insulators. The topologies will be based on time-modulated Wheatstone bridges of varactors connected through filters. We will explore using dual-mode filters that provide independent control over the common and differential modes of the circuit for better alignment of the scattering parameters. We will investigate circuits with multiple stage filters for reducing loss and the modulation amplitude, while keeping the modulation frequency low. Furthermore, we will target making the proposed circuits tunable by adding varactors in the filters. The proof-of-concept circuit will be a non-reciprocal circulator operating in the S-band with isolation better than 20 dB, insertion loss less than 2 dB, and tuning at least 10% of the center frequency. Later in the program, non-reciprocal integrated circuits will be designed for operating at higher frequencies, such as 5G.

Nanohmics Inc. (Austin, TX), in collaboration with Prof. Dimitrios Sounas at Wayne State University (Detroit, MI), propose to continue the development of a new form of time-modulated circulators, with low loss, broad bandwidth, high isolation, and the additional advantage of full autonomy. In Phase I of the program, we explored two approaches for the design of magnet-less circulators. The first one was based on double-balanced bridges of varactors and filters, with a goal of broadening the nonreciprocity bandwidth and increasing the isolation between the RF and modulation signals. This approach was experimentally measured for the case of a gyrator, with fairly good results ( f 0 =1 GHz, IL=-6 dB, BW=3% , f m f 0 =1.5% ). The second approach we explored was the design of fully autonomous circulators, for which the modulation signal is generated on the same board as the modulated circuit. Despite the preliminary nature of our study, the designs of such circulators have shown excellent performance: f 0 =1 GHz, f m f 0 =16% , BW=2.5% , IL=-2.5 dB, IX>20 dB, RL>10 dB, P1dB=26 dBm, IIP3=39 dBm, power consumption = 400 mW. Furthermore, these designs have the unique property of being fully autonomous, in the sense that do not require any external instruments, like modulation sources, for their operations. This property is practically very important, since it demonstrates the feasibility of implementing autonomous circulator modules, that can be included in larger systems. For this reason, in Phase II of the program, we will focus on further development of this approach for low-loss, high-isolation, and high-efficiency circulators in the L/S-band frequencies (1-4 GHz), for applications in mobile communications, navigation and radiolocation.