To address the Navy need for fast, affordable, and reliable tunable notch filters at X-band frequencies, Physical Optics Corporation (POC) proposed to develop a new Tunable, Rapid, Electronically Controlled X-band (T-REX) notch filter, based on a resonating RF structure utilizing ferroelectric-based capacitors for ultrafast-frequency tuning. The innovation in the resonating RF structure provides a large tunable range by using tunable capacitors to quickly (<50 ns) change the impedance to shift the operational frequency. As a result, the initial T-REX Phase I protoype filters offer notch attenuation >-40dB within the 8.8 GHz to 12 GHz range, minimal passband insertion loss (<0.3 dB), and a notch bandwidth from 800 MHz to 1200 MHz with low reflected power (<10%), which directly addressed the Navy need for low-cost electronic warfare and military communications systems that suppress interference. In Phase II, POC will further optimize the T-REX filter design. POC will develop a fully functional prototype, covering the entire frequency range (from 8 GHz to 12 GHz) for demonstration and evaluation at a Navy facility, to reach technology readiness level (TRL)-6/-7.