Indiana Micro designs and manufactures real-time reconfigurable microwave filters (RMFs) that adapt to constantly changing contested and congested RF environments. Tunable filter applications are spectral cleanup and the mitigation of co-site interference and jamming signals. Indiana Micro’s current efforts are focused in the VHF through the Ku Bands (30 MHz to 20 GHz). The need for tunable filters at higher frequencies is steadily increasing.
Designing and manufacturing a wideband, high Q tunable and static filter is significant engineering challenge, requiring extensive modeling and simulation using the sophisticated software tool such as HFSS and Microwave Office. Indiana Micro’s RMFs require five major elements: advanced filter architectures, high Q filter tuning elements (for tunable filters), suitable substrates, high Q lumped element components (capacitors & inductors), and control circuitry. Indiana Micro has been addressing these engineering challenges in these areas thanks to the support of a dozen SBIR and STTR awards from DARPA, the Navy, the Army, the Air Force, the MDA, and NASA. Each of these challenges is discussed briefly below.
- Advanced Filter Architecture: Indiana Micro has significant experience in designing tunable filters based on these advanced architectures developed by a number of leading universities.
- High Q Tuning Element: A high Q tuning element is the heart of any tunable filter. Traditional tuning mechanisms include varactors, piezoelectric discs and MEMS. The latter two are largely unsuitable due to a combination long tuning times and reliability. Commercially available Si and GaAs varactors only have sufficient Q though the X band at most. As a result, Indiana Micro has partnered with a leading university to advance the state-of-the-art in high frequency filter tuning elements.
- Advanced Substrates: For frequencies greater than 10 GHz, Indiana Micro has found that traditional RF substrates such Roger 4350B are inadequate, primarily due to feature sizes within the substrate. Silicon’s (Si) loss tangent is simply too large for higher operating frequencies. Indiana Micro’s favored solution is APEX Glass from 3D Glass Solutions (3DGS), which support very fine feature sizes and support integrated passive devices (IPD) such as inductors and capacitors. These characteristics make integration in a λ/2 environment possible.
- High Q Lumped Element Components: Depending on the frequency of operation, inductors - particularly the inductor portion of resonators - can be realized by discrete components (0201 or 01005 packages), APEX Glass substrate IPDs, or evanescent cavities integrated into the APEX Glass substrates though the use of conductive vias.
- Control Circuitry: Indiana Micro has developed expertise in designing and fabricating the circuitry needed to control tunable filter. These controllers are FPGA-based with the necessary control voltages and DACS to bias the filters’ tuning elements. Future development includes integrating the control circuity onto the filter itself.