GTMR's 2-2006-STX filter project was the result of a quick reaction requirement to mitigate harmonic interference problems noted on sensitive receiver equipment with the installation of a high power transmitter on one of our primary aircraft. An industry search of available equipment suitable to the task exposed the basic fact that no such equipment exists.
Our target was to design and build a system that would allow concurrent operation of both the transmitter and receiver with minimum impact to the receiver and without significantly reducing the transmitter performance across the range from "DC" to 1GHz.
Additionally, the filter system was to be installed on a weight-critical aircraft and had to be necessarily light. The specification requirements included 2dB maximum insertion loss with a nominal 30dB isolation while handling transmitter output of 100+ Watts and generating no reflections back into the power amplifier. The assembly could not to exceed 10 pounds and was required to incorporate fully automatic control when integrated into the parent system.
With a concept-to-flight schedule of only six months because of operational schedules, GTMR successfully completed 3 fabrication and test cycles, refining the design to the current Ser 002 prototype. Bandpass filters, with their high insertion losses, were unacceptable and current design principles for Chebyshev and Butterworth type filters to build High/Lowpass filter pairs results in the generation of reflections back into the power amplifier.
GTMR's John Piri conceived a wholly new design, for which we are applying for a US Patent, which gives the insertion and isolation characteristics of a lowpass filter without the reflections, and meets-and-beats the original specification for this system.
The 2-2006-STX-Ser 002 Prototype Filter has passed all tests required for flight and is now flight certified. Results to date demonstrate a flawless technical performance including continuous operation at full, continuous, transmitter amplifier power over time periods measured in hours. The unit, complete, weighs only 5.5 pounds and fits in a volume 5"x5"x15" in it's prototype form, with production design size reductions possible by 10%.