Mini-Circuits and the National Radio Astronomy Observatory (NRAO) announced that the National Science Foundation (NSF) has awarded a Partnerships for Innovation (PFI) grant to fund the joint proof-of-concept development of low temperature co-fired ceramic (LTCC) reflectionless filters for mmWave applications. The collaboration will combine NRAO’s expertise in the design of reflectionless filter circuits with Mini-Circuits’ industry-leading design and manufacturing capability for LTCC components. 

“The PFI program is a fantastic opportunity to expand our collaboration with NRAO and push the development of reflectionless filter technology to the next level,” said Mini-Circuits global product development strategist, Chris Simmonds, who co-authored the proposal. “We believe bringing together the skills and expertise of both organizations will yield many benefits across all industries using RF circuits, particularly in emerging bandwidth-hungry applications.” 

Bert Hawkins, director of NRAO’s Central Development Laboratory (CDL) commented, “When we licensed the technology to Mini-Circuits in 2015, we were excited at how well our technology transferred from the research world to broader uses. Packaged for use at higher frequencies, reflectionless filters have the potential to positively impact communications like 5G and defense and supercharge the industry for new uses that we haven’t even thought of yet. This support [from the NSF] is a recognition of that potential and gives us the ability to create a proof-of-concept.” 

Reflectionless filters were first developed and patented in 2013 by Dr. Matt Morgan, a tenured scientist and research engineer at NRAO CDL to improve receiver sensitivity in radio telescopes. In 2015, NRAO and Mini-Circuits announced an exclusive patent licensing agreement to develop the technology for commercial use. Since that time, reflectionless filters have been adopted in a wide variety of RF/microwave systems across several industries, and Mini-Circuits now offers over 150 unique reflectionless filter models from its catalog. 

In their current implementation, reflectionless filters are designed and manufactured as MMIC devices using integrated passive device technology on GaAs and packaged in standard over-molded plastic QFN packaging or sold as bare die. While these products have gained broad popularity in the market, they are not yet available in a practical surface-mount format at the higher end of the frequency spectrum. 

“Semiconductor-based reflectionless filters work up to about 30 GHz in package, which is only part way to the low target of 40 GHz,” said Christophe Jacques, also a co-author of the proposal and an engineer and Photonics Group Lead at NRAO. “We can’t use the current manufacturing process because it cannot achieve the performance at high frequency needed for typical commercial applications. That’s where a new manufacturing process comes in.” 

Aaron Vaisman, who leads LTCC product development at Mini-Circuits, explained that for passbands in the neighborhood of 40 GHz and above, standard surface-mount packaging degrades device performance while chip and wire assembly of bare die is costly and impractical for many applications. 

“LTCC is a self-packaged technology, so it doesn’t suffer from the parasitics or other effects of the packaging on RF performance,” said Vaisman. “At the same time, it avoids the high costs of other approaches like chip and wire or air cavity packaging at the same frequencies.” 

Dr. Morgan added, “Reflectionless filters at frequencies this high require a transmission-line implementation with very demanding characteristics. The necessary combination of line impedances, quality factors and dispersion properties could not be achieved with other affordable fabrication approaches. Mini-Circuits’ advanced LTCC technology is the perfect platform for implementing these filters as a cost-effective, compact and low-loss integrated passive circuit.” 

The grant will support an 18-month development timeline to realize surface-mountable LTCC reflectionless filters with passbands in the 40 to 50 GHz range. According to Vaisman, the technology platform that comes out of the collaboration will also have extensions to other passive components reaching 70 GHz and beyond. 

The PFI grant and expanded collaboration with NRAO follows several innovations in Mini-Circuits’ LTCC technology portfolio announced earlier this year. In January, Mini-Circuits introduced the industry’s first LTCC filters supporting the 5G FR2 bands up to 40 GHz, followed by narrow-band substrate-integrated-waveguide filter designs in September, and most recently a new family of filter designs achieving enhanced stopband rejection up to 90 dB. The new reflectionless filter designs will further contribute to Mini-Circuits’ proprietary IP and industry-leading design capability for LTCC components.