The Naval Research Laboratory (NRL) has a long and distinguished history of making important contributions to the development of microwave technology. The inspiration for NRL originally came from Thomas Edison, who, in 1915, stated, “The Government should maintain a great research laboratory… in this could be developed… all the technique of military and naval progression without any vast expense.” War delayed construction of NRL until 1920; it was completed in 1923. Although NRL has long maintained extensive research programs in all areas of the physical sciences, its significant contributions in the microwave area began almost immediately with the development of radar. First came the ability to determine range and bearing of ships in 1922 and aircraft in 1930. Subsequent important radar inventions included the duplexer, the plan positions indicator and the monopulse receiver.
Other NRL microwave-related contributions include the TIMATION satellites (the subject of a talk at Tuesday’s IMS 2011 session “Historical Perspectives on Microwave Development in the Baltimore-Washington Area”) and atomic clocks that led to our current GPS satellites, as well as numerous communications, electronic warfare and radar systems.
While the above examples highlight the system level R&D that NRL is well known for, basic materials research has also played a significant role. For example, at NRL in the 1970s, a focused effort resulted in a method of growing high-purity single crystals of semi-insulating gallium arsenide, the basis for the revolution in microwave semiconductor devices that followed. NRL began making GaN microwave transistors back in the early to mid 1990s and has continued its own in-house R&D program while also being at the forefront in helping to establish the reliability of this technology by working closely with industry. High-power, high-frequency vacuum electronics has been greatly advanced by NRL developments including: rare-earth-iron-boron permanent magnet materials, the Controlled Porosity Dispenser cathode, and gyro-based devices that culminated in 1999’s WARLOC 10 kW average power 94 GHz gyro-klystron.
While NRL has made and continues to make important contributions to the development of microwave materials, devices, components and systems, it is extremely difficult to look ahead and predict which of the many on-going programs may be looked back upon in the future with the same game changing recognition. One of my colleagues keeps Albert Einstein’s quote “If we knew what we were doing, it wouldn’t be called research, would it?” prominently at his desk. And while many of us can extrapolate today’s technology to faster, higher frequency, lower power consumption, etc., I think that quote does summarize the difficulty of predicting breakthroughs. Nevertheless, there is a lot of ongoing microwave materials and device research at NRL that is likely to result in next generation capabilities. In particular, new atomic layer deposition techniques, in conjunction with both wide band-gap and narrow band-gap materials, will lead to complementary circuit capabilities in both of these semiconductor systems. This will push the digital realm much closer to the antenna at higher frequencies on both the transmitter and receiver side. For the narrow band-gap semiconductors one of the big challenges in realizing complementary circuitry will be to raise the hole mobility.
The last few years have seen tremendous interest and investment in carbon-based electronics in the form of both carbon nanotubes as well as graphene. While the electronic properties of these materials are intriguing for microwave applications, there is still much research to be done before conventional semiconductor materials are likely, if ever, to be replaced. Not only do these materials have unique electronic properties, they possess mechanical properties that may prove very useful in future microwave devices and components. This could involve everything from packaging to acoustic wave resonators for high-Q micro-miniature filters. At NRL we have several programs that are developing the electronic and mechanical properties of carbon-based materials for microwave applications.
Another area where NRL has been advancing microwave component technology has been in the area of tunable and reconfigurable filters. While the world in general is beginning to understand how crowded the spectrum is becoming, the Navy has been facing this problem much longer since almost all Navy platforms, ship or airplane, are very compact structures considering all of the equipment they carry that involves transmitting and receiving. Co-site interference is a problem the Navy has been dealing with for a long time and has led to a push to develop new filter architectures that address these concerns. These technologies are likely to be recognized, appreciated and adopted by the commercial providers as these spectrum issues become prevalent in their domain.
NRL is the government center of excellence in vacuum electronics and continues to lead in developing the design tools that enable higher frequency and higher power vacuum electronics oscillators and amplifiers for millimeter-wave frequencies. NRL CAD software is commonly used by industry to design current and next generation vacuum electronics. In addition, NRL has R&D efforts in multiple and sheet beam technologies and advanced cathodes that should result in much greater powers and frequencies in the next few years.
Of course there continue to be active programs in next generation radar, electronic warfare, and communications systems within NRL’s Radar, Tactical Electronic Warfare, and Information Technology Divisions, as well as NRL’s Naval Center for Space Technology. While the details of such programs usually do not become known until decades later, the same level of talent, ingenuity and perseverance that led to NRL’s earliest contributions in radar are hard at work to ensure that the Navy and the country are well served and protected in the future.
Irrespective of which of these R&D efforts bears the greatest return, or if it is one I have not mentioned, NRL will remain a center of microwave R&D. NRL has a special R&D environment where engineers, materials scientists and physicists all work closely together to address the materials, device, component and system challenges that confront Naval radar, communications and electronic warfare systems.
To learn how microwave and mmWave systems are being used in material processing at the Naval Research Laboratory, read the MWJ online exclusive by A. Fliflet and M. A. Iman, NRL.