RF and microwave technology enable networking on the move

June 14, 2005
Designers of RF and microwave technology say low power and small size remain the trend in product designs. Meanwhile, integrators adapt and combine RF and microwave technologies to enable networking on the move.

RF and microwave technology enable networking on the move

Designers of RF and microwave technology say low power and small size remain the trend in product designs. Meanwhile, integrators adapt and combine RF and microwave technologies to enable networking on the move.

Military and aerospace systems integrators that buy radio--frequency (RF) and microwave components are demanding low power, ever-smaller sizes, and increasing integration of components into products with several functions.

RF, in this industry's context, refers to radio frequencies lower than 1 GHz, and microwave refers to radio frequencies from 1 to 300 GHz.

These are the typical trends of today's RF and microwave designs, says Rick -Folio, director of research and development at the Harris Corp. Government Communications Systems Division in Melbourne Fla. Harris customers want to improve performance while saving money; one way to do that is through power efficiency, he says.

They also want to move toward higher frequencies in the spectrum because the lower frequencies are mostly occupied.

"We're finding business in the transformational efforts of the Department of Defense (DOD) such as the Future Combat Systems program," says Bill Graves, chief technology officer, TRAK Microwave Corp. in Tampa, Fla.

What these customers increasingly want is integrated functionality, Graves says, and they want it in a smaller, lighter package for electronic warfare applications. In most cases, he says, this involves combining the functions of different products into one solution. The company has much of the ability to do this in-house but has added expertise in the -areas of millimeter wave and radio.

TRAK offers a C-Band five-channel switched-filter assembly used in airborne defense applications. The switch filter features an ultraminiature, low-profile design with less than 10-dB pass-band insertion loss and 60-dB typical stop-band rejection at plus-or-minus 500 MHz.

The model SWF002 has high-speed switching at less than 100 nanoseconds, is hermitically sealed, and laser welded with a better than 350,000 hours mean time between failures. The switch filter meets quality assurance provisions of Class H hybrid equivalent, TRAC officials say.

Advanced EHF

Harris engineers are using their microwave technology satellites in the U.S. Air Force's next-generation Advanced Extremely High Frequency (EHF) satellite communications (SATCOM) terminal.

Once fielded, the ship-, submarine-, and shore-based terminals will link with Advanced EHF satellites to provide the U.S. Navy with improved command, control, and communications capabilities.

Harris also participated in the Navy's AN/WSC-6(V)9 Multi-band Shipboard SATCOM Terminal (MSSCT) program. Harris will develop four Advanced EHF terminal prototypes.

The Advanced EHF satellite program is a follow-on to the DOD's Milstar communications satellite system. When operational, the Advanced EHF constellation will consist of four cross-linked satellites. The U.S. Navy's Advanced EHF terminals will enable its afloat and shore units to communicate from anywhere in the world via the Air Force satellites, as well as other military and commercial satellites simultaneously.

The multiband, multimode terminals will provide deployed Navy commanders with secure command-and-control capability, as well as enhanced communications such as tactical data and imagery, real-time video, battlefield maps, and targeting information. Harris is also providing phased-array antennas for the DDX, the Navy's next-generation land-attack destroyer.

Gallium nitride

Engineers at BAE Systems Information & Electronic Warfare Systems (IEWS) in Nashua, N.H., are developing gallium nitride (GaN) components to improve power efficiency and chip performance under the Wide Bandgap Semiconductor Technology initiative from the U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va.

Gallium nitride high-electron -mobility-transistor (HEMT) devices provide the relatively high power density and efficiency necessary for high-power phased array radar, electronic warfare, missile seekers, and communications systems. TriQuint Semiconductor Inc. in Hillsboro, Ore., leads the BAE Systems team. The Army Research Laboratory in Adelphi, Md., is the contracting activity.
The program seeks to develop new materials, devices, and properties of wide-bandgap semiconductors for RF applications, DARPA officials say. The program has several specific goals:

� Greater than 100-millimeter semi-insulating, high-quality substrates (Phase I)
� Epitaxial material technologies with better than 1 percent composition, thickness, and doping control (Phase I)
� Robust RF/analog devices (Phase II)
� Microwave and mm-wave circuit demonstrations (3 to 35 GHz) (Phase III)
� High-power electronic integration assemblies (Phase III).

Gallium nitride substrates in a power amplifier enables higher power at a higher frequency, says John Windyka director of Advanced Microwave Devices at BAE Systems in Nashua, N.H. It improves power efficiency by a factor of 10, says Dr. Phil Smith, director of Microwave Devices & Circuits and an Engineering Fellow for BAE Systems.

Gallium nitride has better thermal properties than does gallium arsenide substrates, Smith says. The other teams working on the Wide Bandgap program are Raytheon and Northrop Grumman, Smith says. "Our contribution is the wideband amplifier development," Smith says.

Another program where BAE engineers are lowering power and price is the Metamorphic High Electron Mobile Transistor, Smith says. It uses indium phosphide on a gallium arsenide (GaAs) substrate, Smith says.

The superior high-frequency properties of InP HEMTs result from the favorable transport properties of electrons in InGaAs channels with high indium content. HEMT with a record 562 GHz, while reported InP HEMT with values of 600 GHz, remains the highest of any nontransferred substrate device, Smith says. "Applications for which InP HEMT technology is well-suited include high-speed digital circuits, lightwave communication ICs, and a wide range of microwave amplifiers requiring low noise, high efficiency, low DC power consumption, low-voltage (battery-powered) operation, or operation at very high frequencies.

"Despite their unequalled performance, widespread use of InP HEMTs has been hindered by properties of the InP substrate upon which the devices have historically been grown due to lattice matching considerations," he continues. "As compared to GaAs, these include the limited availability of large (6-inch) InP substrates, their inherent fragility, and the increased difficulty of etching through-substrate via holes. MHEMT is one rapidly emerging solution to the issue of InP HEMT manufacturability, employing a special buffer layer that effects a significant shift (typically up to 5 percent) in lattice constant, thereby allowing InP HEMT device structures with high indium content InGaAs channels to be realized directly on GaAs substrates."

The technology also can scale to large wafer sizes and the price does not go up because the cost per die remains the same regardless of wafer size, Smith says.

BAE Systems also won a contract for the TEAM (Technology for Efficient, Agile Mixed Signal Microsystems) program, which seeks to take advantage of the affordability of silicon to develop low-cost systems-on-a-chip (SoC) that integrate RF and digital circuits onto one semiconductor device. Until now, separate RF and digital circuits have been linked by mixed-signal components like A-D and D-A converters. This multichip approach has limited speed, performance, and system flexibility. TEAM will provide an integrated solution that will link the RF and digital processing chain on a low-cost chip.

"In addition to reducing the overall size of the package, the SoC approach reduces power requirements, and eliminates performance degradation associated with interchip wiring," says Frank Stroili, BAE Systems TEAM Program Manager. "Furthermore, the single fabrication process provides a substantially lower overall cost."

Another program in this space in which BAE Systems is participating is TFAST (Technology for Frequency Agile Digitally Synthesized Transmitters), which is to develop indium phosphide (InP) heterojunction bipolar transistor (HBT) technology to reach levels of micro-circuit performance significantly ahead of anything available today, including a fivefold reduction in power consumption. Higher performance at lower power, in more highly integrated packages, can benefit any defense communications system with challenging weight or power requirements.

"This is the device building-block program for future RF systems," says Tony Immorlica, BAE Systems business development manager. "The TFAST technology will have a direct, high impact on current and future DOD programs. Electronic warfare (EW) systems are particularly suitable for TFAST," he added, because "its digital generation and direct sampling of RF signals would greatly enhance future EW capabilities."

BAE Systems is also involved in the upgrades of F/A-22 and Joint Strike Fighter (JSF) digital receivers, new electronic attack pursuits, mission electronics, defensive avionics, radar warning receivers, and space mission payloads.

Research funding

Many defense electronics designers prefer a climate that revolves around a threat of war rather than actual participation in one. They believe more money for new technology and research and development is available in the presence of a threat, but not during a conflict when government money goes for boots, bullets, and gas.

Harris' Folio says the RF and microwave funding at least for his company is steady through both climates. "We are involved in a stable base of programs that are not affected by the needs of boost and bullets," he says. "It is less cyclical than other areas, Folio adds.

Programs such as Advanced EHF do not typically get cut during times of war.

Asian migration

Funding for military semiconductor technology is getting examined more closely as there is a growing fear in U.S. defense circles that U.S. semiconductor technology could migrate to Asia, or more specifically, China, says Smith of BAE Systems.

"The handwriting is on the wall," he says. Technology is already in Taiwan and it could migrate to China by subterfuge or by force. Right now only three prime contractors have foundries for 3.5-micron semiconductor technology-BAE Systems, Raytheon, and Northrop Grumman, Smith says.
There is a possibility that the government may step in with major funding the way it did for the radiation-hardened foundries of BAE Systems-Manassas and Honeywell in Plymouth, Minn., Smith adds.
A recent Defense Science Board report covered this in detail, Smith says. "The emphasis is on silicon but the same concerns apply to microwave IC technologies such as GaAs, InP, and GaN."
Smith referred to an article in Manufacturing News by Richard McCormack, "Developing A Strategy For Saving High-Tech: Defense Science Board Wrestles A Political Hot Potato."

The article states, "In the semiconductor field, DOD is funding a stopgap measure to assure a continued supply of military specific microprocessors. In a quiet manner, it is providing $60 million a year to a dedicated 'trusted foundry' operated by IBM in Vermont. Suppliers in the industry believe a far more comprehensive strategy is required for the military to secure state-of-the-art semiconductors from U.S companies. DOD and the federal government have substantially reduced funding for research in advanced semiconductor production techniques, they point out."

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