Radio Relays Improve Wireless Products

In order to transmit communications through Earth’s atmosphere, satellites and space vehicles need radio equipment that can operate at higher frequencies than on Earth. These higher frequencies, until recently, have demanded mechanical switches in radio relays. Unfortunately, the mechanical switches had some problems with frequency routing, which inspired NASA to seek more rugged, reliable solutions.

NASA’s Lunar Crater Observation and Sensing Satellite (LCROSS), launched with the Lunar Reconnaissance Orbiter (LRO), communicates between antennas on the spacecraft and large dish antennas on Earth using radio frequency signals. This communication depends on distance, spacecraft orientation, and the physical characteristics of the transmitting and receiving antennas and electronics.
NASA began to design new, lightweight, microelectromechanical systems (MEMS). MEMS are extremely small devices (a fraction of a millimeter long) with moving parts, already used in sensors for airbag accelerometers and video game controllers, as well as radio electronics for cellphones, digital mirror displays, and handheld radios. Switching to MEMS relays for actuators (and not just sensors) from older mechanical switches offered NASA improved performance in higher frequencies. A California company helped NASA create new MEMS relays that offer some new benefits as well.

After developing a radio frequency (RF) MEMS relay under U.S. Department of Defense contracts, XCOM Wireless (Signal Hill, CA) continued its research with a Phase II Small Business Innovation Research (SBIR) contract through NASA’s Jet Propulsion Laboratory (JPL). In order to improve satellite communication systems, XCOM produced wireless RF MEMS relays and tunable capacitors that use metal-to-metal contact — moving microscopic metal beams into contact with special electrodes — operating much like a light switch small enough to fit on the cross-section of a human hair. They have the high speed of solid-state switches, but with mechanical contacts that outperform semiconductor technology. Also, by introducing a MEMS relay with electrostatic — and not electromechanical — actuation, XCOM was able to produce a MEMS relay that consumed less power and was easier to manufacture than earlier relays.

These MEMS relays are used for signal tuning, routing, and phase-shifting circuitry, enabling wireless systems to adapt to changing operating conditions, radar or communications waveforms, and other mission needs. For its work with NASA, XCOM Wireless concentrated on frequencies in the range of 70 GHz–100 GHz, while most commercial radio frequencies use the range from 0.1 GHz–6 GHz. Despite the difference in bandwidth, the NASA technology is a fundamental switching device now incorporated into all of XCOM’s products.

After designing these improved devices, XCOM entered into a partnership with MEMS manufacturer Innovative Micro Technology (IMT) of Santa Barbara, CA. With its NASAderived design improvements and IMT’s manufacturing abilities, XCOM automated its relay manufacturing and testing, and reduced costs to one-tenth the previous amount.

XCOM has two products made possible by the MEMS technology the company developed under the SBIR from JPL. The first is an industrial relay used for high-frequency test equipment and instrumentation: the XW3100 single pole double throw relay. The second is an RF MEMS tuning circuit for the wireless communications industry.

The XCOM Wireless XW3100 MEMS single pole double throw relay, mounted on a radio frequency test coupon.
The XW3100 relays offer faster performance for automated test equipment, with frequency switching as high as 20 GHz — much more efficient than large electromagnetic relays. Typically the size of sugar cubes, electromagnetic relays consume a lot of power, and because of their large size, they are very slow. Conversely, the XW3100s incorporate gold contacts to offer speed in a small footprint. Industrial systems that reconfigure different testing for computer chips or cellphones, for instance, depend on the speed of these relays. Reconfiguration speed can account for half of the total cost of testing final products, so companies are able to cut costs by having faster, smaller relays. The XW3100 relays also offer other advantages, such as linearity, lifetime, and bandwidth. The relays offer a continuous RF current of 400 milliamps.

Although early interest for the RF MEMS technology was primarily for instrumentation for aerospace and defense industries, the opportunities are now far more varied. Newer applications include fixed and wireless broadband data link equipment, wireless network hardware, cellphones, laptop computers, and personal digital assistants.

The second product is an RF MEMS tuning circuit for use in handheld radios and cellphones. These circuits use the lowloss switch technology developed with the NASA funding, and the technology greatly improves interoperability and power consumption in tactical radios. Miniaturizing the circuits and integrating them with filter and antenna subsystems allows older and newer radios to communicate seamlessly, making multi-agency operations more efficient. The relays can switch a phone call from a cellular network to an available broadband wireless network automatically, thereby reducing the use of cellphone minutes, and reducing dependence on overloaded cellular infrastructure. Lastly, the technology can also extend battery life and reduce dropped calls.

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