Millimeter-wave frequencies, traditionally reserved for government and military uses, are being explored for a variety of commercial short-range wireless networking applications.
Millimeter-wave frequencies are difficult to generate and as difficult to test, but the bands above 30 GHz have long intrigued commercial and military spectrum planners because of their amount of available bandwidth. So named because of having wavelengths in the 1 to 10 mm range, frequencies from 30 to 300 GHz have long been used in military and government applications, but only recently been investigated for commercial markets. These explorations, in large part, are prompted by the United States Federal Communications Commission (FCC) move a few years ago to allow the shared use of various millimeter-wave frequency bands through about 95 GHz with existing government/military applications.
Simply receiving the FCC's (www.wireless.fcc.gov) blessing has not opened the floodgates to the widespread use of millimeter-wave-frequency electronics, however. Components are still expensive, as is the test equipment to characterize them. Still, some visionary companies have seen the potential for these higherfrequency signals, including newcomer SiBeam, Inc. (www.sibeam.com). The firm's OmniLink60 system makes use of 7 GHz of bandwidth at 60 GHz (57 to 64 GHz) to provide data rates to 4 Gb/s for use in wireless high-definition- television (HDTV) and wireless personal area network (WPAN) systems. The OmniLink60 system employs adaptive beam-steering technology to detect new wireless devices in the network and direct communications signals to and from those devices to a transceiver at the television. The system maintains communications among its peripheral devices even if directed beams are blocked, by performing non-line-of-sight beam steering. To minimize costs, the OmniLink60 system is based on a transceiver fabricated with low-cost CMOS technology working at 60 GHz.
Terabeam Wireless (www.terabeam/hxi.com), now a division of Proxim Wireless (www.proxim.com), has also put the 60-GHz unlicensed spectrum to use with its QuickBridge 60250 point-to-point communications link. The system is easy to align and provides 200 Mb/s capacity at 60 GHz. It is well suited to not only network operator, enterprise and municipal applications but also for rapid construction of temporary networks for special events and when responding to disasters. The system contains all the components, including the radio units, needed for wireless connections at distances as far as 500 m.
Vubiq, Inc. (www.vubiq.com) has developed a 60-GHz integrated radio on a chip housed in a 10 x 10 mm BGA package. The patent-pending radio module is aimed at applications in the unlicensed band from 57 to 64 GHz, including wireless connection of HD televisions and peripherals and other wireless-local-area-network (WLAN) and WPAN applications. The compact radio module, which provides as much as 1.5-GHz modulation bandwidth at 60 GHz, combines a 60-GHz transmitter and receiver along with integrated antennas. According to Adam Button, Vubiq's CEO, "Just as we saw an incredible maturation of applications in the microwave (1 to 10 GHz) spectrum in the last decade, we will experience a similar explosion of millimeter-wave development in the next, and Vubiq will play a strong leadership role in that growth." The company is currently offering a basic development system that includes a 60-GHz transmitter board and a 60-GHz receiver board, each with a USB controller. The kit has embedded control firmware and a simple graphical user interface (GUI) for developing different applications.
In addition to the use of 60 GHz for broadband WLANs and WPANs, an increasing number of automobile manufacturers are adopting 77-GHz collision-avoidance radar systems and cruise-control systems as safety features for their high-end models. For aviation, millimeter-wave frequencies have long been used in collision-avoidance and other sensing applications, while military systems have employed the frequencies for a wide range of sensors, tactical surveillance systems, as well as for missile seekers and firecontrol functions. With the growing use of millimeter-wave technology comes an increasing demand for lower-cost components achieved by means of smaller packaging, lower-cost semiconductor processes, and even coaxial connectors in place of waveguide flanges.
For example, the model 6229-10 directional coupler from Narda Microwave East (www.nardamicrowave.com) uses 2.92-mm coaxial connectors for continuous coverage from 1 to 60 GHz. The compact component provides 10-dB coupling with +/-2 dB coupling flatness. It also delivers 8 dB minimum directivity and 20 W power-handling capability. The use of coaxial connectors not only supports a wider continuous bandwidth than possible with waveguide connectors, it saves on the cost of machined waveguide housings.
A similar coaxial approach is used by Micro Lambda Wireless (www.microlambdawireless.com) for its line of four-stage millimeter-wave YIG-tuned bandpass filters. The filters are available in bands with coaxial connectors with standard frequency coverage of 7 to 40 GHz, 18 to 40 GHz, and 3 to 50 GHz. For example, the model MLFP-43050 YIG-tuned bandpass filter tunes a 30-MHz 3-dB passband across a frequency range of 3 to 55 GHz with signal input and output ports using K connectors. The passband insertion loss is only 6 dB while the off-resonance isolation is 60 dB or more.
Tyco Electronics, M/A-COM (www.macom.com) developed its model MA4CG6773 single-pole, double-throw (SPDT) GaAs PIN diode switch for use in automotive collisionavoidance radar systems at 77 GHz. The component features rise time of 2 ns with only 1.2 dB insertion loss at 77 GHz. The isolation is better than 24 dB at that frequency, with typical return loss of 15 dB or more.
Spacek Labs, Inc. (www.spaceklabs.com) is a company long synonymous with innovative millimeter-wave engineering and reliable products. For example, a recent addition is the model AW-8X 8X multiplier that accepts input signals from 9.35 to 13.75 GHz at levels of +5 to +10 dBm and provides output signals from 75 to 110 GHz at a typical amplitude of +3 dBm. The component incorporates one of the firm's 57-GHz lowpass filters following the multiplier circuitry to reject unwanted harmonic signals. As a result, spurious levels are typically -20 dBc. In addition to its lines of passive components, Spacek manufactures low-noise and power amplifiers covering 18 to 110 GHz for commercial, military, and space-qualified applications.
Millitech, Inc. (www.millitech.com), another company with a long history of supplying millimeter-wave components and subsystems, expanded its Active Multiplier Chain (AMC) series of amplified frequency multipliers for full coverage from 18 to 140 GHz. For example, the model AMC-10, which is outfitted with WR-10 output waveguide, accepts input signals from 12.50 to 18.33 GHz at maximum level of +13 dBm and delivers output signals from 75 to 110 GHz. Those output signals are at +4 dBm through 100 GHz and at 0 dBm through 110 GHz with typical harmonics of -20 dBc. The latest additions include the models AMC-12 and AMC-08 with WR-12 and WR-8 output waveguide, respectively, and output frequency ranges of 60 to 90 GHz, and 90 to 140 GHz, respectively.
For Homeland Security and other applications, Millivision (www.millivision.com) has developed a technology that it calls "Passive Millimeter-Wave Imaging" for automatic-threat-detection (ATD) applications. The firm's systems employ detectors that operate passively, using the millimeter waves that are naturally emitted by the body and the objects hidden on the body to detect threats, such as firearms. The approach can detect threats through a wide variety of clothing to reveal concealed metallic and nonmetallic objects. In contrast to active systems that emit radiation to form an image, the Millivision approach is safe for system operators and the people being scanned. The system relies on the company's proprietary threat-detection software to translate signal information from the detectors into a viewable image, extract potential threats, and then overlay the threats onto a video image.
Multi-Mix patented multilayer circuit technology from Merrimac Industries (www.merrimacind.com) can be applied to both microwave and millimeter-wave component and subsystem challenges, delivering low signal losses in compact footprints. The company's Multi-Mix filters, for example, can be designed and manufactured with passbands as narrow as 1 percent and require no tuning compared to the external tuning circuits or tuning screws used in conventional filter circuits. For example, the model FBMM-42.0G bandpass filter features a 3-GHz-wide passband centered at 42.9 GHz with only 3.5 dB insertion loss. It achieves 30 dB rejection at 46 GHz and 60 dB rejection at 38.5 GHz. The filter, which measures 0.620 x 0.296 x 0.020 in., handles input power to 1 W.
Additional millimeter-wave suppliers include Ducommun Technologies (www.ducommun.com), ET Industries (www.etiworld.com), Farran Technology Ltd. (www.farran.com), superconductor specialist Hypres, Inc. (www.hypres.com), and Phase Matrix (www.phasematrix.com). For more listings of millimeterwave suppliers, visit the Microwaves & RF Product Data Directory online at www.mwrfpdd.com.