Millimeter-wave frequencies offer a “new frontier” for communications. Realizing the overcrowding taking place at RF and microwave frequencies, the United States Federal Communications Commission (FCC) and other regulatory agencies have looked to higher frequencies as a way to add bandwidth and services. All that is missing is low-cost millimeter-wave components to assemble affordable communications infrastructure and user devices to take advantage of the “wide-open” bandwidth.
Millimeter-wave frequencies are so named for the wavelengths of the signals, ranging from about 10 to 1 mm and covering frequencies from about 30 to 300 GHz. They have traditionally seen use in military radar and missile seeker and guidance systems. But in 2003, the United States FCC, seeking to open millimeter-wave frequencies to commercial communications use, adopted a Report and Order establishing service rules or non-Federal development of certain portions of the millimeter-wave spectrum, notably 71 to 76 GHz, 81 to 86 GHz, 91 to 94 GHz, and 94.1 to 95.0 GHz. Frequency bands were made available in 1.25-GHz blocks on a non-exclusive basis. Coordination of the spectrum use would be performed by the National Telecommunications and Information Administration (NTIA).
As a followup, the Wireless Communications Association International (WCA) filed a Petition for the FCC to reconsider certain aspects of the Report and Order but only for the 70- and 80-GHz bands. Among these considerations, all new 70- and 80-GHz users would have to verify in advance that their systems would not cause harmful interference to any existing link and meet a series of requirements related to antenna and power specifications.
Given the tremendous crowding of bandwidth taking place at lower frequencies (consider the number of communications and heating applications in the 2.4-GHz band alone), the bandwidth represented by millimeter-wave links is attractive for secure data links, video links, backhaul connections between cellular communications stations, and more. One of the companies taking note of the available bandwidth was GigaBeam (www.gigabeam.com), driven by the shared vision of Lou Slaughter (CEO and chairman) and long-time microwave-industry visionary Doug Lockie (CTO and president). The company’s WiFiber® Wireless Fiber product lines employ millimeter-wave transceivers capable of providing high-speed (to 10 Gb/s) and reliable communications links at distances to 1 mile for secure campus-to-campus and building-to-building wireless connections.
Endwave (www.endwave.com) produces compact E-band transceivers at frequencies from 71 through 86 GHz with receiver noise figures to3 dB and transmit output power to 2 W. The company’s designs are available with options for waveguide and coaxial connections as well as with hermetic packaging.
The GigaLink Series of millimeter-wave transceivers from Proxim Wireless (www.proxim.com) operate at unlicensed frequencies from 57 to 64 GHz and in the licensed band from 71 to 76 GHz. Designed as a high-speed alternative to fiber-optic links, the E-band transceivers feature an integrated parabolic antenna with 44-dBi gain, Gigabit Ethernet data rate of 1.25 Gb/s, and extended range in excess of 8 km. Similarly, the WiFiber™ Wireless Fiber solution from GigaBeam Corp. (www.gigabeam.com) is a millimeter-wave alternative to fiber using the FCC-approved 71- to 76-GHz, 81- to 86-GHz, and 92- to 95-GHz bands.
Of course, establishing short-range millimeter-wave links that can be competitive with fiber optics and other technologies requires cost-effective components, a long-time stumbling block for widespread use of millimeter-wave technology. Bringing the technology to “the masses” requires a combination of intelligent design and skillful machining processes. Millitech (www.millitech.com), for example, carries those capabilities in two different divisions to provide both standard and custom components from 18 to 300 GHz. The firm produces a variety of building-block components, which can be used for subsystems or complete systems, including antennas, oscillators, amplifiers, control components and various passive waveguide components. Balanced mixers can be specified from 18 to 100 GHz while subharmonic mixers are available from 50 to 200 GHz. Cassegrain reflector antennas range from 18 to 220 GHz, while standard feed horns are available from 18 to 220 GHz. Gunn oscillators can be ordered with electrical or mechanical tuning from 26.5 to 100 GHz, while LNAs provide high gain from 18 to 110 GHz.
Spacek Labs (www.spaceklabs.com) provides most of the building-block components needed to assemble a millimeter-wave system, including the new model AW-8X, an eight-times multiplier for generating W-band signals. The multiplier accepts input signals from 9.35 to 13.75 GHz at levels from +5 to +10 dBm and provides output signals from 75 to 110 GHz at typically +3 dBm output power. Spurious levels are typically controlled to –20 dBc.
Merrimac Industries (www.merrimacind.com) has applied its innovative Multi-Mix® multilayer circuit technology to the fabrication of high-performance filters and other components for millimeter-wave applications. For example, the firm's model FBMM-42.0G Multi-Mix bandpass filter offers a 3-GHz passband centered at 42 GHz with typical passband insertion loss of 3.5 dB. The typical input/output return loss is 15 dB, while minimum rejection is 60 dB at 38.5 GHz and 30 dB at 46 GHz. In spite of measuring just 0.620 3 0.296 3 0.020 in. and weighing just 0.2 g, the filter handles power levels to typically 1 W.
Channel Microwave (www.channelmicrowave.com) developed the model WR28 three-way power divider for use from 34 to 36 GHz. Designed to handle 10 W average power and 500-W peak power in military systems, it exhibits better than 60 dB reverse isolation. To minimize lost energy due to heating effects, insertion loss is help to typically 1 dB.
Farran Technology Ltd. (www.farran.com) offers the PLO Series of phase-locked Gunn oscillators for generating signals from 60 to 325 GHz. The sources operate with an external 100-MHz reference for stability and provide as much as 50 mW output power from 60 to 90 GHz and 2 mW output power from 250 to 325 GHz.
Insight Product Co. (www.insight-product.com) offers a broad line of millimeter-wave and submillimeter-wave components, including amplifiers with as much as 30 W output power at frequencies through 140 GHz, monolithic balanced mixers for applications through 178 GHz, and solid-state and tube-based signal sources through 370 GHz. The firm’s recently developed line of Terahertz frequency synthesizers includes frequency coverage from 120 to 180 GHz with more than 30 mW output power and options for frequency modulation (FM) and amplitude modulation (AM).
The Millimeter Wave Division of ELVA-1 Ltd. (www.elva-1.com) provides components and subsystems through 180 GHz frequency range, as well as semiconductor devices at frequencies to 1200 GHz. The company’s line of zero-biased detectors includes models from 26.5 to 170 GHz with typical video sensitivity of 3500 mV/mW at 26.5 GHz and 500 mV/mW at 170 GHz.
Dorado International (www.dorado-intl.com) supplies a wide range of millimeter-wave components from international sources, including attenuators, directional couplers, phase shifters, switches, and waveguide sections. The waveguide components are constructed of copper with gold plating on electrically active surfaces. For example, the company’s W-band directional couplers provide full-band coverage from 75 to 110 GHz with coupling of 3, 6, 10, or 20 dB and directivity from 15 to 40 dB.
In the active-device area, Mimix Broadband (www.mimixbroadband.com) recently introduced the model XU1004-BD GaAs MMIC transmitter for applications from 32 to 45 GHz. Based on PHEMT device technology, the transmitter delivers an output third-order intercept point of +14 dBm with 5 dB conversion gain when operating with +4 dBm local oscillator (LO) drive power. According to Product Manager Paul Beasly, “The high level of integration in the XU1004-BD allows our customers to reduce the number of components on their board, facilitating a smaller design area and fewer interconnects.” The transmitter is ideal for point-to-point radios and satellite communications.
For even higher-frequency applications, Virginia Diodes, Inc. (www.virginiadiodes.com) produces lines of detectors, mixers, and frequency multipliers for applications from 18 GHz through 2 THz. Based on in-house-fabricated GaAs Schottky diodes and advanced filter structures, the firm makes devices, components, and systems for commercial and military customers. Because of their products’ high operating frequencies, the company developed a revised extension of the Electronic Industries Association (EIA) waveguide designations, for example, using the WR-1.2 designation for frequencies from 600 to 900 GHz, and other designations for products that don’t exactly match the EIA frequency bands.
Once millimeter-wave components have been manufactured, they must also be tested. The 65th Automative RF Techniques Group (ARFTG) conference, held June 17, 2005 in Long Beach, CA, addressed measurements for millimeter-wave applications, including the use of vector network analyzers (VNAs) and active-device measurements. In support of major VNA suppliers, OML, Inc. (www.omlinc.com) offers modules for extending the frequency range of a customer's VNA to cover 50 to 325 GHz in waveguide bands. Modules are available with a multiplier source, dual directional coupler, reference downconverter, and test downconverter to generate and receive test signals. Additional modules are designed with a downconverter to receive signals only. Combining modules allows all four S-parameters to be measured at millimeter-wave frequencies.
The company has also posted a useful application note on its website, “Using a Millimeter Wave Harmonic Mixer to Extend the Frequency Coverage of a Spectrum Analyzer.” The literature details the use of harmonic mixing to translate millimeter-wave frequencies to the range of commercial RF and microwave spectrum analyzers for testing. OML has also manufactured several frequency block downconverters through 40 GHz for test equipment original equipment manufacturers (OEMs). Damaskos, Inc. (www.damoskisinc.com) offers a variety of testing services, for antennas, RCS targets, dielectric materials, absorbers, and printed-circuit boards (PCBs) through millimeter-wave frequencies.
Of course, all millimeter-wave applications are not in communications systems, as automotive manufacturers have embraced the technology for adaptive-cruise-control (ACC) applications. A number of different frequencies are currently in use, including narrowband (200-MHz bandwidth) and ultrawideband (UWB with 3-GHz bandwidth) versions at 24 GHz in Europe and the United States, narrowband use at 47 GHz in the US, and UWB use from 77 to 81 GHz in Europe. Because of potential interference with radio astronomy, 24 GHz is a temporary allocation (until 2013) for automotive radar use. Roke Manor Research (www.roke.co.uk) has been an innovator in low-cost MMIC-based 77-GHz radar modules as part of the European RadarNet project (www.radarnet.org) to develop a low-cost radar network for automotive applications. Additional partners in the project include Volvo, DaimlerChrysler, Jaguar, BMW, and Siemens VDO Automotive Technology. As part of developing a practical 77-GHz MMIC radar module, Roke Manor employed commercial-off-the-shelf (COTS) MMICs and low-cost PTFE substrate materials.
For evaluating the performance of automotive radar systems, Anritsu Co. (www.us.anritsu.com) developed the ME7220A Radar Test System (RTS) for characterizing radar modules from 76 to 77 GHz. Ideal for checking ACC and collision-warning/avoidance radar components, the test system provides a simulated radar target response at set target ranges and an adjustable radar cross section (RCS). Doppler shifts can be introduced to simulate the speed of a moving target. The system can measure the effective isotropic radiated power (EIRP) of a transmitter as well as its bandwidth, spurious content, and other spectral characteristics.
In pursuit of a less traditional application for millimeter-wave technology, the Harmonix Division of Terabeam Corp. (www.terabeam-hxi.com) and Walleye™ Technologies (www.walleyetechnologies.com) formed an alliance to develop a hand-held portable imaging device capable of looking through solid objects. The design uses millimeter-wave energy to see into and through objects and capture digital images. The “camera” being developed by Walleye employs a millimeter-wave transmitter and receiver from Terabeam. Potential uses include Homeland Security, inspection of construction integrity, and medical applications.
For a complete listing of millimeter-wave component and test suppliers, please consult the online version of the Microwaves & RF Product Data Directory at www.mwrfpdd.com