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Anatech Electronics, a manufacturer of RF and microwave filters, has published its March 2015 newsletter. As always, it includes both company news and some tidbits about relevant industry happenings. This month, Sam Benzacar discusses the increasingly important issue of passive intermodulation (PIM) distortion products that originate in metal-to-metal contacts where dissimilar compositions are involved. New modulation schemes place PIM requirements into the -165 dBc realm, which is a difficult goal. Connector interfaces to cables and components are major sources of PIM interference. Being a major manufacturer of connectorized filters, Anatech Electronics has a vested interest in such things.
Microwave Technology Boosts Solar Power Generation
The Japan Aerospace Exploration Agency (JAXA) has successfully transmitted electric power to a pinpoint target 55 km away using microwave energy in the hope of realizing space-based solar power. Scientists at JAXA were the first to transform 1.8 kW of electric power into microwave energy and transmit it to a remote receiver. The energy was then converted to electrical current. In space, sunlight would be collected in geostationary orbit and transmitted to a receiver on Earth.
Unlike solar panels set on Earth, satellite-based solar panels can capture the energy continuously, and solar-power satellites could be placed about 35,000 km from Earth and transmit energy to Earth where it would be collected with over a 3-km radius, generating 1 GW of electricity. The low energy density of the microwave energy would not incinerate anything getting in its way, according to the researchers, who are hoping to have a system working in the 2030s.
The “Pan Ray” Gun is Back
The Air Force is replacing aging helicopter gunships with a modernized AC-130J called Ghostrider beginning in 2018, armed with a 30-mm chain gun, 105-mm cannon, and precision-strike missiles – and possibly a microwave energy gun. The latter would be a non-lethal addition to the gunship’s other weapons, known for their ability to shred anything in their path. The ground-based version of this directed-energy “heat ray”, known officially as the Active Denial System, was deployed in Afghanistan in 2010 but never used. It operates in the millimeter-wave region and excites the water and fat molecules under your skin, causing painful heating -- and the realization that it’s better to get out of the way.
China’s First GaN Power Transistor on 8-in. Substrate
Skysilicon Co Ltd of Chong Qing City, China has created the country’s first gallium nitride-on-silicon power device manufactured on an 8-in. wafer, a metal-insulator-semiconductor high-electron-mobility transistor (MISHEMT). The ability to create GaN-on-silicon devices on such a large wafer may make it possible to reduce the cost of GaN to the point where it is competitive with existing technology. While the device is designed for power-electronic systems and consumer, automotive, and industrial markets, its applicability to RF power devices is clear.
DoD Conducts Big EW Study
The Defense Department is conducting a broad-based study of electronic warfare throughout all the military services, with a focus on platforms such as the EA-18G Growler and the F-35’s three versions. The study examines the country’s entire capability to control the electromagnetic spectrum, on which our networks, sensors, and precision weapons all depend.
While the Air Force has its enormous, all-encompassing EC-130H Compass Call aircraft (some soon to be mothballed), and the Army and Marines have short-range tactical jammers to defeat IEDs, only the Navy provides a survivable aircraft capable of conducting EW in contested airspace. EW has taken on increased importance of late owing to the fact that well-placed military officials have warned that the U.S. has lost its dominance in the electromagnetic spectrum, and the Defense Science Board has identified $2 billion a year of EW shortfalls
An Impending PIM Crisis?
By Sam Benzacar
Passive Intermodulation Distortion (PIM) has always been a problem for operators of communication systems, especially those on board ship where rust, corrosion, moisture, and other environmental factors play havoc. It didn’t get the name “rusty bolt problem” for nothing. However, the situation today is different, as it’s affecting macro cells of carrier wireless systems, especially those that have been in service for years.
The latest problems are brought to us by the higher-order digital modulation techniques and high data rates employed in today’s wireless systems that are vastly more sensitive to conditions on the communications channel and are intolerant of extraneous signals entering their domain.
For those of you who haven’t yet been plagued with this problem, passive intermodulation distortion is created when spurious signals generated by nonlinearities in otherwise linear passive components produce a mixing effect. This results in new signals that are mathematically related to the originals and if their frequencies are in the receive bandwidth of a communications system, system noise floor rises, receiver sensitivity and bit error rate are degraded, causing dropped calls, lower data rates, and other maladies. If the signal strength of these interfering signals is strong enough, they can block a receiver and shut down an entire sector of a macro cell.
Connectors, switches, isolators, couplers, cables and other common transmission line components are the places where PIM is most likely to occur, although it can arise from an almost unlimited number of sources, from rusted or corroded contacts, junctions between dissimilar metals, surfaces contaminated by dirt, dust, or moisture, loose or misaligned connectors or other junction points, and tiny pieces of metal inside connectors. If the base station is near enough to a high-power transmitter that causes PIM to occur locally, it can affect systems far from the one they are degrading.
Latest concerns about PIM arose with the emergence of the latest wireless standards such as LTE and initially resulted in PIM-level requirements as low as -150 dBc but have now risen to as high as -165 dBc. Only a few years ago, there were few systems that could even measure distortion at such a low level but that as the problem is so severe and widespread, instrument manufacturers have addressed the challenge with PIM-specific instruments. Anatech Electronics has developed a line of component specifically designed to address PIM and are working to achieve the highest possible levels of PIM reduction.
In the long term, the major problem is that there’s just so much you can reduce this type of distortion, and the limit is not far from what’s already been achieved. So the question then becomes what to do next. The answer undoubtedly lies in making wireless signals and systems more robust in the face of PIM, addressing the problem within existing systems, and making passive components that achieve the lowest possible levels of PIM. None of this will be easy.
About Anatech Electronics
Anatech Electronics, Inc. (AEI) specializes in the design and manufacture of standard and custom RF and microwave filters and other passive components and subsystems employed in commercial, industrial, and aerospace and applications. Products are available from an operating frequency range of 10 kHz to 30 GHz and include cavity, ceramic, crystal, LC, and surface acoustic wave (SAW), as well as power combiners/dividers, duplexers and diplexers, directional couplers, terminations, attenuators, circulators, EMI filters, and lightning arrestors. The company's custom products and capabilities are available at www.anatechelectronics.com and standard products are available for purchase at the Anatech Electronics integrated Web store https://www.anatechelectronics.com/index.php/webstore
Anatech Electronics, Inc.
70 Outwater Lane
Garfield, NJ 07026
Posted March 23, 2015