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?
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.