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Antenna Systems and Propagation Effects
As wireless communication systems proliferate and the airwaves become
more crowded, the complexity of antenna systems will increase to meet
the performance demands of more complicated systems. SRI's experience
in antenna development, coupled with specialized tools and equipment for
antenna analysis, enables us to provide complete antenna solutions for
unconventional or demanding antenna problems. In particular, SRI has developed
high-performance feeds and multiple, phased feed structures.
Wideband Propagation Measurement System
Designed and built by SRI, this flexible, automated measurement system
collects experimental data for radio propagation studies. These studies
are important to the development of the high-speed digital and spread-spectrum
signals that will be used in future wireless communication products. Our
system makes high-resolution measurements of several characteristics of
the communication channel: path loss, Doppler shift and spread, the power
spectrum of the received signal, and multipath delay spread (used to compute
the maximum data rate of a communication channel). SRI used the Wideband
Propagation Measurement System for field measurements in a variety of
forested terrains, to gather data for new models that describe the propagation
of radio signals in these environments.
Special Operations Radio Antenna Kit
SORAK was designed,
developed, and tested by SRI, for use with HF and VHF radio systems. This lightweight
kit is in production testing prior to the manufacture of several thousand
units for special forces.
Mobile Testbed
SRI designs, for clients and its own use, mobile communication testbeds. Most
recently, the Mobile Testbed (MTB) was assembled to test the operation of transmitter
and receiver hardware in the field, evaluate communication protocols and modulations,
and develop new signals and signal-processing algorithms.
 The MTB consists of wideband
signal generation, collection, processing, and analysis subsystems, rack mounted in a
commercially transportable van with rack space for the systems under test. The van also
contains generators, environmental controls, and Inmarsat, for fully independent
operations in remote locations. The testbed was constructed primarily from commercial,
off-the-shelf components and configured via customized switch matrices; it is controlled
with custom software.
Receiving Elementary Dipole with Optional Polarization
SRI's RELEDOP
measures antenna patterns and gain for ground-based, high-frequency transmitting
antennas.  RELEDOP combines a
towed airborne synthesized receiver, a helicopter
positioning system, a ground station, and communication links. Data on
the transmitter's input power and the helicopter's position, as well as
field strength measurements from the towed receiver, can be used to calculate
and plot the transmitter's effective radiated power and absolute antenna
gain. RELEDOP has
been used to verify antenna performance for the Voice of America, and
for U.S. Air Force and Navy over-the-horizon radars. Digital C-Band Antenna
For a commercial client, we designed and built a prototype digital C-band
antenna that has the surface area of only a 3-ft antenna, but the
resistance to cross-satellite interference of a much larger dish. As designed,
the antenna is limited to reception but could be modified for both transmit
and receive operation.
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R&D Divisions