Technology Today 2006 Issue 3 - Raytheon

Figure 2. Sample engagement. A close-up
of the irradiance profile mapped onto the
target is shown in the figure inset.
Tactical Target Engagement
Tactical target engagements have been
studied extensively using DEWSEM due to
the topical relevance of the threats. In the
example shown in Figure 2, an attack is
launched on a short, high trajectory, with
the laser close to the protected asset. The
presence of atmospheric turbulence leads to
a speckled irradiance profile shown on the
target in the picture inset. The red and green
lines on the target are used to visually indicate
the spin rate. The target trajectory is
the line shown in blue, the laser beam is
represented by the translucent red swath,
and the laser itself is represented by the
blue hemisphere. After studying a number
of laser weapon systems using commercialoff-the-shelf
lasers, it is believed that such
a weapon system could protect an area
that has a radius of about 1,000 meters.
Summary
This directed energy weapon system simulation,
which has been in used for many
years at RMS, has proven itself to be a
powerful predictor of laser propagation
and laser weapon system performance.
Stephen Dolfini
smdolfini@raytheon.com
onTechnology
Fiber Remoting:
A GPS Example
A growing number of signal remoting
applications require transferring radio frequency
(RF) signals from an often inaccessible
or inhospitable remote location. A fiber
optic solution can offer many advantages
for these types of situations, including complete
electrical isolation; a very small, lightweight
interconnection; and a completely
self-contained power source. This RF/photonics
module technique offers the unique
solution of supplying signals, control and
power — all completely by light.
Early generations of RF/photonic modules
were very expensive, but demonstrated the
feasibility and advantages of photonics. In
recent years, a new generation photonic
module has been developed — one that
offers high performance at greatly reduced
cost and ease of manufacture. In this implementation,
commercial-off-the-shelf (COTS)
components and direct laser modulation
have been the key driving elements.
ANT
YESTERDAY…TODAY…TOMORROW
LNA
RF Switching
and Diplexer
RF SYSTEMS
GPS Photonic Module
For some applications, a method of
obtaining physical location via the global
positioning system (GPS) is of great interest.
Prior photonic module designs have not
been required at RF frequencies above 500
MHz. A straightforward extension of
RF/photonics link performance utilizing the
same core technologies, form factor, and
critical components has been extended to
1.6 GHz to cover the GPS band. An existing
module was modified with higher frequency
designs for all RF circuitry, and a novel,
compact diplexer design encompassing
both standard GPS bands was integrated
in place of existing bandpass filters.
Figure 1 shows the basic block diagram of
the GPS photonic module implementation.
A distributed feedback (DFB) laser is implemented
for direct modulation of the RF
signal. A GaAs photovoltaic cell assembly
LNA
Control and
Test Circuits
Bias and
Current
Source
Directly
Modulated
Laser
Photo
Detector
Photo Voltaic
Cell
Continued on page 24
RF on
Fiber Out
Photonic
Control
Photonic
Power
Figure 1. GPS photonic module diagram. All the interfaces are on fiber, allowing the antenna
and LNA to exist at a distance from the main system, with no wired connections.
RAYTHEON TECHNOLOGY TODAY 2006 ISSUE 3 23