05-09-2012, 03:44 PM
Ultra-Wideband Source and Antenna Research
[attachment=33451]
Abstract
Ultra-wideband (UWB) microwave sources and
antennas are of interest for a variety of applications, such as
transient radar, mine detection, and unexploded ordnance (UXO)
location and identification. Much of the current research is being
performed at the Air Force Research Laboratory (AFRL) at
Kirtland AFB, NM. The approach to high power source development
has included high pressure gas switching, oil switching,
and solid-state-switched arrays. Recent advances in triggered gas
switch technology and solid-state-switched shockline technology
have opened up new possibilities for the development of much
higher power systems and have thus opened the door to many
new applications. The research into UWB transient antennas
has also made significant contributions to the development and
improvement of wideband continuous wave (CW) antenna designs
and has brought new knowledge about the complex behavior of
ferrites, dielectrics, and resistive materials in short pulse, very
high voltage environments. This has in turn led to advances in the
technology of transformers, transmission lines, insulators, and
UWB optics. This paper reviews the progress to date along these
lines and discusses new areas of research into UWB technology
development.
INTRODUCTION
ULTRA-WIDEBAND (UWB) research programs have
been ongoing at Air Force Research Laboratory (AFRL)
for over ten years now, and significant progress is evident in
gas and oil switched sources and in antenna technology. In
a previous article, we discussed the development of UWB
technology over the last decade [1]. In this paper, we will
describe recent progress in sources and antennas and some
exciting new developments in both gas and solid state switching
and in antenna design. Interest in UWB technology is growing
rapidly, and we are now seeing the technology emerging in
several countries in Europe, Russia, and the Ukraine.
Challenges and Future Directions
Future research in this area will focus on continuing
to increase our knowledge of the physics of fast gas and
oil switching, and introducing conventional electrical or
laser-triggered switches. Higher voltage and more power
handling capability continue to be desirable as well as reducing
the trigger time, increasing the repetition rate, and controlling
the jitter. As a part of this, we will continue to investigate new
switching media, especially liquids, in a joint research program
with the AFRL Materials Directorate.
SOLID-STATE SWITCHING
BASS Switches
The bulk avalanche semiconductor switch (BASS) is an
extremely compact device that achieves sub-100 picosecond
switch closure by avalanche photo-conduction through gallium
arsenide (GaAs) bulk material [1]. Several switches can be
illuminated by a GaAs laser diode coupled to an optical fiber
splitter. They achieve 10 ps rms jitter and greater than
shot lifetime, making them particularly suitable for parallel
arraying to achieve greater current handling capability. The
maximum switch gap is constrained by optical absorption and
thermal dissipation in the GaAs, thereby capping the voltage
hold off to about 17 kV. This voltage limitation has lead to
development of the lateral photoconductive semiconductor
switch (PCSS) to increase the operating voltage and hence the
radiated energy from solid-state switched arrays.
CONCLUSION
There has been tremendous progress in the field ofUWBelectromagnetics
in the last decade. In the last year, there have been
two remarkable breakthroughs in fast, high voltage switching
technology: low jitter, triggered gas switching and solid-state
shocklines. Each provides the opportunity for significant increases
in our ability to radiate high voltage transient electromagnetic
energy and thereby achieve substantial improvements
in transient sources.
[attachment=33451]
Abstract
Ultra-wideband (UWB) microwave sources and
antennas are of interest for a variety of applications, such as
transient radar, mine detection, and unexploded ordnance (UXO)
location and identification. Much of the current research is being
performed at the Air Force Research Laboratory (AFRL) at
Kirtland AFB, NM. The approach to high power source development
has included high pressure gas switching, oil switching,
and solid-state-switched arrays. Recent advances in triggered gas
switch technology and solid-state-switched shockline technology
have opened up new possibilities for the development of much
higher power systems and have thus opened the door to many
new applications. The research into UWB transient antennas
has also made significant contributions to the development and
improvement of wideband continuous wave (CW) antenna designs
and has brought new knowledge about the complex behavior of
ferrites, dielectrics, and resistive materials in short pulse, very
high voltage environments. This has in turn led to advances in the
technology of transformers, transmission lines, insulators, and
UWB optics. This paper reviews the progress to date along these
lines and discusses new areas of research into UWB technology
development.
INTRODUCTION
ULTRA-WIDEBAND (UWB) research programs have
been ongoing at Air Force Research Laboratory (AFRL)
for over ten years now, and significant progress is evident in
gas and oil switched sources and in antenna technology. In
a previous article, we discussed the development of UWB
technology over the last decade [1]. In this paper, we will
describe recent progress in sources and antennas and some
exciting new developments in both gas and solid state switching
and in antenna design. Interest in UWB technology is growing
rapidly, and we are now seeing the technology emerging in
several countries in Europe, Russia, and the Ukraine.
Challenges and Future Directions
Future research in this area will focus on continuing
to increase our knowledge of the physics of fast gas and
oil switching, and introducing conventional electrical or
laser-triggered switches. Higher voltage and more power
handling capability continue to be desirable as well as reducing
the trigger time, increasing the repetition rate, and controlling
the jitter. As a part of this, we will continue to investigate new
switching media, especially liquids, in a joint research program
with the AFRL Materials Directorate.
SOLID-STATE SWITCHING
BASS Switches
The bulk avalanche semiconductor switch (BASS) is an
extremely compact device that achieves sub-100 picosecond
switch closure by avalanche photo-conduction through gallium
arsenide (GaAs) bulk material [1]. Several switches can be
illuminated by a GaAs laser diode coupled to an optical fiber
splitter. They achieve 10 ps rms jitter and greater than
shot lifetime, making them particularly suitable for parallel
arraying to achieve greater current handling capability. The
maximum switch gap is constrained by optical absorption and
thermal dissipation in the GaAs, thereby capping the voltage
hold off to about 17 kV. This voltage limitation has lead to
development of the lateral photoconductive semiconductor
switch (PCSS) to increase the operating voltage and hence the
radiated energy from solid-state switched arrays.
CONCLUSION
There has been tremendous progress in the field ofUWBelectromagnetics
in the last decade. In the last year, there have been
two remarkable breakthroughs in fast, high voltage switching
technology: low jitter, triggered gas switching and solid-state
shocklines. Each provides the opportunity for significant increases
in our ability to radiate high voltage transient electromagnetic
energy and thereby achieve substantial improvements
in transient sources.