Defense Intelligence Reference Document Pulsed High-Power Microwave Source Technology

UNCLASSIFIED/ ;raA QFFI~llk YE'lii Si'llk>C
THE GEM II HPM SOURCE
The GEM II source was based on PCSS switch technology using GaAs bulk avalanche
semiconductor switches (BASS). GEM II was built by Power Spectra, Inc., in the mid-
1990s and was evaluated by the AFRL. The source was built from individual modules,
each containing a rectangular horn output with a BASS switch at the feed point. The
modules were assembled in a 12 x 12 array to form a planar radiator measuring 1.6 x
1.6 x 0.85 meters. By timing the switching sequence of each BASS module, the beam
was steerable up to 30 8 off center. The HPM output reached 22 kV/mat a distance of
75 meters and was capable of repetition-rate operation at 3 kHz. The rise time of each
module was about 200 ps, and the pulse width was about 2 ns. The major problem with
GEM II was switch lifetime; typically, a few switches failed during each burst.
THE JOLT HPM SOURCE
The Jolt, shown in Figure 10, was designed especially to feed the half-IRA antenna. The
AFRL refers to this source as hyperband, meaning the frequency band ratio is greater
than 10. On the pulsed-power end, Jolt uses a dual-resonant transformer operating at
1.1 MV. The transformer charges an intermediate capacitance discharged by an oil-
insulated peaking switch at the focal point of the half IRA to two flat-plate transmission
lines terminated at the edge of the dish. The voltage rate of rise is 5 x 1015 V/sec, and
the repetition rate is a maximum of 200 Hz. The radiated electric field waveform
recorded at 85 meters is shown in Figure 11. The half-power point frequencies are an
upper frequency of 2 GHz and a lower frequency of 30 MHz.
-
Figure 10. Jolt Hyperband HPM Source
MESOBAND SOURCES
''' ' '6 104 ____ L ___ L ___ L ___ L __________ _
I I I 1
' ' '' ' '[ 41~ ---~---~- ~-------r---r---
~ ' '] 21if ---r---r-
'" ''E I
" 1-~---4""'="\N~ 0
r-------r---L---
'''''' '' '-21if ---r----- ---------r---
'''4104 -frm+rm~m+rm~m+r"m~n,l
-1 10-~ o 1 10-9 ?. 10-9 3 10-'J 4 10-9 '.> rn-9 6 10-9
TimC' (sec)
Figure 11. Jolt Radiated Electric Field Waveform at
85 Meters
The AFRL has defined mesoband or moderate band sources as those with a bandwidth
ratio between one and three. These sources usually generate HPM energy between 50
and 900 MHz. They are designed using two techniques. The first is to feed a damped
sine wave onto a wideband antenna. The second is to switch a transient pulse onto a
resonant transmission line connected to a wideband antenna. One such system at the
24
UNCLASSIFIED/ )f81il 8ffl&I.«1k W&lii Si'llk¥