High-power microwave bandwidth broadening by air breakdown
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Wideband, high-power microwave pulses are expected to have important applications in ultra-wideband radar. The wide bandwidth should generate increased information for target characterization and identification. The high power should result in increased target detection range for conventional targets and targets with reduced signatures. A way to generate wideband, high-power microwave pulses with relatively conventional technology is to tail erode high-power pulses by passage through a low-pressure air cell. In this process, the tails of short (3$$-$$10ns), high-amplitude (>1 MV/m) pulses are removed. This erosion shortens the pulses and generates transmitted pulses with broadened bandwidths. The pressure must be matched to several incident pulse characteristics to create enough electron density to cause strong tail erosion. The important pulse characteristics are amplitude, frequency, pulse length, and pulse shape. We have shown experimentally that tail erosion from air breakdown broadens the 3 dB bandwidths of 2.8608 GHz incident pulses in a rectangular waveguide at 3.5 torr. The incident pulse amplitude varied from 0.67$$-$$1.16 MV/m. The pulse bandwidth increased from 0.147 GHz by 0.34$$-$$1.4% relative. The incident bandwidth was 5.12% relative to the incident carrier frequency. This experimental broadening was simulated with a 2D, electromagnetic, electron fluid computer code for avalanche ionization. The simulation predicted bandwidth broadening by 0.029$$-$$0.13 GHz or 1.0$$-$$4.4% relative for a peak initial electron density of 10 electrons/cm3. Although the measured and calculated transmitted electric field envelopes were in close agreement, the calculated bandwidths exceeded those measured by 13$$-$$47%. Because the detectors were not fast enough to resolve individual cycles we presently conclude that the simulation gives better estimates of reality than do the measurements.
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 10112470
- Report Number(s):
- UCRL-JC--107442; CONF-920124--5; ON: DE92005246
- Journal Information:
- Proceedings of SPIE - The International Society for Optical Engineering, Journal Name: Proceedings of SPIE - The International Society for Optical Engineering Vol. 1631; ISSN 0277-786X
- Publisher:
- SPIE
- Country of Publication:
- United States
- Language:
- English
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COMPUTERIZED SIMULATION
ELECTROMAGNETIC PULSES
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FREQUENCY ANALYSIS
GHZ RANGE 01-100
HIGH-FREQUENCY DISCHARGES
KLYSTRONS
MATHEMATICS AND COMPUTERS
MICROWAVE RADIATION
PULSE SHAPERS
RADAR
TWO-DIMENSIONAL CALCULATIONS