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Title: Photoconductive switching for high power microwave generation

Abstract

Photoconductive switching is a technology that is being increasingly applied to generation of high power microwaves. Two primary semiconductors used for these devices are silicon and gallium arsenide. Diamond is a promising future candidate material. This paper discusses the important material parameters and switching modes, critical issues for microwave generation, and future directions for this high power, photoconductive switching technology.

Authors:
;
Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (USA)
Sponsoring Org.:
DOE/DP
OSTI Identifier:
6288250
Report Number(s):
UCRL-JC-104841; CONF-9011125-4
ON: DE91005433
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: OPTCON 90: SPIE symposium on laser science and applications of optics, Boston, MA (USA), 4-9 Nov 1990
Country of Publication:
United States
Language:
English
Subject:
45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE; 42 ENGINEERING; MICROWAVE AMPLIFIERS; SWITCHING CIRCUITS; DESIGN; EFFICIENCY; GALLIUM ARSENIDES; PHOTOCONDUCTORS; SEMICONDUCTOR SWITCHES; SILICON; WEAPONS; AMPLIFIERS; ARSENIC COMPOUNDS; ARSENIDES; ELECTRICAL EQUIPMENT; ELECTRONIC CIRCUITS; ELECTRONIC EQUIPMENT; ELEMENTS; EQUIPMENT; GALLIUM COMPOUNDS; MICROWAVE EQUIPMENT; PNICTIDES; SEMICONDUCTOR DEVICES; SEMIMETALS; SWITCHES; 450000* - Military Technology, Weaponry, & National Defense; 426000 - Engineering- Components, Electron Devices & Circuits- (1990-)

Citation Formats

Pocha, M.D., and Hofer, W.W. Photoconductive switching for high power microwave generation. United States: N. p., 1990. Web.
Pocha, M.D., & Hofer, W.W. Photoconductive switching for high power microwave generation. United States.
Pocha, M.D., and Hofer, W.W. Mon . "Photoconductive switching for high power microwave generation". United States. doi:. https://www.osti.gov/servlets/purl/6288250.
@article{osti_6288250,
title = {Photoconductive switching for high power microwave generation},
author = {Pocha, M.D. and Hofer, W.W.},
abstractNote = {Photoconductive switching is a technology that is being increasingly applied to generation of high power microwaves. Two primary semiconductors used for these devices are silicon and gallium arsenide. Diamond is a promising future candidate material. This paper discusses the important material parameters and switching modes, critical issues for microwave generation, and future directions for this high power, photoconductive switching technology.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Oct 01 00:00:00 EDT 1990},
month = {Mon Oct 01 00:00:00 EDT 1990}
}

Conference:
Other availability
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  • Photoconductive switching has been explored at LLNL and demonstrated to be a viable technology for high power microwave (HPM) generation. This technology enables the development of compact, portable, and efficient HPM sources. At LLNL we have successfully switched 35 KV in <200 ps using laser triggered, 1 {times} 5 {times} 20 mm GaAs switches. Based on these results we are developing an HPM generator with applications for HPM weapons and high power, wideband radar. The paper will discuss the physics limits and tradeoffs in the application of this technology. Among the topics discussed will be switching efficiency, candidate switch materials,more » laser requirements, applicable laser technologies, generator configurations, and cooling requirements and techniques. In addition to presenting theoretical and practical considerations, the paper will discuss on-going work at LLNL and elsewhere. 11 refs., 2 figs., 1 tab.« less
  • Laser activated photoconductive semiconductor switching shows significant potential for application in high power microwave generation. Primary advantages of this concept are: small size, light weight, ruggedness, precise timing and phasing by optical control, and the potential for high peak power in short pulses. Several concepts have been suggested for microwave generation using this technology. They generally fall into two categories (1) the frozen wave generator or (2) tuned cavity modulation, both of which require only fast closing switches. We have been exploring a third possibility requiring fast closing and opening switches, that is the direct modulation of the switch atmore » microwave frequencies. Switches have been fabricated at LLNL using neutron irradiated Gallium Arsenide which exhibit response times as short as 50 ps at low voltages. We are in the process of performing high voltage tests. So far, we have been able to generate 2.4 kV pulses with approximately 340 ps response time (FWHM) using approximately a 200..mu..J optical pulse. Experiments are continuing to increase the voltage and improve the switching efficiency. 3 refs., 6 figs.« less
  • Photoconductive semiconductor switches hold significant promise as high-voltage, high-current switches for pulsed power applications. Their most important contributions are picosecond rise time and jitter, and millisecond recovery times. A crucial factor in their development is their surface breakdown strength. Despite the lack of improvement shown to date, there are still many techniques to be tried and we consider the chances of significant improvement to be good. In addition to working on the surface breakdown problem, our plans include the construction of a 1 MV, 5 ..cap omega.. PCSS.
  • We are using solid state photoconductive switches to generate wideband microwave pulses with peak powers to 20 MW. A parallel-plate Blumlein transmission line is used to directly feed an exponential taper antenna to produce single pulses with rise times of 200 ps and pulse durations of 340 ps (FWHM). Voltages up to 21 kV have been generated in a 1 cm tall, 12 cm wide parallel-plate line. With the switches operated in linear mode, we have demonstrated phasing of several switches to generate a coherent wave. Generated and radiated signals agree very well with numerical calculations. Radiation efficiencies approach 30%.more » The Blumlein dielectric can be changed to produce a damped waveform, thereby modifying the bandwidth of the signal. We have generated damped waveforms of up to 3 cycles using this method. The parallel-plate geometry lends itself to coupling to an antenna structure to radiate efficiently. The geometry also lends itself to expanding the generator in height and width. We have stacked two generators to nearly double the output power without degrading the pulse characteristics. Applications of ultrashort microwave pulses (UWB radar, HPM weapons) require a high repetition rate and long life from the generator. Life times of >10{sup 5} shots have been seen occasionally at low to medium power densities. As the power density of a solid state photoconductive switch is increased, device life decreases. We have the capability to test devices at a repetition rate of 30 Hz and voltages to 25 kV. Preliminary data indicates that repeated pulse biasing (without switching) of large LEC grown devices in a slab geometry with fields as low as 30 kV/cm damages the switch and eventually leads to failure. 6 refs., 10 figs.« less
  • Abstract not provided.