The high power microwave program at the Air Force Research Lab (AFRL) includes high power source development in narrow band and wideband technologies. The H2 source is an existing wideband source that was developed at the AFRL. A recent AFRL requirement for a wideband impulse generator to use in materials tests has provided the need to update the H2 source for the current test requirements. The H2 source is composed of a dual resonant transformer that charges a short length of coaxial transmission line. The transmission line is then discharged into an output coaxial transmission line with a self-break Hydrogen switch. The dual resonant transformer is driven by a low inductance primary capacitor bank operating through a sel-break gas switch. The upgrade of the coaxial Hydrogen output switch is the focus of this paper. The Hydrogen output switch was developed through extensive electrical and mechanical simulations. The switch insulator is made of Ultem 2300 and is designed to operate with a mechanical factor of safety equal to 4.0 at 1,000 psi. The design criteria, design data and operational data will be presented.
Gallium arsenide photoconductive semiconductor switches (PCSS) are being studied as enabling technologies for a variety of applications. High grain PCSS can be triggered with small laser diodes or laser diode arrays. Some of the applications require low temporal jitter of the switches relative to the trigger laser. The purpose of this study was to compare the temporal switch jitter times for different systems: we varied the type of trigger laser and its risetime, the type of pulse charger and transmission line that was discharged through the PCSS, and the geometry of PCSS used. One of the PCSS was an opposed contact PCSS geometry used by the Air Force Research Laboratory. The other was a coplanar geometry switch made by Sandia National Laboratories. It is found that the optical trigger laser characteristics are dominant in determining the PCSS jitter while the nature of the contact geometry (opposed or coplanar) is not as important.
Fast rising, high-voltage, low jitter trigger pulses have been in high demand for a variety of applications. A recent application required triggering a compact Marx generator with very low trigger jitter. The lateral gallium arsenide photoconductive semiconductor switch (PCSS) being developed at the Air Force Research Laboratory (AFRL) has been implemented in this application. PCSS technology is an attractive solution because of the very low trigger jitter, high voltage switching capability and inherent trigger isolation properties. The PCSS has been packaged into an integrated unit for triggering a Marx generator. The Photoconductive Trigger Generator (PTG-30) requires external 24 VDC, TTL trigger and pressurized insulating gas for operation. Performance characteristics of the PTG-30 are variable output voltage from 5 to 13 kV, in four discrete steps. At maximum output voltage, the pulse risetime is approximately 350 pS. The high-voltage output pulse has an average of 22 ps rms temporal switching jitter with respect to a fast-rising trigger signal. The PTG-30 incorporates all required support components internal to the unit, including: laser diode and driver assembly, solid state FET-based pulse modulator, high-voltage DC to DC converter, and a pulse forming line. The versatility of this unit also allows for direct connection to a variety of antennas and other loads. This paper will discuss the manufacture and performance characteristics of the PTG-30 as well as experimental results from triggering a coaxial Marx generator.
The Air Force Phillips Laboratory, in collaboration with the Army Research Laboratory, is developing lateral geometry, high-power photoconductive semiconductor switches (PCSS) for use in phased-array, ultra-wideband sources. The current switch utilizes an opposed contact geometry with a 0.25 cm gap spacing and is an extension of previous work on 1.0 cm PCSS devices. This work presents the development and demonstration of the 0.25 cm PCSS under both ideal laboratory conditions and potential source conditions. The laboratory configuration consists of two high-bandwidth transmission lines connected with a PCSS. The potential source configuration consists of a vector-inversion pulse generator (Blumlein) commuted with a PCSS. The 0.25 cm PCSS is shown to operate at 20 kV charge voltage, 65 ps rms switching jitter, less than 450 ps risetime and greater than 1 kHz pulse repetition rate when triggered using a compact, high-power laser diode.
A comparison was conducted of fiber optic links for use in electromagnetic environments. Determining which link is optimum for a particular application is dependent on the environment''s electromagnetic bandwidth and amplitude. the device under test the frequency range of interest the environmental conditions and the link''s characteristics. If electromagnetic parameters tested device and environment cannot be altered the link must be adaptable to the device in its environment and operate over the required frequency range. The comparison determined the bandwidth. magnitude linearity versus frequency and temperature risetime signal-to-harmonic ratio and relative merits of each link. The Nanofast 0P300-2A was judged to be the outstanding low radio frequency (RF) FOL. It had a consistant upper 3 dB point (BW ) of 250 MHz and minimum ripple with changing gain: a near linear temperature versus BWU with minimum ripple: a risetime between 1. 7 is and 2. 1 s and a SHR of 42 dB. For high RF use the EOD Sentinal 1000 was the FOL of choice because of its: consistant 1 GH: BWU and low magnitude ripple coefficient with changing gain and temperature a risetime of 0. 5 its and SHR 47 dB.