Active high-power RF pulse compression using optically switched resonant delay lines

Abstract

We present the design and a proof of principle experimental results of an optically controlled high power rf pulse compression system. The design should, in principle, handle few hundreds of Megawatts of power at X-band. The system is based on the switched resonant delay line theory [1]. It employs resonant delay lines as a means of storing rf energy. The coupling to the lines is optimized for maximum energy storage during the charging phase. To discharge the lines, a high power microwave switch increases the coupling to the lines just before the start of the output pulse. The high power microwave switch, required for this system, is realized using optical excitation of an electron-hole plasma layer on the surface of a pure silicon wafer. The switch is designed to operate in the TE 01 mode in a circular waveguide to avoid the edge effects present at the interface between the silicon wafer and the supporting waveguide; thus, enhancing its power handling capability.

X-band active-passive rf pulse compressor with plasma switches

“…Replacement of the iris with an active component (plasma switch) makes it possible to create an active SLED-II system. As it was noted in [1,2], between the compression ratios of 6 and 32 the active system has a significant advantage over the passive one. In this case an increase in the coupling of the line in active SLED-II system will reduce the amount of energy left over after the output pulse is finished.…”

“…The reflected power starts to increase again as the line becomes almost fully charged. According to [2], efficient output of the energy from the storing cavity requires changing the reflection coefficient from R 0 to R d simultaneously with the phase switching by 180 . The optimal reflection coefficient R d in the calculations was determined from the condition of the absence of the wave reflected from the switch into the cavity at the moment of the phase switching before the last ninth time interval .…”

“…The klystron modulator and the delay generator (10) were synchronized with the same trigger pulses. From the delay generator the trigger pulse was sent to the phase shifter (2) and pulser (9). This synchronization scheme made it possible to create plasma and change the phase of incident wave simultaneously just before the last time interval .…”

“…It should be noted that the intrinsic efficiency of the SLED-II system decreases very rapidly as compression ratio C increases [2,3]. The efficiency is reduced due to two effects.…”

“…As it is known, the SLED-II compression system [1][2][3] makes it possible to increase the peak microwave power by several times by means of shortening the duration of the klystron pulse. This system is passive, in that all elements in the microwave circuit have time-independent properties.…”