Compact rf polarizer and its application to pulse compression systems

Abstract

We present a novel method of reducing the footprint and increasing the efficiency of the modern multi-MW rf pulse compressor. This system utilizes a high power rf polarizer to couple two circular waveguide modes in quadrature to a single resonant cavity in order to replicate the response of a traditional two cavity configuration using a 4-port hybrid. The 11.424 GHz, high-Q, spherical cavity has a 5.875 cm radius and is fed by the circularly polarized signal to simultaneously excite the degenerate TE114 modes. The overcoupled spherical cavity has a Q0 of 9.4 × 104 and coupling factor (β) of 7.69 thus providing a loaded quality factor QL of 1.06 × 104 with a fill time of 150 ns. Cold tests of the polarizer demonstrated good agreement with the numerical design, showing transmission of -0.05 dB and reflection back to the input rectangular WR 90 waveguide less than -40 dB over a 100 MHz bandwidth. This novel rf pulse compressor was tested at SLAC using XL-4 Klystron that provided rf power up to 32 MWand generated peak output power of 205 MWand an average of 135 MWover the discharged signal. A general network analysis of the polarizer is discussed as well as the design and high power test of the rf pulse compressor.