Investigation of a metallic photonic crystal high power microwave mode converter

Abstract

It is demonstrated that an L band metallic photonic crystal TEM-TE11 mode converter is suitable for narrow band high power microwave application. The proposed mode converter is realized by partially filling metallic photonic crystals along azimuthal direction in a coaxial transmission line for phase-shifting. A three rows structure is designed and simulated by commercial software CST Microwave Studio. Simulation results show that its conversion efficiency is 99% at the center frequency 1.58 GHz. Over the frequency range of 1.56-1.625 GHz, the conversion efficiency exceeds 90 %, with a corresponding bandwidth of 4.1 %. This mode converter has a gigawatt level power handling capability which is suitable for narrow band high power microwave application. Using magnetically insulated transmission line oscillator(MILO) as a high power microwave source, particle-in-cell simulation is carried out to test the performance of the mode converter. The expected TE11 mode microwave output is obtained and the MILO works well. Mode conversion performance of the converter is tested by far-field measurement method. And the experimental result confirms the validity of our design. Then, high power microwave experiment is carried out on a Marx-driven Blumlein water line pulsed power accelerator. Microwave frequency, radiated pattern and power are measured in the far-field region and the results agree well with simulation results. The experiment also reveals that no microwave breakdown or pulse shortening took place in the experimental setup.

Mode‐matching analysis for characterization of the sectoral waveguide mode converters

“…where γ SWG is radial propagation constant of SWG. All the field constants were normalized by substituting Equations (6), (7), and (8) in their relevant field expressions for further calculation. To account for all possible modes, the orthogonality relations were applied to find the scattering coefficients at the junctions.…”

“…[2][3][4] SWG mode converter loaded with dielectric and metallic photonic crystals capable of conversion from TM 01 mode to TE 11 mode has been reported. [5][6][7] But these mode converters have a low capability to sustain at high power microwave in comparison to all metal-mode converters. Also by using shorted inner conductor end, mode conversion of TM 01 mode to TE 11 mode is achieved but their conversion efficiency is lower in comparison to SWG mode converter.…”

“…The mode conversion has achieved through the length of the SWG region having two different sectoral angles . SWG mode converter loaded with dielectric and metallic photonic crystals capable of conversion from TM 01 mode to TE 11 mode has been reported . But these mode converters have a low capability to sustain at high power microwave in comparison to all metal‐mode converters.…”

Development of a Ka-Band Circular TM01 to Rectangular TE10 Mode Converter

“…Incumbent conventional mode converters to date employ serpentine, sectoral or dual bent circular waveguide structures which are difficult to fabricate and install [10][11]. New mode converter structure loaded with dielectric, metallic photonic crystals, and coaxial waveguide structures have also been recently reported [12][13][14]. Due to a variety of functional limitations of these structures, including …… and …….., many such mode converters are incapable of sustaining high-power microwave or MMW emission compared with more traditional all-metal mode converters that are better suited for use in potentially high-power radiation sources including Virtual Cathode Oscillators (Vircator) [15], Plasma Assisted Slow Wave Oscillators (Pasotron) [16][17][18], Cerenkov [19], Gyrotron [20], and Travelling Wave Amplifier [21].…”