A Wideband High-Power Microwave Mode Converter Using Vane-Loaded Waveguide

High-power microwave (HPM) sources, like the magnetically insulated line oscillators (MILOs), backward wave oscillators (BWOs), and coaxial vircators, generate a few GW level of power in the TM<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode. When such modes are radiated by an antenna, they form a null at the boresight. This is undesirable, and mode converters (MCs) are used to convert the TM<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode to a TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode, which, when radiated, forms a maxima at the boresight. In this work, the authors report a TM<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub>-to-TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> MC based on a vane-loaded circular waveguide. The vanes are located far from the region of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i>-field maxima, so the fields are minimally perturbed. As a consequence, the MC exhibits high bandwidth and high-power handling capability. A method to calculate the dimensions of the MC is presented. Thereafter, as a case study, the design and performance of a 3-GHz MC is presented. Two specific variants of the design are discussed. One is with a perturbed length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\lambda {_{\text {ga}}}$</tex-math> </inline-formula> and a sector angle of 60°. The simulated bandwidth of this MC is 437.95 MHz (14.59%) with a computed power handling capability of 2.056 GW. This is an improvement in the bandwidth and power handling by a factor of 1.34 and 2.8, respectively. The fabrication of this MC is also carried out using rapid prototyping, as only low-power tests were intended. The second variant is with a perturbed length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7\lambda {_{\text {ga}}}$</tex-math> </inline-formula> and a sector angle of 105°. The simulated results of the MC indicate a bandwidth of 620 MHz (20.68%) and a power handling of 1.12 GW. This is an improvement in the bandwidth and power handling by a factor of 1.9 and 1.75, respectively.