Mode converter based on dielectric phase shift

Abstract

In this paper, mode conversion method in a circular waveguide, based on dielectric phase shift is proposed. Radiation from high power microwave sources generally consists of null or minimum power on the axis, due to presence of TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode. To get the maximum power on the axis, TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode can be converted into dominant TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode. Conventional 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> mode converters are serpentine-profile circular waveguides, while the proposed mode converter is linear-profile circular waveguide. It first converts TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode into coaxial TEM mode and then due to dielectric phase shift, final output is TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode. Proposed mode converter consists of a circular waveguide with centre conductor, and azimuthally divided into two sections by metallic plates. Lower section of the waveguide is loaded with dielectric and upper section with vacuum. An analysis of mode conversion efficiency with respect to different dielectric materials is performed. Selection of PTFE (Polytetrafluoroethylene) or Teflon <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> as dielectric resulted in an optimized design with high conversion efficiency (more than 90%) for 690 MHz (19%) bandwidth at 3.5 GHz operating frequency.