A modified conical cavity for submillimeter wave applications

Abstract

The conical cavity has been modified for use in electron beam devices. In this new cavity resonator a short radial line section couples the beam hole with the conical region providing a suitable interaction gap. Operated in a higher order TM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0p0</inf> mode the cavity size is large compared to wavelength making it attractive for millimeter or submillimeter applications. In this mode, both Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> and R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">shunt</inf> are large. For analysis, the modified conical cavity can be considered as a composite consisting of a circular waveguide at cutoff, a radial waveguide, and a shorted "quasi-wedge" guide. Resonant frequencies are found by impedance matching at a transverse plane in the cavity. Unloaded <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> and R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">shunt</inf> are found by calculating total energy stored and power loss along with an equivalent voltage across the gap. An experimental cavity was tested. This cavity was scaled for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</tex> and Ku bands and operated in TM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0p0</inf> modes from p=5 to p=9. Measured results agreed well with theory. At the p=9 mode, the radial dimension of the cavity was 4.2 λ. Design curves are presented for the modified conical cavity without beam hole.