Rigorous analysis of highly tunable cylindrical Transverse Magnetic mode re-entrant cavities

TL;DR

This paper presents a rigorous FEM-based analysis of cylindrical re-entrant cavities, demonstrating their high tunability from 2 GHz to 22 GHz and exploring the limitations of lumped element models.

Contribution

The study introduces a detailed FEM analysis of re-entrant cavities and designs a highly tunable cavity with a mode transformation from re-entrant to TM mode.

Findings

FEM analysis aligns well with experimental results.

The cavity can be tuned from 2 GHz to 22 GHz.

Mode structure transitions from re-entrant to TM mode during tuning.

Abstract

Cylindrical re-entrant cavities are unique three-dimensional structures that resonate with their electric and magnetic fields in separate parts of the cavity. To further understand these devices, we undertake rigorous analysis of the properties of the resonance using in-house developed Finite Element Method (FEM) software capable of dealing with small gap structures of extreme aspect ratio. Comparisons between the FEM method and experiments are consistent and we illustrate where predictions using established lumped element models work well and where they are limited. With the aid of the modeling we design a highly tunable cavity that can be tuned from 2 GHz to 22 GHz just by inserting a post into a fixed dimensioned cylindrical cavity. We show this is possible as the mode structure transforms from a re-entrant mode during the tuning process to a standard cylindrical Transverse Magnetic (TM) mode.