Comment on "Higher order reentrant post modes in cylindrical cavities" [ J. App. Phys. 122, 144501 (2017) ]

TL;DR

This paper comments on a previous article claiming new higher order reentrant post modes, clarifying that such modes are well-known in existing literature as modes of a foreshortened quarter-wave coaxial resonator.

Contribution

It clarifies that the so-called 'new' modes are actually well-known and documented in classical resonator theory, providing relevant references to existing knowledge.

Findings

Higher order modes are known in quarter-wave coaxial resonators.

The modes discussed are classical and well-documented.

The paper provides references to established literature.

Abstract

A recent article [ B. T. McAllister et al., J. Appl. Phys. 122, 144501 (2017), arXiv:1611.08939] claims to show the existence of "new" higher order reentrant post modes. Indeed, such modes do exist and are known to scientists and engineers for a very long time as modes of a foreshortened quarter-wave coaxial resonator. It is a textbook problem. In this comment, I briefly review the higher order modes in such cavities and provide relevant references.