Roger Pryor - RF Module

RF MODULE

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RF MODULE

The Three Stub Tuner

By

Roger Pryor, PhD

Copyright 2014 by MERCURY LEARNING AND INFORMATION. All rights reserved.

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R. Pryor. RF MODULE: The Three Stub Tuner.
ISBN: 978-1-938549-69-4

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This book is one of the books in the Multiphysics Modeling Series. Each book in the series is designed to model an important Multiphysics problem or process in a highly focused manner. In the case of this book, the problem chosen is that of modeling a component that is widely used in a diverse number of industrial applications. The modeling software employed is COMSOL Multiphysics (version 4.3a) and this model employs the RF Module. The specific model built is upwardly compatible with later versions of the COMSOL Multiphysics software through the import function.

The waveguide device modeled here specifically demonstrates the exploration of a small, but very important, subset of components of the family of microwave hardware devices designed to facilitate the optimized transfer of power from the generating source to the consuming load. Each of those components is called, in electronics terminology, a Tuned Stub.

A stub is a length of transmission line or waveguide that is connected to an active circuit at one end only. This book models a rectangular waveguide with three adjustable stubs distributed along the upper surface of the waveguide. The waveguide stubs are hollow, as is the waveguide, and they are each electromagnetically connected to the inner cavity, at right angles to the central axis of the waveguide via an aperture in the wall of the waveguide. In this model, three (3) stubs have been added, at appropriate locations along the length of the waveguide, to optimize the tuning performance.

The first portion of this book builds the Three Stub Tuner Model using a step-by-step process to ensure that the model is easily and correctly built. The second portion of this book explores the consequences of changing the length of different individual Stubs through Variations on the Three Stub Tuner Model.

Microwave signals need to be clear and undistorted to ensure accurate information transfer. The primary function of many waveguide systems is to convey complex, broad power range, wave-based, electromagnetic signals from the generating or receiving source to the consuming or input load with a minimum of signal dissipation and/or distortion. Because waveguides are of great technological importance and application diversity, they are designed and manufactured in a large range of wave-length-specific, application-dictated, shapes, sizes, and configurations.

In this book, the COMSOL Multiphysics RF Module software (version 4.3a) is employed to perform a two-port S-parameter analysis of a Three Stub Tuner in the range of 2.2 to 3.3 GHz.

The primary advantage of using COMSOL Multiphysics software is the breadth of built-in functions available in the diverse collection of Multiphysics modules. Additionally, when the need arises, another advantage afforded by using the COMSOL Multiphysics software is the inherent capability of the software to allow the modeler to modify or create, as needed, suitable equations for insertion into the model for the calculation of the model parameters or for the incorporation of data into visualization plots.

In the case of this 3D model, the equation for the calculation of the Voltage Standing Wave Ratio (VSWR) was added to those equations normally incorporated into the COMSOL Multiphysics software. The quantity VSWR is a measure of the power transfer match and also, indirectly of the potential signal dispersion and/or distortion.