Summary

In this course, the governing equations of both rectangular and circular waveguides are explained. One example for each waveguide was also simulated in Ansys HFSS

Let’s summarize the key takeaways from each lesson.

Intro to Waveguide Simulation

• A waveguide can be a wire, a hollow rectangular or circular structure, a coaxial cable, an optical fiber, or simply air.
• For the same dimensionalities, an empty air-filled waveguide can handle more power than a waveguide with a center conductor.
• Popular uses of air-filled waveguides include satellite communications, radar, antenna feeds, and communication links.
• Complex math equations are required to analyze a waveguide, which determines the propagation conditions, cutoff frequencies, and propagating modes.
• Simulation decreases time to market and saves money at the same time by eliminating the need to manufacture different prototypes for testing.

Rectangular Waveguide Governing Equations

• A rectangular waveguide is a hollow metal tube filled with dielectric with a rectangular cross-section and is uniform along its length.
• Since the rectangular waveguide is made up of a single conductor, the TEM mode does not exist. Only TE and TM propagations are possible.
• The electric and magnetic fields are sinusoidal in nature in the transverse plane while propagating along the waveguide length.
• General representation of modes in a rectangular waveguide is TE_mn and TM_mn.
• The mode indices m and n represent the number of half-cycle variations of the fields along the longer and smaller dimensions of the cross-section, respectively.
• The propagation constants and cutoff frequencies are dependent on the mode indices and are different for different modes.
• In a rectangular waveguide, the TE10 mode is the dominant mode, which has the lowest cutoff frequency.

Rectangular Waveguide Simulation — Model Creation

• A rectangular waveguide geometry is created by defining the dimensions in terms of local variables.
• The simplest form of geometry is used for simulation with great accuracy.
• The method to create custom material from the existing material library is shown.
• The required simulation steps are covered in detail.

Rectangular Waveguide Simulation — Post-processing

• The cutoff frequencies are determined by plotting the imaginary part of the propagation constant in a 2D rectangular plot.
• The quickest way to see the modes excited at the ports is to look at the Port Field Display.
• The electric and magnetic field plots are also plotted inside the waveguide cavity and are animated over the phase to visualize the mode propagation.
• Mode identification of the propagating modes is done using the field plots.
• The effect of the material properties on the cutoff frequencies of the modes is shown.

Circular Waveguide Governing Equations

• A circular waveguide is a hollow metal tube filled with dielectric with a circular cross-section and is uniform along its length.
• Since the circular waveguide is made up of a single conductor, the TEM mode does not exist. Only TE and TM propagations are possible.
• The electric and magnetic fields are expressed in terms of Bessel’s functions in the transverse plane while propagating along the waveguide length.
• The general representation of modes in a circular waveguide is TE_nm and TM_nm.
• The mode index m represents the number of half-cycle variations of the fields along the radial distance from the center of the cross-section.
• The mode index n represents the number of full cycle variations of the fields along the cross-section’s circumference.
• The propagation constants and cutoff frequencies are dependent on the mode indices and are different for different modes. They are also dependent on the roots of the Bessel’s functions.
• In a circular waveguide, the TE11 mode is the dominant mode, which has the lowest cutoff frequency.

Circular Waveguide Simulation

• A circular waveguide geometry is created by defining the dimensions in terms of local variables.
• The required simulation steps are covered in detail.
• The cutoff frequencies are determined by plotting the imaginary part of the propagation constant in a 2D rectangular plot.
• The quickest way to see the modes excited at the ports is to look at the Port Field Display.
• The electric and magnetic field plots are also plotted inside the waveguide cavity and are animated over the phase to visualize the mode propagation.
• Mode identification of the propagating modes is done using the field plots.
• The effect of the waveguide radius on the cutoff frequencies of the modes is shown.