RF Module Updates

For users of the RF Module, COMSOL Multiphysics® version 5.3a brings a new study step for running adaptive frequency sweeps, a Material Library for microwave and millimeter-wave circuit boards, an extended RF Part Library with edge launch connectors, and an example of a wideband radar cross section (RCS) calculation using time-explicit simulation. Browse all of the RF Module updates in more detail below.

Adaptive Frequency Sweep

The new Adaptive Frequency Sweep study type can be used to run models faster and with a fine frequency resolution by using a reduced-order model in the frequency domain. For example, you could compute the response of a linear or linearized model subjected to harmonic excitation for several frequencies. The asymptotic waveform evaluation (AWE) model reduction is performed by a moment matching technique where Padé approximation or a Taylor series expansion is used for the transfer function in a specified frequency interval. The AWE expressions are automatically chosen based on the port settings, but can optionally be specified by user-defined expressions. A user-defined expression can be entered for the error estimation as calculated by the AWE algorithm. When the expression used for the AWE method represents a sufficiently slowly varying quantity vs. frequency, then the simulation can be run using a very fine frequency resolution without much impact on performance. The AWE method has been available in previous versions, but not in an easy-to-access dedicated study type.

An illustration of the Adaptive Frequency Sweep study type, new with COMSOL Multiphysics 5.3a. For the waveguide iris filter model, an S-parameter comparison between adaptive frequency sweep and regular sweep is shown. The simulation can be run with a 10 times finer frequency resolution in a similar amount of time as with the discrete sweep simulation. For the waveguide iris filter model, an S-parameter comparison between adaptive frequency sweep and regular sweep is shown. The simulation can be run with a 10 times finer frequency resolution in a similar amount of time as with the discrete sweep simulation.

Application Library paths for examples using the new Adaptive Frequency Sweep study step:
RF_Module/Antennas/microstrip_patch_antenna_inset
RF_Module/Antennas/pifa_handheld
RF_Module/Couplers_and_Power_Dividers/wilkinson_power_divider
RF_Module/EMI_EMC_Applications/antenna_ebg
RF_Module/EMI_EMC_Applications/frequency_selective_surface_csrr
RF_Module/Filters/cylindrical_cavity_filter_evanescent
RF_Module/Filters/lumped_element_filter
RF_Module/Filters/notch_filter_srr
RF_Module/Filters/pcb_microwave_filter_with_stress
RF_Module/Filters/tunable_cavity_filter
RF_Module/Filters/waveguide_iris_filter
RF_Module/Passive_Devices/rf_coil
RF_Module/Transmission_lines_and_Waveguides/substrate_integrated_waveguide

New RF Material Library for Substrates

The RF Module now features a Material Library with material properties for more than 60 substrate materials to assist in modeling RF, microwave, and millimeter-wave circuit boards.

RF Part Library Updated with Edge Launch Connectors

The RF Part Library now includes edge launch connectors from Signal Microwave for quick modeling of RF components supporting high-speed data connectivity.


A CPW circuit board model. An edge launch connector test circuit board: the dB-scaled electric field norm (filled contours) and arrow plot of the electric field (surface) shows where the electric field is confined on a coplanar waveguide (CPW) circuit board. An edge launch connector test circuit board: the dB-scaled electric field norm (filled contours) and arrow plot of the electric field (surface) shows where the electric field is confined on a coplanar waveguide (CPW) circuit board.

De-Embedded Ports

Ports can now be de-embedded by specifying a port offset parameter, and the phase of the corresponding de-embedded S-parameters can be adjusted, based on the value of the port offset. De-embedded ports are useful, for example, to partition an assembly of microwave components in a different way than that of the original CAD model. The de-embedding functionality is triggered automatically when the port offset is set to a nonzero value. When active, the de-embedded S-parameter phase is automatically scaled based on the offset value and the propagation constant. The software assumes that the domain between the port boundary and the boundary projected by the port offset is straight, while maintaining a constant cross-sectional shape.

A screenshot of the COMSOL Multiphysics GUI showing a de-embedded port plane. Visualization of the de-embedded port plane (a long blue rectangle) where the S-parameter phase is scaled by the offset setting, set to 0.05 m from the port in this case. Visualization of the de-embedded port plane (a long blue rectangle) where the S-parameter phase is scaled by the offset setting, set to 0.05 m from the port in this case.

Slit Port Visualization: More Intuitive Arrow Direction

Interior ports with an active slit condition now show the direction of the power flow with an arrow symbol. You can easily switch the direction of the power flow by clicking the Toggle Power Flow Direction button.

A demonstration of the Toggle Power Flow Direction button in COMSOL Multiphysics 5.3a.

By clicking the Toggle Power Flow Direction button, you can change the direction of the power flow on an interior slit port.

By clicking the Toggle Power Flow Direction button, you can change the direction of the power flow on an interior slit port.

Physics-Controlled Mesh for Frequency-Dependent Materials

The physics-controlled mesh functionality can now automatically analyze material properties that are characterized by an interpolation function that has a frequency input argument as well as generate an appropriate mesh density.

Tutorial Model Visualization Enhancement

The tutorial models in the Application Library have been updated to present the latest postprocessing features.

A demonstration of the annotated microstrip patch antenna model. The microstrip patch antenna model has been updated to include annotations. The microstrip patch antenna model has been updated to include annotations.

Application Library path:
RF_Module/Antennas/microstrip_patch_antenna_inset

A demonstration of isosurfaces in the microstrip patch antenna model. The microstrip patch antenna model has been updated to show isosurfaces. The microstrip patch antenna model has been updated to show isosurfaces.

Application Library path:
RF_Module/Antennas/microstrip_patch_antenna_inset

A demonstration of using the 3D Grid data set in the mobile device antenna model.

The mobile device antenna model has been updated to show the use of a 3D Grid data set to visualize the far field.

The mobile device antenna model has been updated to show the use of a 3D Grid data set to visualize the far field.

Application Library path:
RF_Module/Antennas/pifa_handheld

New Tutorial Model: Wideband RCS Calculation Using Time-Domain Simulation and FFT

This model shows how to calculate the radar cross section (RCS) of a scatterer over a wide frequency range using the Electromagnetic Waves, Time Explicit interface. Based on the scattered-field formulation in 2D, the model has a temporally modulated Gaussian pulse as a background field. The results present the scattered field in both the frequency and time domains, as well as the RCS per unit length of a circle in the frequency domain.

A plot from the RF Module tutorial model for calculating RCS. Visualization of a bistatic RCS per unit length at 300 MHz in dB. Visualization of a bistatic RCS per unit length at 300 MHz in dB.

Application Library path:
RF_Module/Scattering_and_RCS/rcs_time_explicit

Data Refinement Using a Combine Solutions Study Step

The Combine Solutions study step can be used to filter out and remove unwanted solutions. This functionality can be used, for example, to filter out the first and last 5% of the frequency spectrum for a Time to Frequency FFT study step. Parts of the solution can be excluded based on a user-defined expression.


Application Library paths for examples using the new Combine Solutions study step:
RF_Module/Filters/coaxial_low_pass_filter_transient
RF_Module/Scattering_and_RCS/rcs_time_explicit

Helmholtz-Compliant Gaussian Beam Background Field

A new Gaussian beam background field implementation is available, where the beam focal plane is approximated using a summation of plane waves that are propagating with wave vectors pointing in a distribution around the main propagation direction. The advantage of this implementation as compared to the paraxial approximation implementation is that the plane-wave expansion implementation is a true solution to the Helmholtz equation, as each plane wave is a solution to the Helmholtz equation. As the name suggests, the paraxial approximation is only an approximate solution to the Helmholtz equation that should not be used to represent tightly focused Gaussian beams.

New Effective Index Variable for Boundary Mode Analysis

When a Boundary mode analysis is performed, new variables for the effective indices of the modes are created. The name for those variables follows the pattern <phys>.neff_<x>, where <phys> is the physics interface tag and <x> is the port name. As an example, Port 1 in the Electromagnetic Waves, Frequency Domain interface would have a variable name emw.neff_1.