RF Module
RF Module
For Microwave and RF Design
An evanescent mode cavity filter is realized by adding a structure inside the cavity that changes the resonant frequency below that of the dominant mode of the unfilled cavity. A piezo actuator is used to control the size of a small air gap that provides the tunability of the resonant frequency.
Predicting Microwave and RF Designs Virtually
The RF Module is used by designers of RF and microwave devices to design antennas, waveguides, filters, circuits, cavities, and metamaterials. By quickly and accurately simulating electromagnetic wave propagation and resonant behavior, engineers are able to compute electromagnetic field distributions, transmission, reflection, impedance, Q-factors, S-parameters, and power dissipation. Simulation offers you the benefits of lower cost combined with the ability to evaluate and predict physical effects that are not directly measurable in experiments.
Compared to traditional electromagnetic modeling, you can also extend your model to include effects such as temperature rise, structural deformations, and fluid flow. Multiple physical effects can be coupled together and consequently affect all included physics during the simulation of an electromagnetic device.
Solver Technology
Under the hood, the RF Module is based on the finite element method. Maxwell's equations are solved using the finite element method with numerically stable edge elements, also known as vector elements, in combination with state-of-the-art algorithms for preconditioning and iterative solutions of the resulting sparse equation systems. Both the iterative and direct solvers run in parallel on multicore computers. Cluster computing can be utilized by running frequency sweeps, which are distributed per frequency on multiple computers within a cluster for very fast computations or by solving large models with a direct solver using distributed memory (MPI).
Additional images:
- ANTENNA MODELING: A two-arm helical antenna example tutorial from the Model Library of the RF Module
- ELECTROMAGNETIC FIELD SIMULATION: The distributed heat source is computed in a stationary, frequency-domain electromagnetic analysis. This is followed by a transient heat transfer simulation showing how the heat redistributes in the foodstuff within the microwave oven.
- ELECTROMAGNETIC WAVES: Oblique TM wave incident on a gold wire grating. The unit cells of the periodic structure are shown as wires.
- MICROSTRIP ANTENNA DESIGN: The radiation pattern from a microstrip patch antenna is visualized with the fast far-field plots for 3D, 2D, and 3D cut planes.
Analysis Options for Electromagnetic Simulation
GOVERNING EQUATIONS
The RF Module simulates electromagnetic fields in 3D, 2D, and 2D axisymmetric, as well as transmission line equations in 1D, and circuit (non-dimensional) modeling with SPICE netlists. The 3D formulation is based on the full-wave form of Maxwell's equations using vector edge elements, and includes material property relationships for modeling dielectric, metallic, dispersive, lossy, anisotropic, gyrotropic, and mixed media. The 2D formulations can solve for both in-plane and out-of-plane polarizations simultaneously or separately, as well as for out-of-plane propagation. The 2D axisymmetric formulations can solve for both azimuthal and in-plane fields simultaneously or separately, and can solve for a known azimuthal mode number.
FIELD FORMULATIONS
Both total-wave and background-wave formulations are available. The full-wave formulation solves for the total fields due to all included sources in the model, while the background-wave formulation assumes a known background field from an external source – a common approach for radar cross section and electromagnetic scattering models.
BOUNDARY CONDITIONS
Boundary conditions are available for modeling perfect electrically conducting surfaces, surfaces of finite conductivity, and faces that can represent thin lossy boundaries within the model. Symmetry and periodic boundary conditions allow you to model a subset of your entire model space, and scattering boundary conditions and perfectly matched layers (PMLs) are used to model boundaries to free space. Various different excitation boundary conditions exist for modeling ports: rectangular, circular, periodic, coaxial, approximate lumped, user-defined, and precise numerically computed port excitations are available. You can include boundary conditions representing cable terminations as well as lumped capacitive, inductive, and resistive elements. Line currents and point dipoles are also available for quick prototyping.
SOLUTION TYPES
Simulations can be set up as eigenvalue problems, frequency domain problems, or fully transient solutions. Eigenvalue problems can find the resonances and Q-factors of a structure, as well as the propagation constants and losses in waveguides. Frequency domain problems can compute the electromagnetic fields at a single frequency, or over a range of frequencies. Fast frequency sweeps, using the method of Padé approximants, can dramatically improve solution times when computing the behavior over a frequency range. Transient simulations are available for both the second order full-wave vectorial formulation as well the more memory-efficient first order discontinuous Galerkin formulation. Transient simulations are used for modeling of nonlinear materials, signal propagation and return time, as well as for modeling of very broad-band behavior.
MULTIPHYSICS COUPLINGS
The equations in all models developed in COMSOL Multiphysics can be completely coupled such that the electromagnetic fields can both affect and be affected by any other physics. In particular, a dedicated user interface for microwave heating expands simulation capabilities beyond traditional power deposition analysis, with features such as SAR calculations and precise temperature rise predictions. By solving for Maxwell's equations in the frequency-domain, and the heat transfer equation in the stationary or time-domain, it is possible to compute the rise in temperature over time, and compute the effects of varying material properties with temperature.
Extendable Results from Microwave and RF Simulations
The results of computations are presented using predefined plots of electric and magnetic fields, S-parameters, power flow, and losses. A fast postprocessing tool allows for quick generation of far-field radiation patterns. You can also display your results as plots of expressions that represent physical quantities you define freely, or as tabulated derived values obtained from the simulation. S-parameter matrices can be exported to the Touchstone format, and all data can be exported as tables, text files, raw data, and images.
The workflow is straightforward and can be described by the following steps: define the geometry by creating it using the COMSOL native tools or import a CAD model, select materials, select a suitable user interface and analysis type, define ports and boundary conditions, automatically create the finite element mesh, solve with optional mesh adaptation, visualize, and postprocess the results. All steps are executed from the COMSOL Desktop^{®}. The solver selection step automatically uses default settings that are tuned for each specific RF interface but can also be user-configured.
Many Example Models for RF and Microwave Design
The RF Module Model Library describes the interfaces and their distinct features through tutorial and benchmark examples. The library includes models addressing antennas, ferrite devices, microwave heating phenomena, passive devices, scattering and radar cross-section (RCS) analysis, transmission lines and waveguides in RF and microwave engineering, tutorial models for education, and benchmark models for verification and validation of the RF interfaces.
Absorbed Radiation (SAR) in the Human Brain
Scientists use the SAR (specific absorption rate) to determine the amount of radiation that human tissue absorbs. This measurement is especially important for mobile telephones, which radiate close to the brain. The model studies how a human head absorbs a radiated wave from an antenna and the temperature increase that the absorbed radiation ...
Frequency Selective Surface, Periodic Complementary Split Ring Resonators
Frequency selective surfaces (FSS) are periodic structures with a bandpass or a bandstop frequency response. This model shows that only signals around the center frequency can pass through the periodic complimentary split ring resonator layer.
RF Heating
This is a model of an RF waveguide bend with a dielectric block inside. There are electromagnetic losses in the block as well as on the waveguide walls which cause the assembly to heat up over time. The material properties of the block are functions of temperature. The transient thermal behavior, as well as the steady-state solution, are computed.
Modeling of Pyramidal Absorbers for an Anechoic Chamber
In this model, a microwave absorber is constructed from an infinite 2D array of pyramidal lossy structures. Pyramidal absorbers with radiation-absorbent material (RAM) are commonly used in anechoic chambers for electromagnetic wave measurements. Microwave absorption is modeled using a lossy material to imitate the electromagnetic properties of ...
Plasmonic Wire Grating
A plane wave is incident on a wire grating on a dielectric substrate. Coefficients for refraction, specular reflection, and first order diffraction are all computed as functions of the angle of incidence. The model is set up for one unit cell of the grating, flanked by Floquet boundary conditions describing the periodicity. As applied, this ...
Corrugated Circular Horn Antenna
The excited TE mode from a circular waveguide passes through the corrugated inner surface of a circular horn antenna where TM mode is also generated. When combined, these two modes give lower cross-polarization at the antenna aperture than the excited TE mode. This example is designed using a 2D axisymmetric model.
Parabolic Reflector Antenna
A large reflector can be modeled easily with the 2D axisymmetric formulation. In this model, the radius of the reflector is greater than 20 wavelengths and the reflector is illuminated by an axial feed circular horn antenna. The simulated far-field shows a high-gain sharp beam pattern
Modeling a Dipole Antenna
The dipole antenna is one of the most straightforward antenna configurations. It can be realized with two thin metallic rods that have a sinusoidal voltage difference applied between them. The length of the rods is chosen such that they are quarter wavelength elements at the operating frequency. Such an antenna has a well known torus-like ...
Substrate Integrated Waveguide (SIW) Leaky Wave Antenna
Substrate Integrated Waveguides (SIW) can be used in antenna applications. Leaky waves from a slot array on the top surface of the SIW in this model generate a beam in a certain direction that can be steered by choosing a different operating frequency.
Second Harmonic Generation of a Gaussian Beam
Laser systems are an important application area in modern electronics. With nonlinear materials it is possible to generate harmonics that are a multiple of the frequency of the laser light. This model shows how a second harmonic generation can be set up as a transient wave simulation, using nonlinear material properties. A YAG (lambda=1.06 ...