RF Module
RF Module
Software for Microwave and RF Design
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:
- COSITE INTERFERENCE: Antenna crosstalk, or cosite interference, on a single large platform can be analyzed by S-parameter analysis of different configurations of a receiving antenna installed on an airplane fuselage. This model simulates interference between two identical antennas at a very high frequency (VHF).
- ANTENNA MEASUREMENT: Pyramidal absorbers with radiation-absorbent material (RAM) are commonly used in anechoic chambers for electromagnetic wave measurements. Here, microwave absorption is modeled using a lossy material to imitate the electromagnetic properties of conductive, carbon-loaded foam.
- BIOMEDICAL ENGINEERING: This model uses a low-power, 35-GHz Ka-band millimeter wave and its reflectivity to moisture for noninvasive cancer diagnosis. It detects abnormalities in terms of S-parameters at the tumor locations. An analysis of the fraction of necrotic tissue is also performed.
- POWER DIVIDER / COUPLER: A Wilkinson power divider is a three-port lossless device that outperforms T-junction and resistive dividers. This simulation includes a 100-Ω resistor modeled via a lumped element feature and computes S-parameters, which show good input matching and a -3 dB evenly split output.
- TUNABLE DEVICE: In this tunable device simulation, resonant frequency is controlled by the capacitance inside of the evanescent mode cavity filter. The capacitance is tunable by a piezoelectric actuator.
- WIDEBAND ANTENNA: A tapered slot antenna, also known as a Vivaldi antenna, is useful for wide-band applications. The taper profile can be easily configured by an exponential function. This model shows the radiation pattern from the antenna visualized with a fast 3D far-field plot.
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.
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 ...
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 ...
Log-Periodic Antenna
The shape of a log-periodic antenna resembles that of a Yagi-Uda antenna, but is composed of a coplanar array to achieve a wider bandwidth. It is also known as a wideband or frequency-independent antenna. All metallic parts are modeled using the perfect electric conductor (PEC) boundary conditions. The antenna is excited by a lumped port while a ...
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
Corrugated Circular Horn Antenna
Corrugated circular aperture (conical) horn antennas are popularly used as feed horns for dish reflector antennas due to their low side lobe and cross-polarization level. The excited TE mode from a circular waveguide passes along the corrugated inner surface of a circular horn antenna, where a TM mode is also generated. When combined, these two ...
Circularly Polarized Antenna for GPS Applications
One way to generate circular polarization from a microstrip patch antenna is to truncate the patch radiator. This model is tuned around the GPS frequency range. The axial ratios are calculated to show the degree of circular polarization.
Monopole Antenna Array
It is possible to shape the radiation pattern and steer the beam from an antenna array by controlling the relative phases and magnitudes of the input signal. This example shows how to design an active electronically scanned array (AESA) using arithmetic phase progression on each antenna element.
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 ...
A SMA Connector on a Grounded Coplanar Waveguide
SMA connectors are popularly used on printed circuit boards (PCB) for testing. This model shows how to excite an SMA connector on a microwave substrate and how to terminate a grounded coplanar waveguide (GCPW) with 50 ohm using a lumped port and an air-bridge.
A Low-Pass Filter Using Lumped Elements
Passive devices can be designed using lumped element features if both the operating frequency of the device and the insertion loss of lumped elements are low. This example simulates two types of lumped element filters that are similar to lumped ports, except that they are strictly passive and there are predefined choices for inductances and ...