## RF Module

### New App: Corrugated Circular Horn Antenna Simulator

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 modes give lower cross-polarization at the antenna aperture. By using this app, the antenna radiation characteristics as well as the aperture cross-polarization ratio can be improved by modifying the geometry of the antenna.

*An app showing the far-field radiation of a corrugated circular horn antenna. The geometry parameters and operating frequencies can be changed to optimize the antenna's performance.*

An app showing the far-field radiation of a corrugated circular horn antenna. The geometry parameters and operating frequencies can be changed to optimize the antenna's performance.

### Postprocessing Wave Vector Variable for Periodic Port and Diffraction Order Port

Postprocessing variables are added for the wave vectors for the incident wave and the various diffraction orders (including the reflected wave). These variables can be used in arrow plots for visualization of the various diffraction orders from gratings and other periodic structures.

### Scattering Boundary Condition in 2D Axisymmetry Now Handles Incident and Scattered Plane Waves

The *Scattering* boundary condition for 2D axisymmetric models now includes a plane wave option for the scattered wave type. This means that you can now set up the *Scattering*boundary condition to absorb a wave propagating along a coaxial waveguide, as shown in the example below. Furthermore, it is also possible to enter the field of an incident wave propagating along the symmetry axis. This is useful for exciting and absorbing waves propagating along coaxial waveguides if you do not want to use *Lumped Port* excitation. It is also useful for propagating Gaussian beams in free space.

### New Constitutive Relation to the Frequency Domain Interface: Loss Tangent; Loss Angle; and Loss Tangent, Dissipation Factor

The old loss tangent model has been renamed *Loss tangent, loss angle*. A new electric displacement field model called *Loss tangent, dissipation factor* has been added from which it is possible to enter a value directly for the material dissipation factor.

### Voltage Standing Wave Ratio (VSWR) Postprocessing Variable

Many commercial off-the-shelf (COTS) antennas of one-port devices are characterized by the voltage standing wave ratio (VSWR). VSWR is now available for excited ports. The application example Modeling a Biconical Antenna for EMI/EMC Testing demonstrates a 1D VSWR plot.

### Surface Roughness on Lossy Conductive Surfaces

*Surface roughness* is now available as a subfeature for the *Transition* and *Impedance* boundary conditions. These boundary conditions scale the surface current using either the Sawtooth or the Snowball surface roughness models.

### Surface Current Density on Transition Boundary Condition

This subfeature for the *Transition* boundary condition is a one-sided surface current source that is useful for EMI/EMC applications. It models an imposed current flowing along one side of a thin conductive sheet.

### New Tutorial: Simulating Antenna Crosstalk on an Airplane’s Fuselage

Antenna crosstalk, or cosite interference, is problematic when multiple antennas are used on a single large platform. In this model, the interference between two identical antennas at very high frequency (VHF) is studied with an S-parameter analysis of different configurations of a receiving antenna installed on an airplane fuselage. The 2D and 3D far-field radiation patterns of a transmitting antenna are computed and the highlighted and shaded areas on the airplane surface are also visualized.

*The electric field norm on the airplane surface. The antenna on the top of the airplane is the transmitting antenna, while the receiving antenna is on the bottom.*

The electric field norm on the airplane surface. The antenna on the top of the airplane is the transmitting antenna, while the receiving antenna is on the bottom.

### New Tutorial: Designing a Waveguide Diplexer for the 5G Mobile Network

A diplexer is a device that combines or splits signals into two different frequency bands and is widely used in mobile communication systems. This tutorial model simulates splitting properties using a simplified 2D geometry. The computed S-parameters and electric fields at the lower and upper bands show the diplexer characteristics in the Ka-band.

*The norm of the electric field for a frequency of 28 GHz, where the input power flows into Port 2 only and for a frequency of 30.4 GHz, where the input power flows into Port 3 only.*

The norm of the electric field for a frequency of 28 GHz, where the input power flows into Port 2 only and for a frequency of 30.4 GHz, where the input power flows into Port 3 only.

### New Tutorial: Modeling a Biconical Antenna for EMI/EMC Testing

Biconical antennas are popular for very high frequency (VHF) measurement because they support a wide frequency range. They are also useful for electromagnetic compatibility (EMC) testing where the antenna can be used as an RF source in susceptibility or immunity tests. This model simulates a biconical antenna made of lightweight hexagonal frames that are preferred over solid cones for fabrication. The simulation includes the computation of far-field radiation pattern and voltage standing wave ratio (see feature section above).

### New Tutorial: Fast Numerical Modeling of a Conical Horn Lens Antenna

An axisymmetric 3D structure such as a conical horn antenna can be simulated in a fast and efficient way using only a 2D axisymmetric model. In this example , the antenna radiation and matching characteristics are computed very quickly with respect to the dominant TE mode from the given circular waveguide by simulating the 2D axisymmetric geometry of a 3D antenna structure.

### New Tutorial: Numerical Modeling of a UHF RFID Tag for Animal Identification

UHF RFID tags are widely used for identifying and tracking livestock. This example simulates a passive radio-frequency identification (RFID) tag for the ultra-high frequency (UHF) range. With respect to the chip transponder’s complex impedance, a reflection coefficient is computed. This is done using an approach that differs from the conventional scattering parameter analysis method by a real reference impedance value.

### New Tutorial: Hexagonal Grating

A plane wave is incident on a reflecting hexagonal grating. The grating cell consists of a protruding semisphere. The scattering coefficients for the different diffraction orders are calculated for several different wavelengths.

### New Tutorial: Modeling of a Mobile Device Antenna

Electrical components in wireless communication systems are designed to be small and light while maintaining decent performance and efficiency. Antennas are essential components in mobile devices and are required to fit in the limited space allowed by industrial specifications. To fulfill this requirement, a planar inverted-F antenna (PIFA) is common and a popular choice for miniaturized antennas in cellular phones. The PIFA design can be tuned and extended to cover multiple frequency bands from cellular phones, Wi-Fi, and Bluetooth®. The antenna in this introductory example is tuned only for the Advanced Wireless Services (AWS) band downlink frequency range. The impedance matching properties of the antenna are calculated in terms of S-parameters. The far-field radiation pattern is simulated.

### New Tutorial: Simulating Wireless Power Transfer in Circular Loop Antennas

This model addresses the concept of wireless power transfer by studying the energy coupling between two circular loop antennas tuned for UHF RFID frequency. The size is reduced using chip inductors. While the orientation of a transmitting antenna is fixed, a receiving antenna is rotating and the best coupling configuration is investigated in terms of the S-parameters.

### New Tutorial: Modeling a Conical Dielectric Probe for Skin Cancer Diagnosis

The response of a millimeter wave with frequencies of 35 GHz and 95 GHz is known to be very sensitive to water content. This model utilizes a low-power 35 GHz Ka-band millimeter wave and its reflectivity to moisture for noninvasive cancer diagnosis. Since skin tumors contain more moisture than healthy skin, it leads to stronger reflections on this frequency band. Hence, the probe detects abnormalities in terms of S-parameters at the tumor locations. A circular waveguide at the dominant mode and a conically tapered dielectric probe are quickly analyzed, along with the probe's radiation characteristics, using a 2D axisymmetric model. Temperature variation of the skin and an analysis of the fraction of necrotic tissue are also performed.

*The tapered dielectric probe radiates human flesh for the purposes of finding cancer through reflection properties. It is excited by mm-sized electromagnetic waves coming from the waveguide. Shown is the norm of the electric field in the waveguide and on the dielectric probe, and the temperature variation in the human flesh.*

The tapered dielectric probe radiates human flesh for the purposes of finding cancer through reflection properties. It is excited by mm-sized electromagnetic waves coming from the waveguide. Shown is the norm of the electric field in the waveguide and on the dielectric probe, and the temperature variation in the human flesh.

### Time-Domain Modeling of Dispersive Drude-Lorentz Media

Plasmonic hole arrays have attracted great interest throughout the last decade since the discovery of extraordinary transmission through sub-wavelength hole arrays. The classical Bethe theory predicts that transmittance through a sub-wavelength circular hole in a PEC screen scales as (d/lambda)^4. Yet, transmission through holes in realistic metallic films can exceed 50% and even approach 100%. This phenomenon is attributed to surface plasmon polaritons, which can tunnel EM energy through the hole even if it is very sub-wavelength. This model is intended as a tutorial that shows how to model the full time-dependent wave equation in dispersive media such as plasmas and semiconductors (and any linear medium describable by a sum of Drude-Lorentz resonant terms).

### New Tutorial: Thermal Drift in a Microwave Filter Cavity

Microwave filters are used to eliminate unwanted frequency components in the output from microwave transmitters. They are typically inserted between a power amplifier and an antenna. The amplifiers are nonlinear and produce harmonics that must be eliminated with filters that have a rather narrow passband. Due to high power loads but also possibly from harsh environmental conditions, it is necessary to estimate the drift of the passband frequency due to thermal expansion. It is easy to demonstrate that by using steel for the cylinder, a temperature-driven adjustment of the distance between the cylinder end and the brass box (where the adjustment screw is) can automatically compensate for most of the thermal drift.

*Microwave filters are used to eliminate unwanted frequency components in the output from microwave transmitters. Due to high power loads and perhaps also from harsh environmental conditions, the drift of the passband frequency due to thermal expansion needs to be estimated.*

Microwave filters are used to eliminate unwanted frequency components in the output from microwave transmitters. Due to high power loads and perhaps also from harsh environmental conditions, the drift of the passband frequency due to thermal expansion needs to be estimated.

### New Tutorial: Axisymmetric Cavity Resonator

This benchmark model exemplifies the 2D axisymmetric formulation of the *Electromagnetic Waves, Frequency Domain* interface that is available with the RF Module. The tutorial calls for finding the resonant frequencies and fields inside an axisymmetric cavity with rectangular cross section and perfectly conducting walls. Analytical expressions for the eigenvalues can be obtained using separation of variables. The eigenvalues obtained with the COMSOL simulation are in excellent agreement with the analytical values. The model also contains instructions for plotting the Cartesian components of the electric field in 3D with the correct dependence on the angular coordinate. The plots are animated to illustrate that the modes are traveling waves with right- and left-handed circular polarization.

### Hexagonal Periodic Structures

Hexagonal periodic structures are now correctly analyzed using periodic ports. You only need to specify the incident wave direction to the sides of the hexagonal cell and all periodic boundary conditions will be applied appropriately. Periodic ports have also been improved to handle partitioned port boundaries.

### Time-Domain Modeling of Dispersive Drude-Lorentz Media

For the *Electromagnetic Waves, Transient* interface, you can now use the Drude-Lorentz dispersion model from the available Electric displacement field models. The *Drude-Lorentz polarization* feature can now be added as subfeatures to the wave equation feature. The *Drude-Lorentz polarization* feature adds the following equation to the desired domains:

This equation will be solved together with the time-dependent wave equation for the magnetic vector potential.

### S-parameters Set to Zero for Evanescent Modes

For port modes that are not propagating (evanescent), the S-parameters are now automatically set to be zero. Thus, you do not need to add logical expressions that nullify the S-parameters for frequencies/angles where the corresponding wave is evanescent. This simplifies the use of the S-parameters in postprocessing.