You can calculate either the near electric field (Lab = EF, default) or the near magnetic field (Lab = H) beyond the FEA computational domain using one of the following:

You can obtain the near electric field or near magnetic field at a point (X, Y, Z) in a coordinate system or along a path. When determining the field at a point, you specify a coordinate value in the global or a local coordinate system. You also specify a global coordinate system for the output vector. When determining the field along a path, you define a path using the PATH command and you set VAL to PATH. All previous path items are cleared before HFNEAR executes.

To use HFNEAR, you must first define an equivalent current source surface in the preprocessor. You must issue the HFSYM command to account for symmetry planes in the modeled region.

Far fields and far field parameters are essential for scattering analysis and antenna design. This section describes some useful POST1 operations for these analyses.

Far Electromagnetic Field

To plot far fields, use one of the following:

To print far fields, use one of the following:

You can display the magnitude or the Cartesian or spherical components of the far electromagnetic field.

Radar Cross Section (RCS) and Normalized Radar Cross Section (RCSN)

The bistatic scattering cross section (radar cross section), measures the scattering characteristics of a target for an incident plane wave. The radar cross section (RCS) depends on the dimensions and material properties of the object and the wavelength and incident angle of the plane wave. It is also a function of the polarization of the incident wave. You can calculate the RCS for the pth component of the scattered field for a q-polarized incident plane wave where p and q represent the φ and θ spherical components, respectively.

The RCS can be normalized by the wavelength in a 2-D analysis and the wavelength squared in a 3-D analysis.

To plot RCS or RCSN, use one of the following:

To print RCS or RCSN, use one of the following:

To plot RCS or RCSN, use one of the following:

Using PLHFFAR or PRHFFAR, you can calculate a 3-D RCS for radar echo area, φ-φ polarization, φ-θ polarization, θ-φ polarization, or θ-θ polarization. You can calculate a 2-D RCS using a 3-D computational model. You extrude a 2-D model a distance Δz in the z direction to generate a 3-D numerical model. You can use PLHFFAR or PRHFFAR to calculate a 2-D RCS for a TE or TM incident plane wave.

Refer to High-Frequency Electromagnetic Field Simulation in the Theory Reference for ANSYS and ANSYS Workbench for more information on RCS.

Antenna Parameters

You can obtain various antenna design parameters (for example, radiation pattern, radiation power, directive gain, directivity, power gain and radiation efficiency) based on the far field results. Refer to High-Frequency Electromagnetic Field Simulation in the Theory Reference for ANSYS and ANSYS Workbench for definitions of these parameters.

To print antenna parameters, use one of the following:

To plot antenna parameters, use one of the following:

You can display Cartesian or polar components of the antenna radiation pattern and direct gain.

Before issuing PLHFFAR or PRHFFAR, you need to flag a virtual equivalent current source surface using Lab = MXWF on the SF command in the preprocessor before solution. See Equivalent Source Surface for details. You must issue the HFSYM command if there is a symmetry plane in the modeled region. When calculating antenna parameters, use the HFANG command to define the spatial angles if the radiation space is not the entire spherical domain.

Phased Array Antenna

Before calculating far field or antenna parameters, you need to define the characteristics of a phased array antenna using one of the following:

The total field of a phased array antenna is equal to the product of an array factor and the unit cell field.

E_total = AF (E_{unit cell})

Refer to High-Frequency Electromagnetic Field Simulation in the Theory Reference for ANSYS and ANSYS Workbench for the definition of Array Factor.

You must account for symmetry planes in the modeled domain for postprocessing near or far electromagnetic fields beyond the computational domain. To do so, use one of the following:

The HFSYM command accounts for PEC or PMC symmetry planes that coincide with the X-Y, Y-Z or Z-X planes of the global or a local Cartesian coordinate system. It applies the image principle on the symmetric part of the computational domain to represent the radiation effect of the partial equivalent current source beyond the modeled domain. HFSYM accounts for the radiation that would be present if the entire structure was modeled. If there is a PEC or PMC symmetry plane, you must issue the HFSYM command before issuing HFNEAR, PLHFFAR or PRHFFAR. Although a PMC symmetry plane is a natural boundary condition in a finite element analysis, it must be defined by the HFSYM command.

You can specify the radiation space when calculating antenna parameters. To do so, use one of the following:

The HFANG command defines the radiation space of an antenna in terms of the type of antenna. For example, the solid angle of a dipole antenna is determined by φε[ 0,360°] and θε[ 0,180°] and (Figure 4.25: "Solid Angle - Dipole Antenna"), while the solid angle of a monopole antenna above ground plane is associated with φε[ 0,360°] and θε[ 0,90°] (Figure 4.26: "Solid Angle - Monopole Antenna above Ground Plane"). If the electromagnetic wave is not radiated into the entire space, you must issue the HFANG command before issuing the PLHFFAR or PRHFFAR command.

A phased array antenna is approximated by an infinite array of unit cells with periodic boundary conditions. When you calculate the antenna parameters of the entire array based on the solution of the unit cell , only half a radiation space should be defined (that is, φε[ 0,360°] and θε[ 0,90°]).

You can calculate scattering parameters between a driven port (Port i) and a matched port (Port j) using one of the following:

SPARM returns two S-parameters: S_ii and S_ji, where i represents the driven port and j is the matched port. For a multi-port network, the S-parameters are defined as follows where a and b are the normalized incoming voltage wave and the normalized outgoing voltage wave, respectively.

The condition a_j = 0 indicates a matched port. In your model, you should use an absorbing boundary condition, such as PML or a port with the IMPD option, to truncate the computational domain. It represents the matched ports of the equivalent network.

When the distance from the extraction plane to the reference plane is defined by the HFPORT command, the S-parameter phase shift is calibrated automatically. To de-embed the existing S-parameter data with Touchstone format, use the HFDEEM command.

For a multi-port device, you issue multiple commands to retrieve the required S-parameter matrix terms. The SPARM macro will output the magnitude and phase angle of the S-parameters.

To calculate the voltage reflection coefficient (REFLC), standing wave ratio (VSWR), and return loss (RL) in a COAX fed device, use one of the following:

To calculate the input power, reflected power, return loss, and power reflection coefficient for a driven port, use one of the following:

If you define a matching output port, the HFPOWER macro can also calculate the transmitted power, insertion loss, and power transmission coefficient. For lossy materials and conducting surfaces, you can also use it to calculate the time-averaged dissipated power (from surface impedance or shielding boundary conditions). To calculate dissipated power in a region, you must select the elements that are associated with the lossy material or the conducting surfaces.

For a periodic structure that is used as a frequency selective surface, you need to specify input and output ports. You can then calculate the reflection and transmission coefficients, power reflection and transmission coefficients, and return and insertion loss using one of the following:

Voltage is defined as the line integral of the projection of electric field along the path.

To calculate it you need to define a path from the central conductor to the ground as shown in the following figure for a coaxial waveguide (a), a microstrip line (b), and a coplanar waveguide (c).

You first define the path using the following commands or GUI paths:

You then calculate the voltage using one of the following:

The EMF command macro stores the results as the EMF parameter. All path items clear after EMF executes.

Current is defined as the line integral of the magnetic field H along a closed path containing the inner conductor:

To calculate it you need to define a closed current path contain the central conductor as shown in the following figure for a coaxial waveguide (a), a microstrip line (b), and a coplanar waveguide (c).

After defining the current path using PATH or PPATH, you calculate the current using one of the following:

A counter clockwise ordering of points on the PPATH command will yield the correct sign for MMF. The MMF command macro stores the results as the MMF parameter. All path items clear after MMF executes.

Characteristic impedance is defined as:

To calculate the impedance, you calculate both the EMF (voltage drop) and the MMF (current). The IMPD macro calculates the complex impedance at the specified location. You must define the voltage and current paths before issuing IMPD. The impedance calculation can work with a symmetry sector of a model. For example, if you model only 10 degrees of a coax cable, you can supply a multiplier term on the MMF (current) calculation to account for a full model.

To invoke the IMPD macro, use one of the following:

You can plot scattering, admittance, or impedance parameters on a Smith chart. A Touchstone file provides the input parameters and their type.

To convert and plot any input parameter type to a specified output parameter type, use one of the following:

You can use one of the following to convert and list scattering, admittance, or impedance parameters input by a Touchstone file:

You can also use the PRSYZ command to renormalize S-parameters based on a new port characteristic impedance. The renormalized S-parameters are output to a new Touchstone file jobname_Sparm.snp.

You can use of the following to convert and plot scattering, admittance, or impedance parameters as a function of frequency.

You can also use the PLSYZ command to plot reflection loss, insertion loss, isolation loss, and voltage standing wave ratio.

For more information on Touchstone files, see Starting the Solution. For an example problem, see Postprocessing Scattering, Admittance, and Impedance Parameters.

Macromodels are essential for efficient subsystem and system level simulation and the prediction of complex system performance. They can be generated in terms of equivalent circuits that are compatible with system level simulators such as SPICE. The electromagnetic behavior of a multiport component can be approximated by terms of rational functions and the equivalent circuits can be subsequently synthesized. A system level simulation can then be performed by inserting the macromodel into the system level simulator as illustrated in the following flowchart.

To create a SPICE macromodel, you first generate a Touchstone file from either a high-frequency full-wave electromagnetic solution or the measurement of a high-frequency structure. You can use the SPSWP command to generate the Touchstone file. You then generate the macromodel using the SPICE command.

The following are important points to remember when you are creating a SPICE macromodel.

The generated equivalent circuit is a subcircuit (SUBCKT in SPICE nomenclature) consisting of a set of nested SUBCKTs. The main SUBCKT, and the only one called, is named NPORT 1 2 3 4 … Nodes 1 and 2 define port 1, nodes 3 and 4 define port 2, etc. Hence, there are 2M nodes for an M-port component. All elements in a synthesized subcircuit are standard elements in SPICE. Therefore, total compatibility is expected with most SPICE based circuit simulators.

For more information, refer to RLCG Synthesized Equivalent Circuit of an M-port Full Wave Electromagnetic Structure in the Theory Reference for ANSYS and ANSYS Workbench. For example problems, see SPICE Synthesized Equivalent Circuit for a Line-fed Microstrip Patch Antenna and SPICE Synthesized Equivalent Circuit for a T-type Transmission Line Network

You can apply the Inverse Fast Fourier Transform (IFFT) to frequency domain S-parameters to obtain time domain reflection (TDR) and time domain transmission (TDT) waveforms and an impedance profile. The PLTD command performs these transformations and displays the time domain results. You can also use the PLTD command to display the total waveform. The total waveform at an input port is equal to the sum of the incident wave and reflected waves.

Step and impulse input signal options are available (PLTD command, Lab = STEP or IMPU). The signal propagates through a transmission line at a velocity v_p and arrives at the far end at a time TD = d/v_p, where d is the transmission line length. A reflected signal arrives at the TDR output port at t = 2TD. The maximum frequency of the frequency domain S-parameter data determines the time step of the Fast Fourier Transform (FFT). To capture the transient signal variations, at least 5 time steps are required for the signal rise time. It should be noted that the impulse signal behaves as a periodic signal after using the FFT.

See TDR Display of Shorted Single-Ended Uniform Transmission Line for an example problem.