Home / Examples / Electromagnetic Analysis [Hertz] / Example 22: S-Parameter Analysis of Differential Lines

Example 22: S-Parameter Analysis of Differential Lines

General

The characteristics of differential lines are analyzed.

S-parameters are solved for the differential mode or common mode.

Unless specified in the list below, the default conditions will be applied.

Results will vary depending on Femtet version and the PC environment.

Analysis Space

Item	Settings
Analysis Space	3D
Model Unit	mm

Analysis Conditions

Item	Settings
Solver	Electromagnetic Analysis [Hertz]
Analysis Type	Harmonic Analysis

Harmonic Analysis tab and Open Boundary tab are set as follows.

Tab	Setting Item	Settings
Mesh Tab	Frequency-Dependent Meshing	Reference Frequency: 1x109 [Hz] Select [The conductor bodies thicker than the skin depth constitute the boundary condition].
Harmonic Analysis	Sweep Type	Select [Linear Step by Division Number]
	Sweep Setting	Minimum: 0.1×109 [Hz] Maximum: 5x109 [Hz] Division: 10
	Sweep Setting	Select Discrete Sweep
	Input	1.0 [W]
Open Boundary	Type	Absorbing Boundary
Open Boundary	Order of Absorbing Boundary	1st-order

* Fast sweep is avoided for higher accuracy. The number of frequencies is relatively low, so the calculation will not take long.

Model

Two electrodes are created on a substrate. They function as differential lines.

They are surrounded by a rectangle air space.

Ports are set to both ends of air (AIR) and the substrate as shown below.
An integral path is set to a port.
The locations of the integral path are different between the differential mode analysis and the common mode analysis.
For the differential mode analysis, the integral path is set between two electrodes.
For the common mode analysis, it is set between one of the electrodes and the bottom of the substrate.
The bottom of the substrate contacts the electric wall outer boundary condition.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
0/Solid	SUBSTRATE	006_Glass_epoxy *
1/Solid	AIR	000_Air(*)
2/Solid	LINE	003_Ag *
3/Solid	LINE	003_Ag *
5/Sheet	Imprinting body
6/Sheet	Imprinting body

* Available from the material DB

Boundary Conditions

Boundary condition settings are different between the differential mode analysis and the common mode analysis.
The different settings are shown in red as follows.

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Setting for Differential Mode Analysis	Setting for Common Mode Analysis
PORT1/Face	Electric	Port	Integral Path: Set “PATH” as in the diagram A above Reference Impedance: Select Specify 100 [Ω] Number of Modes: Number of Precalculated Modes: 5 Click Select modes. Select mode01.	Integral Path: Set “PATH” as in the diagram B above Reference Impedance: Select Specify 25 [Ω] Number of Modes: Number of Precalculated Modes: 5 Number of Modes Used in the 3D Analysis: Select Automatic
PORT2/Face	Electric	Port	Same as Above.	Same as Above.
Outer Boundary Condition	Electric	Electric Wall

Results

Propagation Mode

Select Port for [Solver]. From [Mode], select 5 GHz which is the maximum analysis frequency.
As the number of modes to precalculate is set to 5,
five propagation modes are calculated for each frequency.
The diagram below shows the electric fields of five propagation modes calculated 1 at 5 GHz.for PORT.

A part of the Propagation constant dialog box is also shown at the bottom of each diagram below.
Propagation constant dialog box can be opened from Mode Information of the [Chart] button.

Mode

Differential Mode Analysis

Common Mode Analysis

50: 5.000000E+09 Hz: (0)