Home / Examples / Electromagnetic Analysis [Hertz] / Example 14: Coaxial Cable

Example 14: Coaxial Cable

General

The characteristics of a coaxial cable are analyzed.
The propagation constant and the electromagnetic field distributions are solved.
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	2D
Model Unit	mm

Analysis Conditions

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

The waveguide analysis is set as follows.

Tab	Setting Item	Settings
Mesh Tab	Element Type	2nd-order Element
	Multigrid/Adaptive Mesh Method	Select [Use the adaptive mesh method].
	Frequency-Dependent Meshing	Reference Frequency: 1.0x109 [Hz] Select [The conductor bodies thicker than the skin depth constitute the boundary condition]. METAL is thicker than the skin depth. Its surface will be set with the proper boundary condition based on the material automatically.
Waveguide Analysis	Analysis Type	Propagation Constant Analysis
	Sweep Type	Select Linear Step by Divion Number Division: 0
	Propagation Constant Analysis	Maximum Number of Propagation Modes: 1 Minimum frequency: 1x109 [Hz] Maximum frequency: 1x109 [Hz]

Model

AIR and METAL are represented by circular sheet bodies.

The integral path is defined by a wire body. It is an imprinting body connecting the outer and inner perimeters of AIR.

The integral path is used for the calculations of electric potential differences and the characteristic impedances.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
0/Sheet	METAL	003_Ag *
1/Sheet	AIR	000_Air(*)
2/Wire	Imprinting body

* Available from the material DB

Boundary Conditions

As the outer is conductive, the outer boudanry conditon is set to [Electric Wall].

The integral path is set to an imprinting body.

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Settings
INTEG/Edge	Electric	Integral Path
Outer Boundary Condition	Electric	Electric Wall

Results

The calculation results are listed in the table.

The characteristic impedance is 66.3 [Ω] and the phase constant is 21.0.

They are well matched with the theoretical values: Z0 = 65.9 [Ω], β = 21.0.

The electric and magnetic fields are shown below. The first figure shows the electric field vectors. The second figure shows the magnetic field vectors.