Example25 Antenna

General

The impedance characteristics of a loop antenna are solved.
Unless specified in the list below, the default conditions will be applied.

Analysis Space

Item	Setting
Analysis Space	3D
Modelunit	m

Analysis Conditions

Item	Setting
Solver	Electromagnetic Analysis [Hertz]
Analysis Type	Harmonic Analysis
Options	Select “Ignore the influence of face/edge electrode thickness” *

* This is the default setting. It is irrelevant to select it or not as there are no face electrodes with this model.

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

Tab	Setting Item	Setting
Mesh	Frequency-Dependent Meshing	Reference frequency: 13.56×10^6[Hz] Select “The conductor bodies thicker than the skin depth constitute the boundary condition.” As Metal is thicker than the skin depth, boundary condition with copper material loss is applied to the Metal surface.
Mesh	Meshing Control	Tessellations of Periodic Surface Minimum number of tessellations: 12 Loop antenna’s circular shape is approximated as a polygon. Minimum number of tessellations is 6 by default. That is a hexagon. To increase the accuracy, it is changed to 12. That is a dodecagon.
Harmonic Analysis	Frequency	Minimum: 12×10^6[Hz] Maximum: 14×10^6[Hz]
	Sweep Type	Select Linear step by division number. Division number: 50
	Sweep Setting	Select Discrete sweep
	Input	1.0[W]
Open Boundary	Type	Absorbing boundary
Open Boundary	Order of Absorbing Boundary	1st degree

Fast sweep is avoided for higher accuracy.

Graphical Objects

Loop antenna consists of solid bodies. A port and a lumped-constant C are placed on it.

They are sheet bodies set with boundary conditions.

The antenna is covered with spherical air, AIR. Its radius is 6m. 6m is 13MHz and about a quarter of the wavelength.

Open boundary is set on the surface of AIR.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
3/Solid	coil	008_Cu (*)
5/Solid	coil	008_Cu (*)
14/Sheet Body	Imprinting body
15/Sheet Body	Imprinting body
16/Solid	air	000_Air(*)

(*) Available from the Material DB

Boundary Conditions

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Setting
Port_001/Face	Electric	I/O Port	Reference Impedance: select Specify enter 50Ω. Number of Modes: number of precalculated modes: 5 number of modes used in the actual analysis: 1 Select modes: none
C/Face	Electric	Lumped constant	Capacitance: 20.65×10^-12[F]
Outer Boundary Condition	Electric	Open boundary	Select on the open boundary tab of the analysis condition setting.

Results

The impedance characteristic is shown below. The center of Smith chart is 50[Ohm]. S-parameter S11 is shown in the right graph below.

The reflected power is large in the S-parameter S11 graph. We will reduce the reflected power by changing the reference impedance of the port as follows. Impedance at 13GHz is 1.873-j50.502[Ω] in the Smith chart above. To reduce the reflected power, set the reference impedance at (1.873+j50.502[Ω]) which is the conjugate value. The result is shown in the graph below. As the impedance at 13MHz is used as a reference impedance, we can see the matching at 13MHz.

To obtain the same result as shown here, pay attention to the following points. Use the same meshes before and after changing the reference impedance. If the reference impedance is changed, meshes created by the adaptive mesh will also be changed. Create a new project before changing the reference impedance and analyze with the existing mesh. Specify the pdt file of the project with the reference impedance before changing.

See [Exercise 7: Dipole Antenna] for the details of the radiation patterns and settings.

See other Electromagnetic Analysis examples.