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Example30Dipole and Monopole Antennas

General

• Dipole antenna’s characteristics are simulated for a full model, a half model, and a quarter model.

• Analysis of monopole antenna having infinite ground is explained.

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

• Also see [Exercise 7: Dipole Antenna].

Analysis Space

 Item Setting Analysis Space 3D Model unit mm

Analysis Conditions

 Item Setting Solver Electromagnetic Analysis [Hertz] Analysis Type Harmonic Analysis Options: Correction coefficient for the characteristic impedance 1.0 for dipole full or quarter model, and monopole antenna 2.0 for dipole half model 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 Harmonic Analysis Frequency Minimum: 3×10^9[Hz] Maximum: 6×10^9[Hz] Sweep Type Select Linear step by division number. Division number: 100 Sweep Setting Select Fast sweep S-parameter tolerance: 1×10^-3 Input 1.0[W] Open Boundary Type Absorbing boundary Order of Absorbing Boundary 1st degree

Graphical Objects

Dipole antenna’s full model, half model, and quarter model are shown below.
Monopole antennas is the same as the dipole antenna’s half model.
All models consist of copper ANTENNA body, AIR body, and port.

Dipole antenna’s full model is covered with a sphere of air.

Dipole antenna’s half model is covered with a hemisphere of air.
The flat face of hemisphere is on XY plane. It is set with electric wall boundary condition (EWall).
For the half model, this electric wall is a boundary condition indicating the symmetry.

The quarter model is created by cutting the half model with YZ plane.
The face on YZ plane is set with the magnetic wall boundary condition (MWall).
This magnetic wall is also a boundary condition indicating the symmetry.

• Refer to the [Electric tab] for the electric wall and magnetic wall.

Body Attributes and Materials

 Body Number/Type Body Attribute Name Material Name 0/Solid ANTENNA 008_Cu * 3/Solid AIR 000_Air(*) 6/Sheet Imprinting body

* Available from the Material DB

Boundary Conditions

 Boundary Condition Name/Topology Tab Boundary Condition Type Setting EWall/Face Electric Electric wall MWall/Face Electric Magnetic wall PORT/Face Electric I/O Port Reference Impedance: Select “Specify” and enter 50[Ohm]. Number of Modes   Number of precalculated modes: 5 Number of modes used in the actual analysis: 1 Select modes: none Outer Boundary Condition Electric Open boundary Select on the open boundary tab of the analysis condition setting.

Set up Mesher/Solver

 Setting Item Setting Frequency-Dependent Meshing Reference frequency: 5×10^10[Hz]

The resonant frequency calculated from the antenna length is given for the reference frequency.

Result 1: Comparison of Results for the Dipole Antennas with Plane of Symmetry.

Dipole antenna’s characteristics obtained for a full model, a half model, and a quarter model are all matched.

Antenna’s reflection characteristics can be confirmed in the S-parameters and Smith chart of impedance.
Go to the [Results] tab. In the [Chart] , click [SYZ Matrix].
In the [SYZ Matrix] dialog box, click [XY_Graph] or [SmithChart].
The corresponding graphs will appear.

• For the details of [SYZ Matrix] dialog box, see [SYZ Matrix].

The reflection characteristics of the full model, half model, and quarter model are shown in the Figure 1.
They are all well matched.

 Figure 1: The reflection characteristics of the dipole antenna’s full model, half model, and quarter model

Next, we will see the directivity which represents the antenna’s radiation pattern.
Go to the [Results] tab. In the [Chart] , click [Directivity].
In the [Directivity Calculation] dialog box, set the [Electromagnetic Waves Directivity] tab as in the Table 1.
Set Plane of Symmetry and Infinite Ground Plane according to the models as in the Table 2.
Click [Polar Graph], and a polar graph showing directivity like Figure 2 will appear.

• For the details of the [Electromagnetic Waves Directivity] tab, refer to [Electromagnetic Waves Directivity].

The directivity of the full model, half model, and quarter model are shown in the Figure 2.
Comparison is done at 4.5GHz where the reflection is small.
Radiation patterns are well matched too.

Table 1: Setting of [Electromagnetic Waves Directivity] tab

 Tab Setting Item Setting Electromagnetic Waves Directivity Frequency 4.500000 GHz Observation point φ Min: 0 [deg] Max: 0 [deg] Division: 0 θ Min: -180 [deg] Max: 180 [deg] Division: 72 Display Type POWER Unit dBi Plane of Symmetry and Infinite Ground Plane Refer to Table 2. Setup Horizontal axis: θ Other Input type: Division Efficiency Type: Radiation Gain Type: Input power referenced

Table 2: Setting of plane of symmetry and infinite ground plane

 Model XY plane YZ plane ZX plane Dipole Antenna Full Model Asymmetric Asymmetric Asymmetric Dipole Antenna Half Model Electric wall Asymmetric Asymmetric Dipole Antenna Quarter Model Electric wall Asymmetric Magnetic wall Monopole Antenna Infinite ground plane Asymmetric Asymmetric

 Figure 2: The radiation pattern of the dipole antenna’s full model, half model, and quarter model

Result 2: Analysis of Monopole Antenna Having Infinite Ground

Characteristics of the monopole antenna having infinite ground is analyzed.
Comparison is done with a half model of dipole antenna.

First, compare the reflection characteristics of the two antennas.

S-parameters and Smith chart are obtained as in the Figure 3.
The Figure 3 shows that the frequency is 4.59GHz where the imaginary part of impedance is close to 0.
Impedance Z of each antenna at this frequency are as follows.

• Dipole Antenna: Z = 64.019 + j 0.159 [Ω]

• Monopole Antenna: Z = 31.334 + j 1.883 [Ω]

Monopole antenna’s impedance is half of dipole antenna’s.
This means that when the same current flows in the dipole antenna and monopole antenna,
the voltage applied to the monopole antenna is half of that to the dipole antenna.
It can be considered to be a reasonable result.

 Figure 3: Reflection characteristics of dipole antenna (half model) and monopole antenna

Next, the radiation patterns will be compared.
In the [Directivity Calculation] dialog box, set the [Electromagnetic Waves Directivity] tab as in the Tables 3 and 4.
A directivity graph like Figure 4 will be obtained.
The Figure 4 shows monopole antenna’s gain is higher than dipole antenna’s by 3dB.

Table 3: [Electromagnetic Waves Directivity] tab setting

 Tab Setting Item Setting Electromagnetic Waves Directivity Frequency 4.590000 GHz Observation point φ Min: 0 [deg] Max: 0 [deg] Division: 0 θ Min: -180 [deg] Max: 180 [deg] Division: 72 Display Type POWER Unit dBi Plane of Symmetry and Infinite Ground Plane Refer to Table 2. Setting Horizontal axis: θ Other Input type: Division Efficiency Type: Radiation Gain Type: Input power referenced

Table 4: Setting of plane of symmetry and Infinite ground plane

 Model XY plane YZ plane ZX plane Dipole Antenna Half Model Electric wall Asymmetric Asymmetric Monopole Antenna Infinite ground plane Asymmetric Asymmetric

 Figure 4: Radiation pattern of dipole antenna (half model) and monopole antenna

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