Dipole Antenna
Introduction
折戟是什么意思The dipole antenna is one of the most straightforward antenna configurations. It can be realized with two thin metallic rods that have a sinusoidal voltage difference applied between them. The length of the rods is chon such that they are quarter wavelength elements at the operating frequency. Such an antenna has a well-known torus-like radiation pattern.
Conductive radiator PML
特价促销
λ/4
Lumped port
Figure 1: A dipole antenna. The model consists of two cylindrical arms of conductive material with a voltage source in between. A region of free space bounded by a perfectly matched layer (PML) surrounds the antenna.
Model Definition
The model of the antenna consists of two cylinders reprenting each of the dipole arms. The free space wavelength at the antenna’s operating frequency is 4 m. Thus, each of the antenna arms is 1 m long and aligned with the z-axis. The arm radius is chon to be 0.05 m. In the limit as the radius approaches zero, this antenna will approach the analytic solution.
A small cylindrical gap of size 0.01 m between the antenna arms reprents the voltage source. The power supply and feed structure are not modeled explicitly, and it is assumed that a uniform voltage difference is applied across the faces. This source induces electromagnetic fields and surface currents on the adjacent conductive faces.
The dipole arm surfaces are modeled using the Impedance Boundary Condition, which is appropriate for conductive surfaces that have dimensions much larger than the skin depth. This boundary condition introduces a finite conductivity at the surface as well as resistive loss.
人生如棋励志名言The air domain around the antenna is modeled as sphere of free space of radius 2 m, which is approximately the boundary between the near field and the far field. This sphere of air is truncated with a perfectly matched layer (PML) that acts as an absorber of outgoing radiation. The far-field pattern is computed on the boundary between the air and the PML domains.
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The mesh is manually adjusted such that there are five elements per free space wavelength and that the boundaries of the antenna are meshed more finely. The PML is swept with a total of five elements along the radial direction.
Results and Discussion
The magnitude of the electric field around the antenna is shown in Figure 2. The fields appear artificially high near the excitation, as well as at the ends of the arms. The peaks in the intensity are due to local singularities; the fields at sharp transitions in the model are locally artificially high, but they do not affect the results some distance (1–2 elements) away from the regions.
The polar plot in Figure 3 of the far-field pattern in the xy-plane shows the expected isotropic radiation pattern. The 3D visualization of the far-field intensity in Figure 4 shows the expected torus-shaped pattern.
The impedance as en by the port is evaluated to be 119 + 30i Ω, which agrees reasonably with expectations. In the limit as the antenna radius and gap height go to zero and in the limit of mesh refinement, the model approaches the analytic solution for a dipole antenna.
Figure 2: A slice plot of the electric field magnitude around the antenna.
Figure 3: The polar plot of the far field pattern in the xy-plane is isotropic.热面
Figure 4: A 3D visualization of the far-field pattern of the dipole shows the expected torus-shaped pattern.
Model Library path: RF_Module/Antennas/dipole_antenna
Modeling Instructions
M O D E L W I Z A R D
1Go to the Model Wizard window.
2Click Next.涅盘重生的励志句子
3In the Add physics tree, lect Radio Frequency>Electromagnetic Waves, Frequency Domain (emw).
4Click Add Selected.
5Click Next.
6Find the Studies subction. In the tree, lect Pret Studies>Frequency Domain. 7Click Finish.
电热水器哪家好G L O B A L D E F I N I T I O N S
Parameters
1In the Model Builder window, right-click Global Definitions and choo Parameters. 2In the Parameters ttings window, locate the Parameters ction.
3In the table, enter the following ttings:
Name Expression Description
lambda04[m]Operating wavelength
arm_length lambda0/4Dipole antenna arm length
r_antenna arm_length/20Dipole antenna arm radius
gap_size arm_length/100Gap between arms
G E O M E T R Y1
Create a sphere with a layer. The outer layer prents the PML.
Sphere 1
1In the Model Builder window, under Model 1 right-click Geometry 1 and choo Sphere.
2In the Sphere ttings window, locate the Size and Shape ction.
3In the Radius edit field, type 2.5*arm_length.
4Click to expand the Layers ction. In the table, enter the following ttings:
Layer name Thickness (m)
Layer 10.5*arm_length
5Click the Build Selected button.
Choo wireframe rendering to get a better view of the interior parts.
天然海绵6Click the Wireframe Rendering button on the Graphics toolbar.
Then, add a cylinder with layers. The top and bottom parts are the antenna radiators.
A small gap between the antenna radiators is for the voltage source.
Cylinder 1
1In the Model Builder window, right-click Geometry 1 and choo Cylinder.
2In the Cylinder ttings window, locate the Size and Shape ction.
3In the Radius edit field, type r_antenna.
4In the Height edit field, type 2*arm_length+gap_size.
