11

Halfwave Dipole Antenna

High Frequency Analysis

In this model, one half of a dipole antenna has been modeled with a 1-meter length. The excitation at .15 gigahz excites a 2-meter wavelength. The current has been specified to vary from a maximum value at the origin to zero at the end of the wire. The model uses symmetry at the x=0, y=0 and z=0 planes. A PML layer is used to truncate the model at 2 meters. A maxwell surface flag has been applied to the surface between the solution domain and the PML layer to obtain far field calculations. These will be retrieved in post1 [PLHFFAR/PRHFFAR.] The input for the model is contained in dipole.dat. The solution takes about 10 minutes and a workspace of 128 Mb.

GIVEN:

A database, dipole.db, and a results file dipole.rmg

Brief Instructions

  1. Enter ANSYS 5.7 with the default jobname, “file”
  2. Resume dipole.db. Switch to a negative iso view [/VIEW,1,-1,-1,-1] with global z up [/VUP,1,Z]. Unselect the PML layer [ESEL,U,TYPE,,2].
  3. Enter the General Postprocessor and store the first set of results in dipole.rmg (Real results.) After entering Post1, it is necessary to indicate the results file, dipole.rmg, using the first menu item, Data & File Opts…
  4. Request isosurface type contours. PlotCtrls: Style> Contours> Contour Type… [/CTYPE,1]
  5. Display the electric field, Plot Results> Nodal Solution… Flux&Gradient EFSUM [PLNS,EF,SUM] It will appear similar to the display above. To see the field displayed with the symmetry reflection about xy as shown, do PlotCtrls: Style> Symmetry Expansion> Periodic/Cyclic Symmetry: Reflect about xy.
  6. Obtain the farfield value of the electric field at a 20 meter radius

  1. Specify the symmetry planes as PMC, PMC, PEC

  1. Obtain the field values over a 180 angle at 20 meters. Note that the angles start from X toward Y and Z toward X, somewhat different than CSYS,2.

  1. The graphical output will look something like this.

  1. Now display the Antenna Pattern. Re-do Step 7.

  1. It will look something like this. The final plot, “Antenna Pattern,” is more useful if displayed from 5 to 175 degrees.

  1. If you wish to perform some other postprocessing, resume the database again and re-enter post1.

ANSYS 5.7 New Features Workshop Supplement 11-5