Dipole simulation with HFSS



      Dear all,

      I noticed that if we put the dipole (Hertzian-dipole excitation) close to the ground and I measured the E-field at one point far from the dipole, the simulated E-field is different from the one I obtained by using image method.

      Specifically, I did the following HFSS simulations and I noticed some differences

      Working frequency: 200 MHz. E-field observation point  P1: (0, 0, 400) mm

      Working space: free-space with a XY perfect conductor (PEC) plane at z = 0 mm.

      HFSS case #1: One dipole in a free-space space with a XY perfect conductor (PEC) plane at z = 0 mm.

      Dipole information: +y E Hertzian dipole, L=50 mm, Radius: 5 mm, location (0, 0, 30) mm (30 mm above the PEC plane.

      HFSS case #2 (image method): Two dipoles in a free-space space.

      Dipole information :

      1.     +y E Hertzian dipole, L=50 mm, Radius: 5 mm, location (0, 0, 30) mm.

      2.     -y E Hertzian dipole, L=50 mm, Radius: 5 mm, location (0, 0, -30) mm


      It is observed that the total E-field at P1 generated in case #1 and #2 are difference. 


      My questions is:

      1.     Why the differences are observed in Case #1 and Case #2 when the same setting is considered (same working space, same setting for analysis, etc.)

    • Praneeth
      Ansys Employee

      Hi Xinglong,

      Thank you for reaching out to us.

      Please see my observations / comments from your post:

      1. Did you check "infinte ground plane" while setting the PEC boundary condition in Case-1?
      2. Did you excite both the antennas for case-2? Please share the edit sources dialog box for case-2 simulation.

      Please share screenshots of the simulation geometry and setup to help us serve you better.

      Best regards,


      Hi! Praneeth,

      1. Yes. I actived the "Inf Ground Plane".
      2. Yes. see the attached screenshot

      Regarding the simulation geometry and setup, The setings for the two cases are similar.

      The solving space Box1 size:  Position: (-500, -500, 0); (Xsize, Ysize, Zsize) = (1000, 1000, 600). It is larger than the suggested size: Lambda/4.

      Solution types: HFSS-Network Analysis-Terminal (ANSYS 2022 R2)

      Analysis Setup: Freq = 4 GHz, Maximum number of passes: 20, Maximum Delta Energy: 0.1. Others: Default. Sweep: discrete-single point at 200 MHz.

      A screenshot:


      It is also noticed that the sizes of the solving space can affect the result of case 1, but cannot affect the result of case 2. The result of case 2 is constant and is always equal to the one obtained from the theoritical calculations. Therefore, I guess the difference is due to the pec GND of case 1. But I don't know the reason.

      I hope the information is enough and I look forward to your feedback/suggestions.

      Thanks and best regards,


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