Altair Feko: How to Calculate the Time Response for a Given Input Signal in POSTFEKO

Esti Hansmann
Esti Hansmann
Altair Employee
edited August 2024 in Altair HyperWorks

This article describes how to calculate the time response for a given input signal in POSTFEKO.

 

Example

Consider a dipole antenna with a near field sampled from 1 to 30 metres away from the centre of the dipole on its electric symmetry plane.

image

Dipole antenna.

 

The excitation pulse is taken as:

image

 

image The frequency range should match with the signal bandwidth, see Altair Feko: What are the guidelines for defining a time signal in POSTFEKO? for more details.

 

Option 1 - Using Time Analysis

  • Define a time signal in POSTFEKO for the excitation pulse.

image

The Create time signal dialog in POSTFEKO.

 

  • On the Time Analysis tab, from the Near field drop-down list, select the near field result.

image

The time response of the near field for the given input time signal on the x-axis at 10 m.

 

 

Option 2 - Using Math Traces

  • Define the input time signal using math traces in POSTFEKO:
    • Define a ramp function t with duration 1e-6 s and the number of sample points as 201.

image

image

The defined ramp time signal, t.

 

 

  • Define the input time signal u in terms of t:

image

image

The input time signal, u.

 

  • Calculate the complex spectrum of the input time signal u, using an FFT and get the real and imaginary parts using math traces:

image

where the bandwidth was calculated as 200 MHz.

image

 

  • Determine the real and imaginary parts of the z-component of the electric field at 10m distance.
    • Create two near field traces using the near field result.
    •  In the result palette, select the Z-component check box and Real or Imaginary.

 

  • Calculate the Fourier transform of the electric field at 10 m using a math trace:

image

image

The time response of the near field for the given input time signal on the x-axis at 10 m.

 

 
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