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

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.

Dipole antenna.

The excitation pulse is taken as:

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.

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

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.

The defined ramp time signal, t.

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

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:

where the bandwidth was calculated as 200 MHz.

• 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:

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