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

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#### 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.

*The ***Create time signal** dialog in POSTFEKO.

- 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.*

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#### 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.*

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