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