External Antenna Models | ANSYS *.ffd Antenna

ANSYS ffd Format

These sample files provide examples of the Ansys ffd format. STK computes the gain assuming a 50-ohm impedance antenna. If your antenna impedance is different (e.g., 75 ohms), you should include an additional less term, which for a 75-ohm antenna would be -1.7609126 dB.

When using ffd files exported by Ansys HFSS, you needs to be aware of settings that are not logged in the file, but provide important context for the data. For example, an ffd file does not contain the antenna impedance value, so STK assumes 50 ohm as the default. If a different value is used inside of HFSS before exporting the file, however, you would have to account for that with an additional loss term in STK. For an impedance of 75 ohm, the ratio 50/75 would represent an appropriate additional loss term on the object where the file is used. In other cases, HFSS accounts for an antenna connection (or mismatch) loss, a setting that is not exported as part of the ffd file. You need to account for this loss in the additional loss terms.

Frequency-independent far fields

In this case, the file format is simple. No keywords are used. The first two lines contain doubles representing start, stop, and num points for the sweeps of theta and phi. The angle units are degrees. To have a unique coordinate system, theta and phi should be in the range of 0 < theta < 180 and 0 < phi < 360.


ThetaStart ThetaStop ThetaNumPoints
PhiStart PhiStop PhiNumPoints

Then, the next lines give the complex components of electric field in the theta and phi directions. The units of E field is Volts. All these are doubles. For these lines, theta is held constant while phi is swept through all values, then theta increments to the next value, etc. So the lines correspond to (th1, ph1), (th1, ph2), (th1, ph3),…,(th1, phN), (th2, ph1), (th2, ph2), etc… This format enforces a strict uniform grid of theta and phi samples.


E_theta_real E_theta_imag E_phi_real E_phi_imag
E_theta_real E_theta_imag E_phi_real E_phi_imag
...

See the following example file:

			0  180  3
			0  360  5
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0

Frequency-dependent far fields

For frequency-dependent far field links, the data is supplied in blocks. The syntax for a frequency- dependent far field uses the following format:

	ThetaStart ThetaStop ThetaNumPoints
	PhiStart PhiStop PhiNumPoints			
	Frequencies NumFrequencies
	Frequency FrequencyValue
	E_theta_real E_theta_imag E_phi_real E_phi_imag
	E_theta_real E_theta_imag E_phi_real E_phi_imag
	E_theta_real E_theta_imag E_phi_real E_phi_imag
	… repeat for all theta and phi sweep points
	Frequency FrequencyValue
	E_theta_real E_theta_imag E_phi_real E_phi_imag
	E_theta_real E_theta_imag E_phi_real E_phi_imag
	E_theta_real E_theta_imag E_phi_real E_phi_imag

	… repeat for all theta and phi sweep points
	… repeat for a total of NumFrequencies

See the following sample data file:

			0  180  2
			0  360  5
			frequencies 3
			frequency 3.0e9
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			0.0  0.0  0.0  1.0
			frequency 6.0e9
			0.0  0.0  0.0  2.0
			0.0  0.0  0.0  2.0
			0.0  0.0  0.0  2.0
			0.0  0.0  0.0  2.0
			0.0  0.0  0.0  2.0
			0.0  0.0  0.0  2.0
			0.0  0.0  0.0  2.0
			0.0  0.0  0.0  2.0
			0.0  0.0  0.0  2.0
			0.0  0.0  0.0  2.0
			frequency 9.0e9
			0.0  0.0  0.0  3.0

			0.0  0.0  0.0  3.0
			0.0  0.0  0.0  3.0
			0.0  0.0  0.0  3.0
			0.0  0.0  0.0  3.0
			0.0  0.0  0.0  3.0
			0.0  0.0  0.0  3.0
			0.0  0.0  0.0  3.0
			0.0  0.0  0.0  3.0
			0.0  0.0  0.0  3.0

The syntax and their values are as follows:

The values are 0, 180, and 2 for ThetaStart, ThetaStop, and ThetaNumPoints in the first line.
The values 0, 360, and 5 do the same thing for Phi.
NumFrequencies represents the number of blocks defined in the data file. In this example, three frequency blocks are defined.
FrequencyValue represents the value of frequency for which you supply the far field data. In the Data File Example, FrequencyValue is as follows:

3.0e9 Hz for the first block
6.0e9 Hz for the second block
9.0e9 Hz for the third block