Is mismatch loss taken into account in point sources?

Altair Forum User
Altair Forum User
Altair Employee
edited October 2020 in Community Q&A

For electrically large problems it is often more computationally efficient to represent antennas, especially antenna arrays, with point sources. Could someone some light on the mismatch problem experienced with point sources?

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Answers

  • JIF
    JIF
    Altair Employee
    edited June 2017

    Consider two patch antennas some distance apart. The top patch, with regards to its boresight direction, is directed 180 degrees away from the bottom patch.

     

     

    geometry_full.jpg

     

    We are interested in computing the coupling between the two antennas. In the first case we will compute the coupling using the exact geometry for the antennas for reference purposes. In the second case we will replace the antennas with point sources.

    Computing the coupling for the full model using an S-parameter request yields an S21 value of -47.16 dB.

    To use the point sources, we first solve a single patch and for the far fields export the *.ffe file. Then a new model is created whereby a radiation pattern point source is set up for the bottom patch, and a radiation pattern point receiver for the top patch. For both the source and receiver, the *.ffe file previously exported is imported.

    The transmit and receive power in the point sources are given in the OUT file or available under 'Power' in POSTFEKO:

    • The source power for the radiation point source is obtained as 8.72e-4 Watt.
    • The received power for the radiation pattern point receiver is 3.43e-7 Watt.
    • The coupling is then given as 10*log10(3.43e-7 / 8.72e-4) = -36.8 dB.

     

    We see the radiation pattern point sources report some 10 dB stronger coupling than the full wave model (S-parameter S21). The difference is due to mismatch: the S21 parameter takes into account the mismatch losses, but the radiation patterns do not.

    We can include the mismatch losses in the coupling for the radiation patterns as follows:

    • The reflection coefficient for the patch is -1.63 dB or 0.829.
    • This gives a transmission coefficient of 0.559 or -5.05 dB.
    • Therefore adding 2x -5.05 dB to the coupling for the radiation patterns (we assume both patches have the same reflection coefficient) yields the coupling with mismatch taken into account as -46.5 dB.

     

    All of the above calculations can be performed directly in POSTFEKO using the 'Add Math' functionality on the result palette.

     

    The example files are available ().

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