Loading a log-periodic antenna in 2 different models

Georgios Kyriakou
Georgios Kyriakou Altair Community Member
edited November 2021 in Community Q&A

Hi, 

I would like to pose a question regarding the design of a Log-Periodic Antenna configuration which I have defined as a multiport network, as described in the relevant example of the FEKO User Guide. For the improvement of a specific characteristic of the antenna (narrow band gain response), I have introduced R-L parallel loads in some of the ports, which have been defined as in the first image I attach. Although this works as expected in this simple model, I would like to also confirm the result in a more complex model where the log-periodic antenna boom is implemented as 2 parallel rectangular conductors providing the desired Z0. In this case, I thought that the equivalent circuit would be to connect the 2 conductors at the height of the dipole of interest with a wire, define a port and the use the same load as in the transmission-line (TL) model. That does not seem to work properly though. The only way I could imitate the performance of the TL model was by defining 2 ports, calculating the 2x2 S-matrix of the R-L circuit and loading it as a touchstone file in a general network element (second image, right, there are 2 conductors although they cannot clearly be seen because I wanted to show the ports).

My question is, why does this distinction exist in the more complicated model? Shouldn't there be a voltage drop on a wire connecting 2 points when a load has been defined on its corresponding wire port, or is the electrical connection preserved and the R-L load is "branching out", as I depict on the left of the second image? That would mean I might have to modify other models too, so I would like to clearly understand how the load works.

Thank you,
George

 

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Answers

  • Mel
    Mel Altair Community Member
    edited November 2021

    All loads, including a parallel circuit, is placed in series with the port.
    If you would load a port with the below circuit and add a voltage source to the port, you would have (1) voltage source (2) circuit (3) antenna geometry (e.g. 1st wire segment or connecting triangle) all in series with each other.
    And every port connection is a differential (plus/minus) connection.

    image

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