Far Field Patterns of Aperture Antennas with Central Shadow from the Feed

Joachim Köppen DF3GJ ... Kiel, Aug 2017

- This tool computes the antenna pattern of square and circular dishes,
illuminated uniformly, but also with shadowing by the feed in the focal
point, which gives the theoretical pattern.
One enters the relevant data and clicks the
**point source**button. The result is shown as a blue curve, with a light blue curve to indicate the pattern of the unobscured antenna. - The pattern can also be computed for a few types of extended sources
which are specified by their angular diameter. If a point source pattern
is displayed, one clicks the
**extended source**button, and the result is shown as a red curve. The gray curve indicates the brightness across the face of the source. - The 1 D source patterns are computed somewhat more quickly than the 2 D patterns.
**overplot**permits to superpose different plots, in order to compare different patterns.**Display**: one may set the**maximum offset angle**and choose between**linear**and**logarithmic**ordinates (factor of 10 corresponds to 10dB). One may choose between**true gain**which shows how much the main lobe loses because of the shadowing, and**adjust gains to same peak**.- The mouse position gives the coordinates of that point, allowing to read numerical values from the plot. In some browsers, these values may not correspond to the plot. If this happens, keep this page in its initial top-left corner position.
- Please note that due to the finite accuracy chosen to get reasonably fast computations, one may get weird results if one pushes the tool to extreme choices of parameters! For example, a source diameter larger than 10 times the antenna's HPBW - which nobody really needs to compute - leads to perturbations in the central part of the pattern ...