AN-SOF Top Loaded Vertical

Some Mastodon posts about top loaded, shortened verticals raised enough interest to put together a quick model to see how they behaved compared to standard 1/4 wave verticals. Without regard to actual frequencies covered, constructed a 0.2m vertical with the upper half being a cylinder of ~ 0.045m diameter. Then just ran the analysis to see how it behaved (and where it might be resonant).

Running the analysis yields the following tabular results.

Here's the VSWR plot.

Here's the return loss (S11, db) plot.

The results tab for this analysis is below.

The simulation was run over the 300 to 1,200 MHz frequency range. Far field results at 300 MHz are below.

Far field results at 700 MHz are below.

Far field results at 1,200 MHz are below.

It's interesting that the lowest elevation angle lobe appears to be where the antenna is resonant. Need to look at this a little closer.

Conclusions: The operating bandwidth of the top loaded vertical appears to be greater than that of a standard 1/4 wave vertical over ground. More experimentation is needed to determine the optimal dimensions that might yield a VHF/UHF band (144-450 MHz) antenna using this technique.

Want to try simulating your antenna designs? Try AN-SOF from https://antennasimulator.com/ and begin your learning journey into the fascinating world of antenna analysis and design.

Here is the main page for my AN-SOF antenna simulations.