How to calculate/simulate a rubber ducky spring antenna?

Hello everyone,

I am quite confused about the calculation of spring antenna (or rubber ducky antenna defined by Wikipedia). I tried with an online spring/helix antenna calculator to determine the parameters however the results do not seem like a rubber ducky antenna at all. Also, I tried to simulate a such antenna (by measuring its pitch, turns and radius etc.) with HFSS and the frequency response is far from what I desired.

The spring antenna that I am using is like this.


However, according to the online antenna calculator the size of a 433 MHz helix antenna is much larger than the one that I am using.

I hope you have already found out mistakes in my logic. I really have very limited knowledge about antennas however I want to know how to calculate and how to simulate the spring antenna that I am using.

Thanks a lot.

The spring antenna that I am using is like this.
https://www.alibaba.com/product-det...17019.html?spm=a2700.7724857.29.19.6MMDf1&s=p

A "rubber duck" or "spring" (helical wire) hasn't much to with a helix antenna with dimensions in the order of wavelength. In so far you can safely forget about using the online calculator.

It should be nevertheless possible to evaluate the antenna parameters with an EM solver, e.g. HFSS. Can you show a Smith chart and magnitude curve of S11 obtained in your simulation?