# How to model passive elements when simulating an antenna?

So I started writing an antenna simulator program to design antennas for my needs. To calculate the electric field vector at every point, I split the active element of the antenna into a large number of smaller parts and the calculate the electric field generated by each element at that point - taking into account speed of light. In the program I simulated a dipole antenna and it worked well.

Now I'm thinking how could I add support for passive element? If I would like to simulate a yagi-uda antenna, I need to somehow take into account a passive element which does not fit into my model.

• This would be a very broad question, and books are written on this. Can you narrow your question down to a specific function/algorithm/calculation which you have a problem with ? -- furthermore, there are some (free and paid) downloadable apps which do precisely this :: can you explain the shortcommings of those which prompted you to write your own ? Jan 8, 2019 at 9:50
• As a ham (or electronics hobbiest or student), building you own radio (or software) does not require that commercial solutions have a shortcoming! (versus: appliance operators) Jan 8, 2019 at 14:28
• Thank you. You said exactly what I was about to say. I love programming and I need to learn about electromagnetic field for Olympic so I thought I will write this program. Jan 8, 2019 at 16:48
• How are you calculating the currents on the small parts of the antenna? Are you using a prior assumption about it being sinusoidal distribution as expected on a dipole? If so, it's fairly simple to apply that to the other elements. Or are you building a full interaction matrix between the elements? in which case parasitic elements are almost as simple as driven ones...? Jan 9, 2019 at 5:28

## 1 Answer

Without any insight into the design of your program, I can only offer some basic guidance.

The parasitic elements in a yagi design are shorted dipoles that can also be modeled as a collection of infinitesimal dipoles. A shorted dipole will re-radiate nearly all of the power that it intercepts. This re-radiation will interact with the driven element. The conditions of this interaction depend upon the relative spacial phase separation of the parasitic element from the driven element (and other elements).

The parasitic elements are also slightly shortened or lengthened compared to their resonant frequency. This is done so that the current to voltage phase relationship of the elements simulate the progressive spacial phase shift of a plane wave intercepting, or emanating from, the yagi antenna.

I would think you would find it beneficial to first understand the details of the design theory of a yagi type antenna. There are many references in text books on this subject as well as Internet resources. Here is one of many credible Internet sources.

• So from you explanation I understand that passive elements can be simply interpreted as shorted dipoles? Jan 8, 2019 at 16:50
• @atomd Correct. Jan 8, 2019 at 16:51
• So for every point on passive element I shall assign charge proportional to electric field in that spot? What about direction of that electric field? Or maybe I should make charge proportional to electric potential. And what about proportion factor? Jan 8, 2019 at 16:53
• in this simple model, the direction of the electric field would be given by the direction of the conductor. If you need to consider the conductor as anything but infinitesimally thin, you'll end up with a full finite-elements simulation of the EM field. I'd argue that even if you're insistent on writing your own, reading up on the design decisions and the theory behind OpenEMS should really be done before you venture too deep. Jan 8, 2019 at 18:55