Simulation of antennas in Low Frequency

[rooby84]

Hey everybody!
I wanted to simulate an antenna in Low Frequency, but I don't know any suitable software for this purpose. I'll appreciate if anybody could help me out...
Thanks

 

[f95toli]

Can't most software packages that can simulate antennas go to low frequencies?
My only experience with antenna design was with Zeland IE3D (which is now part of a software package sold by Mentor) and that could down to very low frequencies (a few Hz), this was for on-chip antennas (patch antennas etc).

What software have you looked at?

 

[vk6kro]

There is a free simulation program called Eznec.
http://www.eznec.com/demoinfo.htm
Get the free "demo" version to try it out.

It is easy to use and accurate.

Low frequency antennas can be simulated but effects due to ground proximity have to be allowed for.

If you want to explore the theory of low frequency antennas, you can use "free space" mode which ignores ground proximity.

 

[Baluncore]

… to simulate an antenna in Low Frequency, …

Welcome to PF.
What approximate frequency are you referring to?
What type of antenna do you want to model?

 

[rooby84]

Can't most software packages that can simulate antennas go to low frequencies?

honestly I don't know that...Can they? I meant softwares like CST and HFSS

 

[rooby84]

Welcome to PF.

Thank you so much.

What approximate frequency are you referring to?
What type of antenna do you want to model?

I want to simulate a crossed-loop antenna at 100 KHz.

 

[Baluncore]

I want to simulate a crossed-loop antenna at 100 KHz.

Sounds like a Bellini-Tosi direction finding system to me.
http://en.wikipedia.org/wiki/Radio_direction_finder#Bellini-Tosi

At 100KHz the wavelength will be 3 Km, so I expect your loop diameter will be small when measured in wavelengths. The field pattern will therefore be that of a simple dipole.

Because your loops are orthogonal, (at 90°), they will not interact. For fixed stations it is usual to mount the two loops, one with N-S alignment, the other with E-W. On a ship one is mounted in the fore-aft plane, the other in the port-starboard plane.

This antenna configuration is not usually modeled with NEC type software. Analysis is best done by treating each loop independently, as an inductive loop with a capacitance to bring it to resonance.

There is a problem that comes from 100 KHz being in the middle of the “switching power supply” band. As a single turn loop you will pick up the local LF electric field noise. But if you have an even number of turns in each loop you can Earth the mid point where you take the balanced feed from the ends of the loop, usually at the bottom of the supporting tower. A single capacitor between the balanced feed points will bring the antenna to resonance.

A Faraday shield, (screen), can be installed in the form of a conductive tube or coaxial braid about the wire loop, that is also earthed at the base, but must have a short insulated gap symmetrically positioned, to prevent circulating currents. That system will respond only to the LF magnetic component of the signal. Most local electrical noise will then be rejected.

You will need to know the shape of the loop, it's size and the number of turns. That will permit calculation of loop self inductance and the value of the neutralisation capacitor required. I have equations to solve for regular polygon shapes, but to give the right ones, I will need to know;

What shape and size will your loops be?

You will also need to decide on the bandwidth. That can be adjusted by selecting the diameter and resistivity of the wire used to make the loop, or by using a resistor at the tuning capacitor to lower the Q of the resonance.

If you want to tune to a narrow band or channel you will want high Q. But if you want to use the output of the two loops on an x-y display to get the direction of signals or thunderstorms, you will need to use a much lower Q so as to reduce sensitivity to the phase error between the loops.

What bandwidth do you require?

It is common with crossed DF loops to have a very small third loop at 45° to the two main loops. That small loop is used to generate a milliwatt of test signal while trimming the capacitance to tune the loops to the same phase.

I'm sorry about the protracted process, but it will all be worth it in the end.

 

[rooby84]

Hey Baluncore!
Thank you so much.
I'm so sorry that I replied late. actually I'm working on your proposed process, and it will take some time. below is the antenna shape I want to work on:

Besides I have no idea of it's bandwidth :shy:

 

[Baluncore]

I think you inserted the image thumbnail, rather than the image.
Ah ha! US patent 6,014,111 .pdf attached.

 

[rooby84]

yes, that's it!
and fig 1a and fig 1b is the structure that I want to simulate ;)

 

[sophiecentaur]

For a receiving antenna at lf, a pair of crossed ferrites could give good sensitivity and be very compact. (Had to laugh. My auto spell kept trying to make it "crossed ferrets". Annoyed rodents?)