dispersion diagram measuring

[R@SE]

hi

can anyone say how to measure the dispersion diagram of an antenna. please reply

 

[jiripolivka]

Dispersion of any object or medium means that a beam of energy is dispersed .i.e. reflected, lost or directed anywhere else.
To measure this effect you need a test range like for antenna pattern measurement. By rotating the device under test and locating test detectors around one can get the dispersion diagram in 3D.

 

[PlanarMetamaterials]

Hi R@SE,

I'm not sure if we're on the same page about what dispersion diagram you're referring to, but if you're looking for the modal frequencies inside the G-X-M Brillouin Zones, I've written up a summary of how to do this in HFSS at https://www.edaboard.com/threads/265560/#post1140645

Good Luck

 

[R@SE]

Thank You PlanarMetamaterials.

I read your summary at 'understanding field plots of MNG metamaterial' . i have done that sort of solving in HFSS on my antenna. But the thing is, my antenna has lumped elements in it, due to that it was not getting correct result. So i turned to experimentally measure the structure for dispersion diagram, which i don't know how to do.

it will be very helpful if u can say how to simulate as well as measure the dispersion diagram for a lumped element loaded antenna.

 

[jiripolivka]

I described the way to measure the dispersion diagram.

 

[PlanarMetamaterials]

Hi R@SE,

I use lumped elements inside my eigenmode solver all the time, there should be no problem in simulation.

Measuring the dispersion of an antenna would be an interesting thing to do; I feel like jiripolivka may be able to provide more insight into this, as I have no idea where to begin.

Edit: Are you familiar with effective medium parameter retrieval? As far as I know, this requires a two-port network, but perhaps someone has developed a way to obtain such parameters for a dispersion diagram using only one?

Good Luck

 

[R@SE]

Hi jiripolivka

How i can measure the dispersion diagram in 2D?
And also do dispersion diagram characterizes the propagation through a periodic media consisting of unit cell only??

 

[jiripolivka]

In a plane, rotate the dispersing object and record the dispersed power by a receiving antenna (horn) while irradiating the object by another antenna. Before the test record the directly coupled signal between antennas without the object and deduct this signal later.

- - - Updated - - -

I think any object does disperse the incident power. Certain effects are named e.g. forward and backward scatter, absorption and reradiation.

 

[R@SE]

if the dispersing object is antenna , then also we have to do the same test?... if so how we can feed that antenna?

 

[amntt]

Hi R@SE,

I use lumped elements inside my eigenmode solver all the time, there should be no problem in simulation.

Measuring the dispersion of an antenna would be an interesting thing to do; I feel like jiripolivka may be able to provide more insight into this, as I have no idea where to begin.

Edit: Are you familiar with effective medium parameter retrieval? As far as I know, this requires a two-port network, but perhaps someone has developed a way to obtain such parameters for a dispersion diagram using only one?

Good Luck

whenever i want to use lump element in eigen mode solver simulator error that eigen mode solver doesnt support descrete port ? do you put lump element without descrete port??

 

[PlanarMetamaterials]

whenever i want to use lump element in eigen mode solver simulator error that eigen mode solver doesnt support descrete port ? do you put lump element without descrete port??

Hi amntt,

I think you misunderstand how the eigenmode solver works. It solves for resonant modes in a structure. As such, no ports of any kind are required. I'm also not sure what connection you're making between lumped elements and lumped ports.

 

[jiripolivka]

if the dispersing object is antenna , then also we have to do the same test?... if so how we can feed that antenna?

Concerning the termination of a tested antenna, the best should be to use the nominal feed line impedance, e.g. 50 Ohms (or 300 Ohms for a symmetrical feed line).
Interesting can also be to use a short or open antenna load. All depends on the purpose of the real test.
I have not seen any suitable "simulation" of such dispersion test; I think it must be measured as I described.
As far as I remember, dispersion diagrams were of interest of the military when they needed to estimate target cross-section under various real situations. Airplane models were used, irradiated by radar signals and 3D angular dispersion was obtained. Propeller rotation was found having a strong effect back in WWII.
When satellite communication started, there was a lot of interference caused by reflecting terrestrial signals by aircraft above earth stations. Again an investigation was done, best results by using airplane models illuminated by light and dispersion diagrams measured. The "final" solution to the interference problem (still existing in C-band) was found by the ITU by giving satellite service special frequency bands, 11-12, 14 and 18 GHz where no terrestrial communication is not allowed.