Can Antenna Pattern be modified without taking the Antenna apart?

[AndreyG]

The antenna in question is dual polarized directional Panel, operates at 5GHz ISM band.
Horizontal beamwidth 60 degrees.
How to modify the pattern to make beamwidth ~120 deg (both polarizations) without disturbing radiating structure (structure is corporate-fed unidirectional patch array)?
Is there systemized, methodical way to design such modification?

Thank you,

Andrey

 

[Azulykit]

An "antenna" is in actually what most people consider "the antenna" as well as the material in the immediate vicinity. It is likely that modifying the immediate surroundings will change the radiation patterns.

Faced with this and looking for a civilized design approach I would do some testing in the lab to get a feeling for what might work and then consider one of the high end simulators. In your case, some sort of scattering element in the main beam would probably spread the beam. A roll of copper tape is your friend here. You might try covering part of the panel with absorber to make it appear smaller. That could also widen the beam and hopefully it will not screw up the feed too badly. Expect about a -6 dB decrease in the gain, that is what happens when you increase beamwidths.

 

[AndreyG]

I tried some modeling to see what works.
I modeled single patch instead of the array.

According to the modeler placing scatterer strategically widens pattern very effectively ... for one polarization.
Another polarization gets worse.

Also, match goes off.

 

[Azulykit]

Try moving the scatterer a bit further from the aperture or choose a shape that does not reflect directly back into the aperture. That might help improve s11.

Is your antenna linear or more square shaped? For linear arrays I would try long elements like wedges and cylinders. For a more symmetric (n by n array) cones, spheres or pyramids would be what I would try.

Narrowing one polarization and not the other seems strange. Try a sheet of parallel wires if you want to effect one polarization more than the other (polarization parallel to the wires are more strongly reflected).

I am curious about your results. PM me if you want a more private discussion.

 

[AndreyG]

>> Is your antenna linear or more square shaped?
the antenna is linear array of patches. Right now I am just testing single patch, study what to expect.

>> Narrowing one polarization and not the other seems strange.
Not only that, it seems no matter how i orient the scatterer - parallel or perpendicular to E-Field I always increase width of B-plane of the pattern. This is contr-intuitive but i keep repeating the same result. I switched to apertures - the same. I made square aperture roughly 3/4 wavelength, placed roughly wavelength away from square patch - B-plane becomes wide and E-plane - narrow. If I excite perpendicular side of the patch - switch E and B, pattern rotates 90 degrees.

 

[Azulykit]

Hmmm. Describe the scatterer. Have you had a chance to try any of the shapes yet?

Starting with a simple model to figure out how things work is a good way to start.

Are you simulating or making brassboard measurements. The thought is "Do I believe the simulation yet?"

 

[AndreyG]

I used strips of different widths, always in pairs located vertically and symmetrically with respect to the patch.
I tried long strips and resonant sections
After your advice I switched to cylindrical scatterers.
Then I switched to apertures - vertical slots in front of the patch, square openings in front of the patch.
The width of the openings and distance between scatterers I varied from width of the patch (~ 1/2 wavelength) to 2 wavelengths.
Position of the openings I varied from immediate proximity to the patch to 3/4 wavelength away
Also tried circular openings.
I always see the same trend: B-plane of the Pattern (perpendicular to E-field) is affected significantly, E-plane - not
Typical - axi-simmetrical setup: patch is square, aperture is square, Aperture size ~3/4wavelength
I excite with two orthogonal feeds. The resulting pattern is wide in B-plane and narrow in E-plane. I get two pattern orthogonal to each other.

>> Are you simulating or making brassboard measurements. The thought is "Do I believe the simulation yet?"
I simulate - got no measurement equipment at present.

I tend to trust the simulator - did several projects with it including patches, array of patches and Yagi-patch. In all cases experimental results matched simulation well.

 

[Azulykit]

OK. Here is what I understand about what you are trying to accomplish:

You have a panel antenna in the 5 GHz ism band. (5.725 GHz to 5.875 GHz. Right?)
The panel has 60 degree beamwidth in one plane. (How about the other plane?)
The panel is dual polarized. (I assume dual linear)

You would like to increase the beamwidth to 120 degrees. (Just one plane and not the other? 60 degrees to 120 degrees? I understand this to be the E plane for one polarization and the H plane for the other.)

You would like to not disturb the panel. Do you have additional information about the panel? Size? Gain? E and H plane patterns for each polarization? I assume that it is some sort of an array? Element description? Layout? ( 60 degrees seems a bit wide for an array. I would have expected a more narrow patten. Is the panel just a single element? Is it producing a wide patten in one and a narrow one in the other, a linear array for example?)

Is the 120 degree target in just one plane? Which one? Do you care about pattens in the orthogonal plane?

Do you have other physical constraints?

You have been able to increase the B plane patterns but not E plane patterns with scattering elements.

You are using a simulator and do not have an antenna range available. You have correlated measurements and simulations on similar antennas. That is reassuring and I would proceed with your simulator.

So far the experiments with the scattering elements have increased the magnetic field plane patterns but not the electric field plane. ( I am trying to make sure I understand your description relative to feed polarization, pattern plane, antenna panel and the final objective.)

I am still bothered by what you are telling me about how you see spreading in the B plane and not the E plane. Maybe I am missing something in your description. Many years ago I had some success with a turnstyle antenna radiating into a cone to spread the pattern. It produced an "circularly polarized omni" from a teardrop shaped feed patten. That you are having trouble here perplexes me.


Regards,

Azulykit

Another thought: You might consider taking two panel antennas and squint the boresight directions about 60 degrees in the horizontal plane relative to each other. Then feed the to antennas in phase. I would expect that you would also see significant (e. g. close to 120 degree) increases in the horizontal plane pattens.

 

[AndreyG]

You have a panel antenna in the 5 GHz ism band. (5.725 GHz to 5.875 GHz. Right?)
5.1 to 5.8 - it is WiMax
The panel has 60 degree beamwidth in one plane. (How about the other plane?)
Another plane is 4 degrees I believe

The panel is dual polarized. (I assume dual linear)
Yes, vertical and horizontal

You would like to increase the beamwidth to 120 degrees. (Just one plane and not the other? 60 degrees to 120 degrees? I understand this to be the E plane for one polarization and the H plane for the other.)
Correct.

You would like to not disturb the panel. Do you have additional information about the panel? Size? Gain? E and H plane patterns for each polarization? I assume that it is some sort of an array? Element description? Layout? ( 60 degrees seems a bit wide for an array. I would have expected a more narrow patten. Is the panel just a single element? Is it producing a wide patten in one and a narrow one in the other, a linear array for example?)
It is linear vertical array of 16 patches.

Is the 120 degree target in just one plane? Which one? Do you care about pattens in the orthogonal plane?
Ideally one plane only. Another plane should stay 4 deg.

Do you have other physical constraints?
In placement of augmenting structure I am limited with the surface of existing antenna

You have been able to increase the B plane patterns but not E plane patterns with scattering elements.
Correct.

You are using a simulator and do not have an antenna range available. You have correlated measurements and simulations on similar antennas. That is reassuring and I would proceed with your simulator.
Correct

So far the experiments with the scattering elements have increased the magnetic field plane patterns but not the electric field plane. ( I am trying to make sure I understand your description relative to feed polarization, pattern plane, antenna panel and the final objective.)
Correct

I am still bothered by what you are telling me about how you see spreading in the B plane and not the E plane. Maybe I am missing something in your description. Many years ago I had some success with a turnstyle antenna radiating into a cone to spread the pattern. It produced an "circularly polarized omni" from a teardrop shaped feed patten. That you are having trouble here perplexes me.
I thought more about it and I believe it makes sense.
If we think how scatterer works, in the core of it's function is the fact the EM field induces current on the scatterer. This current causes re-radiation of EM field.
When E field vector coincides with direction of the scatterer it works effectively.
When E-field vector is perpendicular to the direction of the scatterer, it is not.
This hints the simulator shows the right thing.

It does not help me to solve the problem

 

[Azulykit]

Ok, I have been thinking in terms of scattering elements "some distance above" the radiating patch. It sounds like you have been modeling elements in the same plane as the patch radiator. You said you were constrained to be in the plane of the patch in your last note. I was not thinking in that space.

You might consider modeling shapes above the patch plane to see if that works for you. If it pans out maybe the specification could be negotiated. Think of it as scatters imbedded in a radome for example. I suspect that an elevated, "wedge" scatterer would show widening of both polarizations.

Did you consider the idea of adding a second array? squinting one relative to the other would increase your 60 degree bemwidth and leave the 4 degree beam relatively undisturbed. Angle between the two antennas and spacing are parameters to adjust and it would not require antenna modifications. Some additional cable and a power divider would of course be needed.

 

[AndreyG]

Funny ... of course I modeled scatterers above the patch. in front of the patch. In the direction of main beam i.e. bore-sight.
I guess I did not express myself clear enough

Second array. structurally and cost-vice it adds a lot.
Are you sure it will result in wider beam?
In the extreme case when both patches point in he same direction and close to each other (1/4 to 1 wavelength) The beam width will half.
When they are under an angel ... not sure.
I will try modeling this, thank you.

 

[Azulykit]

The point is to not point the two antennas in the same direction. If they were pointing the same direction the array beamwidth would narrow as you described above. Start with the antennas about a half wavelength apart and pointed so that the beams just barely overlap. +/- 30 degrees might be a good place to start. I would expect to see a pattern that starts looking like a difference pattern as you increase the angle between the element boresight directions.

Certainly a 2x cost and volume increase will not be popular. Nothing is ever easy.

 

[AndreyG]

I might do this experiment. I let you know then.

Though it is still disappointment - I was expecting I stick scatterer in front of it and will be done.
Nothing is ever easy as you said


Stay tuned...