What is the function of so many squares in Antenna Area?

[tony_lth]

HI, Gurus,
In one antenna design, there are so many squares filled around the antenna.
I am curious about the function of so many squares (As the yellow lines circled area)?
Do they need to be grounded through vias?
Best,
Tony Liu

 

[volker@muehlhaus]

Doesn't look like RF functionality. I guess this is a manufacturing topic, to reach some minimum copper density on the top layer.

 

[tony_lth]

Hi, volker,
It seems not so.
Attachment is another antenna design.
I seems to isolate the antennas.
I just wonder if it is grounded, and how to decide its size?
Best,
Tony Liu

 

[vfone]

I think is just a bad design. There are just few printed antenna types that needs objects or ground planes nearby.
And patch antennas are not one of them, especially when they are part of an array antenna (increase coupling between antenna elements, affect edge elements behaviour, etc).
If you can keep clear the space around array patch antennas, is better.

 

[volker@muehlhaus]

Attachment is another antenna design.
I seems to isolate the antennas.

Hi Tony,

as written above, it reminds me of "dummy metal fill" used in IC technologies to fulfill metal density rules.

If it serves an RF purpose, these floating metal islands (smaller than 1/2 wavelength) might be to reduce/avoid surface waves.

 

[FvM]

Metal fill for PCB uses different shapes and less copper occupation, e.g 25 %. If individually grounded by via, the pads would behave very similar to massive copper pour. If they serve a purpose at all, they would be floating. The nearest correspondence that I see is with the pad arrays provided in power amplifiers to tune matching circuits by solder bridging.

 

[tony_lth]

Hi, Gurus,
I guess its function is similiar to fake antenna between working antennas.
I have done the simulation to insert several fake antennas between working antennas.
The results shows the main lobe gain increases about 1dB,while sidelobe not increasing.
And the ripple in the band increases to about 1.5dB.
So it seems that the beam pattern is fixed and more stable and can't be interfered by other factors.
Best,
Tony Liu

 

[vfone]

I have done the simulation to insert several fake antennas between working antennas.
The results shows the main lobe gain increases about 1dB,while sidelobe not increasing.

So you have done the test inserting dummy antennas between working antennas.
But what are the reults with and without the metal fill pattern?
Usually the dummy antenna elements are placed at the edges of the array, and always they are at the same distance as the active antenna elements.
In the second picture you posted, the metal fill is placed at higher distance from the array.

 

[tony_lth]

Hi, Gurus,
I have done the simulation with floating copper.
It seems the floating copper increasing the beamwidth, while increasing the ripple in the band.
With optimizing on the antenna dimensions, the antenna beamwidth should be increased markably.
Best,
Tony Liu

 

[KlausST]

Hi,

I'm no HF guy. I'm not able to say if it has a function at all.

If it has a function:
In acoustics one could use such pattern as absorber.
My idea: Copper has it's impedance, air has it's impedance ... and with the geometries you may create a new "impedance" between copper and air.

Don't know if this sounds plausible..

Klaus

 

[vfone]

Tony, can you post please the surface currents of the entire structure, including floating copper?

 

[tony_lth]

Hi, vfone,
Check the attachment.
Best,

--- Updated Oct 21, 2022 ---

PS:
I am a newbie in design antenna, could you comment on the antenna design from Jsurf?

 

[vfone]

Thanks for posting, but unfortunately this surface current density picture (Jsurf) doesn't tell much, why the antenna pattern is so much affected by the nearby metal pattern (when practically are no currents in the small pieces of metal).
Or maybe this is the main idea, the small pieces of metal (fraction of wavelength) to behave like a "chaff" for the antenna.
Spreading "chaff" was (is) a radar countermeasure, in which an aircraft spread many small pieces of aluminium foils which provides multiple returns, to confuse the radar systems.

 

[PlanarMetamaterials]

I have done the simulation with floating copper.
It seems the floating copper increasing the beamwidth, while increasing the ripple in the band.
With optimizing on the antenna dimensions, the antenna beamwidth should be increased markably.

They are possibly electromagnetic bandgap structures. As some have noted, the primary function is likely to prevent radiation/leakage in certain direction, e.g., to isolate the antennas from the rest of the circuitry. They may also be used to enhance radiative performance. If you're lucky, they will do both.

 

[vfone]

It happen to find a paper from Bosch where is written that those structures are for reflection reduction.
Actually here the topology is even smarter, they use both, H and V polarization for those patches.

 

[tony_lth]

Hi，
So I guess this structure is how to work, to reduce the reflection wave from the target. If without these, the reflection wave would incidence these area, then reflected by the 2nd layer GND, and forming multipath effect between radar and targets. With these, the reflection wave would be reduced. So I have two questions:
1. These rectangular copper should not be grounded by vias, right?
2. How to design these rectangular copper? Obviously, the length and width should be related with the lamda. Evenly, I found they are almost aligned with the combs. And how to simulate it in HFSS?
Best,
Tony Liu

 

[vfone]

Yes, I think your assumption about reflections is correct.
The rectangular parasitic patches should not be grounded by vias, could say that they are floating.
Can be seen from the picture that their dimensions are pretty much the same as the dimensions of the patch antenna elements placed in the middle of the series arrays.
The antenna elements of the series arrays have the length (the longer side) equal to half-lamda, and the width side is tapered, to minimize the side lobes.
The parasitic patches use half-lamda for all lengths, and the same width for all elements. The spacing between elements is not anymore half-lamda (as is between the elements of the series arrays), but smaller, most probably to get more mutual coupling between elements.