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#### micro_tech

##### Member level 1
slot antenna finite ground plane

Hi all,

but I hope there's someone in this forum who have experience in designing slot antenna. OK, as mentioned, I'm trying to design the slot antenna which feed by microstrip line.

The question are:
- First for the feed line, from the reference I only got impression that the width of the microtsrip line, contribute to the impedance. but what about its length? how can I figure it? I mean, what is the length value I should chose/use. because there's no explanation regarding it.

- I'm simulating using IE3D, so I made slot in the infinite ground plane, and then I add the microstrip line for the feed on top of the dielectric. And the I add edge-feed on it. Is that what I'm done is correct. If not please assist me.

- At first when I'm simulating I use infinite ground plane, but of course it's inpractical, so if I want to use finite ground plane. How I can determine its dimension? Is there any "guidance" on it.

Thank you for your time and help.

Regards,

ground plane size and stacked patch antenna

You have asked a number of questions. Slots are often used to feed patch antennas, particularly when one tries to increase the bandwidth. I mention this because there is information on slots in the technical literature associated with patch antennas.

The impedance of a microstrip is a function of the width, dielectric, and height but not the length.

As to feeding a slot, if you cross the slot with the line and leave about a quarter wavelength of line (assuming an open termination) you should at least be in the ball park for exciting the slot. You might also look into "radial stubs" as an alternate feed structure. A coax with the shield on one edge and the center connected to the opposite side isn't too bad as an alternative.

Going down a different path, radiating slots may be cut in a waveguide. From your question this may not be what you had in mind.

As a rule of thumb you need at least three line widths of ground plane under a microstrip. My view is that more is better. As to the minimum size for the groundplane around a slot, I have not seen any guidance. As a first guess I would think that anything less than a half wavelength would need to be studied very carefully. After several wavelengths I would expect the performance to come very close to an infinite plane. It really depends on your particular set of requirements as to how big you need for the groundplane..

Eng. Esraa

### Eng. Esraa

Points: 2
antenna slot

micro_tech said:
Hi all,

but I hope there's someone in this forum who have experience in designing slot antenna. OK, as mentioned, I'm trying to design the slot antenna which feed by microstrip line.

The question are:
- First for the feed line, from the reference I only got impression that the width of the microtsrip line, contribute to the impedance. but what about its length? how can I figure it? I mean, what is the length value I should chose/use. because there's no explanation regarding it.

"there is no fix length for microstrip line. you should design it to the actual length that you are going to use. But then, during design, you have to look at the smith chart. you will notice that as you lengthen the m/s line, the smith chart plot will just circulate accordingly. So the best bet is to simulate to the length you are going to use or where you are going to mount your connector to it. Also, as you lengthen your m/s line, you will notice an increase in your inductance."

- I'm simulating using IE3D, so I made slot in the infinite ground plane, and then I add the microstrip line for the feed on top of the dielectric. And the I add edge-feed on it. Is that what I'm done is correct. If not please assist me.

"For a start, simulating in infinite ground plane is ok. You need to at least get the design you wanted in n ideal situation first to get a hang of how the slot antenna will match to your port. With you start to define a finite ground plane, the result will shift a litte, but since you already know the trend of the shift, you should be able to tune it back. So no worries. "

- At first when I'm simulating I use infinite ground plane, but of course it's inpractical, so if I want to use finite ground plane. How I can determine its dimension? Is there any "guidance" on it.

"1/2 wavelength is the bare minimum i would say, don't go less than that. You can try to reduce your gnd plane size in steps to see the effect of it. Once it goes beyond the point where you cant tune your slot back to the operating freq, thats more or less your limit."

Thank you for your time and help.

Regards,

slotted antenna infinite plane

quarter lambda ground plane antenna

Hi, micro_tech:

Slot antennas (SA) are different from microstrip antennas (MSA). The input impedance Zin of MSA is not affected much by the size of the gnd because most of the field is concentrated between the patch and the gnd. Using infinite gnd and finite gnd will yield about the same results.

For slot antennas, the gnd can be an important part of the resonantor. When the gnd is not extremely big, you should try to consider the finite size of the gnd. Regards.

Eng. Esraa

### Eng. Esraa

Points: 2
slot antenna current distribution

I've been working on slotted patch antennas.. how can I help u?

Can u tell me something about the dimensioning of a stacked patch antenna in linear polarization?
I lost my notes.. :-(

Lupin

### micro_tech

Points: 2
explanation of slot antenna

Hi jian,

btw, I've simulated in IE3D for the slot antenna using finite ground plane, when I want to see the current distribution on it, why I can't see the magnetic one (only electric) contrary when I simulated using the infinite ground plane I can clearly see the magnetic distribution inside the slot?
whould you please describe how I can do this.

Btw, can we see the current phase in IE3D?

thanks before. I hope you could help me

regards,

jian said:
Hi, micro_tech:

Slot antennas (SA) are different from microstrip antennas (MSA). The input impedance Zin of MSA is not affected much by the size of the gnd because most of the field is concentrated between the patch and the gnd. Using infinite gnd and finite gnd will yield about the same results.

For slot antennas, the gnd can be an important part of the resonantor. When the gnd is not extremely big, you should try to consider the finite size of the gnd. Regards.

Hi Lupin,

I hope you could....
OK, I want to obtain an slot antenna that give Circular polarization actually...
so I design a slot with the shape of an L-shape that feed by microstrip line...
If you something about it (to obtain the CP), please do help me...
I mean how I can figure the appropriate length, width of sloth and stub or length of microstrip line. What parameters that affect it.

Thanks before,

Lupin said:
I've been working on slotted patch antennas.. how can I help u?

Can u tell me something about the dimensioning of a stacked patch antenna in linear polarization?
I lost my notes.. :-(

Lupin

the feed line, from the reference I only got impression that the width of the microtsrip line, contribute to the impedance.

yes, i have the same question. It seams to happen just in IE3D(compared with CST and HFSS), now i'd like to use the formula below to explain it, is it correct or not, you may have different idea.
Zin=Z0（（Zl+jZ0tan（βz））/ (Z0-jZl tan（βz）))

Hi, micro_tech:

If you use infinite ground plane, IE3D allows you to model the slots on infinite gnd as magnetic current represented by the polygons. If you use finite gnd, IE3D allows you to model the finite gnd as electric current represented by the polygons. You are visualizing either the e-current or m-current on the polygons.

Hi, amigo_pp:

The formula is ok for shifting reference plane transmission line except there is a typo there. You use - sign instead of + in the denominator. Here is the correct one.

Zin=Z0（（Zl+jZ0tan（βz））/ (Z0+jZl tan（βz）))

The issue is that Zl of the antenna is affected by the width of the feed line, the gnd size. Regards,

hi mircrotech,

i remember that there's a paper from Pozar dealing with microstrip line exciting a slot.. I have to look for it..

One question: do you need also the ground plane? in that case, I can tell u that the microstrip has to be lambda / 4 high on the gp.

As soon as I find the paper I send it to u..

However, something on the search engines should be available.

Regards,

Lupin

PS: Any idea on the stacked patch probe-fed dimensioning?

hi Lupin,

I really appreciate if you could provide me the paper you mentioned...
yes I use the ground plane the same layer as the slot...
so as brief, the antenna has 3 layer:
- top layer : ground plane and the slot
- dielectric layer
- bottom layer: microstrip line

did you mean the height between the top layer and bottom layer should be at least
quarter lambda?

btw, do you have any idea, for generating circular polarization?

I'm sorry I don't understand your PS mean, cause I don't use stacked patch nor the probe feed

regards,

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