How to find the feed location for a rectangular patch antenna?

[khilji3774]

Can anyone help me to find the feed location for a rectangular patch antenna, coaxially feed.. any formula if please

 

[khaled.ayman]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

Check out this post, it has everything you need:

https://www.edaboard.com/threads/166237/#post1177847

and let me know if you need further assistance

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I'm attaching an excel file that I've prepared with all the necessary formulas to design a square patch with coaxial feed.

 

[khilji3774]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

Thank You so much for your post, it was really helpful for me... furthermore if u kindly specify me that how we take tha height of patch? is there any formula for that or not? and also about ground plane height?

 

[khaled.ayman]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

No problem

If you're referring to the thickness, then ideally for the patch and the ground they can be modeled as PEC (Perfect Electric Conductors) or metal sheet with 0 height.

And, practically they should have thickness of around 0.035mm (35um)

 

[khilji3774]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

let supose i am using a substrate with thickness 1.5mm, so the ground plane thickness is not affected by the substrate? it can be any value for which we get good results. am i right?

 

[khaled.ayman]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

No ground plane thickness is not affected by substrate thickness. You just have to keep in mind that practically when fabricating this ground plane you will use a Copper sheet with thickness of around 35um as previously mentioned. So if you want to have a design which is close to reality take this into consideration. If you just want a quick design to check for some parameters then just model your ground or patch as a flat metal sheet with 0 thickness.

 

[1132]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

use CST microwave studio software

 

[khilji3774]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

Thank you for your help... it helped alot ... i am using CST microwave studio.

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Will you please guide me further more, when we have to feed a patch antenna coaxially, then how to find the impedance of the antenna at the feeding point?

 

[khaled.ayman]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

Ok, so I assume now you know how to get the optimum feed location right?

To find the current input impedance in CST, wait after the solver has finished running, click the "2D/3D Results" in the navigation tree --> "Port Modes" --> "e1". On the drawing pane you will find Line imp. which is giving you the current impedance, this should be in the range of 50 ohms.

In my example attached you can see that I get an impedance of around 48 ohms which is satisfactory.

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A quick note, the equations and excel file I've provided will give you the feed location. Yf is on the y-axis and should be in the middle of your patch. But for Xf after calculating the position, you will only reach your optimum feed point after some trials and error by manually moving your feed along the X-axis till you get the lowest S11.

 

[khilji3774]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

View attachment MSA @2.1GHz.zipSir, i have designed a microstrip antenna for 2.1 GHz using substrate permitivity of 1.39 and the height of 1.5mm. when i feed it , almost everytime i am getting the error of waveguid eport 1 is too small and so on. what should i do for removing this error and one thing more how to add shield to the waveguide.... I am also attaching the CST file please check it.. it would be a great favour with me.

 

[khaled.ayman]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

Hi Khilji,

I modified your structur:

- set the frequency range
- modified your feeding structure

Results are better now, but you need to increase your substrate size, maybe it'll improve the results.

 

[khilji3774]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

Dear Mr Khaled A hope u would be fine.
I checked the updated cst file, and now the problem is not present. sir can u guid eme how to feed the antenna in CST via coaxial feed, i mean how to construct it with shield and that of dielectric material, i didnt know the correct method as u have done in the CST file. and further more are u referring the substrate size as thickness of substrate or the length and width of substrate? and is there any rule regarding the thickness of substrate?
Thank You so much

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Dear K A
i am not able to find your email. please if u could provide me ur e mail

 

[khaled.ayman]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

Hi Khilji,

I will send you my email in a PM.

For the substrate I'm referring to LxW not height, I normally have substrate dimensions with 3-4 times the patch size.

Regarding the coaxial cable here are the steps taken:
1- "Feed probe" with material PEC, with radius 0.635 and with height 5mm in the negative direction

2- "Teflon" with material teflon, outer radius= 2.075, inner radius= 0.6375, height should start from the ground and end at the same location as the feed probe. You should first cut out a circle from the ground with radius 2.075

3- "shield" with material PEC, inner radius= 2.075, outer radius= 2.375, height shoud be the same as teflon

If you cross check these steps with my design you should understand the concept. If not then reach me on my email and I'll try explaining further.

 

[khilji3774]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

So nice of you sir...
Regarding the length and width of substarte i am following a formula i.e. Length of Substrate= Length of patch +6*thickness of substarte and Width of Substrate= Width of patch +6*thickness of substarte. is this wrong?

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Also clear me plaease. i have run the updated file which you sent me, the S 1-1 is almost -3db at the operating frequency, idoes it mean that the feeding point should be changed? and also is this a necessary condition that the Y axis feed should be at the center of the patch?

 

[khaled.ayman]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

Your formulas are ok.

In all my trials for MS Patch with coaxial feed, yes Yf is in the middle. But you can still move it around as an exercise to see the impact.

S11 should be in the range of -15 or much less even. -3dB means your antenna isn't matched, so try to move the Xf until you get the lowest possible S11.

Use the "parametric sweep" option in CST by changing Xf.

 

[khilji3774]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

where can i find the parametric wep option in CST and how to use it?

 

[khaled.ayman]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

I suggest you go through the tutorial found in C:--> program files--> CST STUDIOS SUITE --> Documentation. Inside there is a pdf file named "CST MICROWAVE STUDIO - Workflow and Solver Overview"

Go through the full tutorial, you will learn a lot of essentials in CST as well as the parametric sweep option.

Let me know if you have difficulties finding it, I can email the document.

 

[khilji3774]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

Thank u soo much sir...
let me know one thing, when we have to change the position of Xfeed, we have to reconstruct the whole coaxial probe. is it any other way to move that already existed feed point without reconstructiing it?

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Thank u soo much sir...
let me know one thing, when we have to change the position of Xfeed, we have to reconstruct the whole coaxial probe. is it any other way to move that already existed feed point without reconstructiing it?

 

[khaled.ayman]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

Of course there is!!!

First of all, you need to go through the CST tutorials I told you about, because you will discover some options that will make your life easier.

Second, check my example, you will find that in almost every dimension I am assigning a variable (e.g. W for width L for length..) in order to be able to modify my structure more efficiently.

If you do this, then you can simply change the parameter value for Xf in the parameter window and the whole coaxial cable will be automatically shifted to the new location.

So bottom line, when building a new structure do not assign numbers for every dimension, rather assign a variable (e.g. "r" for radius) and then assign the value to this variable.

 

[khilji3774]

Re: How to find the exact location for feeding coaxially a rectangular patch antenna

Thank you so much sir....
It really helped me and feeling v easy now