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# square patch antenna

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#### arjun1991

##### Newbie level 3
hai sir this is arjun,
I have a designed a square patch antenna.I have to give a probe feeding for my antenna and i dont know where to keep the feeding.
can you just show me how to sort this problem

You mean at what position the probe feeding should be placed?
Complex formulas are provided in antenna books like Microstrip antenna design handbook or Antenna theory.
When you have a simulation tool, you could use a optimization to find the best feed position.

arjun1991

### arjun1991

Points: 2
hai,
Actually i am using CST STUDIO SUITE , and i want to know like where my feeding should be exactly kept for square patch antenna..!!

First, you need to know what feeding impedance you want, I assume 50Ohm.
Is the feed included in the simulation?
Then you could use the optimizer to vary the feed position (for example in x and y coordinate) in order to get a good match to 50Ohm.
If this doesn't work you could change the size of your patch.

arjun1991

### arjun1991

Points: 2
Hai again,
See my patch i have calculated from em talk: epsilon(εr)=2.2 ;Dielectric Height (h):31mil so i got length: 8.9925 ;width :11.08
so can u please say me from the begning like how much i need to take substrate thickness,height, and probe feeding .

The input impedance of the patch is highly affected by the feeding point. You need to consider what input impedance you want to match to and then select a feed point based on that.

I think that you need to start from the fundamentals on the operation of patch antennas. A good introductory book like the Balanis text or Microstrip antenna design handbook should be where you should start.

Alternatively, at least read through this https://www.antenna-theory.com/antennas/patches/antenna.php

This is an excellent source - and as you'll find, an inset or 1/4 wave transformer will help with matching. The question is, what is the edge impedance?? I was wondering this myself a little while ago and came across this after a lot of looking around... I'm sorry I don't have any reference (it took a fair amount of digging):

${Z}_{edge} = \frac{\lambda}{2 \times 0.00836 \times\ W}$​

You'll still need to simulate after all this though...

arjun, it seems that you now have the size of your patch.
With that you can simulate your antenna and then find a good feed position!

blambrec, what do you mean with edge impedance? Sounds interesting.

At the antenna-theory.com site there is a page that talks about the impedance looking into the patch based on different feed methods, but they all are derived with respect to the edge impedance. Rather than a guess-and-check method, or depending solely on the output of an optimizer, using these equations should give an idea of what to expect. The edge impedance formula I found seems consistent with all the designs I found online, so I figured it must be ok.

Btw, the alternative feed methods for a patch are found here:

https://www.antenna-theory.com/antennas/patches/patch3.php

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