square patch antenna

[arjun1991]

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

 

[flanello]

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]

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..!!

 

[flanello]

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]

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 .
please please!!!

 

[jeeudr]

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

 

[blambrec]

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...

 

[flanello]

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.

 

[blambrec]

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