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help please,it's urgent: double inset feed patch antenna

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bvik

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hello everybody,
i am supposed to design a rectangular microstrip patch antenna for 2GHz and 2.5GHz with double inset feed. The patch length should be the resonating length for 2GHz and the width for 2.5 GHz. When i do it for individual frequency it is ok. but whenever i am using two inset feeds(one along length for 2 GHz and the other along width for 2.5 GHz) the frequencies shifts about 0.3-0.5 GHz to the origin. I have got no idea how to implement double inset feed. the project needs to be completed in 1 week.
i am using IE3D from Zealand for simulation.

i have searched the internet but i could not find a single example of double inset feed.
Please help.
Thank you in advance.
 

zorro

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Hi bvik,

When you test one of the insets, is the other one loaded with the matched impedance?
Can you show a drawing of the antenna?
Regards

Z
 

bvik

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hello Z,
Thanks for your reply.
Here is the drawing of the antenna:


---------- Post added at 14:40 ---------- Previous post was at 14:02 ----------

the length parallel to port 1 is 28.241mm(2.5 GHz). Width parallel to port 2 is 36.6 mm(2 GHz). Width of inset feed=3mm, each gap in between=0.2mm. Dielectric constant=4.4, substrate thickness=1.59mm.
 

zorro

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Hi bvik,

When you say "When i do it for individual frequency it is ok", are you speaking about this same design, or to something different?
For example, do you test feed 1 without the gaps of the other one? In that case, the effect of the gaps of the feed 2 cutting the currents would be different.
Regards

Z
 

bvik

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hello Z,

thanks for your reply.
I have got the dimensions. patch length 20mm, width 28mm. inset feed at 6mm and 9mm from edge. It gives good result.
 

zorro

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Hi,

The dimensions you gave now are quite different from the first patch. I don't understand with respect to which condition "the frequencies shifts about 0.3-0.5 GHz to the origin". Can you clarify?

In your case, the gaps necessary for the port 1 (or 2) inset cut the patch where the current is maximum when you feed by port 2 (or 1). So the current distribution is no more that of the cavity model, but much more complicated.
A double probe-fed patch is more common and does not have that problem.

Regards

Z
 

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