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

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bvik

Newbie level 3
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.

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

hello Z,
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.

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

hello Z,

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

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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