[Ask] how to increase bandwidth of 1*8 patch array antenna

Hi everyone,,
i have design a 1*8 microstrip patch array antena. I want to make it work in 3.3-3.7 Ghz. But when i measured the antena, it became dual band antena work in 3.3-3.5 and 3.6-3.7 Ghz.
I'm using inset feed and corporate feed network.
do you have any idea why the antenna become dual band antena,and how to make it work in 3.3-3.7 Ghz ?
Thanx

The array spacing might be less than that needed. Look into the mathematics of antenna.

you did not publish the details of your patch, but it sounds like it is a double tuned patch. You need to adjust the double tuned portion (near the feedpoint) so that the vswr does not get bad in the middle.

Complete design :

and the result :

i don"t understand about double tuned portion (near the feedpoint), is it similar to single stub matching ?
could you explain to me please
Thanx

Hello,

Did the single Patch showed desired behavior? If so, try two patches together (with the feed) and see what happens. You may feed them separately to see possible interaction.

When no interaction, maybe the problem is in the feed system.

i have designed 1,2 and 4 element before,and they showed desired behavior.
Yes i also thought that the problem is in the feeding system.
Is it necessary if i added resistor for isolation ?

Hello,

When I understand you well, up to 4 elements combined show desired behavior.

When 1, 2 and 4 patches (with feed) goe well, there must be something with the last combiner (that combines the 4 element arrays).

Place the 4 elements array together in there final configuration, and feed them from two sources (each 4 elem. array its own source). Check S11 and S21/12. If S11 is still OK (as with the seperate 4 element araays) and S12 is low, then the problem is in the combining, not mutual interaction.

Regarding isolation resistor. As the arrays are similar, they will show similar S11,S22 and similar S12,S21. Of ocurse assumming that you have strict production tolerances. In that case there will be no voltage across the resistor in a Wilkinson divider.

Other question, Did yuo also check whether current and current phase is OK for the 4 element array?

i have done what you said,,the S11 is still fine and S12 is low,so the problem as you said, in the combining.
Do you have any advice for me to make it better ?
Thanx before