aparture coupled patch antenna bandwidth problem

[yefj]

Hello,I have tried to create a wideband patch antenna using aparture coupled feeding.
e_r=2.2 and h=0.787mm was used for both layers with the measues shown bellow for central frequency of 10GHz.
I have tried to use bowtie and straight slots and to play with the width .
but nothing makes it wide band.
In one manual i red that one layer needs to be with higher dielectric constant then the other.
but i cant see why?
how can i physicaly investigateusing current of field to see where exactly did i go wrong in the aparture coupling mechnism?
Thanks

 

[PlanarMetamaterials]

What bandwidth are you looking for?

 

[Azulykit]

Broad bandwidths are difficult but practical with aperture coupled patches. I designed one using parasitic patches, stacked that reached 50% bandwidth (s11 -10 dB, about 6 dBi gain, around 3 GHz to 6 GHz ) and lots of fiddling with the feed and patch spacing. As I recall I found a reference in one of David Pozar's books to get me started.

 

[yefj]

could you please give me a good refrence with physics explanantions?
Thanks.

 

[Azulykit]

I would look in (ieee) APS and MTT. As I mentioned above articles (and books) by David Pozar have additional useful bits. I do not know of one specific reference. For a while, a lot of work was done for UWB applications but not so much now. Older reference material in the literature can still be helpful.
You also might look fro articles by R. B. Waterhouse. He also has useful work on the increasing bandwidth subject.

The problem with patches is that they are inherently narrow band and to make things worse they detune easily if the ground plane is small and/or there are changes in the nearby environment. Note that many of the articles address matching and are mute about radiation characteristics. In real applications I am usually most interested in the latter.

I think of a patch as radiating because of the fringing fields at the edges. Think of the patch and ground plane as a cavity with radiation leaking at opposite edges. The dimensions of the patch are adjusted so that the opposite edges are in phase and radiate in the "broadside" direction away from the ground plane. With a good simulator you can see this characteristic. There are numerous ideas for adding parasitic slots and elements to increase the bandwidth of the antenna. I was most successful with stacked parasitic patches. R do not recall a reference with this particular physical description of a patch but it is nevertheless a common description of how a patch radiator "works".

I have generally had best luck with low dielectric constant material and wide spacing. I ended up with air gaps (rohacell supports) for the parasitic patches. You still have not said what you are looking for in the way of bandwidth,

 

[yefj]

Hello Azulykit, Pozar only says what parameter is good and what parameter is bad.
there is no field analysis so i can understand why..

for example why thin slot makes good coupling (field explanation)
Thanks.