patch antenna and surface current

edge currents of patch antenna

Hi!

I tried to simulate a patch antenna using FDTD. This patch is fed by a microstrip line.
In general it is working fine. but there is one unwanted effect: the currents flowing along the resonant length on the patch are not of the same size along the width of the patch. there is a strong and sudden increase towards the edges. the width of the patch or the frequency have no influence on this increase.
Does anybody know what might be the problem?

Thanks for your help
elm

If i understand ur question correctly its true. The currents in patch antenna are different in patch directions and the radiation is actually because of this. In one side the currents are in same direction and other size varies oppoiste to patch size. consequently leading to resonate at the particular frequency.
Kraus and Milligen are good for you to have a look

f i understand ur question correctly its true. The currents in patch antenna are different in patch directions and the radiation is actually because of this. In one side the currents are in same direction and other size varies oppoiste to patch size. consequently leading to resonate at the particular frequency.
Kraus and Milligen are good for you to have a look

thanks for your answer, but unfortunateley I didn't get it.
Let's define directions.the resonant length L= lambda/2 is in x-direction, the width W in y-direction. so currents are flowing in x-direction as expected: maximum current in the center x=L/2 and minimum current at the edge x=0 and x=L. What I was talking about is the fact that the current in x-direction at y=0 and y=W is much larger than the one at y=W/2. but all of them are flowing in the same direction. which currents have you been talking about?

The radiation of patch antenna is due to fringing fields from transmission line model. The current varies in width depending upon patch type. As an example the equvanlent currents in square patch in diagram varies sinθ and oppoiste in other direction.
This field also varies depending upon the type of resonant mode that depends on the antenna size, substrate heignt etc

i the As an example you can see the following diagram from Milligen