Branch Line Coupler Problem

[kent81]

I have design a branch line coupler for 5.8GHz
I have the structure of about 14mm X 50mm.
Then i sumulate it with EM simulator.

I dont know what happen to my design as result not same as theory. Firstly I though because of coupling problem between two lines as they close together (7mm).

However that, got people do research to reduce the dimension and there is 25GHz branch line coupler for MMIC (5um). The dimension so small and gap between line should be very small too, but they still can get good result.

Anyone can tell me any possible problem to my design??

 

[flyhigh]

Hi,

theory doesn't take into account the effect of discontinuities (basically T junctions). If aspect ratio (line width/line length) is mild, i.e. length is considerably larger than width, you could try re-optimizing the coupler. Otherwise discotinuities are coupled (meaning that they are not seperated enough to allow Q-TEM wave to become uniform after it) so cut and try is basically the only way to optimize it.

flyhigh