Updated May 11,
here to go to our main page on couplers and splitters
here to go to our main page on branchline couplers
here to go to our page on quadrature couplers
New for May 2011! And
under construction... The patch coupler is a form of quadrature
coupler, related to the branchline. It looks sort like a branchline
with the center filled in. We came across this topic at the request
of one of our readers.
Her is one reference to the patch
coupler, there are surely many more. In this article an elliptical
coupler was proposed.
A Quadrature-Hybrid Design
Using a Four-Port Elliptic Patch, Kin-Lung Chan et al,
IEEE MTT, Vol. 45, No. 3, March 1997.
We didn't want to follow the
math for now, so we used trial and error to come up with a patch
coupler that works. We started with a GaAs substrate in an electromagnetic
simulator, drew a rectangle (just like an ellipse, it is asymmetric),
then played around with the dimensions until quadrature coupling
occurred. This is no way to design a circuit in real life, we didn't
have a target frequency in mind, just got lucky at around 120 GHz...
The port numbers are hard to
read, P1 is upper left, then P2, P4 and P3 when you move clockwise.
The rectangle measures 15 mils high x 13.5 wide, while the connections
are 3.0 x 7.5 mils (and are slightly higher than fifty ohms impedance
at 120 GHz). Overall dimension is 28.5 x 15 mils. The use of mils
rather than microns was out of laziness, these were default units
in the project.
Here is the coupled and direct
ports excited from P1. There is approximately 0.25 dB loss due to
the metal conductivity.
Here's the return loss and isolation:
The relative phases of the two
3dB ports are approximately in quadrature:
We'd appreciate another example,
especially if it included measured data!