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I have designed a directional coupler in ADS, and when simulating it in Momentum, I realized that depending the type of port calibration (checked on Calibration TML and Calibration None) the isolation of the coupler changes. Why is this happening?

Any help is appreciated!

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According to this Application Note from Keysight, the difference between those two calibrations is as follows...

TML:

The TML port calibration (known as Single Mode in earlier versions of ADS) is used when a transmission line will be connected to the port. For this port calibration type, Momentum extends the transmission line (or any edge of the layout in contact with the port). A calibration standard (a transmission line of twice the length) is simulated to de-embed the effect introduced by the transmission line. This calibration technique reduces the impact of higher-order modes around the source and adds the mutual coupling effect of the transmission line current with the circuit. It is recommended when the circuit is fed through a long transmission line(s).

None:

There is also the option to use uncalibrated ports in Momentum. These ports were previously called Internal ports in older versions of ADS, but are now simply called None. Uncalibrated ports can be placed anywhere within the circuit (not limited to boundaries between dielectrics and conductors) and may excite a single point, edge or area. Uncalibrated ports may be de ned using a single pin referenced to implicit ground (Gnd), or by using multiple positive pins and/or multiple negative pins. Sometimes, uncalibrated ports are the best choice for modeling how devices are connected to a circuit.

So it seems that each calibration will set different boundary conditions in the interfaces (ports) of your coupler, and that's why you're getting different results.

Just select the calibration type that better suits how the coupler will actually be integrated in the rest of your circuit. If you plan to access the ports of your coupler through transmission lines, the results of the TML calibration may be more accurate and correlate better with actual measurements when you build it.

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  • \$\begingroup\$ Thanks for the answer @enric-blanco !. Regarding to what you have commented, TML calibration will probably be more close to reality so the simulation with this port calibration type may be more plausible than the uncalibrated one. All I needed was answered, so thank you again! \$\endgroup\$ – euskadi Mar 30 '17 at 8:48

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