mtee in ads

Hi all,

I am designing an oscillator at 8 GHz using HBTs on a microstrip substrate. I have designed the input and output matching networks in ADS using tlines and the circuit oscillates as expected as shown in the figures. However, when I add the MTEE_ADS component, the oscillation frequency jumps to 5 GHz unexpectedly! I know that there is a junction susceptance at the tee and hence expect some changes. I feel that this change is too drastic!

Please let me know if anybody finds what I am doing wrong!

Thanks!

Hi
As the mtee has physical size (it's a 3.9 by 3.9 mm square shaped patch) you are making your lines longer. Take it into account.

Agreed, except you missed a 0!. Reduce all line lengths by 1.547 mm (3.094 mm/2).

Thanks! I also have another question regarding the MTEE component. The documentation says that this model is valid only when f(GHz) x height of subs (mm) <= 0.4. Anybody know the reason for this?