resonace of the Y-shape circulator

Hello guys,


I have some questions regarding the circulator.


1. By my understanding, circulator could be considered an inreciprocal and low-Q (BR especially) filter. So the resonace of circulator is the same as that of filter? The centre frequency of Circulator is just one of his resonant frequencies?


2. so when we do the HFSS simulation for a Y-shape circulator, we should first set the initial dimensions to match/meet one of its resonant frequencies, and then fine-tune the circulator near this resonance frequency. But this resonace frequency (working mode) doesn't have to be the cutoff frequency (main mode), correct?

(e.g. WR75's cut-off is around 7.8GHz, but it is always used in the 10~15GHz range.)



3. HFSS eigenmode doesn't make sence for circulator!


I designed a WR62 circulator.

As can be seen in attached Figure1, the centre frequency is around 14.77GHz

But in eigenmode results, the modes frequency is 5.65GHz,11.06GHz,12GHz, 13.93Ghz, 15.85Ghz, 17.33GHz.



5.65GHz is even smaller than the cutting-off for WR62(9.5Ghz)?

so many resonations near 14.77GHz, which mode we are actually using?





4. If we use one of these above resonance frenquency, we can notice other resonation are so close, which means higher-order mode may be possible affect the in-band performace?



I am so confused. Really appreciate any advice.



Regards,

Lee