HFSS simple ring resonator filter

Hello

I am trying to design a simple one port ring resonator filter. I have calculated and simulate the band pass prototype filter using circuit level simulator and now trying to design using HFSS to get the similar result. I am designing a one port ring resonator filter which is 1 wavelength long at 1.8GHz using suspended substrate stripline. However I didn't get similar results as the one using circuit level simulator. The ring resonator resonate at 2.8GHz instead of 1.8GHz. My calculated radius for one wavelength long ring resonator was 26.5mm. I did play around with eigenmode and found that the radius of resonator should be somewhere around 26mm so that it resonate at 1.8GHz. However, when using Driven modal solution and after putting the 50ohm transmission line and considering coupling gap, i didn't get the similar result. I am very lack of experience on this and really want to learn if anyone can help me with this. I really want to know what went wrong with my design. Please find attached of my design and results

DEGREE ONE.pdfTg.pdfDEGREE ONE TEST 26.5.hfss.zip

Have you ever take the dielectric coefficient of the substrate into account while you're calculating the wavelength ??

Hello bigboss,

I am using substrate with dielectric coefficient of 2.23 in my design. Let say i took into account the dielectric coefficient, the radius should be around 17mm. Using this radius, my design resonate even further away from 1.8Ghz. I did try to play around with the radius and found that my radius should be around 40mm so that it will resonate at 1.8GHz which is way too big as compared to what i got from eigenmode solution. I really want to know what wen wrong with it.
Please help

Thanks!

Resonator sides should be far enough from electrical magnetic walls of the cavity to avoid proximity effects of the walls.
I'm not HFSS expert but your structure seems so close to the walls.Try to simulate by moving all walls far..



What is the purpose of the inner copper sheet circle in the outer metallic loop ???

Hello bigboss,

I'll try to change the box dimension and will update on the outcome later.
sorry, i've wrongly assigned the inner copper sheet, it supposed to be 'vacuum' instead of 'copper' because i am designing a ring resonator.
Let me try and see the outcome.

Thanks anyway.

Hello Bigboss,

I've tried to change the wall into few different dimensions. However, the results looks not much different from the previous one. And this conclude that the dimensions doesn't give much effect on the resonance. From my observation, the only thing that influence the resonance are the radius of the ring resonator as well as the gap capacitance. To make it resonate at 1.8GHz, the ring resonator has to be about 44mm radius which is not tally with the calculation taking into account the radius is one wavelength long at 1.8GHz. I am wondering what should cause the difference, do you have any idea?

Thanks