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HFSS simulation problem: CPW with interdigital capacitors

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abhi_kolkata

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HFSS simulation problem

hi,

i was trying to simulate a grounded CPW with interdigital capacitors over quartz(permittivity = 3.8)substrate.when i simulate only the grounded CPW , without the interdigital capacitors, it gives result that is quite close to the designed value(Z0 = 98 ohm).but when i put the interdigital capacitors (in the gap between the centerconductor and coplanar ground on both the sides of center conductor) to load the line and bring its Z0 down , the simulation results show no (almost none) difference from that without capacitors, while theoritically Z0 should come down.

i don't understand why is that happening.anybody plz help me with it.

eagerly waiting for replies.

with regards

abhi
 

jallem

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HFSS simulation problem

I think it may be because the integration line
is not defined or poorly defined. If the vector
is not touching the "metal" then there is not
connection. When usually happens to me the
first thing I check is the integration line when you
define the capacitor.
 

burton

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Re: HFSS simulation problem

I think you should pay attention to these notes as follows:

(1) I donot know the way by which you get the impedance. The Z0 you can get from the solutions->matrix is the port impedance, which is computed by 2D eigen value problem. So the Z0 of port impedance without capacitors is the same as with capacitors.
(2)You should try Ansoft ensemble for 3D planar structures, not HFSS.

Best wishes.
 

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