input impedance of substrate integrated waveguide

good evening my dear
I am designing a microwave network in HFSS which I need to know the input impedance of a substrat integrated waveguide and because Zin = Z11 when I2 = 0 (open port), I have placed a LumpedRLC in port 2 by choosing R = 50 GOhms, in fact I had some result that I am not sure if it is correct or not. my questions are;

1- in HFSS is there a way to directly simulate the input impedance of a waveguide?

2- is it correct to place a LumpedRLC to simulate an open port?

thank you very much

Why don't you use s-parameters ??

BigBoss said:

Why don't you use s-parameters ??

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thank you for your reply
actually I need to know input impedance at resonant frequency to use it later in another impedance matching procedure but, it's possible to deduct input impedance from S-parameter ?

Are you sure that input impedance is the parameter you want? This assumes that one of your ports always has a certain condition (i.e., open). Are you sure you aren't looking for something like a characteristic impedance?

Nassimovitch said:

is it correct to place a LumpedRLC to simulate an open port

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It's probably better to have nothing.

I think result may be incorrect when putting small lumped element on large waveguide port. There must be transition from SIW to GCPW or microstrip line. Although it may be ok in HFSS. You can look into some HFSS waveguide examples. SIW port must be defined the same way as for rectangular waveguide. If you have difficulties making such 3d model and port, you can add small dielectric filled waveguide after last via of SIW, and then attach standard waveguide port to it. Or you are doing some kind of 2D schematic from HFSS microwave blocks?

You can check your result following way: make frequency sweep or change SIW length by one quarterwave. If your ports are ok, then impedance (or point on Smith chart) will be at the same position, with some insignificant change. If impedance value / point on a Smith chart changes significantly, then your ports have wrong impedance or defined incorrectly.