While simulating SIW filter I am getting a graph of reference impedance vs frequency as shown in the figure.
I am not able to identify what is the cause of this peak in the impedance and why is this varying with the frequency. Also, what does it signifies?
One thing that I observed is that while changing the dimensions of the waveguide port, the peak of the impedance graph is shifting.
I will be helpful if you can explain this.
Regards,
Anand
The waveguide won't let low frequencies through. In waveguide, the impedance changes with frequency. For the mode you are propagating, the impedance increases as the frequency drops, until it is infinite at the cut-off frequency. Read about waveguide and cut-off frequency.
I'm little bit confused. Are you asking about wave impedance inside the hollow wabeguide or input impedance of the waveguide. From your graph as provided here, it is found that you have given input impedance curve (w.r.t to port 1 and port 2). Therefore, it is not wave impedance. To calculate input impedance at fixed frequency, you have evaluate current and voltage at the port and as a result of that, you can find input impedance at the port. The peak is due to cut-off frequency. When you change the dimensions of the wabeguide, its cut-off frequency changes. As a result of that, this peak changes.
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