Septum Dudes

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Pablo_UDEC

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Hello everyone, I need help. This is my first experience working on my undergraduate project in HFSS. I am designing a septum OMT that will allow me to measure circular polarization at two frequencies: 1.42 and 1.65 GHz, so I need a perfect or stable 90° phase shift over 200 MHz. I haven't been able to achieve this using the HFSS optimizer, and I'm struggling to set the GOALS correctly. I’ve read a lot but still have doubts. I’m attaching my project. If you could give me some recommendations to improve it, regarding parameters like the axial ratio output function, measuring the 90° phase shift between Ex and Ey, scattering parameters, etc., I would be very grateful. Thanks in advance.
 

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Pablo_UDEC said:
I need a perfect or stable 90° phase shift over 200 MHz
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In theory a series capacitor gives you a 90 deg shift between sine wave voltage and current. Explore how to choose a Farad value and type of construction so you can get optimum performance.

An inductor may create the same 90 deg difference in theory, with a sine wave.
 
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I understand, but the models for the heights and lengths of the septum based on documentation are a function of a coefficient between 0 and 1 multiplied by the wavelength. From this, I need the models to maintain a good axial ratio through 90° phase shifts between the linear modes (TE01 and TE10). That said, I find it difficult to understand how each step has a dimension (a x b) and behaves like a capacitor and inductor. If you could help me with that, I would greatly appreciate it. I have seen some designs where, for example, n=5 (number of steps), the first steps affect the high frequencies, and the second and third steps are optimized for objectives like their scattering parameters and axial ratio, for example. Thanks for your response.
 

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