How to determine the bandwidth of a horn antenna feeding by WR28?

[imtiaz369]

I recently simulated a horn antenna in HFSS using the WR-28 waveguide. As we know, the WR-28 waveguide has its TE10 mode cutoff frequency at 21 GHz, and the next mode cutoff frequency at 42 GHz. To evaluate the bandwidth of my horn antenna, I ran a frequency sweep from 1 GHz to 70 GHz.

And my observations:

1. The S11 parameter appears to be very stable and consistently around -20 dB starting from 21 GHz.
2. The gain is above 15 dB across the entire frequency range after the cutoff frequency.

I guess that higher-order modes are contributing to the behavior, which might explain S11's strange stability across a wide range of frequencies. My goal is to determine the horn antenna's real bandwidth for its fundamental mode and filter out any higher-order modes.

Questions:​

1. Is my assumption about higher-order modes affecting the results correct?
2. How can I effectively filter out the higher-order modes to observe the performance of the fundamental mode only?
3. Is there a recommended method or metric to precisely determine the practical bandwidth of my design in a simulation?

Thanks in advance!

 

[ahsrabrifat]

You can use Eigenmode analysis in HFSS to verify mode distribution within the waveguide. Plot the E-field distribution in the waveguide cross-section to confirm that only TE10 is propagating up to 42 GHz.