Broadband Horn Antenna Input Impedance Matching

Hello everyone,

I am trying to design a 1GHz-2GHz rectangular waveguide fed horn antenna. I simulated the horn antenna into HFSS, here are the input impedance and S11 reflection results.

The antenna will be fed through a coaxial-waveguide adapter, so coaxial characteristic impedance is 50 ohms, and since there is air inside the waveguide, hence the characteristic impedance of the adapter is 377 ohms, then comes the antenna whose impedance is given in the figure above. I am wondering how can I design the impedance matching network? The idea that occured to me(might be wrong), place a chebyshev (tapered) transformer between the coaxial cable and the coaxial-waveguide adapter. Or is there any other way to do it? Any help will be greatly appreciated.

Thanks.

P.S. Someone else in the forum wrote that if S11 is below -10dB, the reflections will be small enough and the antenna will be matched, but as we can see above, the impedance at 1GHz is about 1096.9908 ohms. I am confused.

How did you conclude this? What equation did you use?