antenna array S11 problem

I have designed a waveguide 1:16 power divider with s11 <-30dB in required band i.e 13.75-14.5 GHz. in the same band I have designed a dual polarized square horn antenna with s11<-30db. however when I simulate the power divider and antenna array together my s11 drops from -30dB to -15dB. I cant figure out the reason for drop in s11. the waveguide dimensions for power divider are same as input of waveguide. Need some urgent help.

Thanks in advance.

It sounds like a convergence issue, are you adequately meshing all three simulations?

It could also be the case that there is higher than anticipated coupling between the horns which would de-tune the return loss -- can you plot the fields between them and observe coupling?

The meshing is good, In CST it is 10 per wavelength. for coupling I simulated the 2 horns separately with same array separation and S12 was better than 55dB.

I dont know how to plot fields between 2 antennas?