Hello,
there is four fed patch for best circular pol simulated in CST. When 1 port is excited the S31 is about -4dB, S21=S41=-13dB, S11=-15dB. It means that total efficiency of antenna is less than 60% (in one port fed mode) because ~40% of power return to the port 3. When all ports simultaneous excitation (with phases 0°, 90°, 180°, 270° for ports 1, 2, 3, 4 respectively) are performed the efficiency more than 95% by CST. Why efficiency calc doesn't connected with S-parameters for one port fed mode? With real feeding network the transmitted power between ports will come back to devider and total efficiency of antenna+devier will reduce.
When all the ports are excited, the signal exiting port 3 is S31+S32+S33+S34, with differing phases for each because of the different feed phases. These can add up to less than S31 because they are vectors (or alternatively phasors or complex numbers), so the efficiency can be 95%.
I think because of the split if you excite one port, you lose 3 dB in every other port, so when you excite all four ports you add up your transmitted power. I hope I understand your question. Good luck
due to the power passing through the transmission line will have different values if the dimension selection is not correct.
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