Re: mutual impedance of two dipole antenna array
1. It is quite possible that the resonant frequency will shift due to another conductor is put near the radiator. In this case, two identical dipole wires are put closer than lamda/2. The mutual coupling may change the characteristic LC of your original (single Dipole antenna), and its half-lamda resonant frequency might change even though they two has the same length. I have to check the text book again to learn if the freq will shift up or down.
2. I think mutual coupling can be described in many aspects, I do not explicitly know why you need to measure Y12, which is still valid I think. But I normally measure S21 to describe cross talk level (which can be understood as mutual coupling as well).
Hello Rodger.
You can measure S-parameters and convert them to Z-parameters, so actually it doesn't matter what you measure, it is just a matter of presentation.
Knowing the mutual impedance is good to know the impedance of both dipoles when you feed them together. You will see that both dipoles have same impedance (bot not equal to a single antenna) if you feed them in phase, or opposite phase. However when feeding them with other phase, each antenna has different impedance.
Getting the phase and dipole current as you want can be a time consuming task, because your are right, both impedance and resonant frequency changes (in other words both Re(Z) and Im(Z) ).
I want to measure Y21 first,because in fdtd is simpler.then you can convert it to S parameter.
finally rodger and wim!
do you think that my results are true?shift in Z12 (in peak frequency) is reasonable?
You have already demonstrated by the diagrams in post #7 and #11 that mutual impedance Z21 has the least intuitive connection to antenna coupling, because it emphasizes the "anti-resonance" points. Y21 shows the resonances, but still combines dipole self impedance and coupling into a single quantity. Thus S21 is my preferred coupling measure.
Hi Fvm.
can you explain me your answer?what is your mean from "mutual impedance Z21 has the least intuitive connection to antenna coupling, because it emphasizes the "anti-resonance" points"?
High Z21 value means the driving voltage casues about no current in the other antenna = apparently no coupling.