Can you please clarify which quantity is shown as "Y" in the diagrams? The impedance of a passive component, e.g. an antenna can be expected a complex value with non-negative real part. So if Y is the reactive (imaginary) impedance part, how about the real component (the so called radiation resistance)?
P.S.: I see, that the first plot is showing reactive impeddance, it looks quite common in this case. For the second plot, you need a reasonable impedance scale.
Thanks FvM
In both the figure X axis shows the frequency and Y axis shows Z11 of real and imaginary. almost flat line at 0 shows Real part and other buch of lines shows imaginary part at the different distance between antenna and parasitic element.
For the other figure i don't have access to lab for now so i can't do anything. but i can send you as soon as i can.
You can of course plot antenna impedances as real and reactive impedance R and X (Z = R + jX). But the plot scale must allow to see both values, which isn't the case in your second diagram. In the first, the important real impedance part representing the radiation resistance is missing.
You'll find R + jX plots in many antenna text books, e.g. Ballanis. I also agree with enjunear, that a Smith chart plot of s11 is most informative. Most engineers will use it to display empirical antenna measurements. It's also the usual starting point to design a matching network.
but i have plot Z11 Vs frequency not S11. i guess Z11 will give me the input impedance not the S11, if i am wrong than please guide me.
The Smith chart isn't very meaningful, because it has too few points around the antenna's resonance frequency.
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