I have designed a rectangular patch antenna with co-axial feed and observed that the impedance is more in the inductance region.
But, I expect that the impedance at feed of patch be symmetrical with the real axis(resistance line) of smith chart i.e half the frequencies in capacitance region and the rest in inductance region with zero reactance at resonance.
In the simulation , is the discrete port excitation the reason behind the shifting to inductance region.?
OR
Something else is actually contributing which I am ignoring?
Perhaps your discrete port excitation is inductive, because it is so narrow. If it were a 50 ohm microstrip it would be considerably wider than that. You could try a waveguide port the same width as 50 ohm microstrip would be - or whatever impedance you matched to. Perhaps take a microstrip line to the edge of the ground plane and use a waveguide port there.
Srinaga
Discrete ports are usually set up to be 50 Ohm resistive. I would recommend you leave the port as such.
It generally does not matter what quadrant the S11 resides in, unless you are considering amplifier load-pull performance, in which case you would have a target region on the Smith chart you wish to occupy for the in-band (and sometimes out of band) S11 contours.
If you really must have symmetry about the real axis, you just need to rotate the above S11 profile by 90 degrees using a 1/8 wave transmission line.
I think that discrete ports have the impedance you ask for, in the middle of a wire or strip joining it to the two ends that you define. The port will be resistive, but the wire joining it to the end points is inductive, and introduces a series inductance. I think this description of the discrete port is in the help files.
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