2.4/5.8 GHz Microstrip Antenna Design
Your port setup looks incorrect for the structure you're simulating. Note that your substrate does not have a ground plane, but simply two layers: cond and M2. Your port editor shows that you're using a global Gnd for the negative reference for your EM port (this is what &lt;Implicit&gt; is referring to), which in the case of Momentum for a substrate without a bottom/top cover, uses infinity as the implicit reference.
Try setting the Gnd Layer column to the yellow layer in your layout (I assume that is M2) and re-simulating.