Why we talk about Quasi TEM instead of TEM in patch antennas?

[Albeiro]

I was just wondering about this. Why we always talk about quasi TEM when we treat patch antennas?

Thanks in advance!

 

[kellys_eye]

http://www.rfwireless-world.com/Terminology/difference-between-TEM-wave-and-quasi-TEM-wave.html

...explains it very well. Basically the differences in dielectric medium 'surrounding' the radiative conductor. In coaxial cable the dielectric is 'constant' but for strip lines (patch antennas) it's a mix of 'air' and the pcb material.