I am a bit out of my area of expertise. I have done the Google search etc. came up with nothing. Any pointers to microstrip OMNI design descriptions would be very much appreciated.
You also may find some additional information by searching for "inverted F" antennas or "Planar Inverted F Antenna" (aka "PIFA" These aren't completely a microstrip type, but consist of a two-dimensional patch conductor above another two-dimensional patch conductor(Gnd). They are sometimes made using double-sided circuit board material that may be extra thick or with a substrate having a higher dielectric value.