can you give a brief explanation why they are not omni directional?
"varuniyengar" said in a earlier post that "Yes, a patch antenna can have omni radiation pattern in Azi and Ele planes.
These antennas are used for aerospace applications (as an array), mobile phones use PIFA and can have omni radiation pattern"
I found a IEEE article that demonstrates the design of a microstrip omnidirectional antenna. This should help you. The solutions seem somewhat practical. Good Luck......
Hello,
You can to designed the microstrip antenna with Omni radiation pattern by without a ground plane. Usually the microstrip antenna consisted of a radiator, a substrate and a ground is uni-directional beam.