printed antenna with omnidirectional pattern

[myata]

Hello, I should make planar antenna at 20 GHz with donut RP. It should cover with good gain all 360 in azimuth and at least 90 degrees in elevation. I tried lots of designs of monopole, loop, U-shape antennas with or without ground plane. But they are omnidirectional only when they are electrically small(poor matching), but not in normal resonating size. Monopole array gives me small angle in elevation.
Please give me an advice what can be wrong in my designs or some good examples of omni printed antennas. Probably there are some tricks how to match electrically small antennas.

Thanks in advance