Circularly Polarised Omni Antenna

Hi,

can anyone help me out with some ideas on how i could achieve the attached specifications.

This is not an omni antenna, it has beamwidth in az and el of 160 degrees. It may be a helical design, although the dimensions seem a little small for 400 MHz. But the beamwidth is very wide, so the numbers may work out.

http://en.wikipedia.org/wiki/Helical_antenna

Might be that your antenna is Quadrifilar helix? Although I agree, the AZ angle spec should be 360 deg.