quadrifilar helix antenna with backlobe

Hello
How can possible to get a back lobe with quadrifilar helix antenna?Is there any reference that mentioned design rule?
Thanks

A quadrifilar helix antenna's radiation pattern is symmetrical in the horizontal plane and so there is no "back" (as such) for a lobe to go.
Susan

Thank you dear Susan
but as my instructor told me when we remove ground plane and change the excitation of different lobe we can get back lobe.

i think he is right. of you remove the ground plane, you will get back the backlobe. you can implement it the way you wanted so get the response you wanted.

Use a thin dielectric instead of a metal ground plane. You'll get your back lobe.