  We present a design to generate structurally propagation invariant light
beams carrying non-integer orbital angular momentum (OAM) using
Hermite-Laguerre-Gaussian (HLG) modes. Different from previous techniques, the
symmetry axes of our beams are fixed when varying the OAM; this simplifies the
calibration technique for beam positional measurement using a quadrant
detector. We have also demonstrated analytically and experimentally that both
the OAM value and the HLG mode orientation play an important role in the
quadrant detector response. The assumption that a quadrant detector is most
sensitive at the beam center does not always hold for anisotropic beam
profiles, such as HLG beams.
