  The success of a given inflationary model crucially depends upon two
features: its predictions for observables such as those of the Cosmic Microwave
background (CMB) and its insensitivity to the unknown ultraviolet (UV) physics
such as quantum gravitational effects. Extranatural inflation is a well
motivated scenario which is insensitive to UV physics by construction. In this
five dimensional model, the fifth dimension is compactified on a circle and the
zero mode of the fifth component of a bulk $U(1)$ gauge field acts as the
inflaton. In this work, we study simple variations of the minimal extranatural
inflation model in order to improve its CMB predictions while retaining its
numerous merits. We find that it is possible to obtain CMB predictions
identical to those of e.g. ${\cal R} + {\cal R}^2$ Starobinsky model of
inflation and show that this can be done in the most minimal way by having two
additional extra light fermionic species in the bulk, with the same $U(1)$
charges. We then find the constraints that CMB observations impose on the
parameters of the model.
