  Orbital angular momentum (OAM) has attracted great interest in the past few
decades due to its helical phase characteristics. It has been proved that Plane
spiral OAM (PSOAM) has potential in pattern reconfiguration of azimuthal domain
because it solves the difficulty of mode superposition caused by different main
lobe directions of different modes. However, the absence of a compact
high-purity multimode PSOAM antenna hinders the development of PSOAM
applications. In this paper, a compact high-purity 8-mode PSOAM antenna
consisting of a coaxial resonator group (CRG) and a rotating parabolic
reflector (RPR) is designed. It works in the X-band with the bandwidth of 140
MHz, and its efficiency is greater than 90$\%$. Amplitude and phase of each
PSOAM beam generated by this antenna can be controlled independently owing to
its feed network and separate resonators design, hence any target pattern in
azimuthal domain can be approximately reconfigured by modes weighting. The
simulation and experiment results show that this antenna can make the PSOAM
based pattern configuration possible, which will have potential in the OAM
based applications.
