Computer-aided design software and additive manufacturing provide flexibility in the direct fabrication of multi-material devices. This design and fabrication versatility has been investigated for the manufacture of dielectric spiral phase plates (SPP) to generate electromagnetic waves with helical wave-fronts. Three types of SPPs designed to produce an orbital angular momentum (OAM) mode number l=|1| were additively manufactured using multi-material extrusion and multijet fabrication methods. The phase mode and mode characteristics of transformed helical microwaves as a function of the SPP geometrical features was investigated experimentally in the 12 to 18 GHz frequency range, providing high purity at characteristic frequencies. The SPPs were further combined with an additively manufactured dielectric lens that provided a marked improvement in OAM mode purity. Finally, multiplexing and de-multiplexing of two OAM modes were demonstrated successfully using the optimum SPP geometry and design.

Two oppositely directed horns were fed by commercial Ku-band SMA coax via waveguide adaptors (Flann Microwave) connected to a vector network analyzer (Rhode&Schwarz ZNB20) for excitation and response measurement in the frequency range 12 to 18 GHz. A computer-controlled X-Y gantry system was used to move the receiver horn in a pre-programmed pattern to map complex scattering parameters in the plane perpendicular to the beam direction, positioned at approximately 35 wavelengths from the stationary source horn.

The raw experimental data presents the table of the view (x, y, S21(12.0GHz), S21(12.5GHz), S21(13.0GHz), … S21(17.5GHz), S21(18.0GHz)  ) where x and y are the scans coordinate and S21(F) is the complex transmission parameter measured in this coordinate point at the frequency F (in the range 12–18 GHz with 0.5 GHz step).
The data has simple naming such TypeSPP.txt (for the type of the SPP please refer the manuscript).
The *.mat files contain the centre position of the S21 phase for corresponding SPP and need to be used in the SPP_Mode_Ratio.m script accordingly.

Files organised as follows:
// main code //
| - SPP_Mode_Ratio.m        
// Raw data //
| - GRINSPP.txt
| - GRINSPP_lens.txt
| - SmoothSPP.txt
| - SmoothSPP_lens.txt
| - StepSPP.txt
| - StepSPP_lens.txt
| - MPlex_Mode2.txt        // modulation l=2
| - DeMPlex_Mode0.txt    // demodulation l=0
// minimum amplitude table //
| - T_GRIN.mat
| - T_Smooth.mat
| - T_Step.mat
| - T_Mod.mat
| - T_DeMod.mat

The graphical representation of the data can be done using Matlab script.