Analysis of continuous transverse stub (CTS) array by Floquet mode method

Abstract

A continuous transverse stub (CTS) array antenna is a low-cost, low-profile, easy-to-fabricate, innovative two-dimensional aperture antenna invented by W. Milroy (1993) of the Hughes Aircraft Company. A CTS array is eventually an array of long slots (stubs) which are fed by a parallel plate waveguide. An analysis using one-dimensional periodic Floquet mode expansion and method of moments to solve the active reflection coefficient of the continuous transverse stub (CTS) array radiated to free space has been formulated and solved. A computer program based on this solution has been developed and validated by comparing the results with HFSS/Eminence model. This Floquet mode solution of the CTS array can take care of the two-dimensional scan coverage in arbitrary continuous scan angles, which is not possible for HFSS/Eminence model. The solution also incorporates the multiple-layer superstrate matching radome effect. By using this Floquet mode solution for active reflection coefficient of the CTS stub radiated to space and the solution of the E-plane waveguide tee junction, a scattering matrix formulation can be obtained for each stub section of the CTS array. Thus, the far-field patterns, beam pointing angles, the antenna gain (or loss), and the input VSWR of the entire CTS array can be predicted. Computer programs based on the above scattering matrix cascading formulations for the end-fed or center-fed series-feed CTS antenna arrays have been developed.