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Continuous transverse stub (CTS) arrays represent a high-performance and affordable solution for fixed-beam and scanning flat antenna systems, though intrinsically linearly polarized. In these systems, the polarization is controlled using add-on polarization converters or combining cross-connected CTS arrays. This two-part article presents a novel parallel-fed CTS antenna which achieves dual-linear polarization using, instead, a single array and two orthogonally polarized excitation fields. In this article, it is shown that, due to modal coupling, standard parallel-plate waveguides (PPWs) are not suitable as building blocks of the proposed antenna. Therefore, an alternative waveguide, the corrugated PPW (CPPW) is introduced. The dispersion characteristics of such CPPW are investigated. Guidelines to independently design the dispersion properties of the two propagating modes and avoid the excitation of higher order modes are provided. Based on this study, the design and simulated performance of a $Ka$ -band array of eight long slots parallel-fed by a dual-mode CPPW corporate-feed network are described. An extensive experimental validation of the concept is presented in Part II. [ABSTRACT FROM AUTHOR]

We present the experimental validation of the dual-mode, polarization-agile parallel-fed continuous transverse stub (CTS) antenna architecture introduced in Part I of this two-part paper. The Ka-band dual-mode CTS array described in Part I is characterized when it radiates in horizontal and vertical polarization. To this end, it is combined with two different quasi-optical beamformers operating in a quasi-transverse electromagnetic (quasi-TEM) and in a quasi-transverse electric (quasi-TE1) mode, respectively. The scanning capabilities of both multibeam antenna systems are demonstrated. The CTS array and its feed network comprising corrugated parallel-plate waveguides (CPPWs) are fabricated by additive manufacturing. Measurements show that the dual-polarized CTS antenna works between 29 and 32 GHz in a field of view of about 45°, achieving a peak gain of 31.3 dBi and very low cross polarization. These promising results pave the way for the realization of dual-circularly polarized beam-scanning antennas with application to broadband and compact Ka-band ground terminals. [ABSTRACT FROM AUTHOR]