Dual-Linearly Polarized Leaky-Wave Patch Array With Low Cross-Polarization Levels Using Symmetrical Spoof Surface Plasmon Polariton Lines

A dual-linearly polarized (LP) leaky-wave antenna (LWA) with low cross-polarization levels is proposed. The LWA with 14 circular patches is fed by symmetrical spoof surface plasmon polariton (S-SSPP) lines. When the S-SSPP lines are excited by a common mode, {z} -components of the magnetic fields are out-of-phase, and those of the electric fields are in-phase, due to the symmetrical structure. The radiation generated by the magnetic couplings (M-couplings) between these two SSPP transmission lines and the patch array strengthens each other, while the cross-polarized radiation produced by the electric couplings (E-couplings) cancels each other out. From another perspective, the M-couplings excite the horizontally polarized (H-pol) TM 11 mode. The E-couplings excite the TM 21 mode; thus, the E-couplings mainly appear at higher frequencies. As a result, the M-coupling and E-coupling mechanisms are separated successfully. Specifically, the LWA radiates H-pol waves with high purity. On the contrary, with the differential-mode excitation, the E-coupling patch array radiates vertically polarized (V-pol) waves. Finally, a dual-LP LWA with frequency-controlled scanning beams and suppressed cross-polarization levels is designed. Measured results show that the dual-LP beams scan from backward to forward. In the whole band, the cross-polarization levels are less than −30 dB in the scanning plane.