A Wideband and High-Polarization-Purity Leaky-Wave Antenna with Continuous Backward-to-Forward Scanning based on Mode Modulation

In this communication, a mode-modulated leaky-wave antenna (LWA) composed of alternating arrangement of substrate integrated coaxial lines (SICL) elements and microstrip lines (MSL) elements is proposed. This LWA can not only achieve continuous backward-to-forward scanning without open-stop band (OSB) effect, but also has the characteristics of both wide bandwidth and high polarization purity. The radiation of the LWA is excited by mode discontinuities introduced between the transverse electromagnetic (TEM) waves supported by SICLs and quasi-TEM waves supported by MSLs, and continuous backward-to-forward beam-scanning can be achieved by optimizing the spacing between the two discontinuities formed by the two modes in each period to suppress the in-phase superposition effect of reflected waves. Meanwhile, in this design, SICLs and MSLs have the same characteristic impedance and surface impedance, as well as the low dispersion, so that a wide operating bandwidth can be achieved due to wideband impedance matching. In addition, due to the fully symmetric electric-field distributions of TEM and quasi-TEM modes, a high level of cross-polarization suppression can be achieved. Experiment results show that the proposed LWA can achieve continuous backward-to-forward scanning with 66% large relative impedance bandwidth (6.4-12.7 GHz) and 65% large pattern bandwidth (6.5-12.7 GHz), as well as a high cross-polarization ratio (XPR), which is measured to be about 27 dB.