Contents I. Introduction
The leaky-wave antenna (LWA) is a common type of traveling-wave antenna with the merits of simple structure, broad bandwidth, high gain, and frequency-scanning capability. Recently, this type of antenna has been widely investigated for its demand in automotive radar [1], imaging systems [2], analog signal processing [3], and other applications [4], [5]. LWAs have been implemented in various forms/technologies. These include substrate integrated waveguide (SIW) [6], [7], stripline [8]–[10], Goubau line [11]–[13], composite right-/left-handed (CRLH) line [14], [15], and spoof surface plasmon polariton-based structures [16], [17]. However, most of the reported designs cover only a limited spatial range, with a varying peak gain. A full-space scanning LWA with flat gain remains a research challenge. Its realization has important applications and these include computational imaging [18]. Full-space scanning implies that the main beam of LWA can be steered continuously from backfire to endfire directions, covering a 180° angular span. Major challenges exist in obtaining continuous scanning around both broadside and endfire directions.
