A compact low-profile wideband omni-directional microstrip patch loading composite right/left-handed transmission line

A compact and low-profile wideband omni-directional microstrip patch antenna is proposed. The antenna is loaded by a novel spiral composite right/left-handed (CRLH) transmission line (TL), which is realized by replacing the interdigital capacitors of the conventional CRLH-TL with the spiral inductors. The antenna is composed with a four arms spiral line, a circle patch, four stubs connecting the patch and the ground. The antenna is fed by a standard SMA coaxial connector from the bottom. The bandwidth of the proposed antenna is up to 25.3% (VSWR<2). The antenna has a field pattern with a vertical electric field polarization, and has an omni-directional radiation pattern. The omni-directional radiation pattern is stable in desired operating band.