Broadband Omnidirectional Antenna with Stable Radiation Patterns for Indoor Data-Intensive Regions

In this letter, a broadband horizontally-polarized omnidirectional antenna (HPOA) with stable radiation patterns in vertical plane is presented. In this design, sector-like slots are loaded at the end of slotline structures to improve impedance matching and to reduce gain variation at high frequencies by changing current path on the ground. Metamaterial-based slow-wave structures, complementary split ring resonators (CSRRs), are introduced to improve impedance matching at low frequencies and to stabilize main beam direction at high frequencies. A prototype of this antenna is fabricated and tested. The designed antenna has stable main beam direction of 30°±5° in vertical plane, and small gain variation less than 1.78 dB in horizontal plane within 1.6-5 GHz (103%).