Effective Magnetic-Loop Array Antennas With Enhanced Bandwidth

Effective magnetic-loop array antennas with coupling feed structures are proposed in this communication. Two effective magnetic loops with constant magnetic currents are formed to produce omnidirectional radiation pattern in the azimuth plane. The gains in the plane are enhanced by interference effect of the fields formed by the two loops. The TM01 mode and TM02 mode are excited simultaneously by adjusting the parameters of feeding structures to form a wide band. Prototype antennas working at 5 GHz are designed, optimized, fabricated, and measured, and bandwidths of 5% are achieved. The radiation patterns are stable in the operation band, and gains larger than 2 dBi in the azimuth plane at most frequencies can be observed. The elevation angles are about 30° at various frequencies, lower than that for typical omnidirectional patch antennas. All these performances are realized on a low-profile ($\lambda $ /30) structure, which makes them possible elements in conformal applications.