Electromagnetically coupled small broadband monopole antenna

The paper presents a small broadband monopole antenna. The proposed structure consists of a circular disk-loaded monopole and a probe with a circular spiral strip line monopole. Broad bandwidth can be achieved through electromagnetic coupling between these two monopoles that generate two resonances closely spaced in frequency. The antenna occupies a cylindrical volume with a radius of /spl rho/ /spl cong/ 0.04/spl lambda//sub o/ (5.5 mm) and a height of h /spl cong/ 0.08/spl lambda//sub o/ (11 mm) and has 430 MHz of impedance bandwidth for VSWR<2 with a center frequency at 2.185 GHz, which is fractional bandwidth of approximately 19.7%. The gain of the antenna is more than 1.7 dBi within the entire bandwidth with good omnidirectional radiation characteristics.