A flat four-beam switched antenna

Multipath fading is a serious problem for land mobile communication in urban areas. Methods to reduce the the effects of fading are antenna diversity such as space, energy density, polarization and antenna pattern. The antenna pattern diversity proposed by Ikegami (1986) is carried out by switching antenna beams. In particular, four-beam diversity is the most desirable method, and a beam pattern is required to be 90/spl deg/ of half-power beamwidth in the horizontal plane. In experiments, a vertical monopole with four 90/spl deg/ corner reflectors has been used. However it is not appropriate for practical use such as a mobile antenna, and it is necessary to develop a flat antenna. This paper presents a four-beam switched antenna, consisting of four planar elements and two 3 dB hybrids. We analyze its characteristics using a model of magnetic line current array and a cavity model using the finite element method (FEM). As a result we obtain the required radiation pattern from the flat antenna structure.<>