This paper addresses the problem of cochannel interference (CCI) generated in a mixed cell architecture in microcellular systems. In this type of microcellular systems in which both microcells and macrocells coexist in the same geographical urban area, the base station antennas mounted on the rooftops of buildings to cover wide circular radio zones suffer severe CCI from the surrounding low base stations. A dielectric-loaded slotted-cylinder antenna (DSCA) is applied to horizontally polarized omnidirectional array antennas in a height-diversity configuration with the high gain of 8？dBi, which is comparable to that of a collinear antenna, to reduce the CCI. The measurements conducted in a suburban area clarify the reduction in the CCI for three techniques. The beam-tilt technique reduces the CCI level by approximately 10？dB for both collinear antennas and the DSCA array antennas. The use of horizontal polarization reduces the CCI level by approximately 13？dB for the DSCA array antennas with and without beam tilt. The combination of the beam tilt and horizontal polarization or the DSCA array antennas with beam tilt significantly reduces the CCI level by approximately 23？dB. 1. Introduction The number of subscribers to the personal handy-phone system (PHS) [1], which was developed and successfully implemented in Japan as a wireless personal communication service (PCS), has continued to increase beyond 80 million mostly in middle South American, African, and Asian countries especially China [2]. PHS supplies not only public wireless services but also wireless local loop (WLL) and fixed wireless access (FWA) systems [3] and has recently been applied to new services such as logistics [4] and ETC [5]. In a PHS system with a street microcell [6], all base station (BS) antennas are installed at locations lower than the surrounding buildings. The buildings form a radio zone called a street microcell along the street. As a fundamental concept in PHS design, the street microcell does not assume the occurrence of cochannel interference (CCI) between BSs. This is because the buildings act as obstacles and as a result increase the propagation loss compared to that of elevated BSs because of the low BS height. Attention should be paid to the fact that commercial PHS with a street microcell basically uses vertically polarized antennas; therefore, the polarization of the CCI waves is mainly vertical as reported in [7]. One of the disadvantages of the PHS street microcell is that numerous BSs are needed to cover all service areas and installing many BSs is costly. When we
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