Flat antennas for indoor cellular system

A leaky coaxial-line for a telephone system under indoor environments is not suitable for a frequency range of 900 MHz and up, because of large transmission loss. A micro cellular system is necessary for indoor wireless telephone service at underground shopping malls, subway stations and inside tunnels. Flat antennas are required for these applications, because base station antennas installed on the ceiling or on the wall should have a low profile structure. For compatibility with present cellular system, a vertical polarization is required for these flat antennas in the frequency band of 900 MHz and 1.5 GHz used in the Japanese cellular system. The flat antennas should have a pattern of sine/spl theta/ in the azimuth plane to increase a dynamic range inside a coverage area. The antenna is used separately for a transmitting and a receiving with a frequency band width more than 9%, which requires layered and integrated structure. For 900 MHz band, the transmitting frequency is 810-885 MHz, and the receiving frequency is 885-956 MHz. The VSWR (voltage standing wave ratio) less than 1.5, and the isolation more than 15 dB are required. For 1.5 GHz, the transmitting frequency is 1477-1501 MHz, and the receiving frequency is 1429-1477 MHz. This paper presents three flat antennas on the ceiling and an antenna on the wall to satisfy the above requirements.<>