Double-sided printed strip antenna for dual frequency operation

Public land mobile communications have become very popular and the number of base stations has been grown rapidly. Multiple mobile radio systems operating at different frequencies have been also introduced. In many urban areas, the base station antennas of different mobile systems are often installed on the same buildings. It is desirable to have a dual frequency antenna for use by two different mobile radio systems. In this way the space occupied by antennas mill be halved and the production cost lowered. This paper describes a dual frequency antenna consisting of two double-sided printed narrow strips connected through a balanced stripline. The proposed configuration has several advantages including reasonably wide bandwidth and polarization purity offered by strip dipole elements and very simple construction of both the radiating elements and the feed network. A method for analyzing these structures is also presented using a simplified model based on the generalized concept of equivalent radius of cylindrical antennas. This approach has been used for designing dual frequency antennas operating in 900 MHz and 1500 MHz frequency bands. Two design examples of dual frequency antennas with the H-plane half-power beam widths of 120/spl deg/ and 60/spl deg/ suitable for 3 sector and 6 sector zone use, respectively, are shown.