Multiband dipole antenna with reflector comprising additional reflector composed of FSS

The increase of data rate of mobile communication services has pushed to assign more frequency resources for wireless communication systems. ITU-R has assigned 3.5GHz band to the IMT systems in WRC2007, the frequency band is more than 4 times compared to 800MHz band which is the lowest IMT frequency band. In view of base station antenna installation, since the spaces for establishing base station antennas are limited, multi-band antenna configurations are demanded for the base station antennas.Dipole antenna with reflector (it is called `DAR´ hereafter) is commonly used for a base station antenna applied to a sector cell. To form sector radiation pattern with the DAR, the spacing between dipole element and reflector should be less than 0.25 wavelengths. Here we consider multi-band DAR using multi-band resonant dipole element in this paper. When the spacing between the dipole element and the reflector in the multi-band DAR is set to around 0.25 wavelengths at a high frequency band, the spacing at a low frequency becomes too narrow so that the operating bandwidth is degraded. On the other hand, when the spacing is set to 0.25 wavelengths at a low frequency band, the spacing at a high frequency band exceeds 0.25 wavelengths, it causes the distortion in the radiation pattern. The distortion increases as increasing the frequency separation increases. To solve the problem, this paper proposes multi-band DAR comprising additional reflector composed of FSS (Frequency Selective Surface) designed for high frequency bands. 850MHz and 4GHz dual-band configuration is considered in this paper and band-rejection FSS at 4GHz is used as the FSS reflector. The effectiveness in the radiation property is analyzed by FDTD calculation.