Achievement of inverse frequency-dependent phase shift by using composite right/left-handed phase shifter

In the conventional base station antenna, a linear array antenna is used. For suppressing the interference between neighbouring cells, the main beam is down-tilted to the cell edges of own radio zones [1]. Recently, the multi-frequency base station antenna is used due to a limited space in the base station [2]. The beam tilt angle is usually designed by conventional phase shifters. For example, in the dual-frequency (1.5 GHz and 2 GHz) base station antenna, the beam tilt angle becomes frequency-independent. However, the half-power beamwidth at 1.5 GHz is broader than that at 2 GHz. Therefore, the interference to the neighbouring cell becomes large at 1.5 GHz. To suppress the interference at 1.5 GHz, the composite right/left-handed (CRLH) phase shifter has been proposed for achieving inverse phase shift at each frequency by using the dispersion relation of the CRLH transmission line [3]. The variation of the dispersion curve can be obtained by mechanically-shifting the patch for series capacitance. This paper presents the dispersion design of the unit cell and the experimental verification of the inverse phase shift at each frequency.