This paper presents analytical derivations and simulation results for signal-to-noise ratio (SNR) when a linear array antenna is used in a CDMA base station with beam forming (BF) algorithms. The roles of two design factors effecting performance, the direction selectivity of an array antenna and the direction-of-arrival (DOA) accuracy in the BF algorithm, are examined not only for SNR but also to determine the robustness of a BF algorithm due to error factors of spatial scattering of radio waves and DOA. From the study, it is found that there is a trade-off between the SNR and the robustness with respect to these design factors. The trade-off can be used to achieve an economical implementation of the BF in the CDMA system, which does not have severely deteriorated SNR performance while ensuring its robustness to the error factors.