We segregate a region of interest into several zones, and consider the problem of estimating the zone of target sensor node using received signal power at the sensor node corresponding to the transmitted signal from each anchor node. Contrary to typical indirect zone estimation methods (location estimation followed by zone mapping), we propose direct zone estimation with maximum likelihood approach for Rayleigh and Nakagami-Rice fading channels. The advantage of the proposed approach is confirmed via computer simulations. However, the performance evaluation using measurement data has revealed the impact of non-uniform antenna beam patterns of practical sensor nodes. Thus, we also propose to incorporate the effect of the directivity of practical sensors in the evaluation of likelihood function, and demonstrate the validity of the proposed approach using measurement data.