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- Adapted raised cosine window function for array factor control with dynamic range ratio limitationPublication . Santos, Filipe E. S.; Azevedo, Joaquim A. R.The use of window functions to improve the side lobe level of antenna arrays is hindered by high value of excitation currents dynamic range ratio. This paper proposes a fast and iterative window function generation strategy aimed at achieving improved side lobe level starting from a preset current dynamic range ratio. Based on this strategy a new window function is developed for standard set of conditions.
- An empirical propagation model for forest environments at tree trunk levelPublication . Azevedo, Joaquim A. R.; Santos, Filipe E. S.The estimation of the received signal strength inside forest environments is very dependent on the vegetation density. However, most published empirical models only provide calculation of the path loss as a function of distance and frequency. The importance of these models is their simplicity. This paper presents a model that was developed from an extensive measurement campaign carried out for different vegetation densities and types of trees. Noting the typical decaying behaviour of signal propagation, the objective was to estimate the main parameters of the log-normal model that fits the measured data. Since in many applications both the transmitter and the receiver are inside the forest, the propagation path is mainly characterized by tree trunks. In this case, it was found that the signal attenuation is dependent on the vegetation density, defined by the product of the tree density and the average diameter of the trunks. In addition to the measurements used to develop the model, other experiments were conducted to test it. The study also included a comparison with other methods in order to evaluate the performance of the model.