Analysis of the impedance changes of a HF/VHF monopole antenna in a Brazilian Atlantic rainforest urban site

This work analyzes the impact of vegetation coupling on the impedance of a monopole antenna operated in a Brazilian Atlantic rainforest site, in the HF and low VHF bands. A theoretical analysis was performed in order to have a first order estimate of the differences between the impedance responses in a forest spot and in an open area. Next, the impedance of a 3-m monopole was measured in those sites and compared. It was found that the reflection coefficient in forest was slightly shifted in frequency to the left in respect to the open area, as expected from the theoretical estimation.