Co-polar and cross-polar measurements of the re-radiation signal at 20 GHz from a tree and their analysis in the region around the nulls

The effects of single trees on the propagation of radiowaves in the 20 GHz microwave band on radio design and planning are being investigated. Deep nulls in the signal strength have been observed on the re-radiated signals from a tree at a certain angular positions when both the transmitter and receiver are aligned on either side of the tree. This paper outlines further investigation carried out around the vicinity of the nulls in terms of the behaviour of both the co-polar and cross-polar components of the received signal. Analysis of the measurement results which include average signal levels and correlation between the two components of the received signal have resulted in the identification of three regions of interest. These regions are discussed in the paper where it is shown that good agreement exists between the measured signals behaviour and that which may be predicted qualitatively from the radiative transfer energy theory described by Johnson and Schwering (1985)