Antenna Wave Tilt page 11

4.4) Radiation Path 4    Tx tip to Rx base

  This radiation path and source is easier to establish because it traverses from The Tx Antenna tip to the Rx Antenna base and therefore shows little variation in delay time as the Rx antenna is rotated. First the data points for the relevant peaks are used to construct a graph which also displays the calculated path for comparison as shown in figure 38.

Figure 38

  The received signal magnitude is extracted from the original data files and entered into a graph as shown in figure 39. It can be seen from this graph that there is a sharp null at 15° and a much flatter one at 180° that extends into 195° and this suggests that the polarisation, which is at right angles (90°) to the null, is at 105° to the horizontal and the Tx Antenna tip radiation has a 15° ± 7.5°wave tilt. The radiation polarisation is generally upwards because it has a time delay of 8.45 ns which indicates that it is mainly sourced from the incident current in the Tx antenna. It is worth noting that this path gives the highest magnitude of received signal of all of the analysed paths which suggests that there is no polarisation cancellation caused by there being both an INCIDENT and REFLECTED current at the Tx antenna tip.

Figure 39

4.5) Radiation Path 5    Tx tip to Rx tip

  This radiation path and source shown in figure 40 is intended to show the radiation from the Tx tip to the Rx tip but selects the path from the Tx tip to the Rx base for the points where the Rx Antenna is pointing away from the Tx Antenna as the radiation will take this shorter path. This approach still reveals the radiation null.

Figure 40

  After the path delay is selected, the received signal magnitude is extracted from the original data files and entered into a graph as shown in figure 41. It can be seen from this graph that there are nulls at 15° and 195° and this suggests that the polarisation, which is at right angles (90°) to the null, is at 105° to the horizontal and the Tx Antenna tip radiation has a 15° wave tilt. The radiation polarisation is of course upwards because the measured time delay of 8.45 ns related to the antenna spacing of 1974 mm shows that this is the first signal that originates from the Tx Antenna tip and therefore has to be in an upward direction. This result agrees with the radiation polarisation from the Tx tip achieved in Radiation Path 4 which is also 15° ± 7.5° wave tilt.

Figure 41

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