A study on the effect of building on the HF direction finding
The effect of new building on the high-frequency (HF) direction finding (DF) is analyzed. Commercially available software is used to get array manifold of the HF DF system taking the effect of the new building into account. The terrain, building and the array antenna system are modeled. The new building near the antenna system is also modeled to see whether it actually has an effect on the performance of the DF system. Interferometer DF algorithms has been employed.
Effect of Buildings on the Radiation Characteristics of MF Broadcast Antennas
This study aims to investigate the impact of the presence of buildings on the radiation characteristics of MF broadcast antennas. Two different antennas are considered: a monopole operating at 1494 kHz and a two-element linear array radiating at 1008 kHz. The buildings were modeled as wire-grids and the total electric field intensity was calculated as the sum of the scattered field by the wire-grid and the field radiated from the antenna in free space. The radiation pattern of the antennas, when one or two buildings were situated in their vicinity, were the end result of the analysis, and they were compared to the corresponding patterns in free space. The results demonstrate that the radiation characteristics of antennas are mostly affected by the heights of buildings. If these heights are less than a critical value, the buildings do not significantly obstruct the operation of the antenna, despite the value of other parameters, such as the length and the width of the buildings, as well as their distance from the antenna.
An experimental investigation of the reflection and absorption of radiation of 9-cm. wave-length
The paper, which was circulated as a confidential report to the Radio Research Board in October 1944, describes measurements on the reflecting power of various surfaces at a wave-length of 9 cm and angles of incidence ranging from 80° to 45°; these included level and uneven bare ground, vegetation-covered ground, tap water and a 4% salt solution approximating to sea water. Specular reflection was found to occur only from very level surfaces; the absorptions of these surface media were measured, and from the combined measurements of reflection and absorption their electrical constants were derived. Rough surfaces, either of bare ground or vegetation-covered ground, gave values of reflection coefficient in general agreement with the optical rule that regular reflection is only observed from an uneven surface if the product of the depth of the surface irregularities and the cosine of the angle of incidence is a small fraction of the wave-length. If this fraction exceeded ½λ, the values of reflection coefficient measured were about 0.1. The calculated values of reflection coefficient corresponding to dry soil, wet soil and sea water for angles of incidence varying from 0° to 85° are given in an appendix to the paper.