Abstract
In the first report of experimental studies on the wireless beam of short electric waves of few metres, it has been shown that the electric field due to the oscillator itself used by the author, in which the plate and the grid coils in the oscillation circuit form the radiators, is directive, namely the field intensity being a maximum in the plane of the coils. But in this case the radiation energy from such closed circuit coils is too small to be taken into service. And also it has been stated that if a single vertical rod antenna of nearly half a wave length is employed, the energy of radiation from the oscillator will be much increased, but at the same time the strength of the field will become nearly equal in all directions.
In order to incresse the radiative power still greater in a desired direction and moreover to maintain the directive property of electric field, metallic rods of finite length may be used as reflectors. Further experiments in connection with this line of investigations are made and some of the results are described in this paper.
For the explanation of the behavior of reflector rods used in the beam system of wireless tele raphy, it is convenient to consider simple cases at first in which merely one or two reflector rods are employed and the length of these rode is equal to or slightly longer than half a wave leugth.
A single reflector rod placed a quarter wave behind a radiating antenna is sufficient to cause directive radiation of radio waves. When the distance between the antenna and the rellector is equal to half a wave length, the electric waves will be radiated chiefly in the direction normal to the line joining the antenna and the reflector. Again, if this distance is equal to three times as a quarter wave length, maximum radiation will exist in three directions.
Two reflector rods are now vertically erected at the distance of half a wave, or a quarter wave length from the antenna, one being on the left and the other on the right side of it. In both cases, the wave energy is projected chiefly in the forward and the backward direetions of the antenna, but the former case gives better directivity than the latter.
Of course it is evident that whether each rod will act effectively as a reflector or not, depends not only upon its relative position with the antenna, but also upon its length. Therefore for a complete consideration of the action of reflector rods, their lengths at diferent values must be taken into account, but since this makes the problem so complicate to understand, the author want to write further descriptions of this point in another paper.
In our experiments, 4.4 metres wave length is employed and the lengths of antenna and reflector rods are all equal to half a wave length, i. e. 220 cms. The intensity is measured with a receiving system comprising a crystal detector and a micro ammeter. It has been very carefully ascertained that this crystal system gives the most consistent results throughout the long time of experiments.
The simplest and comparatively effective reflector may be formed as stated below. A reflector rod is placed a quarter wave behind the antenna and two more reflectors, one being on the left and the other on the right side of it, are placed a half wave distant from the antenna. (see Fig.) These three rods form a tri-antennary reflecting system which will hereafter be called a fundamental "Trigonal reflector". Two more reflector rods CC are shown in the figure. These are not as efficient as a reflector as A and B's, but their existence enables closer screening of waves in the backward direction, and when this reflector system is employed in a receiving station, they are specially effective to eliminate external disturbances from behind.
Comhined with these screening rods, the trigonal reflector is now formed of five rods.
