Abstract
The paper describes the results of experiments made on the directional property of horizontal antennas with special reference to the high angle radiation of horizontally polarized short waves.
In our experiments, short waves of 260 cms. in length were emcloyed, and the sending antenna of nearly a half-wave in length was placed horizontally above the ground. (see Fig. 18) The receiving antenna forming a Hertz's resonator was also supported horizontally and made to move up and down along a vertical line by means of a pulley device as shown in Figure 19. The field intensity .due to the horizontal antenna was measured in various angular directions above the ground level by placing the receiver at various heights.
The observed polar diagrams show that the radiation from the horizontal antenna is generally directed in certain high angular directions and is very small along the earth surface. (see Fig. 3) If the height h of the antenna is made equal to λ/8 or λ/4 λ representsthe wave-length, maximum radiation will occur just in vertical upward direction, whereas if its height is equal to 3/8λ or λ/2, the radiation will be maximum in the direction making the angle about 45°or 30° with the horizontal line respectively. Now if the height h is more increased so as to equal to 5/8λ, 3/4λ, two maxima of radiation will exist: one is at vertical upwards, and the other is at about 25°, 20° respectively. Furthermore, if h is equal to 7/8λ or λ, there will be also two maxima of radiation at about 60°, 15° or 50°, 13°respectively. These are illustrated by the polar diagrams in Figure 3.
Now if several wave directors are arranged in front of the radiating antenna along an inclined line making a certain angle with the horizontal, the radiatedd energy along this line will become much augmented due to the existence of wave directors, but the direction of maximum radiation will not strictly ecincide the line of directors but somewhat higher angle than this line. (see Fig. 8, Fig. 9 and Fig. 10) And the sharpness of the beam can be much improved by increasing the number of wave directors.
