Radiation Pattern from Two Antennas Wave interference patterns created by two adjacent an- tennas. Radio waves from two adjacent sources of the same frequency reinforce or cancel each other to pro- vide wave pattern in space adjoining the antennas. Midway between these lines the waves cancel each other. This pattern represents an antenna array having five lobes. Antenna Pattern of Directional Array Polar plot shows antenna radiation as compared to an omnidiredional antenna.
Signal gain varies with the number and adjustment of antenna elements in the ar- ray.
The effedive power gain of an antenna is the ratio of power required in the antenna and the power required in an isotropic radiator to achieve the same field strength in the favored diredion of the antenna under measurement. The power gain of a half-wave dipole over an isotropic radiator is 1.64. The gain of a direc- tional antenna over an isotropic radiator is expressed by the formula in the illustration. The power gain over an isotropic radiator, or over a simple dipole, is the measuring stick for antenna per- formance. Closely allied to the concept of power gain is the problem of suppressing unwanted radiation from the sides and rear of a directive antenna system.