coax cable attenuator.Front to back ratio of antenna

　　In the directional pattern, the ratio of the maximum level of the front and back lobes is called the front to back ratio, denoted as F/B. The larger the front to back ratio of the antenna, the smaller the backward radiation (or reception).

　　F/B=10 Lg {(forward power density)/(backward power density)}

　　When there is a requirement for the front to back ratio of the antenna, the typical value of F/B is (25-30) dB, and in special cases, it is required to reach (35-40) dB.

　　The use of reflector plates can control the radiation energy to one side direction: the reflector plane is placed on one side of the array to form a fan-shaped coverage antenna. Below is a horizontal directional diagram to illustrate the function of the reflective plate.

　　In a fan-shaped coverage antenna, the reflector reflects power to one side, increasing gain. The gain of a typical fan-shaped coverage antenna is around G=(11-17) dBi.

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