rf interference filter.The basic principles and functions of antenna radiation of electromagnetic waves

　　(1) The function of an antenna is to control the direction of radiated energy, with a single symmetrical oscillator having a "bread circle" shaped pattern.

　　(2) On the ground level, in order to concentrate the signal to the desired location, it is required to press the "donut" flat.

　　(3) Symmetric oscillator arrays can control radiation energy to form a "flat bread circle"

　　(4) Gain refers to the ratio of the square of the field strength generated by the actual antenna and the ideal radiation unit at the same point in space under the condition of equal input power, which is the power ratio. The gain is generally related to the antenna pattern, where the narrower the main lobe, the smaller the back lobe and side lobe, and the higher the gain.

　　At this gain=10log (4mW/1mW)=6dBd

　　(5) By using a reflector, radiation energy can be controlled and focused in one direction

　　The reflector is placed on one side of the array to form a fan-shaped coverage antenna.

　　Omni Antenna's operating frequency range

　　Whether it is a transmitting antenna or a receiving antenna, they always operate within a certain frequency range. Generally, when operating at the center frequency, the antenna can deliver the maximum power, and when deviating from the center frequency, the power it delivers will decrease. Based on this, the frequency bandwidth of the antenna can be defined.

　　There are several different definitions:

　　One refers to the bandwidth when the antenna gain decreases by three decibels;

　　One refers to the operating bandwidth of an antenna at a specified standing wave ratio.

　　In mobile communication systems, it is defined according to the latter definition, specifically, when the input standing wave ratio of the antenna is ≤ 1.5, the working bandwidth of the antenna.

　　When the working wavelength of the antenna is not optimal, the antenna performance will decrease

　　Within the operating frequency band of the antenna, there is not much decrease in antenna performance, which is still acceptable.

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