The so-called antenna, in fact, refers to a converter that can transform the guided wave propagating on the transmission line into electromagnetic waves propagating in an unbounded medium (usually free space), or vice versa. Transform. Its classification is as follows:

       1. Yagi directional antenna
       Yagi directional antenna has the advantages of high gain, light structure, convenient erection and low price. Therefore, it is particularly suitable for point-to-point communication, for example, it is the preferred antenna type for outdoor receiving antennas of indoor distribution systems.
       The more the number of cells of the Yagi directional antenna, the higher the gain. Usually, the Yagi directional antenna of 6 - 12 units is used, and the gain can reach 10-15dBi.

       2, indoor wall mount antenna
       The indoor wall-mounted antenna must also have the advantages of light structure, beautiful appearance and convenient installation.
       The indoor wall-mounted antennas seen on the market today have many appearances, but the purchase of the cores is almost the same. The internal structure of such a wall-mounted antenna belongs to an air medium type microstrip antenna. Thanks to the auxiliary structure of the widened antenna bandwidth, the computer aided design and the use of the network analyzer for debugging, the working broadband requirements can be satisfactorily met. Incidentally, the indoor wall mount antenna has a certain gain, which is approximately G = 7 dBi.

       3, plate antenna
       Whether it is GSM or CDMA, the plate antenna is the most popular type of base station antenna. The advantages of this type of antenna are: high gain, good sector pattern, small back lobes, convenient control of the vertical angle of the vertical plane, reliable sealing performance and long service life.
       The plate antenna is also often used as a user antenna for the repeater. Depending on the size of the sector, the corresponding antenna model should be selected.

       4, plate antenna
       A plurality of half-wave oscillators are arranged into a vertically arranged linear array, and a reflector is added to one side of the linear array (for example, a vertical array of two half-wave oscillators with a reflector), and the gain is G = 11 ~ 14 dBi. In order to increase the gain of the plate antenna, it is also possible to further adopt eight half-wave oscillator arrays
       As mentioned above, the gain of the four half-wave oscillators arranged in a vertically placed linear array is about 8 dBi; the quaternary linear array with a reflector on one side, that is, the conventional plate antenna, has a gain of about 14 ~ 17 dBi.
       An eight-element linear array with a reflector on one side, an elongated plate antenna with a gain of approximately 16 to 19 dBi. It goes without saying that the length of the elongated plate antenna is twice that of the conventional plate antenna, which is about 2.4 m.

       5, indoor ceiling antenna
       The indoor ceiling antenna must have the advantages of light structure, beautiful appearance and convenient installation.
       The indoor ceiling antennas seen on the market today have many appearances, but the structure of the inner core is almost the same. The internal structure of the ceiling antenna, although small in size, is well suited to work in a very wide range because it is based on the antenna        wideband theory, aided by computer aids, and debugged using a network analyzer. The VSWR in the frequency band requires that the VSWR of the antenna operating in a wide frequency band according to national standards is VSWR ≤ 2 . Of course, it is better to achieve VSWR ≤ 1.5. Incidentally, indoor ceiling antennas are low gain antennas, typically G = 2 dBi.

       6, high gain grid shape
       From the performance price ratio, the grid parabolic antenna is often used as the donor antenna of the repeater. Because the paraboloid has a good focusing effect, the parabolic antenna has a strong collection capability and a 1.5 m diameter grid-shaped parabolic antenna. In the 900 mega band, the gain can reach G = 20 dBi. It is especially suitable for point-to-point communication, for example it is often chosen as the donor antenna for repeaters.
       The paraboloid adopts a grid structure, one is to reduce the weight of the antenna, and the other is to reduce the wind resistance.
       Parabolic antennas generally give a front-to-back ratio of no less than 30 dB, which is a technical specification that must be met for the receiving antenna when the repeater system is self-excited.
       
       7, loop antenna
       The loop antenna is very similar to the human body and has a common monopole or multi-stage antenna function. Together with the small size, high reliability and low cost of the small loop antenna, it makes it an ideal antenna for micro-communication products. A typical loop antenna consists of an electrical circuit consisting of copper traces on a circuit board, or it may be a loop made of a loop. Its equivalent circuit is equivalent to the series connection of two series resistors and one inductor. Rrad is the resistance model of the actual energy emitted by the loop antenna. The power it consumes is the transmit power of the circuit.
       Assuming that the current flowing through the antenna loop is I, then the power consumption of Rrad, that is, the RF power is Pradiate=I2· Rrad. The resistor Rloss is a resistance model in which the loop antenna consumes energy due to heat. The power consumed is an unavoidable energy loss, and its magnitude is Ploss=I2· Rloss. If Rloss > Rrad, then the power lost is greater than the actual transmitted power, so this antenna is inefficient. The power consumed by the antenna is the sum of the transmitted power and the lost power. In fact, the design of the loop antenna is almost impossible to control Ploss and Prad, because Ploss is determined by the conductivity of the conductor making the antenna and the size of the wire, and Prad is determined by the size of the area enclosed by the antenna.