Antennas are one of the many factors that affect the reliability and performance of all wireless communication systems. It is very important to choose an antenna that fully satisfies the system performance specifications. However, today's small handheld devices also pose challenges for antenna design engineers. The antennas should be as thin as possible, compact in structure, high in performance, and meet a variety of technical standards. Time to market and cost are also two important factors that manufacturers must consider. The two main conditions for selecting the best antenna for the system are the electrical and mechanical characteristics of the antenna. These indicators are limited by the design and mechanical structure of the equipment. The basic electrical characteristics that should be considered are the antenna's operating frequency, bandwidth, maximum gain, average gain, efficiency, return loss, or voltage standing wave ratio (VSWR), as well as polarization direction, directivity, side and back lobes. , front-to-back ratio, phase pattern, impedance and power rating. The constituent materials of the antenna and the actual RF RF design also determine the final electrical performance of the antenna. The constituent materials of the antenna should have very low loss and good conductivity. The range of operating frequencies is determined by the type of application. For example, Wi-Fi 802.11b/g, ZigBee, and BlueTooth all use the same 2.4 GHz ISM band, which has a bandwidth of approximately 80 MHz (2.4 to 2.48 GHz). The commercial GPS system uses the L1 1.575 GHz band with a bandwidth of 2 MHz (1575.42 MHz ± 1 MHz). The GSM system uses the 850/1900 MHz band, or the 900/1800 MHz band, depending on the operator in the corresponding region. The 3G system also uses different frequency bands and is also regionally relevant. For example, the WCDMA system in Europe uses the 2.1 GHz band. The antennas of four- or five-band mobile phones are mainly used for global roaming and communication between different communication systems, as shown in Figure 1. They can transmit and receive signals in quad-band GSM systems and W-CDMA 2100 systems to enable interworking in all mobile phone bands. Other applications include WiMax, UWB, ISM900, ISM5/5.8GHz, DVB-H, MediaFLO, DECT, RFID, VHF, UHF, AM, and FM. Multiple antenna systems, such as diversity and multiple antenna systems (MIMO), are used in applications that require increased data rates. When using a multi-antenna system, it is critical to design and characterize the entire antenna system, including isolation and correlation testing between the antenna and the antenna. Maximum gain, average gain, and efficiency determine the bandwidth and performance of the antenna. The higher these metrics, the better the bandwidth and performance of the antenna. Moreover, the antenna should have sufficient VSWR over its operating frequency range. Typically, a 10 dB return loss (2.0: 1.0 VSWR) or better is an expected indicator. In order to obtain a better phase map of the overall performance of the antenna, the maximum gain or average gain of efficiency should be considered. But don't get stuck and just consider one of these features to come to a conclusion. The maximum peak gain is a good indicator of antenna directivity, but it can be misleading if it is used as the primary criterion for determining conventional antenna performance. In general, the more complex the device, the lower the gain, so losses occur when the antenna is installed in an actual device. This is because a high peak gain always means a certain strength of directivity and may result in a lower gain of the antenna in a certain direction due to zero intensity in a certain direction in the phase pattern. One should choose an antenna with a margin above the recommended decibel value to ensure it meets the system requirements in the real world. Most wireless systems have a 50Ω impedance and the antenna should match this value as much as possible to reduce mismatch/loss in the system. In order to fully characterize the characteristics of the antenna, other factors to be considered include the polarization direction (vertical polarization, horizontal polarization, or circular polarization), and the phase pattern (in the xz plane, the zy plane, and the xy plane). Most handheld portable devices require a linearly polarized antenna and have an omnidirectional phase pattern for covering 360° omnidirectional, but the true omnidirectional phase pattern is theoretical only. Typically, the mechanical structure of the device affects the shape of the antenna phase pattern and produces zero intensity and directivity in the phase pattern. As shown in Figure 2, in many cases, the best way to determine the performance of a real antenna is the complete three-dimensional radiation efficiency of the antenna, as it shows how much of the antenna's energy is converted into radiated waves for transmission, and because the antenna impedance does not match. What is the loss and radiation loss caused? Especially in small portable or handheld devices, three-dimensional efficiency is a better parameter than maximum gain since the device actually used may be in any direction. In addition, since the maximum gain peak beam may be toward the user's body, the gain may be reduced due to body attenuation. The mechanical layout of the device determines the size and type of antenna required, and the size and type of the antenna also limits and determines the electrical characteristics of the antenna. Therefore, the mechanical design of the device should also take into account the choice of antenna. Semiconductor Fuse And Ferrite
Fuse refers to an electric appliance that, when the current exceeds the specified value, melts the fuse and disconnects the circuit with the heat generated by itself.When the current exceeds the specified value for a period of time, the fuse melts and disconnects the circuit with the heat generated by the fuse itself.A current protector made from this principle.The fuse is widely used in high and low voltage power distribution system and control system as well as power equipment.
Ferrite is a metal oxide with ferrous magnetism.As far as electrical properties are concerned, the resistivity of ferrite is much larger than that of single metal or alloy magnetic materials, and it has higher dielectric properties.Ferrite magnetic energy also shows high permeability at high frequencies.As a result, ferrite has become a non-metallic magnetic material widely used in the field of high frequency and weak current.Due to the low ferrite magnetic energy stored in the unit volume, saturated magnetic induction strength (Bs) and low (usually only pure iron 1/3 ~ 1/5), and thus limits its higher requirements in the low-frequency magnetic energy density in the field of high voltage and high power applications.
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