The development of microwave is inseparable from the development of wireless communication. In 1901, Marki used the 800KHz medium wave signal to conduct the first transatlantic radio wave communication test from the United Kingdom to Newfoundland and North America, creating a new era of human wireless communication. In the early days of wireless communication, people used long-wave and medium-wave to communicate. Short-wave communications were discovered in the early 1920s until the rise of satellite communications in the 1960s. It has been the primary means of international long-distance communications and is still important for current emergency and military communications.
An electric wave used for spatial transmission is an electromagnetic wave that propagates at a speed equal to the speed of light. Radio waves can be classified and named according to frequency or wavelength. We refer to electromagnetic waves with frequencies above 300 MHz as microwaves. Since the propagation characteristics of each band are different, it can be used in different communication systems. For example, the medium wave mainly propagates along the ground and has a strong diffraction ability, which is suitable for broadcasting and maritime communication. The short wave has strong ionospheric reflection capability and is suitable for global communication. Ultrashort wave and microwave have poor diffractive ability and can be used as line-of-sight or over-the-horizon relay communication.
The history of microwave development (1)Microwave communication was the product of the 1950s. Due to its large communication capacity and low investment cost (about one-fifth of the cable investment), the construction speed is fast and the disaster resistance is strong, and rapid development has been achieved. In the 1940s and 1950s, microwave communication with wide transmission band and stable performance was produced, which became the main means of wireless transmission of long-distance and large-capacity ground trunk lines. The analog FM transmission capacity is up to 2700 channels, and high-quality color can also be transmitted simultaneously. TV, and then gradually into the medium capacity or even large-capacity digital microwave transmission. Since the mid-1980s, with the discovery of the effects of frequency selective dispersion fading on digital microwave transmission disruption and the development of a series of adaptive fading countermeasures and high-state modulation and detection techniques, digital microwave transmission has revolutionized. In particular, it should be pointed out that the rapid development of a set of high-speed multi-state adaptive coded modulation and demodulation technology and signal processing and signal detection technology developed in the 1980s and 1990s for today's satellite communications, mobile communications, and all-digital HDTV transmission. Universal high-speed wired/wireless access, and even high-quality magnetic recording and other signal design and signal processing applications have played an important role.
The proportion of microwave relay communication in foreign developed countries in the long-distance communication network is as high as 50%. According to statistics, the United States is 66%, Japan is 50%, and France is 54%. Since the introduction of the first microwave communication equipment from East Germany in 1956, China has made great achievements through the imitation and spontaneous development process. In the 1976 Tangshan earthquake, the coaxial cable between Beijing and Tianjin In the case of a break, all six microwave channels are safe. In the devastating floods of the middle and lower reaches of the Yangtze River in the 1990s, microwave communication once again showed its great power. In the communication revolution of today's world, microwave communication is still one of the most promising means of communication.
In terms of satellite communications, since Clarke proposed in 1945 that three geosynchronous satellites can cover the globe, satellite communications have actually become a reality for about 20 years. First of all, the experiments of many low-orbiting satellites, and the first artificial earth satellite in the world that was successfully launched by the former Soviet Union on October 4, 1957, was about 1600 km away from the Earth, and realized communication with the Earth. This is a history in the history of satellite communications. An important milestone; the "Early Bird" geostationary satellite launched on April 6, 1965 marks the real commercial phase of satellite communications and incorporates the world's largest commercial satellite organization tel/' target='_blank '>INTELSAT's first generation satellite system IS-I. GEO commercial satellite communication is exemplified by tel/' target='_blank'>INTELSAT satellite system. Since the IS-I in 1965, the satellite system officially commercialized has gone through eight generations and 12 types. Currently, the ninth generation satellite system IS-IX is being developed. It is expected to be launched in 2001.
The history of microwave development (2)In terms of mobile communications, its development has gone through five stages: the first stage was from the early 1920s to the end of the 1950s, mainly used for ships and military, using short-wave band and tube technology, and the end of the period was 150MHz. The simplex car public mobile phone system MTS, the second stage is not from the 1950s to the 1960s, when the frequency band is extended to UHF450MHz, the device technology has been excessive to the semiconductor, mostly for the dedicated system in the mobile environment, and solved the mobile phone and public telephone. The continuation problem; the third stage is from the early 1970s to the 1980s, when the frequency band has been extended to 800MHz, the US has carried out the AMPS test, and the fourth stage is from the 1980s to the mid-1990s, the second generation of digital mobile communication has arisen and is large. Development and progressive development towards personal communication. Various systems such as D-AMPS, TACS, ETACS, GSM/DCS, cdmaOne, PDC, PHS, DECTPACS, PCS, etc., have been expanded to 900MHz to 1800MHz, and in addition to public mobile phone systems, wireless paging systems, cordless phones System, cluster system and other mobile communication means adapt to the user and market demand at the same time; the fifth stage is from the mid-1990s to the present, with the development of data communication and multimedia business needs, adapt to mobile data, mobile computers and mobile multimedia The third generation of mobile communications began to rise cdma2000, WCDMA, LAS-cdma and other corresponding standards came into being. The future of wireless communication technology is bright.
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