The development of microwaves is inseparable from the development of wireless communications. In 1901, Marconi used 800KHz medium wave signals to conduct the world's first transatlantic radio wave communication experiment from Britain to Newfoundland in North America, ushering in a new era of human wireless communications. In the early days of wireless communications, people used long waves and medium waves to communicate. Shortwave communications were discovered in the early 1920s. Until the rise of satellite communications in the 1960s, it has been the main means of international long-distance communications, and it is still important for current emergency and military communications.
The radio waves used for space transmission are a type of electromagnetic waves, which propagate at a speed equal to the speed of light. Radio waves can be classified and named according to frequency or wavelength. We call electromagnetic waves with a frequency higher than 300MHz microwaves. Because the propagation characteristics of each band are different, they can be used in different communication systems. For example, medium waves mainly propagate along the ground, have strong diffraction capabilities, and are suitable for broadcasting and maritime communications. Short waves have strong ionospheric reflection capabilities and are suitable for global communications. Ultrashort waves and microwaves have poor diffraction capabilities and can be used as line-of-sight or beyond-line-of-sight relay communications.
In 1931, the world's first microwave communication circuit was built between Dover, England and Calais, France. After World War II, microwave relay communication developed rapidly. In 1955, tropospheric scatter communication was successfully tested in North America. Satellite communication experiments began in the 1950s and were put into use in the mid-1960s. Since the microwave band frequency resources are extremely rich and the spectrum below the microwave band is very crowded, mobile communications have also developed towards the microwave band. In addition, the development of digital technology and microelectronics technology has also promoted the gradual transition of microwave communication from analog microwave communication to digital microwave communication.
Microwave communication is a product of the 1950s. It has achieved rapid development due to its large communication capacity and low investment cost (about one-fifth of cable investment), fast construction speed, and strong disaster resistance. From the 1940s to the 1950s, microwave communication with a wide transmission bandwidth and stable performance was produced, becoming the main means of long-distance and large-capacity ground trunk wireless transmission. The analog FM transmission capacity is as high as 2,700 channels, and it can also transmit high-quality color TV at the same time, and then gradually enters medium-capacity and even large-capacity digital microwave transmission. Since the mid-1980s, with the discovery of the impact of frequency selective dispersion fading on digital microwave transmission interruption and the development of a series of adaptive fading countermeasure technologies and high-state modulation and detection technologies, digital microwave transmission has undergone a revolutionary change. It should be particularly noted that the rapid development of a set of high-speed multi-state adaptive coding modulation and demodulation technologies and signal processing and signal detection technologies developed from the 1980s to the 1990s has played an important role in signal design and signal processing applications in many fields such as today's satellite communications, mobile communications, all-digital HDTV transmission, universal high-speed wired/wireless access, and even high-quality magnetic recording.
The proportion of microwave relay communications in long-distance communication networks in developed countries abroad is as high as more than 50%. According to statistics, the United States is 66%, Japan is 50%, and France is 54%. Since my country introduced the first set of microwave communication equipment from East Germany in 1956, it has made great achievements through imitation and spontaneous research and development. In the Tangshan earthquake in 1976, when all the coaxial cables between Beijing and Tianjin were broken, all six microwave channels were safe and sound. In the 1990s, during the severe flood in the middle and lower reaches of the Yangtze River, microwave communication once again demonstrated its great power. In today's world's communication revolution, microwave communication is still one of the most promising communication means.
