Long-line Transmission Antenna
When the wavelength of the electromagnetic wave propagating along the transmission line can be compared with the geometric length of the transmission line, the transmission line in this case is usually referred to as LT, LT has uneven distribution of the current and voltage: make a transmission line and the length of 10 meters, when the online high-frequency current passes to line, such as F = 150MHz. (wavelength) = 2m, due to the shorter wavelength, in this transmission line, the current changes in the several cycles of the thus at the same moment line, each point of the current the large and small and direction is different; the long-term is a distributed parameter system: the lte antenna long-term, with the length of the transmission line or along the propagation of electromagnetic waves of different wavelengths, the transmission line itself has a distributed capacitance and inductance parameter and the parameters of these distributions is large, in the case of long-term, due to the line length with different or different wavelengths, the transmission line itself is showing the different nature of the impedance (capacitance, inductance or pure resistance), while the short-term capacitor has an electric field in the coil to generate a magnetic field, and there is no relationship with the line length.
Open-ended transmission antenna
When the wifi antenna transmission line receives the signal, the electrical signal will be transferred at the speed of light by the cosine distribution law transmitted to the terminal due to the open-end, the signal cannot continue to propagate forward, total reflection is formed to the direction of the starting end, at this time it is equivalent to a terminal of the transmission line access to a signal source to an electrical signal by the terminal to the beginning of the end to travel at the speed of light. Generally, it is said that the propagation of radio waves transfer from the beginning of the end to the terminal is the incident; and the reflected radio waves reflected back from the terminal is reflected wave. Incident and reflected waves are traveling waves.
The Terminal Shorted Transmission Antenna
The terminal short-circuited transmission line is contrary to the open-end transmission line, it's VSWR characteristics are the same phase of the incident current and the reflected wave current, the opposite phase of the incident voltage and the reflected voltage wave. Its impedance characteristic is that the less than a quarter-wavelength transmission line was purely resistive inductive; and the equal to a quarter wavelength was capacitive greater than a quarter-wavelength; reactance is zero or equal to the half wavelength. Under normal circumstances, the transmission line terminal is connected with a load, and its load usually both resistance component reactive components, thus one db load absorption by the energy of the signal source output, another part of the times reflected back, so the transmission line traveling wave and standing wave coexist.
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