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Golden beacon: what is an RF transmission line? You know what?

Release date:2021-12-28Author source:KinghelmViews:475

    Shenzhen jinhangbiao Electronics Co., LtdFounded in 2007, shenzhenkinghellmelectronco., Ltd. is a national high-tech and dual soft certification enterprise, "senior member unit of China satellite navigation Association", an enterprise with ISO9001 (04617q13625ros) quality management certification system, and is improving iatf16949 automobile quality management system. Its main business is the R & D, production and sales of Beidou satellite navigation and IOT terminal application hardware, and www.bds666.com Com logistics information intelligent system solution.

Then, the next little editor of golden beacon Electronics will talk to you: what isRF transmission line? You know what?

1、 Basic concepts

1. In the field of high frequency / radio frequency, the most important basic concepts are incident wave, reflected wave and transmission wave transmitted along the transmission line.

In fact, understanding these concepts can be compared with the propagation of light (I learned this knowledge in junior high school). A beam of light propagates along a straight line in the same medium, but the light is incident from air to water (the medium changes), some light is reflected and some light is refracted; If the medium consists of a material with great loss, all the incident light is reflected (such as a mirror).

Similarly, RF signal is like light (in fact, light is also a wave), and transmission line is like medium. Its characteristic impedance characterizes this material.

When the transmission line is infinitely long, the RF signal has no reflection, that is, the incident signal = the transmission signal, but there is no infinitely long transmission line, the impedance ZL connected to the terminal of the transmission line is very important (usually the characteristic impedance Z0 of the transmission line is a positive real number: 50 or 70 Ω):

2、ZL!= At Z0 (equivalent to different media, such as air and water), reflection will occur at the terminal of the transmission line. Transmission signal = incident signal - reflected signal, which is also called impedance mismatch.

2、 Why are these concepts so important at HF / RF?

Compare low and high frequency signals:

1. Low frequency (the wave length is longer than the line length): the current is easier to propagate along the wire to obtain effective power transmission. The measured voltage and current do not depend on the position of the wire, that is, the current and voltage of a wire are equal everywhere (learned in junior middle school);

2. High frequency / radio frequency (the signal wave length is less than the transmission line length, generally less than or equal to 10 times the transmission line length): This requires the transmission line to transmit the signal. At this time, in order to reduce the reflected signal and obtain the maximum power transmission, it is very important to match the characteristic impedance of the transmission line. The voltage measured on the transmission line depends on the position along the measuring point (i.e. the voltage on the transmission line is not equal everywhere).

The reason why these concepts are particularly important is that we can use a specific load to match the characteristic impedance of the transmission line to replace the infinite transmission line, and the maximum power is transmitted to the load. What a magical thing.

The above is all the content sharing brought by the small series of golden navigation mark electronics. I hope it will help you. Thank you for reading!


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