Golden Navigation: What is a radio frequency transmission line? Did you know?

    Shenzhen Jinhangbiao Electronics Co., Ltd.(SHENZHENKING HELMELECTRON CO., LTD.) was established in 2007. It is a national high-tech and dual-software certified enterprise, a senior member of the "China Satellite Navigation Association", an enterprise that has obtained the ISO9001 (04617Q13625ROS) quality management certification system, and is improving the IATF16949 automotive quality management system. The main business is the R&D, production and sales of Beidou satellite navigation and Internet of Things terminal application hardware, and the provision of www.BDS666.com logistics information intelligent system solutions.

So, next, the editor of Golden Navigation Electronics will talk to you: What isRF transmission line? Did you know?

1. Basic concepts

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

In fact, to understand these concepts, we can compare it to the propagation of light (this knowledge was learned in junior high school). A beam of light propagates along a straight line in the same medium, but when the light is incident from air to water (the medium changes), part of the light is reflected and part of the light is refracted; if the medium is composed of a material with great loss, all the incident light is reflected (such as a mirror).

Similarly, the radio frequency signal is like light (in fact, light is also a wave), and the transmission line is like the medium, and its characteristic impedance characterizes the material.

When the transmission line is infinitely long, the radio frequency signal has no reflection, that is, the incident signal = the transmission signal. However, there is no infinitely long transmission line in practice. 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 ohms):

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

2. Why are these concepts so important under high frequency/radio frequency?

Compare low-frequency and high-frequency signals:

1. Low-frequency situation (wavelength is much longer than the wire length): the current is more likely to propagate along the wire to obtain effective power transmission. The measured voltage and current do not depend on the position of the wire, which means that the current and voltage of a wire are equal everywhere (junior high school);

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

The reason why these concepts are particularly important is that we can replace infinitely long transmission lines with specific load and transmission line characteristic impedance matching, so that the maximum power can be transmitted to the load. What a magical thing this is.

The above is all the content shared by the editor of Jinhangbiao Electronics. I hope it will be helpful to everyone. Thank you for reading!