Impedance Matching Box

Introduction

Impedance matching box is a part of microwave electronics. It is mainly used in transmission lines to achieve the purpose that all high-frequency microwave signals can be transmitted to the load point, and no signal will be reflected back to the source point, thus improving energy efficiency.

Impedance matching means that during energy transmission, the load impedance is required to be equal to the characteristic impedance of the transmission line. At this time, the transmission will not generate reflection, which indicates that all energy is absorbed by the load. On the contrary, there is energy loss in transmission.

Type

■Change impedance force

The capacitance or inductance is connected in series with the load to increase or decrease the impedance value of the load. The points on the diagram will move along the circle representing the real resistance. If the capacitance or inductance is grounded, the point on the diagram will first rotate 180 degrees in the center of the diagram, then walk along the resistance coil, and then rotate 180 degrees in the center. Repeat the above method until the resistance value becomes 1, then the impedance force can be directly changed to zero to complete the matching.

■Adjust transmission line

Lengthen the transmission line from the load point to the source point. The dot on the diagram will move counterclockwise along the center of the diagram until it reaches the circle with a resistance value of 1. Then add capacitance or inductance to adjust the resistance to zero to complete the matching.

Matching method

In high-speed design, the matching of impedance is related to the quality of signal. Impedance matching box technology can be said to be rich and diverse, but how to reasonably apply it in a specific system needs to measure many factors. For example, in our system design, many of them use serial matching of source segments.

1. Series terminal matching

The theoretical starting point of series terminal matching is that when the impedance of the signal source end is lower than the characteristic impedance of the transmission line, a resistor R is connected in series between the source end of the signal and the transmission line, so that the output impedance of the source end matches the characteristic impedance of the transmission line, and the signal reflected back from the load end is restrained from being reflected again

2. Parallel terminal matching

The theoretical starting point of the parallel terminal matching is that when the impedance of the signal source terminal is very small, the input impedance of the load terminal matches the characteristic impedance of the transmission line by increasing the parallel resistance, so as to eliminate the reflection of the load terminal. The implementation forms are divided into single resistance and double resistance.

3. Other matching methods

Of course: AC terminal matching; Diode based voltage clamping and other matching methods.

Effect

Impedance matching refers to a suitable match between the signal source or transmission line and the load. It has two main functions: adjusting load power and suppressing signal reflection.

1. Adjust load power

Assuming that the excitation source has been determined, the load power is determined by the impedance matching box between the two. For an idealized pure resistance circuit or low-frequency circuit, the reactance value caused by inductance and capacitance can be basically ignored, and the impedance source of the circuit is mainly resistance.

2. Suppress signal reflection

When a beam of light shoots from the air to the water, it will be reflected, because the light and water have different photoconductive properties. Similarly, when the characteristic impedance of the transmission line changes suddenly during signal transmission, reflection will also occur. The wavelength is inversely proportional to the frequency, and the wavelength of the low-frequency signal is far greater than the length of the transmission line, so the reflection problem is generally not considered. In the high frequency field, when the wavelength of the signal and the length of the transmission line are of the same order of magnitude, the reflected signal is easy to mix with the original signal, which affects the signal quality. High frequency signal reflection can be effectively reduced and eliminated by impedance matching.

Certificate

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Delivery

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