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Impedance matching (Impedance matching) is a part of the microwave electronics, mainly used for transmission line, microwave signal to achieve all the high frequency can be transmitted to the load point, will not have the reflected signal source, so as to enhance the energy efficiency.

In general, there are two kinds of impedance matching, one is through the change of resistance (lumped-circuit matching), another is to adjust the transmission lines (transmission line matching).

To match a set of line, the point of load impedance, characteristic impedance divided by the value of transmission line to normalization, and then the numerical paddle in the Smith chart.

Change in resistance

The series capacitor or inductor and load, can increase or decrease the load impedance, the point on the graph represents the real resistance along the circle around. If the capacitance or inductance to ground, the first point on the graph to the center can rotate 180 degrees, and then along the resistance ring around, and then along the center of rotation of 180 degrees. Repeat the above process until the resistance value becomes 1, can be directly to the impedance force becomes zero matches.

Adjust the transmission line

From the point to the source point load long transmission line, in the chart dot along the center of the picture in the counterclockwise direction around, until the resistance value of 1 circles, can add capacitance or inductance to resistance is adjusted to zero, complete matching

The impedance matching of transmission power, for a power supply, single its resistance equal to the load

At this time, maximum output power, impedance matching. Maximum power transfer theorem, if it is of high frequency words, is no reflection wave. For broadband amplifier common, output impedance of 50, consider the need of impedance matching power transmission circuit, but if the signal wavelength is much greater than the length of the cable, the cable length can be ignored, need not consider the impedance matching. Impedance matching refers to the transfer of energy, the characteristic impedance and load impedance equal requirements to transmission line, transmission will not at this time of reflection, suggesting that all energy is load absorption. And vice versa energy losses in the transmission. High-speed PCB layout, in order to prevent the reflection signal, is the line impedance is 50 ohms. This is a ballpark figure, the general provisions of baseband 50 ohm coaxial cable, band 75 ohm, twisted pair is 100 ohms, just take a whole, in order to match the convenience.

Impedance literally and resistance are not the same, of which only one stop words are the same, and the other one - word? Simply put, impedance is the resistance and reactance, so called impedance; distribution point to say, impedance is the resistance, capacitance and inductance and resistance against in the vector and the. In the current world, objects called resistance on current hinder it, all the world's matter has resistance, just the size difference resistance value. Small resistance material called a good conductor material resistance, great called non conductor, and more recently in the field of high technology known superconductors, is a kind of resistance value is close to zero. But in the alternating current field in addition to hinder current resistance, inductance and capacitance will hinder the flow of the current, the effect is called reactance, meaning the resistance current effect. Capacitance and inductance reactance are respectively called capacitance resistance and inductive reactance, referred to as the capacitance and inductance. Units of measurement and the resistance they are OM, and the value of the size and the frequency of the alternating current frequency is, the higher the smaller inductance capacitance is bigger, the lower the frequency capacitance and inductance and smaller. In addition, capacitance and inductance and resistance against phase angle, has the relation vector, so would say: impedance resistance and reactance is in the vector and the.

Impedance matching refers to the internal impedance and load impedance source mutual adaptation, a state of maximum power output. For circuits with different characteristics, the matching condition is not the same.

In the pure resistance circuit, when the load resistance equal to the excitation source resistance, the output power is maximum, the working state is called matching, otherwise known as mismatch.

When the excitation source impedance and load impedance contain reactance component, in order to obtain the maximum power load, the load impedance and resistance must satisfy the conjugate relation, i.e. a resistance component reactance components only equal, equal in magnitude but opposite sign. The matching conditions for the conjugate matching.