Impedance matching In electrical engineering, impedance is the ratio of voltage to current with the consideration of phase angle. According to Ohm’s law V= IR, where V – voltage, I is the current and R is the resistance of the network. In RF, the idea of impedance matching is to equalizing the source and load impedance for maximum power transfer. Impedance is represented as Z and is complex than just the resistance of the network. In simple explanation, impedance matching is to making source and load impedance as similar as possible in order to minimize losses.
Purpose of impedance matching
Maximizes power transfer from the transmitter to the load and increases efficiency. At low power level, avoiding any signal loss is very important and perfectly matched network is required.
Protect the devices from reflection. In high power transmission system, any power reflection may cause severe damage to the equipments like amplifiers and other devices.
Matching networks
In network analysis, two most common matching networks are Pi network and T-network. The main idea of this network is to get full control of the Q of the circuit. It is very useful in most of the cases where the design specifications are tighter and lesser option to implement. Pi and T-network offers the variety to handle different situations and optimize the network for maximum efficiency. Most common network impedance standard is 50 Ohm another standard is 75 Ohm standard. In order to have a better matched network, it is necessary to have all the components in the circuitry matched to 50 Ohm such as PCBs, cables, connectors etc. Inductors, capacitors and impedance transformers are the most commonly used components for matching of network.
Q = f/BW : Q is the quality factor of the network described as the ratio between the operating frequency (f) over bandwidth (BW).
Pi -network often used as a solution to match a high impedance source to lower load impedance and to match a low impedance source to higher impedance load. Pi -networks are good for wide frequency range and impedance transformation.
T-networks are another common topology used for impedance matching usually known as LLC circuits with combination of two inductors and capacitor in shunt. Conversion from a Pi-network to T-network is also possible and it will be necessary during some complex network analysis.
Smith ChartSmith chart is a chart representation of impedance and admittance grid developed by Philip Smith in Bell’s radio research lab during 1930s. Since then Smith chart is widely popular among electrical and electronic network engineers to solving problems and illustrate a complex network condition. Since the early stages of network analyzer, Smith Chart is one of the most important format to show the reflection of individual ports and easy to figure out mismatch in the network.
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