Impedance matching

Impedance matching adjusts connected electrical systems so their impedances meet a chosen condition, commonly to maximize power transfer or minimize signal reflection.

Maximum power transfer theorem: A theorem stating the load receives maximum power when its impedance matches the source impedance appropriately. Conjugate matching follows this theorem for AC sources with complex impedance.
Electrical impedance: A frequency-dependent measure of opposition to alternating current, combining resistance and reactance. It is the quantity adjusted when connecting sources, loads, and transmission lines.
Antenna tuner: A circuit that transforms an antenna's input impedance to suit a transmitter or feed line. It presents a more suitable load to the transmitter despite antenna mismatch.
Impedance bridging: Connecting circuits with a high input impedance relative to the preceding circuit's output impedance. It prioritizes voltage transfer and low loading rather than maximum power transfer.
Conjugate matching: Matching a load impedance to the complex conjugate of a source impedance. This is the condition for maximum average power transfer in linear AC circuits.
Electrical resistance: The property that dissipates electrical energy and opposes current flow. For purely resistive circuits, matching reduces to choosing an appropriate load resistance.
Quarter-wave impedance transformer: A transmission-line section one quarter wavelength long that transforms one resistive impedance into another. It provides a simple narrowband match between a line and a resistive load.
Voltage divider: A circuit that divides an input voltage across series-connected impedances. A mismatched load can alter a divider's output, unlike an ideal matched-power setup.
Reflection coefficient: A complex ratio describing the amplitude and phase of a reflected wave relative to an incident wave. Impedance mismatch at a transmission-line boundary determines the reflected wave.
Reactance: The frequency-dependent opposition to alternating current caused by capacitance or inductance. Reactive mismatch must be canceled or transformed in narrowband matching networks.

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