This issue was addressed by the stepped transmission line, where multiple, serially placed, quarter-wave dielectric slugs are used to vary a transmission line's characteristic impedance. In many cases, there is a need to use the same circuit to match a broad range of load impedance and thus simplify the circuit design. If the load impedance becomes capacitive, the matching element must be replaced by an inductor. For example, in order to match an inductive load into a real impedance, a capacitor needs to be used. Most lumped-element devices can match a specific range of load impedances. Power loss is an unavoidable consequence of using resistive networks, and they are only (usually) used to transfer line level signals. Resistive impedance matches are easiest to design and can be achieved with a simple L pad consisting of two resistors. Z l o a d = Z s o u r c e ∗ Z_ Resistive network In the following summary we will consider the general case when resistance and reactance are both significant, and the special case in which the reactance is negligible.Ĭomplex conjugate matching is used when maximum power transfer is required, namely In simple cases (such as low-frequency or direct current power transmission) the reactance may be negligible or zero the impedance can be considered a pure resistance, expressed as a real number. In general, impedance (symbol: Z) has a complex value this means that loads generally have a resistance component (symbol: R) which forms the real part and a reactance component (symbol: X) which forms the imaginary part. Electrical impedance, like electrical resistance, is measured in ohms. The concept of electrical impedance is perhaps the most commonly known. The energy involved can be electrical, mechanical, acoustic, magnetic, optical, or thermal. For varying signals, it usually changes with frequency. For constant signals, this impedance can also be constant. Impedance is the opposition by a system to the flow of energy from a source. The concept of impedance matching is widespread in electrical engineering, but is relevant in other applications in which a form of energy, not necessarily electrical, is transferred between a source and a load, such as in acoustics or optics. Practical impedance-matching devices will generally provide best results over a specified frequency band. Techniques of impedance matching include transformers, adjustable networks of lumped resistance, capacitance and inductance, or properly proportioned transmission lines. Signals on a transmission line will be transmitted without reflections if the transmission line is terminated with a matching impedance. For example, impedance matching typically is used to improve power transfer from a radio transmitter via the interconnecting transmission line to the antenna. Often, the desired value is selected to maximize power transfer or minimize signal reflection. In electronics, impedance matching is the practice of designing or adjusting the input impedance or output impedance of an electrical device for a desired value. For the computer science concept, see object-relational impedance mismatch.
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