Impedance Matching Networks

Impedance matching networks are electrical circuits which, when connected between two networks, match the output impedance of the source (the first network) to the input impedance of the load (the receiving or second network). The purpose of matching these two impedances is to minimize wave reflection and/or to maximize the transfer of power between the system and the load. In this product area, impedance matching networks are complete systems with either manual or automatic modes of operation. Manual devices must be set by the user to monitor or tune a particular load. Automatic devices monitor or tune loads automatically. Typically, both types of impedance matching networks are used in large systems such as telecommunications and computer networks. 

Selecting impedance matching networks requires an analysis of cooling types and performance requirements. Typically, devices are cooled by either forced air or water.  Frequency range, rated power range, input impedance, tuning range, output current rating and output voltage rating are important performance specifications to consider. In a system, impedance mismatches cause some of the transmitted energy to be reflected back to the source. The signal frequency determines the amount of energy that is reflected. Voltage standing wave ratio (VSWR), a unit-less ratio ranging from 1 to infinity, represents the amount of reflected energy at the input or output of the device. A value of 1 indicates that all the energy passes through the impedance matching networks. Any other value indicates that a portion of the energy is reflected.

Impedance matching networks carry specifications for input voltage, phase, frequency, operating temperature, and features. Choices for input voltage include 115 VAC, 208 VAC, 230 VAC, and 24 VDC. Some impedance matching networks are single-phase devices. Others use three-phase power. Choices for frequency include 50 Hz and 60Hz. Operating temperature is defined as a full-required range. In terms of features, impedance matching networks may provide remote control operation or a preset capacitor capability. They may also allow microprocessor control or include so-called intelligent software. Impedance matching networks that are destined for sale in Europe should comply with all relevant European Union (EU) directives, including Restriction of Hazardous Substances (RoHS) and Waste Electrical and Electronics Equipment (WEEE). 

• AN721: Impedance Matching Networks Applied to RF Power Transistors, Courtesy of Motorola
  Some graphic and numerical methods of impedance matching will be reviewed here. The examples given will refer to high frequency power amplifiers. Although matching networks normally take the form of...
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• Design of an Input Matching Network for a DC Biased 850 MHz Small Signal Detector - App Note
  This application note describes the use of the HSMS-2820 in small signal detector applications at 850 MHz. The single series diode (HSMS-2820) has a detection sensitivity [1] of about 30 mV /µW; i.e.,...
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