Stubs and Its Types
Stub
In microwave and radio-frequency engineering, a stub is a length of transmission line or waveguide that is connected at one end only. The free end of the stub is either left open-circuit or (especially in the case of waveguides) short-circuited. Neglecting transmission line losses, the input impedance of the stub is purely reactive; either capacitive or inductive, depending on the electrical length of the stub, and on whether it is open or short circuit. Stubs may thus be considered to be frequency-dependent capacitors and frequency-dependent inductors. Because stubs take on reactive properties as a function of their electrical length, stubs are most common in UHF or microwave circuits where the line lengths are more manageable. Stubs are commonly used in antenna impedance matching circuits and frequency selective filters. Smith charts can also be used to determine what length line to use to obtain a desired reactance.
In their simplest form, stubs that are some multiple of a quarter wavelengths are used to kill harmonics or sub-harmonics of the operating frequency. One property of a transmission line is that it inverts the impedance every quarter wavelength, so a quarter-wave stub with a short at one end looks like an open circuit at the other end. At the second harmonic, that same stub is two quarter-waves long, so the short is inverted twice, and looks like a short circuit to the harmonic. At the third harmonic, it 's three quarter-waves, so it 's an open circuit again, then at a full wavelength it 's a short circuit again. Likewise, a quarter wave stub that is open at the far end looks like a short circuit, but an open circuit at the second harmonic.
A stub works by placing a short circuit across the line at the frequency of interference. Placing a stub on a line forms a voltage divider between the line impedance and the stub impedance. The higher the line impedance at the point of connection, the greater the attenuation. If the line is well matched
In microwave and radio-frequency engineering, a stub is a length of transmission line or waveguide that is connected at one end only. The free end of the stub is either left open-circuit or (especially in the case of waveguides) short-circuited. Neglecting transmission line losses, the input impedance of the stub is purely reactive; either capacitive or inductive, depending on the electrical length of the stub, and on whether it is open or short circuit. Stubs may thus be considered to be frequency-dependent capacitors and frequency-dependent inductors. Because stubs take on reactive properties as a function of their electrical length, stubs are most common in UHF or microwave circuits where the line lengths are more manageable. Stubs are commonly used in antenna impedance matching circuits and frequency selective filters. Smith charts can also be used to determine what length line to use to obtain a desired reactance.
In their simplest form, stubs that are some multiple of a quarter wavelengths are used to kill harmonics or sub-harmonics of the operating frequency. One property of a transmission line is that it inverts the impedance every quarter wavelength, so a quarter-wave stub with a short at one end looks like an open circuit at the other end. At the second harmonic, that same stub is two quarter-waves long, so the short is inverted twice, and looks like a short circuit to the harmonic. At the third harmonic, it 's three quarter-waves, so it 's an open circuit again, then at a full wavelength it 's a short circuit again. Likewise, a quarter wave stub that is open at the far end looks like a short circuit, but an open circuit at the second harmonic.
A stub works by placing a short circuit across the line at the frequency of interference. Placing a stub on a line forms a voltage divider between the line impedance and the stub impedance. The higher the line impedance at the point of connection, the greater the attenuation. If the line is well matched
References: * http://en.wikipedia.org/wiki/Stub_(electronics) * http://www.winnerscience.com/transmission-lines/impedance-matching-using-stub/ * http://www.winnerscience.com/transmission-lines/impedance-matching-using-stub/ * http://personal.ee.surrey.ac.uk/Personal/D.Jefferies/jefferies-stub.html * http://personal.ee.surrey.ac.uk/Personal/D.Jefferies/stubs.html * http://www.fnrf.science.cmu.ac.th/rf/Stub%20matching.html * http://www.enel.ucalgary.ca/People/Archive.June2010/okoniews/ENEL619-50/Projects2003/RPATCH/WBReactiveLoad_web2.htm