- #Single stub and double stub matching using smith chart pdf generator#
- #Single stub and double stub matching using smith chart pdf series#
The second possible location has line admittance with positive imaginary part. If the normalized load admittance falls inside the unitary conductance circle (see next figure), the first possible stub location corresponds to a line admittance with negative imaginary part.
#Single stub and double stub matching using smith chart pdf series#
The second solution corresponds to an admittance value with negative imaginary part, in the lower portion of the chartĪmanogawa, 2006 Digital Maestro Series 201 The first solution corresponds to an admittance value with positive imaginary part, in the upper portion of the chartĪmanogawa, 2006 Digital Maestro Series 200 Within the first revolution, the two intersections provide the locations closest to the load for possible stub insertion.Īmanogawa, 2006 Digital Maestro Series 199 Every circle of constant |(d)| intersects the circle Re = 1 (unitary normalized conductance), in correspondence of two points. The value of the admittance rides on the red circle which corresponds to constant magnitude of the line reflection coefficient, |(d)|=|R |, imposed by the load.
#Single stub and double stub matching using smith chart pdf generator#
If one moves from load to generator on the line, the corresponding chart location moves from the reference point, in clockwise motion, according to an angle (indicated by the light green arc) Notice that in this case the load admittance falls outside the unitary conductance circle. This provides on the admittance chart the physical reference for the load location on the transmission line. The red arrow on the example indicates the load admittance. Second location suitable for stub insertionĪmanogawa, 2006 Digital Maestro Series 198 It is very convenient to analyze the possible solutions on a Smith chart.Īmanogawa, 2006 Digital Maestro Series 197įirst location suitable for stub insertion ( )stub stubdB B= Depending on the length of the transmission line, there may be a number of possible locations where a stub can be inserted for impedance matching. ( ) ( )stub 0 stubd dY Y jB= + For matching, we need to have Stub stubY jB= A stub should be placed at a location where the line admittance has real part equal to Y0 Note that the input admittance of a stub is always imaginary (inductance if negative, or capacitance if positive) In order to complete the design, we have to find an appropriate location for the stub. Line admittance at location dstub before the stub is appliedĪmanogawa, 2006 Digital Maestro Series 196 Since the circuit is based on insertion of a parallel stub, it is more convenient to work with admittances, rather than impedances.Īmanogawa, 2006 Digital Maestro Series 195 On the other hand, an open circuited stub may be more practical for certain types of transmission lines, for example microstrips where one would have to drill the insulating substrate to short circuit the two conductors of the line.Īmanogawa, 2006 Digital Maestro Series 194 A short circuited stub is less prone to leakage of electromagnetic radiation and is somewhat easier to realize. The choice of open or shorted stub may depend in practice on a number of factors. In many cases it is also convenient to select the same characteristic impedance used for the main line, although this is not necessary. The transmission line realizing the stub is normally terminated by a short or by an open circuit. The drawback of this approach is that if the load is changed, the location of insertion may have to be moved. The length of the stub line Lstub Any load impedance can be matched to the line by using single stub technique. The location of the stub with reference to the load dstub
There are two design parameters for single stub matching:
Single stub impedance matching Impedance matching can be achieved by inserting another transmission line (stub) as shown in the diagram belowĪmanogawa, 2006 Digital Maestro Series 193 Amanogawa, 2006 Digital Maestro Series 192
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