double stub matching
Double stub impedance matching
Impedance matching can be achieved by inserting two stubs at specified locations along transmission line as shown below
There are two design parameters for double stub matching:
The length of the first stub line Lstub1
The length of the second stub line Lstub2
In the double stub configuration, the stubs are inserted at predetermined locations. In this way, if the load impedance is changed, one simply has to replace the stubs with another set of different length.
The drawback of double stub tuning is that a certain range of load admittances cannot be matched once the stub locations are fixed.
Three stubs are necessary to guarantee that match is always possible.
The length of the first stub is selected so that the admittance at the location of the second stub (before the second stub is inserted) has real part equal to the characteristic admittance of the line
If one moves from the location of the second stub back to the load, the circle of the allowed normalized admittances is mapped into another circle, obtained by pivoting the original circle about the center of the chart.
At the location of the first stub, the allowed normalized admittances are found on an auxiliary circle which is obtained by rotating the unitary conductance circle counterclockwise, by an angle
Given the load impedance, we need to follow these steps to complete the double stub design:
(a) Find the normalized load impedance and determine the corresponding location on the chart.
(b) Draw the circle of constant magnitude of the reflection coefficient |Γ| for the given load.
(c) Determine the normalized load admittance on the chart.
This is obtained by rotating -180° on the constant |Γ| circle, from the load impedance point.
From now on, all values read on the chart are normalized admittances.
(d) Find the normalized admittance at location dstub1 by moving clockwise on the constant |Γ| circle.
(e) Draw the auxiliary
Impedance matching can be achieved by inserting two stubs at specified locations along transmission line as shown below
There are two design parameters for double stub matching:
The length of the first stub line Lstub1
The length of the second stub line Lstub2
In the double stub configuration, the stubs are inserted at predetermined locations. In this way, if the load impedance is changed, one simply has to replace the stubs with another set of different length.
The drawback of double stub tuning is that a certain range of load admittances cannot be matched once the stub locations are fixed.
Three stubs are necessary to guarantee that match is always possible.
The length of the first stub is selected so that the admittance at the location of the second stub (before the second stub is inserted) has real part equal to the characteristic admittance of the line
If one moves from the location of the second stub back to the load, the circle of the allowed normalized admittances is mapped into another circle, obtained by pivoting the original circle about the center of the chart.
At the location of the first stub, the allowed normalized admittances are found on an auxiliary circle which is obtained by rotating the unitary conductance circle counterclockwise, by an angle
Given the load impedance, we need to follow these steps to complete the double stub design:
(a) Find the normalized load impedance and determine the corresponding location on the chart.
(b) Draw the circle of constant magnitude of the reflection coefficient |Γ| for the given load.
(c) Determine the normalized load admittance on the chart.
This is obtained by rotating -180° on the constant |Γ| circle, from the load impedance point.
From now on, all values read on the chart are normalized admittances.
(d) Find the normalized admittance at location dstub1 by moving clockwise on the constant |Γ| circle.
(e) Draw the auxiliary