71032

Procedurę

For single stub matching, Figurę 3.10 gives an illustration on the Smith Chart of the procedurę. We work in normalized admittances on the chart.

The steps of the design procedurę are as follows.

1.    Normalize Yl with respect to Yo, and enter an admittance Smith Chart at the point yiso found. This point will represent the normalised admittance seen looking to the right at the reference piane shown as A in Figurę 3.9.

2.    Draw the locus of the normalised admittance looking toward the load through various

lengths of transmission linę, i.e. at variously positioned reference planes B as shown in Figurę 3.9. This locus will be the circle of centre the origin which passes through yi. We denote this locus, which is shown in Figurę 3.10, as locus B. We notę that various values of normalised conductance g and normalisedsusceptanceb are encountered as we move along the locus, and that the locus must at some point intersect the circle g = 1, in fact at two places.

At either of these places we have achieved the desired normalised conductance g = 1, but we have an unwanted susceptance which we will cali jb.

3.    Read off the susceptancejbwhich results at that point of intersection. If we remove this susceptance by the parallel connection of a susceptance-jbfrom a stub, we will the have achieved at the reference piane D the desired result of having a normalised conductance of unity, accompanied by zero susceptance.

4.    The problem is now to find the length s of a stub of susceptance-jb. To do this we enter as shown in Figurę 3.11 a second Smith Chart at the short Circuit point y-)°°on the periphery and travel clockwise, i.e. towards the input end of the stub, until we get to the point y = 0- jb.

In the example given, the rotation to get from the short Circuit point to the point y = -jbis about seven eighths of a revolution, so the length of the short circuited stub will be about seven sixteenths of a wave length.

To determine the actual length in metres of the stub we must know the wavelength on the stub linę at the operating frequency.