CHAPTER 2 - Conveying Power at Radio Frequency
34
One thing to notice however is that, just as deceasing the frequency of the signal would
improve the phase offsets and the issues that they may bring about, increasing the frequency would
have the opposite effect.
Let us now see what happens when the frequency of our signal is increased by considering a 100
MHz signal in an analogous circuit to that shown in Figure 2.2-1.
Earlier on we showed how to calculate the length that a line needs to be for there to exist a
90⁰ phase difference between the generator and load signals. For a 100 MHz signal, this distance is
clearly shorter since the period of this signal is only 10 ns. This means that it takes a much shorter
time for the generator phase to reach 90⁰. By using equation (2.2-1) and the period of our 100MHz
signal (
⁄
), we can calculate this length
The effect of this length of line on V
S
and V
L
is shown in Figure 2.2-5.
Figure 2.2-5 Phase difference between generator and load voltage at 100 MHz over a 0.75m line
In a similar fashion we may calculate the length of the line for other phase offsets
Figure
2.2-6 (a)-(c) shows the phase offset between generator and load voltages for these lengths of
line.
Conquer Radio Frequency
34 www.cadence.com/go/awr
