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CHAPTER 2 - Conveying Power at Radio Frequency 74 Figure 2.8-3 Incident, Reflected and Transmitted voltage for a line terminated with (a) 25 Ω (b) 100 Ω However, when a finite load, whose impedance does not match the characteristic impedance of the line, is placed at its end the reflection is not quite as severe. A fraction of the voltage, proportional to the mismatch between Z L and Z 0 gets reflected but the remainder does get delivered to the load. This is shown in Figure 2.8-3. In the following subsections the graphs will only show the incident and reflected voltages along the line to avoid crowding the graphs. However the transmitted voltage is easily derived since it will have an identical phase to the incident voltage and an amplitude equal to the amplitude difference between incident and reflected voltage. This is demonstrated in Figure 2.8-3. Now let us examine each termination in more details by taking a snapshot of incident and reflected voltages along the line at different instants in time between zero and seconds. represents the period of the signal travelling down the line. A useful indicator of the proportion of the signal which gets reflected is the reflection coefficient . This quantity is extremely useful at Radio and Microwave frequencies and we will define it and describe it appropriately in section 2.14. is a complex number, however, for the time being, we will just look at its modulus | | and interpret it as an indicator of the relative magnitudes of reflected and incident signals. is defined in such a way that when the entire incident signal gets reflected its modulus is 1 whereas when no reflection occur its modulus is zero. is clearly stated on every graph in sections 2.8.1 to 2.8.5. These graphs are snapshots taken from a transmission line animation, designed by the author, which may be downloaded for free at http://docfrankie.com/index_files/matlab_anim.htm ──── Incident ──── Reflected (a) (b) ──── Incident ──── Reflected Conquer Radio Frequency 74 www.cadence.com/go/awr