 2.2.7 Example 2.2.8 is instructive because it shows the following. Calculate the voltage reflection coefficient for the case If you want to transfer an incident voltage wave with where ZL (80 - j10) and Zo = 50 Q. no reflections then the terminating load (ZL) must match the characteristic impedance (Zo) exactly. See Given: ZL = (80 - j10), Z = 50 $ case (a). This is the desired condition for efficient Required: transfer of power through a transmission line. Maximum in-phase voltage reflection occurs with an Solution open circuit and maximum antiphase voltage reflec- Using Equation 2.2.28 tion occurs with a short circuit. See cases (b) and (c). This is because there is no voltage across a short cir- cuit and therefore the reflected wave must cancel the TOTAL incident wave. Intermediate values of terminating impedances pro- 14.03° duce intermediate values of reflection coefficients. 130.38 4.40° See case (d). Example 2.2.8 2.2.11.3 Return loss Calculate the voltage reflection coefficients at the ter- minating end of a transmission line with a characteristic Incident power (Pinc) and reflected power (Pref) can be impedance of 50 S when it is terminated by (a) a 50 O related by using the magnitude of the voltage reflection termination, (b) an open-circuit termination, (c) a short- coefficient (T). Since F = Vref/Vinc, it follows that circuit termination and (d) a 75 O termination. Given: Z = 50 S, ZL = (a) 50 S, (b) open-circuit = (2.2.30) 80, (c) short-circuit = 00, (d) = 75 0. Transmission lines CHAPTER 2.2 The return loss gives the amount of power reflected from a load and is calculated from (2.2.36a) return loss (dB) = -10 log r2 = -20 log Equation 2.2.36a is the form you frequently find in some (2.2.31) articles. 2.2.11.4 Mismatched loss 2.2.11.6 Voltage standing wave ratio (VSWR) The amount of power transmitted to the load (PL) is determined from Cases often arise when the terminating impedance for a transmission line is not strictly within the control of the PL = Pinc - Pref = Pinc(1 - 12 = (2.2.32) designer.