Microwave and Wireless Communications Technology

The Smith Chart 123

VSWRdB = 20 log (20)

(6-28)

VSWRdB = (20)(0.510)= 10.2 dB

(6-29)

These points are plotted at C in Fig. 6-5. Shortly, we will work an example to show

how these factors are calculated in a transmission line problem from a known com-

plex load impedance.

Transmission loss

is a measure of the one-way loss of power in a transmission

line because of reflection from the load.

Return loss

represents the two-way loss and

so is exactly twice the transmission loss. Return loss is found from

= Lossr~, = 10 log

(Ppwr)

(6-30)

and, for our example in which Ppwr = 0.28,

= LosSre t = 10

log (0.28)

(6-31)

= (10) (-0.553) =-5.53 ...