Attenuators 76922.1.2 LossThe term loss is constantly used in attenuator and pad
design. Loss is a decrease in the power, voltage, or
current at the output of a device compared to the power,
voltage, or current at the input of the device. The loss in
decibels may be calculated by means of one of the
following equations:(22-3)(22-4)(22-5)where,
P 1 is the power at the input,P 2 is the power at the output,
V 1 is the voltage at the input,
V 2 is the voltage at the output,
I 1 is the current at the input,
I 2 is the current at the output.The insertion loss is created by the insertion of a
device in an electrical circuit. The resulting loss is
generally expressed in decibels.
A minimum-loss pad is a pad designed to match
circuits of unequal impedance with a minimum loss in
the matching network. This minimum loss is dependent
on the ratio of the terminating impedances.
The minimum loss for attenuators of unequal imped-
ance may be read from the graph in Fig. 22-5.
The graph is entered at the bottom at the desired
impedance ratio and then followed vertically until it
intersects the diagonal line. The minimum loss in deci-
bels is then read at the left margin. For instance, assume
an impedance of 600: is to be matched to an imped-
ance of 150:; this is an impedance ratio of four. For
this ratio, the graph indicates a minimum loss of
11.5 dB, which is the lowest value for which a passive
attenuator can be designed. In actual practice the
network would be designed for a loss of 12–15 dB.22.1.3 Impedance MatchingAn impedance-matching network is a noninductive,
resistive network designed for insertion between two or
more circuits of equal or unequal impedance. When
properly designed, the network reflects the correct30.0 0.031623 31.623 1000.0 0.93869 1.0653 0.031655 31.591 1.00200 0.96836 1.03266 0.032655 30.0
32.0 0.025119 39.811 1584.9 0.95099 1.051 5 0.025135 39.786 1.00126 0.97488 1.02577 0.025766 32.0
34.0 0.019953 50.119 2511.9 0.96088 1.04072 0.019961 50.099 1.00080 0.98005 1.02036 0.020359 34.0
36.0 0.015849 63.096 3981.1 0.96880 1.03221 0.015853 63.080 1.00050 0.98415 1.01610 0.016104 36.0
38.0 0.012589 79.433 6309.6 0.97513 1.02550 0.012591 79.420 1.00032 0.98741 1.01275 0.012750 38.0
40.0 0.0100000 100.000 10,000. 0.98020 1.02020 0.0100010 99.990 1.00020 0.99000 1.01010 0.010101 40.0
42.0 0.0079433 125.89 15,849. 0.98424 1.01601 0.0079436 125.88 1.00013 0.99206 1.00801 0.0080070 42.0
44.0 0.0063096 158.49 25,119. 0.98746 1.01270 0.0063096 158.49 1.00008 0.99369 1.00635 0.0063496 44.0
46.0 0.0050119 199.53 39,811. 0.99003 1.01007 0.0050119 199.53 1.00005 0.99499 1.00504 0.0050370 46.0
48.0 0.0039811 251.19 63,096. 0.99207 1.00799 0.0039811 251.19 1.000032 0.99602 1.00400 0.0039970 48.0
50.0 0.0031623 316.23 100,000. 0.99370 1.00634 0.0031623 316.23 1.000020 0.99684 1.00317 0.0031723 50.0
60.0 0.0010000 1000.0 106 0.99800 1.00200 0.0010000 1000 1.000002 0.99900 1.00100 0.0010010 60.0
70.0 0.00031623 3162.3 107 0.99937 1.00063 0.00031623 3162.3 1.000000 0.99968 1.00032 0.00031633 70.0
80.0 0.00010000 10,000.0 108 0.99980 1.00020 0.00010000 10,000 1.000000 0.99990 1.00010 0.00010001 80.0
90.0 0.00003163 31,623.0 109 0.99994 1.00006 0.00003162 31,623 1.000000 0.99997 1.00003 0.000031624 90.0
100 0.00001000 105 1010 0.99998 1.00002 0.00001000 105 1.000000 0.99999 1.00001 0.000010000 100Table 22-1. K” Factors for Calculating Attenuator Loss Values (Continued)
abcdef ghij l
n
(dB)n
r (dB)
1
K--- -= K K^2 K 1–
K 1+------------- K 1+
K 1–------------- K
K 2 1–----------------- K^2 1–
---------------KKr–=K^2 1+
K^2 1–----------------K 1–
K-------------1 –= rK
K 1–-------------1
1 – r-----------=1
K 1–-------------dBloss 10P 1
P 2= log----- -dBloss 20V 1
V 2= log----- -dBloss 20I 1
I 2= log----