dB在缺省情况下总是界说功率单位，以 10lg 为计。
d B = 10 l g ( B ) dB = 10lg(B) dB=10lg(B)
P o w e r G a i n ( d B ) = 10 l g ( P o u t P i n ) Power Gain(dB) = 10lg(\frac{P_{out}}{P_{in}}) PowerGain(dB)=10lg(PinPout)
2. 级联情况的噪声系数计算公式
N F = N F 1 + N F 2 − 1 G 1 + N F 3 − 1 G 1 G 2 + ⋯ NF = NF1+\frac{NF2-1}{G1}+\frac{NF3-1}{G1G2} +\cdots NF=NF1+G1NF2−1+G1G2NF3−1+⋯
数字表示第n级，所有以dB为单位的变量需要转换成数值表示。
3. 输出P1dB
O P 1 d B ( d B ) = 10 l o g ( 1 1 O P 1 d B 1 × G 2 × G 3 + 1 O P 1 d B 2 × G 3 + 1 O P 1 d B 3 ) OP1dB(dB)= 10log(\frac{1}{\frac{1}{OP1dB1\times G2\times G3} +\frac{1}{OP1dB2\times G3} +\frac{1}{OP1dB3} } ) OP1dB(dB)=10log(OP1dB1×G2×G31+OP1dB2×G31+OP1dB311)
式中均要将dB转为十进制计算
4. 在级联情况下，整个系统的IP3三阶交截点
1 I P 3 2 = 1 I P 3 2 + 1 G 2 × I P 3 1 \frac{1}{IP3_2} = \frac{1}{IP3_2}+\frac{1}{G_2\times IP3_1} IP321=IP321+G2×IP311
1 I P 3 3 = 1 I P 3 3 + 1 G 3 × I P 3 2 + 1 G 3 × G 2 × I P 3 1 \frac{1}{IP3_3} = \frac{1}{IP3_3}+\frac{1}{G_3\times IP3_2}+\frac{1}{G_3\times G_2\times IP3_1} IP331=IP331+G3×IP321+G3×G2×IP311
1 I P 3 4 = 1 I P 3 4 + 1 G 4 × I P 3 3 + 1 G 4 × G 3 × I P 3 2 + 1 G 4 × G 3 × G 2 I P 3 1 \frac{1}{IP3_4} = \frac{1}{IP3_4}+\frac{1}{G_4\times IP3_3} +\frac{1}{G_4 \times G_3 \times IP3_2} + \frac{1}{G_4 \times G_3 \times G_2 IP3_1} IP341=IP341+G4×IP331+G4×G3×IP321+G4×G3×G2IP311
式中均要将dB转为十进制计算
5. 耗散功率
