Matched T-Attenuator Network

Instructions: To design an attenuator, fill in Zi, Zo and Attenuation (a positive dB value) and click the compute button next to R1, R2 and R3 to compute the resistor values. You can skip that and go to the next paragraph if you want to analyze an existing attenuator. If you get a negative resistor value the attenuator is not realizable. Then, either increase attenuation, decrease Zi, increase Zo or get an active circuit. Check also the results further below that the computed Z(Uin)=Zi, Z(Uout)=Zo and attenuation are correct.

You can now tweak, modify or enter from scratch the resistor values R1, R2 and R3 and press the compute button next to Atten(Uout/Uin) to analyze the attenuation and impedances of the network. Remember to keep Zi and Zo at correct values even here. The Atten(total) result reflects the true attenuator including the effect of impedance mismatch at the source causing a different attenuation than the 6dB, which is the case of an ideal match. The source coupling attenuation (typically 6dB) is not included in the attenuator design value as the attenuation of the attenuator is specified as the attenuation of voltage Uin to Uout.

Zi=	ohm
Zo=	ohm
Attenuation=	dB	(Uout/Uin)

R1=	ohm
R2=	ohm
R3=	ohm

Z(Uin)=	dB
Z(Uout)=	dB
Atten(Uout/Uin)=	dB
Atten(total)=	dB	(including Z mismatch)