Free T-Pad Attenuator Calculator
Calculate series and shunt resistor values (R1, R2, R3), power dissipation, and standard 1% resistor selections for T-network attenuators.
📡 T-Pad Attenuation & Impedance
📊 Resistor Values & Thermal Ratings
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How T-Pad Attenuators Work
A T-pad attenuator consists of two series resistors ($R_1$ and $R_2$) and one central shunt resistor to ground ($R_3$), forming a "T" network. It is a symmetrical two-port network that attenuates signal amplitude while presenting a constant characteristic impedance $Z_0$ at both ports.
1. The Symmetrical T-Pad Formulas
Let $K = 10^{A / 20}$ be the linear voltage ratio:
R3 = Z_0 × [2 × K / (K² - 1)]
2. Power Dissipation Analysis
When RF transmitter power enters the T-pad, the input series resistor $R_1$ carries the full forward line current plus the shunt current, experiencing higher dissipation than the output series resistor $R_2$.
Frequently Asked Questions
When should I use a T-pad instead of a Pi-pad?
T-pads are superior for low attenuation values (1 dB to 6 dB) because their resistor values remain in standard, readily available ranges. Pi-pads are better suited for deep attenuation (10 dB to 30 dB) where T-pad series resistors approach Z0 and the shunt resistor becomes tiny.
Can I cascade multiple attenuator stages?
Yes! Because a properly designed T-pad presents an exact 50-ohm input and output impedance, you can cascade multiple stages (e.g. 3 dB + 6 dB + 10 dB = 19 dB total attenuation) without any impedance mismatch or interactive reflection.
Why are RF attenuators built with 1% metal film or thick-film chip resistors?
Standard carbon composition or wirewound resistors have high inductive reactance and poor temperature stability. Precision 1% thin-film or thick-film chip resistors have near-zero parasitic series inductance, remaining flat in impedance up to several gigahertz.
How does a 3 dB attenuator affect transmitter power?
A 3 dB attenuator cuts transmitter power exactly in half (50% reduction). A 6 dB attenuator cuts power to 25%, and a 10 dB attenuator cuts power to 10%.